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The Chemical Synthesis of D -Glucuronic Acid
THE CHEMICAL SYNTHESIS OF D-GLUCURONIC ACID
BY C. L. MEHLTRETTER Northern Regional Research Laboratory, * Peoria, Illinois CONTENTS I. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11. Reduction of 1,4-~-Glucosaccharolactonc.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111. Oxidation of D-Glucose Derivatives by Various Agents.. . . . . . . . . . . . . . . . . . 1. Potassium Permanganate. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2. Nitrogen Dioxide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3. Catalytic Oxidation by Oxygen.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4. Use of Other Oxidants.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
231 233 236 236 239 242 247
I. INTRODUCTION D-Glucuronic acid in conjugate form was first detected in the urine of animals in 1874.' Five years later Schmiedeberg and Meyer2 isolated crystalline D-glucuronolactone from the glucuronoside excreted by dogs that had been fed camphor. It was not until 1891, however, th a t the first chemical synthesis of D-glucuronic acid was effected by Fischer and Pi10ty.~ I n this synthesis Fischer's method for the reduction of aldonic acid lactones by sodium amalgam to the corresponding aldoses4 was applied t o D-glucosaccharolactone. Other methods for preparing D-glucuronic acid were devised during the next forty-eight years, chiefly through the oxidation of derivatives of D-glucose by halogens, hydrogen peroxide, and potassium permanganate. In some of these reactions, only the aldehyde function of D-glucose was protected from oxidation, and in others the secondary hydroxyl groups also were blocked. Even the best of these syntheses6was tedious, however, and gave an overall yield of n-glucuronolactone from D-glucose of only twenty percent. The inadequacy from a preparative standpoint of the early methods
* One of the laboratories of the Bureau of Agricultural and Industrial Chemistry, Agricultural Research Administration, U. S. Department of Agriculture. (1) M. Jaff6, Ber., 7 , 1673 (1874). (2) 0. Schmiedeberg and H. Meyer, Z. physiol. Chem., 3, 422 (1879). (3) E. Fischer and 0. Piloty, Ber., 24, 522 (1891). (4) E. Fischer, Ber., 22, 2204 (1889). (5) M. Stacey, J . Chem. SOC.,1529 (1939). 23 1
232
C. L. MEHLTRETTER
for obtaining D-glucuronic acid by either chemical means6or by hydrolysis of polyuronide natural gums' fostered use of the relatively simple biological synthesis developed by Quicks and by Williams.@ These investigators were able to obtain yields of forty t o forty-five percent of D-glucuronic acid by hydrolysis of the D-glucuronosides obtained from the urine of animals that had been fed borneol or menthol. The quest for a satisfactory chemical synthesis of D-glucuronic acid was renewed with increased vigor when Petermanlo reported in 1947 that this compound showed promise in the treatment of rheumatic diseases. The search was stimulated also by the development of more efficient techniques for the preferential oxidation of primary alcohol groups to carboxyl groups in carbohydrates. Dalmer and Heyns" in 1940 had selectively oxidized the more active primary hydroxyl group of L-sorbose with oxygen in the presence of platinized carbon catalyst, thereby obtaining 2-keto-~-gulonicacid, the precursor of L-ascorbic acid. Shortly thereafter, the use of nitrogen dioxide for the oxidative preparation of uronic acid derivatives from carbohydrates having the aldehyde function protected through a glycosidic linkage was discovered independently by Maurer12 and by Kenyon,lS with their respective coworkers. Application of the catalytic oxidation procedure of Dalmer and by Mehltretter, AlexHeynsll to 1,2-isopropy~idene-~-~-g~ucofuranose ander, Mellies and Ristl4 has resulted in the preparation of 1,2430propylidene-D-ghcuronic acid in a t least fifty percent yield. Mild hydrolysis of the latter substance eliminated acetone and produced D-glucuronic acid nearly quantitatively. This convenient method for preparing D-glucuronic acid possesses the advantages of simplicity and high yield of product. The procedure should be useful also for synthesizing other uronic acids from appropriately substituted monosaccharides. I n the present chapter, the more significant methods which have been reported for the chemical synthesis of D-glucuronic acid will be described and discussed. They are reductive and oxidative procedures and will be (6) (a) M. Stacey, Aduances in Carbohydrate Chem., 2, 161 (1946);(b) J. W. Green, ibid., 8, 164 (1948). (7) F. Weinmann, Ber., 62, 1637 (1929);J. K. N. Jones and F. Smith, Advances i n Carbohydrale Chem., 4,243 (1949);E.Anderson and Lila Sands, ibid., 1,329 (1945). (8) A. J. Quick, J . BioE. Chem., 74, 331 (1927). (9) R.T.Williams, Nature, 143, 641 (1929). (10) E. A. Peterman, Journal-Lancet (Minneapolis Medical Society), 67, 45 1 (1 947). (11) 0.Dalmer and K. Heyns, U. S. Pat. 2,189,778and 2,190,377 (1940). (12) K.Maurer and G. Drefahl, Ber., 76, 1489 (1942). (13) E.C. Yackel and W. 0. Kenyon, U. S. Pat. 2,232,990(1941). (14) C. L. Mehltretter, B. H. Alexander, R. L. Mellies and C. E. Rist, J. Am. Chem. Soc., 78, 2424 (1951);C.L. Mehltretter, U. S. Pat. 2,659,652(1951).
CHEMICAL SYNTHESIS O F D-GLUCURONIC ACID
233
reviewed in that order. No attempt will be made t o elucidate the chemistry of o-glucuronic acid, since the subject has been adequately treated elsewhere.6(a).16 11. REDUCTION OF
1,4-D-GLTJCOSACCHAROLACTONE
Sodium amalgam has been extremely useful in the synthesis and determination of structure of carbohydrates. KilianilB utilized its reducing action, resulting from liberation of nascent hydrogen from water, to convert the double lactone of a sugar acid to a polyhydric alcohol. Unfortunately, he overlooked the application of sodium amalgam to the partial reduction of the lactone of a sugar acid to form the intermediate aldose. It remained for Fischer4 to discover this synthesis and its utility, in combination with the cyanohydrin reaction, l7 for lengthening the sugar chain. In an extension of this work, Fischer and Piloty3found in 1891 that a monolactone of D-glucosaccharic acid could be reduced to D-glucuronic acid by sodium amalgam. Although the reducing power of the sirup obtained after reduction showed that approximately twenty percent of the D-glucosaccharolactone presumably had been converted t o D-glucuronic acid (11),only a small quantity of crystalline D-glucuronolactone (111) was isolated. The fact that D-glucuronolactone was obtained, however, proved that at least a part of the D-glucosaccharolactones had the 1,4-lactone structure (I). Using an analogous procedure, Kilianil9
ocHbOH
b
c:
HO H H 0-
CHO
H 0
HCloH
HAOH
+HO H
HObH
I
I
HCOH HAOH
HAOH
I
1
COOH
COOH
I
CHSOH
I1
111
T
IV
was able t o obtain a thirty percent reduction of D-glucosaccharolactone but he could not crystallize the product, which again was presumed to be (15) N. E. Artz, and Elizabeth M. Osman, “Biochemistry of Glucuronio Acid,” Academic Press, Inc., New York, 1950. (16) H. Kiliani, Ber., 20, 2714 (1887). (17) Reviewed by C. S. Hudson, Adva?aces in Carbohydrate Chem., 1, 1 (1945). (18) 0. Sohst and B. Tollens, Ann., 246, I (1888). (19) H. Kiliani, Ber., 68, 2344 (1925).
234
C. L. MEHLTRETTER
D-glucuronic acid. Recently Serchi and ArcangeliZ0reported an eightyeight percent reduction t o sirupy glucuronic acid from which D-glucuronolactone was claimed to have been crystallized in nearly quantitative yield. An explanation for the difficulty experienced in obtaining D-glucuronic acid by reduction of D-ghcosaccharolactone was provided by a detailed investigation of the structure of Sohst and Tollens’ D-glucosaccharolactone, first by Rehorst and ScholzZ1and later by Schmidt and his coworkers.22 Their results indicated a 3,6-lactone (V) configuration for the substance. This was substantiated by Sutter and ReichsteinZ3 through reduction of the saccharolactone supplied by Schmidt. Halfreduction with sodium amalgam yielded appreciable amounts of L-guluronic acid (VI), isolated as the phenylhydrazide of the phenylhydrazone. Further reduction gave a good yield of D-gluconic acid (VII) which was characterized as the phenylhydrazide. It was considered significant that L-gulonic acid (IV), the final reduction product of 1,4-~-glucosaccharolactone (I), wa8 not found. Sodium amalgam half-reduction
gHjHoH COOH
HAOH
I
COOH
HAOH
A
COOH
HAOH
c:
HCOH I - t HHLOH oH HCOH I
v
bHO
VI
HLOH
LH,OH VII
of authentic l14-lactone (I)24 by the same investigators2a produced crystalline D-glucuronic acid in forty-one percent yield. Smithz6subsequently attempted t o show that the saccharolactone of Sohst and Tollens was a mixture of 1,4- (I) and 3,6-~-glucosaccharolactone (V). Prolonged treatment of the saccharolactone with methyl iodide and silver oxide had given the tetramethyl derivatives of I and V. The interpretation of this result was criticized by ReichsteinZ6who was of the opinion that a partial isomerization of the 3,6-lactone to 1,4-lactone had occurred during the methylation procedure. I n a succeeding report, (20) G. Serchi and L. Arcangeli, Sperimentale Sez. chim. biol., 2, 108 (1951). (21) K. Rehorst and H. Schola, Be?., 69, 520 (1936). (22) 0. T. Schmidt, H. Zeisser and H. Dippold, Ber., 70, 2402 (1937); 0. T. Schmidt and P. Giinthert, Ber., 71, 493 (1938). (23) M. Sutter and T. Reichstein, Helv. Chim. Acta, 21, 1210 (1938). (24) T. Reichstein, A. Grussner and R. Oppenauer, Helv. Chim. Acta, 16, 1019 (1933). (25) F. Smith, J . Chem. Soc., 571 (1944). (26) T. Reichstein, J . Chem. Soc., 320 (1945).
CHEMICAL SYNTHESIS O F D-QLUCURONIC ACID
235
however, Smithz7 confirmed his original view by separating the two lactones from the saccharolactone preparation, by acetone extraction, and identifying them. His pure 3,B-lactone melted a t 149" as compared with 130-132" observed by Rehorst and Scholz21and 135" reported by Sutter and ReichsteinZ3for Schmidt'szz compound. The 1,blactone monohydrate which he obtained melted at 98" (sintering a t 85") while Reichstein's product melted a t about 85". It would appear from the melting points alone that the D-glucosaccharolactones prepared by Rehorst2' and by Schmidtzz were mixtures. Similar preparations by Mehltretter and Rankin,28which were composed predominantly of 3,6-lactone1 also contained small quantities of 1,4-lactone, which was isolated by extraction with acetone. The recent discovery that aldonic acid lactones may be reduced to aldoses by electrolysis a t a mercury cathodezQrepresents a n improvement over the sodium amalgam method and merits trial in the reduction of 1,4-~-glucosaccharo~actone t o D-glucuronic acid. The electrolytic process was developed t o avoid the hazards associated with the handling of large quantities of sodium amalgam, in connection with the chemical synthesis of riboflavin. Its efficiency was demonstrated by the reduction of ~-ribonolactonelZ9in aqueous solution with sodium sulfate and boric acid, to D-ribose in fifty percent yield. In this case, the sugar was isolated as the crystalline p-bromophenylhydrazone. An alternative method for recovering the D-ribose was reported by Berger and Lee130who treated the catholyte mixture with aniline (or 3,4-dimethylaniline) to obtain an insoluble complex of sodium sulfate with the arylamine D-pentoside that was formed. The isolated aniline D-ribopyranoside, on boiling with dilute acetic acid, decomposed to D-ribose and aniline, the latter of which was removed by steam distillation or extraction of its benzal derivative. Analogously, i t should be possible t o separate D-glucuronic acid from an electrolysis mixture as the insoluble sodium salt of aniline D-glucuronoside. Such a method has been successfully employed t o recover D-glucuronic acid from acid hydrolyzates of ~-glucuronosides.3 1 In the final analysis, however, an efficient synthesis of D-glucuronic acid from 1,4-~-glucosaccharolactone is dependent upon a satisfactory procedure for obtaining the latter compound. Although Reichstein and (27) F. Smith, J. Chem. SOC.,633 (1944). (28) C. L. Mehltretter and J. C. Rankin, unpublished work. (29) (a) 1%.Spiegelberg, U. S. Pat. 2,457,933 (1049); (b) T. Sato, J . Chem. SOC. Japan, 71, 194 (1950); Chem. Abstracts, 46, 9483 (1951). (30) L. Berger and J. Lee, J . Org. Chem., 11, 84 (1946); R. W. Jeanloz and H. G . Fletcher, Jr., Advances in Carbohydrate Chem., 6 , 135 (1951). (31) M. Bergmann and W. Wolff, Ber., 66, 1060 (1923); C. L. Mehltretter, U. S. Pat. 2,562,200 (1951).
236
C. L. MEHLTRETTER
his coworkersz4stated that the desired lactone can readily be crystallized by appropriate seeding of supersaturated solutions of D-glucosaccharic acid, Mehltretter and RankinZ8obtained only a mixture consisting of the isomeric lactones when authentic seed crystals of 1,4-D-glUCOSaCcharolactone were used. A contributing factor to this phenomenon, no doubt, was contamination from the atmosphere of the laboratory with 3,6-~-glucosaccharolactone in microcrystalline form. This lactone is more rapidly crystallized a t room temperature than its l14-isomer.
111. OXIDATIONOF D-GLUCOSEDERIVATIVES BY VARIOUSAGENTS 1. Potassium Permanganate
The preparation of D-glucuronic acid from D-glucose by oxidation requires t ha t the reaction be limited t o the primary hydroxyl group (on carbon atom 6). This has been accomplished both by protection of the other oxidizable groups through formation of derivatives and by the use of selective oxidants. Potassium permanganate, which has been employed for the oxidation of a number of carbohydrate derivatives, is non-specific in its action. Thus, studies with 1,2-isopropylidene-~~-~g l u c o f ~ r a n o s showed e ~ ~ th at oxidation of the secondary hydroxyl group on carbon atom 5 was accomplished readily in neutral solution, a thirty percent yield of potassium 1,2-isopropylidene-~-xyluronate being attained. An optimal synthesis of D-glucuronic acid through oxidation with potassium permanganate therefore requires that all positions in D-glucose be protected, except the primary alcohol group. The protecting groups, however, must be removed easily, since extensive degradation of D-glucuronic acid can result from too strenuous conditions of hydrolysis for their elimination. This limitation is met by isopropylidene, benzylidene, and ethylidene derivatives, which have been established as useful intermediates in the preparation of specifically substituted monosaccharides. 9 3 The lability of such cyclic acetals in acid solution necessitates, of course, that their reactions be carried out under neutral or alkaline conditions. A cyclic diacetal of this type was employed by Ohle and Berend34ca) and by Link and his c ~ w o r k e r s ~ ~in ( ~the ) , ( ~synthesis ) of D-galacturonic acid. These investigators found that 1,2 :3,4-diisopropylidene-~-galactose was converted by permanganate oxidation in alkaline solution to the (32) (a) H. Ohle, G. Coutsicos and F. Garcia y Gonzalez, Ber., 64, 2810 (1931); (b) S. Akiya and T. Watanabe, J . Pharm. SOC. Japan, 64, 37 (1944); Chem. Abstracts, 46, 5629 (1951). (33) E. J. Bourne and 5. Peat, Advances i n Carbohydrate Chem., 6, 145 (1950). (34) (a) H. Ohle and Gertrud Berend, Ber., 68, 2585 (1925); (b) C. Nieman and K. P. Link, J. BioZ. Chem., 104, 195 (1934); (c) H. M. Sell and K. P. Link, J . Am. Chem. Soc., 60, 1813 (1938).
CHEMICAL S Y N T H E S I S O F D-GLUCURONIC ACID
237
corresponding D-galacturonic acid derivative in sixty-five percent yield. Mild hydrolysis of the substituted galacturonic acid with aqueous acid and concentration t o a sirup gave crystalline D-galacturonic acid. 34(c) I n 1933, Zervas and SessleF used potassium permanganate to prepare 1,2-isopropylidene-3,5-benzylidene-~-glucuron~c acid ( I X ) in fifty percent yield from 1,2-isopropylidene-3,5-benzylidene-~-glucose (VIII). I I
HGO-
I
CHI
I
VIII
Nearly quantitative removal of the acetal groups of I X by hydrolysis with 0.1 N hydrochloric acid in fifty percent ethanol a t 100" for one hour gave D-glucuronolactone in an overall yield from D-glucose of sixteen percent of theory. Alternatively, the acetal groups could be eliminated stepwise, the yield being lowered by several percent. I n this case the benzylidene group in I X was removed with hydrogen in the presence of palladium-black catalyst. The crystalline 1,2-isopropylidene-~-glucuronic acid, which was isolated from the reaction mixture in eighty-eight percent yield, was then easily hydrolyzed with aqueous acid to D-glucuronic acid. The 1,2-isopropylidene-3,5-benzylidene-~-glucose (VIII) used by Zervas and Sessler was made by the reaction of l12-isopropylidene-a-D-glucofuranose with benzaldehyde and phosphorus pentoxide a t room temperature. The procedure was a modification of the method of Brigl and Grune1-3~ who used zinc chloride as the condensing agent in the original synthesis of this substance. Recently Akiya and Watanabe3? claimed to have improved Zervas and Sessler's36 method for the synthesis of D-glucuronic acid through ll2-iso~ro~ylidene-3,5-benzyl~dene-~-g~ucof~ranose. These investigators prepared the latter compound by the following series of reactions: 1,2-isopropylidene-a-~-glucofuranose -+ 1,2-isopropylidene-~-glucose3,5(35) L. Zervas and P. Sessler, Ber., 66, 1326 (1933). (36) P. Brigl and H. Griiner, Ber., 66, 1428 (1932). (37) S. Akiya and T. Watanabe, J . Pharm. SOC.J a p a n , 67, 99 (1947); Chem. Abstracts, 45, 9483 (1951).
238
C. L. MEHLTRETTER
boric ester -+1,2-isopropylidene-6-acetyl-~-glucose + l12-isopropylidene3,5-benzylidene-6-acetyl-~-glucose -+ 1,2-isopropylidene-3,5-benzylideneD-glUCOSe. Permanganate oxidation of 1,2-isopropylidene-3,5-ben~ylidene-~glucose, and hydrolysis of the resulting n-glucuronic acid derivative by essentially Zervas and Sessler’s procedure, gave a twelve and one-half percent overall yield of D-glucuronolactone from n-glucose. 37s An attempt t o oxidize directly the intermediate 3,5-boric acid ester doubtless was discouraged by the result obtained by v. VarghaS8in 1933, wherein potassium permanganate oxidation of the 3,5-monoborate of IJ-isopropylidene-D-glucofuranose in acetone solution had produced potassium 1,2-isopropylidene-~-xyluronaterather than the expected D-glucuronic acid derivative. In 1951 Ishidate and Okada39 prepared l12-cyclohexylidene-3,5benzylidene-D-glucuronic acid in eighty-eight percent yield from 1,2cyclohexylideize-3,5-benzylidene-~-glucoseby permanganate oxidation, Subsequently hydrolysis of the glucuronic acid derivative by a mixture of ethanol and hydrochloric acid produced D-glucuronolactone from D-glucose in an overall yield of approximately twenty-two percent. Acid hydrolysis under less stringent conditions, as well as catalytic reduction, in crystalgave the intermediate 1,2-cyclohexylidene-~-glucuronolactone line form, This compound appears to be identical with that prepared by Mehltretter40 by catalytic, air oxidation of 1,2-cyclohexylidene-cu-~glucofuranose. Protection of the hydroxyl groups in D-glucose in the preparation of D-glucuronic acid has also been effected by derivatives other than cyclic acetals. I n an earlier synthesis Stacey4I had prepared 1,2,3,4-tetraacetyl-6-trityl-~-ghlcose (X) from D-glucose by a modification of the procedure devised by Helferich, Moog and Junger. 42 Detritylation by the procedure of Helferich and Klein43yielded 1,2,3,4-tetraacetyl-j3-~glucose (XI), which upon oxidation in glacial acetic acid-acetone solution with permanganate gave 1,2,3,4-tetraacetyl-~-glucuronicacid (XII). (37a) For comparison of yields of D-glucuronolactone obtained by the methods which utilize 1,2-isopropylidene-a-D-glucofuranoseas an intermediate, all calculations are based on D-glucose with the assumption of a yield of sixty-nine percent, as obtained by Zervas and Sess1er,86for the preparation of l,%isopropylidene-a-D-gIucofuranose. (38) L,v. Vargha, Ber., 66,704 (1933). (39) M. Ishidate and M. Okada, J . Pharm. SOC.Japan, 71, 1163 (1951); Chem. Abstracfs, 46,4996 (1952). (40) C. L. Mehltretter, unpublished work. (41) M. Stacey, J. Chem. SOC.,1529 (1939). (42)L. Helferich, L. Moog and A. Jiinger, Ber., 68,872 (1925). (43) B. Helferich and J. Klein, Ann., 460,219 (1926).
CHEMICAL SYNTHESIS O F D-GLUCURONIC ACID
239
Deacetylation of the substituted glucuronic acid with aqueous barium hydroxide yielded barium D-glucuronate. After removal of barium with sulfuric acid, the aqueous solution of D-glucuronic acid was evaporated in vacuo to a sirup, which crystallized upon seeding with authentic D-glucuronolactone. An overall yield of D-glucuronolactone of twenty percent was obtained.
-I
AcOCH
HbOAc
b
AcobH
H OAc
b-
AcO H HbOAc
+ ACOAK
b-
AcobH + b
H OAc
AcO H
HAoAc
HbOAc
Derivatives of D-glucose in which all the secondary hydroxyl groups are not blocked have been used chiefly in attempts to devise an economical process for the large-scale manufacture of D-glucuronic acid. Recent patents report methods for producing D-glucuronic acid by alkaline permanganate oxidation of soluble starch, 4 4 and of D-glucose derivatives in which the aldehyde function is protected. 4 6 Gallagher claimed t o have effected some degree of preferential oxidation of the primary alcohol group in both methyl a-D-glucopyranoside and 1,2-isopropylidene-a-D-glucofuranose under conditions of relatively high alkalinity and low temperature. Yields of methyl D-glucuronoside and of 1,2-isopropy~idene-~-g~ucuron~c acid were reported to be, respectively, sixty and thirty-four percent of theory as determined by colorimetric analysis of the reaction mixture by the naphthoresorcinol method. However, t.he claims are not convincing, since the products were not8 isolated and characterized. Furt,hermore, by-product uronic produced by oxidative degradation of the D-glucose derivatives at unshielded positions, are also capable of giving a positive naphthoresorcino1 test erroneously indicative of the presence of D-glucuronic acid. 2. Nitrogen Dioxide Maurer and ~ o w o r k e rfound s ~ ~ ~that ~ ~nitrogen dioxide in non-aqueous solution is capable of selectively oxidizing the primary alcohol group (44) T. Ohmori, Japanese Pat. 179,069 (1949); Chem. Abstracts, 46, 1585 (1952). (45) D. M, Gallagher, U. S. Pat. 2,592,266 (1952). (46) (a) K. Maurer and H. Reiff, J . Makromol. Chem., 1, 27 (1943); (b) K. Maurer and G. Drefahl, Ber., 80, 94 (1947).
240
C. L. MEHLTRETTER
of carbohydrates. Their initial experiment indicated that acetal formation, with the aldehyde function of glycolaldehyde, adequately protected that portion of the molecule from oxidation by nitrogen dioxide in chloroform or carbon tetrachloride solution. Accordingly, they oxidized methyl a-D-glucopyranoside,12 and upon hydrolysis of the reaction mixture presumed to have obtained barium D-glucuronate in sixty-seven percent yield. Their conclusion, however, was based solely on barium analyses of the salt, rather than on unequivocal proof by the isolation of crystalline D-glucuronolactone or some other suitable derivative of D-glucuronic acid. The oxidation of methyl a-~-galactopyranoside~~(~) in the same manner was more precise, in that the galacturonoside was recovered as amorphous calcium (methyl wga1actopyranosid)uronate in a yield of eighty percent and was obtained in crystalline form from the latter salt. In spite of numerous trials, Mehltretter4’ was unable to achieve the yield of barium n-glucuronate reported by Maurer and Drefahl.I2 Hardegger and spit^,^^ likewise, obtained only a small quantity of D-glucuronic acid as the lactone, through nitrogen dioxide oxidation of methyl a-D-glucopyranoside, and stated that the synthesis in its present form is not suitable as a preparative procedure. Considerably more oxidation occurred with the P-an~rner*~ but only small amounts of crystalline derivatives of methyl P-D-glucopyruronoside were isolated, while a seventy percent yield of organic acids was reported. A substantial portion of the latter was found t o be wglucosaccharic acid, which was not observed in the oxidation products from methyl a-D-ghcopyranoside. In 1950, two patents were issued to Peterman on methods for synthesizing D-glucuronic acid by nitrogen dioxide oxidation of glucosides. In one processlLoG) methyl D-ghcopyranoside was oxidized with a mixture of nitrogen dioxide gas and oxygen. The crude methyl D-glucuronoside obtained was hydrolyzed with one percent sulfuric acid at 90’ for one hour, to produce n-glucuronic acid. A theoretical yield of D-glucuronic acid was claimed. This is surprising, since it is known that approximately fourteen hours is required to hydrolyze completely the hemiacetal linkage in methyl a-D-hexuronosides with half-normal sulfuric acid at reflux temperature, 61 and that extensive degradation of the liberated uronic acid occurs during this period. The high yield of D-glucuronic (47) C. L. Mehltretter, unpublished work. (48) E. Hardegger and D. Spits, Helu. Chim. Aetca, 32, 2165 (1949). (49) E. Hardegger and D. Spite, Helu. Chim. Acta, 33, 337 (1950). (50) (a) E. A. Peterman, U. 5. Pat. 2,520,255 (1950);(b) U. S. Pat. 2,520,256 (1950). (51)F. Ehrlich and R. Guttmann, Ber., 66, 220 (1933).
CHEMICAL SYNTHESIS O F D-GLUCURONIC ACID
241
acid claimed by Peterman is in marked contrast to that found by previous investigator^.^^.^^ A second p r o c e ~ s describes ~ ~ ( ~ ) the oxidation of ethyl D-glucopyranoside by nitrogen dioxide in chloroform solution over a period of eight days at 20°C. When the reaction was completed the supernatant liquor was decanted and the residual gummy ethyl D-glucuronoside was dissolved in absolute alcohol. The solution was vacuum distilled to a dry product, which was claimed t'o be eighty to one hundred percent ethyl D-glucuronoside. Acid hydrolysis of the glucuronoside with one percent sulfuric acid at elevated temperature produced a mixture of D-glucuronic acid and furfural, the latter of which was removed by condensation with barbituric acid. A more recent patentb2 relates to the production of D-glucuronic acid by oxidation of methyl D-glucopyranoside with liquid nitrogen dioxide. An optimum yield of ~-glucuronicacid was obtained when the reaction was carried out at 20°C. for nine hours. The crude methyl D-glucuronoside was removed from aqueous solution by an anion-exchange resin. It was then eluted from the resin with dilute sulfuric acid, and the resulting solution was refluxed for sixteen hours t o produce D-glucuronic acid. After impurities were removed by extraction with l-butanol, the aqueous solution was concentrated to small volume and D-glucuronolactone crystallized by the addition of glacial acetic acid. From the data given, the yield of crystalline product was seventeen percent of theory. The use of nitrogen dioxide for the selective oxidation of polysaccharides to polyuronic acids was introduced by Kenyoii and his c ~ w o r k e r s ' ~ ~ ~ ~ in 1941. By this means extensive oxidation of the primary alcohol groups in cellulose was obtained, through the mechanism of preferential nitration followed by decomposition of the nitric acid ester with carboxyl format i ~ n . ~ ~ ( ' )Apparently *(~) some undissociated nitration products also were formed, since infrared absorption studies54 indicated the presence of nitrate radicals in the polyuronic acid. Side reactions produced carboxyl, (52) D. H. Couch and E. A. Cleveland, U. S.Pat. 2,592,249 (1952). (53) (a) E. C. Yackel and W. 0. Kenyon, J . Am. Cheni. SOC.,64, 121 (1942); (b) C. C. Unruh and W. 0. Kenyon, ibid., 64,127 (1942); ( c ) E. W. Taylor, W. F. Fowler, Jr., P. A. McGee and W. 0.Kenyon, ibid., 69, 342 (1947); (d) 1'. A. McGee, W. F. Fowler, Jr., and W. 0. Kenyon, ibid., 69, 347 (1947); (e) C. C. Unruh, P. A. McGee, W. F. Fowler, Jr., and W. 0. Kenyon, ibid., 69, 349 (1947); (f) P. A. McGee, W. F. Fowler, Jr., E. W. Taylor, C. C. Unruh and W. 0. Kenyon, ibid., 69, 355 (1947); ( 9 ) P. A. McGee, W. F. Fowler, Jr., C. C. Unruhand W. 0. Kenyon, ibid., 70,2700 (1948); (h) E. C. Yackel and W. 0. Kenyon, U. S. Pat. 2,448,892 (1948); (i) W. 0. Kenyon and W. F. Fowler, Jr., Abstracts Papers Am. Chem. SOC.,118, 4R (1950). (54) J. W. Rowen and E. K. Plyler, J . Research Nall. Bur. Standards, 44, 313 (1950).
242
C. L. MEHLTRETTER
aldehyde, and ketone groups from the secondary hydroxyl positions of the polysaccharide.6a(g)t66 Although the uronic acid content of cellulose oxidized by nitrogen dioxide was found to be high,6s(a),(d),(n),66,66(a),(b) satisfactory acid hydrolysis to D-glucuronic acid has not yet been achieved. Starch also has been oxidized with nitrogen dioxide.67 As expected, the product obtained by oxidation with nitrogen dioxide in carbon tetrachloride at room temperature gave a qualitative naphthoresorcinol test for D-glucuronic acid. No quantitative data are available, however, on the hydrolysis of such polyglucuronosides to D-glucuronic acid. A wider variety of oxidation products can be anticipated from corn starch, since it is composed of a linear or amylose fraction, present to the extent of about twenty-five percent and containing predominantly a-ll4-glucosidic linkages, and a branched or amylopectin fraction whose branches are considered to be formed mostly through a-1,6-glucosidic linkages. Kerr6’cd)has shown that amylose oxidized with gaseous nitrogen dioxide has significantly more anhydroglucuronic acid units than amylopectin that had been similarly treated. Whole starch, oxidized in the same manner, gave an amount of uronic acid intermediate between those obtained with the two fractions. From a practical point of view, nitrogen dioxide is not a satisfactory oxidant for the preparation of D-glucuronic acid. Anhydrous conditions of reaction are generally necessary and the oxidation progresses slowly. Periods of a t least nine hours are required for completion of an oxidation when liquid nitrogen dioxide is used. Reactions with nitrogen dioxide in chloroform solution or in the gaseous state take a number of days. Side reactions occur to some extent, and lower the yield of the main product. 3. Catalytic Oxidation by Oxygen The oxidation of aliphatic aldehydes and primary alcohols t o acids by use of oxygen in the presence of noble-metal catalysts, has long been known.68 Its application, however, to the preferential oxidation of aldehyde and primary alcohol groups in carbohydrates is quite recent. In 1941 B u s ~ hquantitatively ~~ converted D-glucose to D-gluconic acid with air, using a palladium-impregnated, calcium carbonate catalyst and (55) T. P. Nevell, J . Textile I d . , 43, T91 (1951). (56) (a) A. S. Perlin, Can. J . Chem., SO, 278 (1952); (b) P. Hirsch, Rec. truu. chim., 71, 999 (1952). (57) (a) W. 0.Kenyon and C. C. Unruh, U. S. Pat. 2,472,590 (1949); (b) J. W. Mench and E. F. Degering, Proc. Indiana Acad. Sci., 66, 69 (1945); (c) J. E. Pierce and E. F. Degering, Abstracts Papers Am. Chem. Soc., 113, 17D (1947); (d) R. Kerr, J . Am. Chem. Soc., 73, 816 (1950). (58) J. Houben, “Die Methoden der Organischen Chemie,” 3rd ed., 1952, p. 22. (59) M. Busch, German Pat. 702,729 (1941).
CHEMICAL SYNTHESIS O F D-GLUCURONIC ACID
243
the theoretical amount of alkali for neutralization of the acid. Somewhat later, Heyns and Heinemannso prepared D-gluconic acid in analogous manner with a platinized-carbon catalyst. With this more active catalyst, Dalmer and Heynsll*slwere able to oxidize L-sorbose, under neutral or slightly alkaline conditions, to 2-keto-~-gulonic acid for the production of ascorbic acid. Similarly, Trenners2 converted 2,3-isopropylidene-L-sorbose in aqueous solution to 2,3-isopropylidene-2-ketoL-gulosaccharic acid. The oxidation of D-glucose to D-glucosaccharic acid in fifty-four percent yield also has been carried out with this catalyst,68although Heyns and HeinemannG0were unable to detect D-glucosaccharic acid as an oxidation product of D-glucose in their experiments. Mehltretter, Alexander, Mellies and Rist l 4 then prepared D-glucuronic acid through catalytic oxidation of 1,2-isopropy~idene-a-~-glucofuranose (XIII). The intermediate 1,2-isopropylidene-~-glucuronic acid (XIV), obtained in fifty to sixty percent yield, was hydrolyzed quantitatively to D-glucuronic acid, which was isolated as the crystalline lactone. An overall yield of t,hirty percent of D-glucuronolactone, based on D-glucose, has consistently been realized by these investigators. A similar study reported at approximately the same time by Col6n and his associatesa4 7
-
I
HCOH
I CHzOH XI11
1
I
I
HCOH
bOOH XIV
Direct hydrolysis attained only half' this amount of D-glucuronolactone. of the oxidation mixture, after the removal of cations by ion exchange, produced a sirup from which an overall yield of approximately fifteen percent of crystalline D-glucuronolactone, based on D-glucose, was obtained. (60) (61) (62) (63)
K. Heyns and R. Heinemann, Ann., 668, 187 (1947). K. Heyns, Ann., 668, 177 (1947). N. R. Trenner, U. S. Pat. 2,428,438 (1947); 2,483,251 (1949). C. L. Mehltretter, C. E. Rist and B. H. Alexander, U. S. Pat. 2,472,168
(1949). (64) R. Fernandez-Garcia, L. Amoroa, Hilda Blay, E. Santiago, Hilda SolteroDiaz and A. A. Col6n, El Crisol, 4, 40 (1960).
244
C. L. MDHLTRETTER
Because the synthesis by catalytic oxidation represents the most satisfactory preparative method t o date for D-glucuronolactone, it will be described more elaborately than the previously mentioned procedures. The oxidation of 60 grams of 1,2-isopropy~idene-a-n-glucofuranose in 900 milliliters of water was carried out in the presence of 6.8 grams of platinum-activated carbon catalyst which contained 13 percent of platinum by weight. After being heated to 50°C., the mixture was vigorously stirred at about 3,500 r.p.m., while introducing air at the rate of 112 liters per hour. A volume of 10 percent sodium hydroxide solution, which represented the theoretical quantity of alkali for the complete conversion of 1,2-isopropy~idene-a-~-glucofuranose t o sodium 1,2-isopropylidene-~glucuronate, was immediately added dropwise to maintain the pH of the reaction mixture at 8-9 throughout the addition. All of the alkali generally was introduced in one to two hours, after which the pH of the oxidation mixture was allowed to decrease to 7. The reaction was then stopped, the light-brown solution filtered from catalyst, and the latter washed with hot dilute sodium chloride solution to prevent colloid formation and loss of platinum. The combined filtrate and washings were concentrated in vucuo t o approximately 200 milliliters and oxalate ions were precipitated by the addition of 2 grams of calcium chloride. The addition to the filtered mixture of 13 grams of calcium chloride in concentrated aqueous solution caused almost immediate crystallization of calcium 1,2-isopropylidene-~-glucuronate.After filtration, the product was washed with 50 percent ethanol and air dried, t o yield 41.8 grams hydrate. . (fifty-three percent) of calcium 1,2-isopropylidene-~-glucuronate The fairly pure calcium salt was treated with the theoretical quantity of oxalic acid to precipitate calcium oxalate and liberate 1,24sopropylideneD-glucuronic acid. Hydrolysis of the filtered solution at 90-100" for two hours gave D-glucuronic acid quantitatively, as determined by the reducing power of the solution. The nearly colorless hydrolyzate was concentrated on the steam bath to crystallization of D-glucuronolactone in eighty percent yield. Slightly more D-glucuronic acid was obtained when barium 1,2-isopropylidene-~-glucuronatewas precipitated from the oxidation mixture in lieu of the calcium salt. were Calcium, barium and sodium 1,2-isopropylidene-~-glucuronates prepared from authentic 1,2-isopropylidene-~-glucuronicacid. The crystalline calcium salt contained 5.5 molecules of water and had [a],z6 - 1-54" ( 6 , 1.97, water), while the barium salt was a monohydrate insoluble in water. The anhydrous sodium salt had [aIDz6-2.58' (c, 10.74, water). Catalytic oxidation of 1,2-cyclohexylidene-~-glucofuranoae~~ in an (65) R. C. Hockett, R. E. Miller and A. Scattergood, J . Am. Chem. Soc., 71,3072 (1949).
CHEMICAL SYNTHESIS O F D-GLUCURONIC ACID
245
analogous manner yielded the sodium salt of 1,2-cyclohexylidene-~glucuronic acid in solution. Addition of calcium chloride to the filtered and concentrated oxidation mixture precipitated relatively insoluble crystalline calcium 1,2-cyclohexylidene-~-glucuronate.Removal of calcium with sulfuric acid and concentration of the solution to dryness gave a sirup, which was extracted with hot ethanol. On cooling the extract, 1,2-cyclohexylidene-~-glucuronolactonec r y ~ t a l l i z e d . ~D-Glucuronolac~ tone was prepared from this substance by hydrolysis and evaporation to crystallization. Oxidation of the anomers of methyl D-glucopyranoside, D-galactopyranoside, D-mannopyranoside,6E(8)~(”) Z-menthyl ~-glucopyranoside,~’ and of 2-naphthyl P-D-g1ucopyranosidee8to their corresponding D-glycuronosides has also been readily achieved by this method. Acid hydrolysis of the glucuronosides, however, left much to be desired, and produced D-glucuronolactone in relatively low yield. In Mehltretter’s synthesis66(8) the oxidation mixture containing the sodium salt of methyl a-D-glucuronoside was adjusted to pH 2 with sulfuric acid and concentrated in vacuo to dryness. The crude methyl a-D-ghcuronoside was separated from sodium sulfate by extraction with hot methanol. After removal of solvent, the glucuronoside was hydrolyzed with N sulfuric acid at 95-100” for fifteen hours to yield a relatively small quantity of n-glucuronic acid. Sulfuric acid was removed as barium sulfate and the crude D-glucuronic acid solution was neutralized wit.h sodium hydroxide and concentrat.ed in vacuo to small volume. An alcohol solution of aniline was then introduced and the mixture adjusted to approximately pH 4 with acetic acid to enhance crystallization of the sodium salt! of aniline D-glucuronoside. The salt in dilute acetic acid solution was heated to generate aniline, which was removed by solvent extraction or steam distillation. The aniline also could be eliminated by Schiff-base formation with benzaldehyde, followed by ether extraction of the benzalaniline. The resulting aqueous soIution was concentrated, and sodium D-glucuronate monohydrate was conveniently crystallized by the addition of ethanol, a yield of fourteen percent, based on methyl D-glucopyranoside, being obtained. Neutralization with potassium or ammonium hydroxide instead of sodium hydroxide, before reaction with aniline, resulted in the precipitation of potassium6g or ammonium salts of aniline D-ghcuronoside. (66) (a) C. L. Mehltretter, U. S. Pat. 2,562,200 (1951); (b) S. A. Barker, E. J. Bourne and M. Stacey, Chemistry & Industry, 970 (1951). (67) C. A. Marsh, Nature, 168, 602 (1951); J. Chern. SOC.,1578 (1952). (68) K. C. Tsou and A. M. Seligman, J . Am. Chem. SOC.,74, 5605 (1952). (69) H. Thierfelder, 2.physiol. Chem., lS, 275 (1889).
246
C. L. MEEILTRETTER
Recently Smith and William~'~described a p-toluidine-ammonium D-glucuronate complex, containing one mole of toluidine and one mole of the toluidide of ammonium D-glucuronate, which might have utility in the recovery of D-glucuronic acid from glucuronoside hydrolyzates. Little is known about the configuration and properties of the salts of arylamine D-glucuronosides, and investigations paralleling those of Howard, Kenner, Lythgoe and Todd7' with amine glycosides would appear t o be desirable. The catalytic oxidation of methyl- a-D-glucopyranoside by Barker, Bourne and Staceys6ch)yielded eighty-seven percent of the glucuronoside, which upon hydrolysis gave an overall yield of sixteen percent of D-glucuronolactone. Methyl p-D-glucopyranoside upon oxidation produced glucuronoside to the extent of sixty-eight percent of theory. Formic acid hydrolysis of the latter subst,ance gave an overall yield of D-glucuronolactone of fifteen percent. Only a small amount of D-glucuronolactone was obtained by hydrolysis of the glucuronate secured through oxidation of dipotassium a-D-glucose 1-phosphate. The weak link in any synthesis of D-glucuronic acid which employs methyl a-D-glucopyranoside is the degradation of D-glucuronic acid which takes place during the hydrolysis step. To obtain a more efficient hydrolysis, Barker, Bourne and Stacey66(b)have suggested oxidation of the more easily cleaved methyl D-ghcofuranosides, or enzymic splitting of a salt of D-glucuronic acid 1-phosphate. p-D-Glucuronidase has been utilized for the hydrolysis of phenolphthalein p-D-glucuronoside,T2 I - m e n t h ~ l ~and ~ ( ~phenyl ) & ~ - g h c u r o n o s i d e s , and ~ ~ ~2-naphthyl ~) 8-D-glucopyranuronoside. 68 The successful application of catalytic oxidation by air or oxygen t o the preparation of uronic acids depends on a number of factors which are discussed below. (1) The activity of the platinum-carbon catalyst is of prime concern in obtaining maximum yields of product in a minimum of time. It was found by Mehltretter and his associatesI4that a modification of Trenner's procedures2consistently produced an effective catalyst. In the modified method, platinum from an aqueouR solution of chloroplatinic acid was deposited on acid-washed Darco (2-60brand of activated carbon by means of formaldehyde and sodium carbonate. To maintain high activ(70) J. N. Smith and R. T. Williams, Biochem. J., 44, 250 (1949). (71) G. A. Howard, G. W. Kenner, B. Lythgoe and A. R. Todd, J . Chem. SOC.,855
(1946). (72) P. Talalay, W. A. Fishman and C. Huggins, J . Biol. Chem., 166, 757 (1946). (73) (a) G. A. Levvy, Biochem. J., 42,2 (1948); (b) L. M. H. Kerr, A. F. Graham and G. A. Lewy, Biochem. J . , 42, 191 (1948).
CHEMICAL SYNTHESIS O F D-GLUCURONIC ACID
247
ity of the catalyst the reactants in the oxidation must be extremely pure. Mehltretter has used the same catalyst for at least five oxidations of 1,2-isopropy~idene-a-~-glucofuranose before it became sufficiently inactive to require replacement. Poisoning of the catalyst was relatively insignificant in repeated oxidations of recrystallized methyl a-D-glucopyranoside. (2) Heterogeneous reactions of this type require vigorous agitation t o obtain increased contact of the catalyst with the aerated aqueous solution of the carbohydrate. The use of creased flasks and high-speed stirring enabled oxidations to be carried out efficiently in small-scale experiments. For the oxidation of several liters of solution, however, the employment of 8 turbo-mixer was more practical. In such cases the heat of reaction was great enough to require cooling of the mixture t o maintain a constant temperature of 50-60” throughout the oxidation. Satisfactory oxidations were obtained with stirrer speeds of 3,500 r.p.m. but doubtless the rate of reaction can be increased significantly by even greater a g i t a t i ~ n . ’ ~Other ways to enhance the reaction rate are t80 increase (a) the ratio of catalyst t,o t.he subst,ance being oxidized, (b) the air flow or air pressure during the reaction, and (c) the temperature of the reaction. The extent of their use, however, is limited by such factors as cost, design of equipment, and the occurrence of majorside reactions. 4. Use of Other Oxidants
Early methods for preparing D-glucuronic acid from D-glucose or D-glucosides utilized hydrogen peroxide or the halogens as oxidizing agents, in neutral or alkaline solution. The syntheses developed, however, proved to be unsat,isfactory because of the low yields obtained in both the oxidation and hydrolysis stages. One of the first attempts to use hydrogen peroxide in such a synthesis was made by J01les.’~ A two-percent solut,ion of D-glucose was oxidized over an extended period of time but only an insignificant quantity, if any, of D-glucuronic acid was detected in the oxidation mixture. I n 1924 Smolenski7Bdevised a procedure in which a twenty to thirty percent yield of methyl a-D-glucuronoside was obtained by hydrogen peroxide oxidation of methyl a-D-glucopyranoside. Fifteen years elapsed before the use of hydrogen peroxide was again reported for the preparation of D-glucuronic acid. By means of hydrogen peroxide generated at, the cathode of an electrolytic cell, Leutgoeb and Heinrich7I converted (74) (75) (76) (77)
A. W. Hixson, Ind. Eng. Chern., 36,488 (1944). A. Jolles, Biochem. Z., 34, 243 (1911). K. Smolenski, Roczniki Chemji, 3, 153 (1924); Chem. Abstracts, 19,41 (1925). R. A. Leutgoeb and H. Heinrich, J . A m . Chem. Soc., 61, 870 (1939).
248
C.
L. MEHLTRETTER
methyl a-D-glucopyranoside to the corresponding wglucuronoside. PGlucuronic acid was recovered as its cinchonine salt in low yield after hydrolysis of the glucuronoside. The preparation of D-glucuronic acid by hydrogen peroxide oxidation of soluble has also been investigated. Hydrolysis of the polyuronide with sulfuric or oxalic acid gave D-glucuronic acid, which was isolated as the crystalline lactone. The preparation of glucuronosides by halogen oxidation of D-glucosides was first reported by Bergmann and Wolff ,78 Menthyl a-D-glucopyranoside in pyridine solution was subjected to the action of sodium hypobromite in dilute aqueous alkali, and gave only a low yield of the glucuronoside. When methyl a-D-glucopyranoside was treated with proportionately more barium hypobromite in aqueous barium hydroxide solution, the hydrolyzed reaction mixture gave a high reducing value and a pronounced naphthoresorcinol test for D-glucuronic acid, However, only the crystalline benzylphenylhydrazone of glyoxylic acid could be isolated from the hydrolyzate. The following year, Sm0lenski7~claimed the preparation of methyl D-ghcuronoside in nearly thirty percent yield by alkaline hypobromite oxidation of methyl a-D-glucopyranoside. Further illustration of the inadequacy of hypobromite oxidation for the conversion of glycosides to uronides is the work of Jackson and Hudson.79 Only a twelve percent yield of the brucine salt of methyl a-D-mannuronoside was obtained because of oxidative cleavage of the carbon chain of methyl a-D-mannopyranoside. A number of workers have investigated the oxidation of dextrinssO and starchs1 with halogens in neutral and alkaline solutions and have reported the presence of significant amounts of anhydroglucuronic acid units in the products obtained, as determined by furfural formation. No attempt has been made, however, to develop a practical synthesis of wglucuronic acid by this means. Sowden82recently has prepared n-glucuronic acid isotopically labeled a t carbon atom 6 for certain chemical and biochemical studies. In this novel synthesis, 5-aldehydo-1,2-isopropylidene-~-xylofuranose** (XVI), prepared by periodate cleavage of 1,2-isopropy~idene-a-~-glucofuranose (XV), was condensed with V4-1abeled sodium cyanide. Alkaline (78) M.Bergmann and W. Wolff, Ber., 66, 1060 (1923). (79)E.L. Jackson and C. S. Hudson, J . Am. Chem. Soc., 69,994 (1937). (80) W.Syniewski, Ann., 441, 277 (1925). (81) G. Felton, F. F. Farley and R. M. Hixon, Cereal Chem., 16, 678 (1938); F. F. Farley and R. M. Hixon, I d . Ens. Chem., 34, 677 (1942);C. Dumazert and H. Lehr, Trav. membres. soc. chim. biol., 23, 1284 (1941), B i d . Abatrmts, 21, 2373 (24202)(1947). (82)J. C. Sowden, J . Ana. Chem. Soc., 74,4377 (1952). (83) K.Iwadare, BUZZ. Chem. SOC.Japan, 16, 40 (1941).
CHEMICAL SYNTHESIS O F D-GLUCURONIC
ACID
249
hydrolysis of the cyanohydrin (XVII) gave sodium 1,2-isopropylidene-~glucofuranuronate (XVIII). Ion exchange of this salt to remove sodium ions produced the free acid, which was lactonized to 1,2-isopropylidene-~glucofuranurono-y-lactone (XIX). Isolation of XIX in high yield indi-
HCOH I
CHO
I
k*N
~H,OH
xv
XVI
XVII
I
1 y\
H c o l/CH3 I
HO~H
I
HCO-O&H
HCO
I HCO.
HLOH
H~OH
I
C*OONa XVIII
I
I
-c*o
XIX
CHs
I--*
HC HboH
I -c*o xx
cated that only a minor quantity of the diastereoisomeric nitrile was formed during the cyanohydrin reaction. Hydrolysis and lactonization of X I X gave, quantitatively, ~-glucuronolactone-6-C'4 ( x x ) .
BY C. L. MEHLTRETTER Northern Regional Research Laboratory, * Peoria, Illinois CONTENTS I. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11. Reduction of 1,4-~-Glucosaccharolactonc.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111. Oxidation of D-Glucose Derivatives by Various Agents.. . . . . . . . . . . . . . . . . . 1. Potassium Permanganate. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2. Nitrogen Dioxide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3. Catalytic Oxidation by Oxygen.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4. Use of Other Oxidants.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
231 233 236 236 239 242 247
I. INTRODUCTION D-Glucuronic acid in conjugate form was first detected in the urine of animals in 1874.' Five years later Schmiedeberg and Meyer2 isolated crystalline D-glucuronolactone from the glucuronoside excreted by dogs that had been fed camphor. It was not until 1891, however, th a t the first chemical synthesis of D-glucuronic acid was effected by Fischer and Pi10ty.~ I n this synthesis Fischer's method for the reduction of aldonic acid lactones by sodium amalgam to the corresponding aldoses4 was applied t o D-glucosaccharolactone. Other methods for preparing D-glucuronic acid were devised during the next forty-eight years, chiefly through the oxidation of derivatives of D-glucose by halogens, hydrogen peroxide, and potassium permanganate. In some of these reactions, only the aldehyde function of D-glucose was protected from oxidation, and in others the secondary hydroxyl groups also were blocked. Even the best of these syntheses6was tedious, however, and gave an overall yield of n-glucuronolactone from D-glucose of only twenty percent. The inadequacy from a preparative standpoint of the early methods
* One of the laboratories of the Bureau of Agricultural and Industrial Chemistry, Agricultural Research Administration, U. S. Department of Agriculture. (1) M. Jaff6, Ber., 7 , 1673 (1874). (2) 0. Schmiedeberg and H. Meyer, Z. physiol. Chem., 3, 422 (1879). (3) E. Fischer and 0. Piloty, Ber., 24, 522 (1891). (4) E. Fischer, Ber., 22, 2204 (1889). (5) M. Stacey, J . Chem. SOC.,1529 (1939). 23 1
232
C. L. MEHLTRETTER
for obtaining D-glucuronic acid by either chemical means6or by hydrolysis of polyuronide natural gums' fostered use of the relatively simple biological synthesis developed by Quicks and by Williams.@ These investigators were able to obtain yields of forty t o forty-five percent of D-glucuronic acid by hydrolysis of the D-glucuronosides obtained from the urine of animals that had been fed borneol or menthol. The quest for a satisfactory chemical synthesis of D-glucuronic acid was renewed with increased vigor when Petermanlo reported in 1947 that this compound showed promise in the treatment of rheumatic diseases. The search was stimulated also by the development of more efficient techniques for the preferential oxidation of primary alcohol groups to carboxyl groups in carbohydrates. Dalmer and Heyns" in 1940 had selectively oxidized the more active primary hydroxyl group of L-sorbose with oxygen in the presence of platinized carbon catalyst, thereby obtaining 2-keto-~-gulonicacid, the precursor of L-ascorbic acid. Shortly thereafter, the use of nitrogen dioxide for the oxidative preparation of uronic acid derivatives from carbohydrates having the aldehyde function protected through a glycosidic linkage was discovered independently by Maurer12 and by Kenyon,lS with their respective coworkers. Application of the catalytic oxidation procedure of Dalmer and by Mehltretter, AlexHeynsll to 1,2-isopropy~idene-~-~-g~ucofuranose ander, Mellies and Ristl4 has resulted in the preparation of 1,2430propylidene-D-ghcuronic acid in a t least fifty percent yield. Mild hydrolysis of the latter substance eliminated acetone and produced D-glucuronic acid nearly quantitatively. This convenient method for preparing D-glucuronic acid possesses the advantages of simplicity and high yield of product. The procedure should be useful also for synthesizing other uronic acids from appropriately substituted monosaccharides. I n the present chapter, the more significant methods which have been reported for the chemical synthesis of D-glucuronic acid will be described and discussed. They are reductive and oxidative procedures and will be (6) (a) M. Stacey, Aduances in Carbohydrate Chem., 2, 161 (1946);(b) J. W. Green, ibid., 8, 164 (1948). (7) F. Weinmann, Ber., 62, 1637 (1929);J. K. N. Jones and F. Smith, Advances i n Carbohydrale Chem., 4,243 (1949);E.Anderson and Lila Sands, ibid., 1,329 (1945). (8) A. J. Quick, J . BioE. Chem., 74, 331 (1927). (9) R.T.Williams, Nature, 143, 641 (1929). (10) E. A. Peterman, Journal-Lancet (Minneapolis Medical Society), 67, 45 1 (1 947). (11) 0.Dalmer and K. Heyns, U. S. Pat. 2,189,778and 2,190,377 (1940). (12) K.Maurer and G. Drefahl, Ber., 76, 1489 (1942). (13) E.C. Yackel and W. 0. Kenyon, U. S. Pat. 2,232,990(1941). (14) C. L. Mehltretter, B. H. Alexander, R. L. Mellies and C. E. Rist, J. Am. Chem. Soc., 78, 2424 (1951);C.L. Mehltretter, U. S. Pat. 2,659,652(1951).
CHEMICAL SYNTHESIS O F D-GLUCURONIC ACID
233
reviewed in that order. No attempt will be made t o elucidate the chemistry of o-glucuronic acid, since the subject has been adequately treated elsewhere.6(a).16 11. REDUCTION OF
1,4-D-GLTJCOSACCHAROLACTONE
Sodium amalgam has been extremely useful in the synthesis and determination of structure of carbohydrates. KilianilB utilized its reducing action, resulting from liberation of nascent hydrogen from water, to convert the double lactone of a sugar acid to a polyhydric alcohol. Unfortunately, he overlooked the application of sodium amalgam to the partial reduction of the lactone of a sugar acid to form the intermediate aldose. It remained for Fischer4 to discover this synthesis and its utility, in combination with the cyanohydrin reaction, l7 for lengthening the sugar chain. In an extension of this work, Fischer and Piloty3found in 1891 that a monolactone of D-glucosaccharic acid could be reduced to D-glucuronic acid by sodium amalgam. Although the reducing power of the sirup obtained after reduction showed that approximately twenty percent of the D-glucosaccharolactone presumably had been converted t o D-glucuronic acid (11),only a small quantity of crystalline D-glucuronolactone (111) was isolated. The fact that D-glucuronolactone was obtained, however, proved that at least a part of the D-glucosaccharolactones had the 1,4-lactone structure (I). Using an analogous procedure, Kilianil9
ocHbOH
b
c:
HO H H 0-
CHO
H 0
HCloH
HAOH
+HO H
HObH
I
I
HCOH HAOH
HAOH
I
1
COOH
COOH
I
CHSOH
I1
111
T
IV
was able t o obtain a thirty percent reduction of D-glucosaccharolactone but he could not crystallize the product, which again was presumed to be (15) N. E. Artz, and Elizabeth M. Osman, “Biochemistry of Glucuronio Acid,” Academic Press, Inc., New York, 1950. (16) H. Kiliani, Ber., 20, 2714 (1887). (17) Reviewed by C. S. Hudson, Adva?aces in Carbohydrate Chem., 1, 1 (1945). (18) 0. Sohst and B. Tollens, Ann., 246, I (1888). (19) H. Kiliani, Ber., 68, 2344 (1925).
234
C. L. MEHLTRETTER
D-glucuronic acid. Recently Serchi and ArcangeliZ0reported an eightyeight percent reduction t o sirupy glucuronic acid from which D-glucuronolactone was claimed to have been crystallized in nearly quantitative yield. An explanation for the difficulty experienced in obtaining D-glucuronic acid by reduction of D-ghcosaccharolactone was provided by a detailed investigation of the structure of Sohst and Tollens’ D-glucosaccharolactone, first by Rehorst and ScholzZ1and later by Schmidt and his coworkers.22 Their results indicated a 3,6-lactone (V) configuration for the substance. This was substantiated by Sutter and ReichsteinZ3 through reduction of the saccharolactone supplied by Schmidt. Halfreduction with sodium amalgam yielded appreciable amounts of L-guluronic acid (VI), isolated as the phenylhydrazide of the phenylhydrazone. Further reduction gave a good yield of D-gluconic acid (VII) which was characterized as the phenylhydrazide. It was considered significant that L-gulonic acid (IV), the final reduction product of 1,4-~-glucosaccharolactone (I), wa8 not found. Sodium amalgam half-reduction
gHjHoH COOH
HAOH
I
COOH
HAOH
A
COOH
HAOH
c:
HCOH I - t HHLOH oH HCOH I
v
bHO
VI
HLOH
LH,OH VII
of authentic l14-lactone (I)24 by the same investigators2a produced crystalline D-glucuronic acid in forty-one percent yield. Smithz6subsequently attempted t o show that the saccharolactone of Sohst and Tollens was a mixture of 1,4- (I) and 3,6-~-glucosaccharolactone (V). Prolonged treatment of the saccharolactone with methyl iodide and silver oxide had given the tetramethyl derivatives of I and V. The interpretation of this result was criticized by ReichsteinZ6who was of the opinion that a partial isomerization of the 3,6-lactone to 1,4-lactone had occurred during the methylation procedure. I n a succeeding report, (20) G. Serchi and L. Arcangeli, Sperimentale Sez. chim. biol., 2, 108 (1951). (21) K. Rehorst and H. Schola, Be?., 69, 520 (1936). (22) 0. T. Schmidt, H. Zeisser and H. Dippold, Ber., 70, 2402 (1937); 0. T. Schmidt and P. Giinthert, Ber., 71, 493 (1938). (23) M. Sutter and T. Reichstein, Helv. Chim. Acta, 21, 1210 (1938). (24) T. Reichstein, A. Grussner and R. Oppenauer, Helv. Chim. Acta, 16, 1019 (1933). (25) F. Smith, J . Chem. Soc., 571 (1944). (26) T. Reichstein, J . Chem. Soc., 320 (1945).
CHEMICAL SYNTHESIS O F D-QLUCURONIC ACID
235
however, Smithz7 confirmed his original view by separating the two lactones from the saccharolactone preparation, by acetone extraction, and identifying them. His pure 3,B-lactone melted a t 149" as compared with 130-132" observed by Rehorst and Scholz21and 135" reported by Sutter and ReichsteinZ3for Schmidt'szz compound. The 1,blactone monohydrate which he obtained melted at 98" (sintering a t 85") while Reichstein's product melted a t about 85". It would appear from the melting points alone that the D-glucosaccharolactones prepared by Rehorst2' and by Schmidtzz were mixtures. Similar preparations by Mehltretter and Rankin,28which were composed predominantly of 3,6-lactone1 also contained small quantities of 1,4-lactone, which was isolated by extraction with acetone. The recent discovery that aldonic acid lactones may be reduced to aldoses by electrolysis a t a mercury cathodezQrepresents a n improvement over the sodium amalgam method and merits trial in the reduction of 1,4-~-glucosaccharo~actone t o D-glucuronic acid. The electrolytic process was developed t o avoid the hazards associated with the handling of large quantities of sodium amalgam, in connection with the chemical synthesis of riboflavin. Its efficiency was demonstrated by the reduction of ~-ribonolactonelZ9in aqueous solution with sodium sulfate and boric acid, to D-ribose in fifty percent yield. In this case, the sugar was isolated as the crystalline p-bromophenylhydrazone. An alternative method for recovering the D-ribose was reported by Berger and Lee130who treated the catholyte mixture with aniline (or 3,4-dimethylaniline) to obtain an insoluble complex of sodium sulfate with the arylamine D-pentoside that was formed. The isolated aniline D-ribopyranoside, on boiling with dilute acetic acid, decomposed to D-ribose and aniline, the latter of which was removed by steam distillation or extraction of its benzal derivative. Analogously, i t should be possible t o separate D-glucuronic acid from an electrolysis mixture as the insoluble sodium salt of aniline D-glucuronoside. Such a method has been successfully employed t o recover D-glucuronic acid from acid hydrolyzates of ~-glucuronosides.3 1 In the final analysis, however, an efficient synthesis of D-glucuronic acid from 1,4-~-glucosaccharolactone is dependent upon a satisfactory procedure for obtaining the latter compound. Although Reichstein and (27) F. Smith, J. Chem. SOC.,633 (1944). (28) C. L. Mehltretter and J. C. Rankin, unpublished work. (29) (a) 1%.Spiegelberg, U. S. Pat. 2,457,933 (1049); (b) T. Sato, J . Chem. SOC. Japan, 71, 194 (1950); Chem. Abstracts, 46, 9483 (1951). (30) L. Berger and J. Lee, J . Org. Chem., 11, 84 (1946); R. W. Jeanloz and H. G . Fletcher, Jr., Advances in Carbohydrate Chem., 6 , 135 (1951). (31) M. Bergmann and W. Wolff, Ber., 66, 1060 (1923); C. L. Mehltretter, U. S. Pat. 2,562,200 (1951).
236
C. L. MEHLTRETTER
his coworkersz4stated that the desired lactone can readily be crystallized by appropriate seeding of supersaturated solutions of D-glucosaccharic acid, Mehltretter and RankinZ8obtained only a mixture consisting of the isomeric lactones when authentic seed crystals of 1,4-D-glUCOSaCcharolactone were used. A contributing factor to this phenomenon, no doubt, was contamination from the atmosphere of the laboratory with 3,6-~-glucosaccharolactone in microcrystalline form. This lactone is more rapidly crystallized a t room temperature than its l14-isomer.
111. OXIDATIONOF D-GLUCOSEDERIVATIVES BY VARIOUSAGENTS 1. Potassium Permanganate
The preparation of D-glucuronic acid from D-glucose by oxidation requires t ha t the reaction be limited t o the primary hydroxyl group (on carbon atom 6). This has been accomplished both by protection of the other oxidizable groups through formation of derivatives and by the use of selective oxidants. Potassium permanganate, which has been employed for the oxidation of a number of carbohydrate derivatives, is non-specific in its action. Thus, studies with 1,2-isopropylidene-~~-~g l u c o f ~ r a n o s showed e ~ ~ th at oxidation of the secondary hydroxyl group on carbon atom 5 was accomplished readily in neutral solution, a thirty percent yield of potassium 1,2-isopropylidene-~-xyluronate being attained. An optimal synthesis of D-glucuronic acid through oxidation with potassium permanganate therefore requires that all positions in D-glucose be protected, except the primary alcohol group. The protecting groups, however, must be removed easily, since extensive degradation of D-glucuronic acid can result from too strenuous conditions of hydrolysis for their elimination. This limitation is met by isopropylidene, benzylidene, and ethylidene derivatives, which have been established as useful intermediates in the preparation of specifically substituted monosaccharides. 9 3 The lability of such cyclic acetals in acid solution necessitates, of course, that their reactions be carried out under neutral or alkaline conditions. A cyclic diacetal of this type was employed by Ohle and Berend34ca) and by Link and his c ~ w o r k e r s ~ ~in ( ~the ) , ( ~synthesis ) of D-galacturonic acid. These investigators found that 1,2 :3,4-diisopropylidene-~-galactose was converted by permanganate oxidation in alkaline solution to the (32) (a) H. Ohle, G. Coutsicos and F. Garcia y Gonzalez, Ber., 64, 2810 (1931); (b) S. Akiya and T. Watanabe, J . Pharm. SOC. Japan, 64, 37 (1944); Chem. Abstracts, 46, 5629 (1951). (33) E. J. Bourne and 5. Peat, Advances i n Carbohydrate Chem., 6, 145 (1950). (34) (a) H. Ohle and Gertrud Berend, Ber., 68, 2585 (1925); (b) C. Nieman and K. P. Link, J. BioZ. Chem., 104, 195 (1934); (c) H. M. Sell and K. P. Link, J . Am. Chem. Soc., 60, 1813 (1938).
CHEMICAL S Y N T H E S I S O F D-GLUCURONIC ACID
237
corresponding D-galacturonic acid derivative in sixty-five percent yield. Mild hydrolysis of the substituted galacturonic acid with aqueous acid and concentration t o a sirup gave crystalline D-galacturonic acid. 34(c) I n 1933, Zervas and SessleF used potassium permanganate to prepare 1,2-isopropylidene-3,5-benzylidene-~-glucuron~c acid ( I X ) in fifty percent yield from 1,2-isopropylidene-3,5-benzylidene-~-glucose (VIII). I I
HGO-
I
CHI
I
VIII
Nearly quantitative removal of the acetal groups of I X by hydrolysis with 0.1 N hydrochloric acid in fifty percent ethanol a t 100" for one hour gave D-glucuronolactone in an overall yield from D-glucose of sixteen percent of theory. Alternatively, the acetal groups could be eliminated stepwise, the yield being lowered by several percent. I n this case the benzylidene group in I X was removed with hydrogen in the presence of palladium-black catalyst. The crystalline 1,2-isopropylidene-~-glucuronic acid, which was isolated from the reaction mixture in eighty-eight percent yield, was then easily hydrolyzed with aqueous acid to D-glucuronic acid. The 1,2-isopropylidene-3,5-benzylidene-~-glucose (VIII) used by Zervas and Sessler was made by the reaction of l12-isopropylidene-a-D-glucofuranose with benzaldehyde and phosphorus pentoxide a t room temperature. The procedure was a modification of the method of Brigl and Grune1-3~ who used zinc chloride as the condensing agent in the original synthesis of this substance. Recently Akiya and Watanabe3? claimed to have improved Zervas and Sessler's36 method for the synthesis of D-glucuronic acid through ll2-iso~ro~ylidene-3,5-benzyl~dene-~-g~ucof~ranose. These investigators prepared the latter compound by the following series of reactions: 1,2-isopropylidene-a-~-glucofuranose -+ 1,2-isopropylidene-~-glucose3,5(35) L. Zervas and P. Sessler, Ber., 66, 1326 (1933). (36) P. Brigl and H. Griiner, Ber., 66, 1428 (1932). (37) S. Akiya and T. Watanabe, J . Pharm. SOC.J a p a n , 67, 99 (1947); Chem. Abstracts, 45, 9483 (1951).
238
C. L. MEHLTRETTER
boric ester -+1,2-isopropylidene-6-acetyl-~-glucose + l12-isopropylidene3,5-benzylidene-6-acetyl-~-glucose -+ 1,2-isopropylidene-3,5-benzylideneD-glUCOSe. Permanganate oxidation of 1,2-isopropylidene-3,5-ben~ylidene-~glucose, and hydrolysis of the resulting n-glucuronic acid derivative by essentially Zervas and Sessler’s procedure, gave a twelve and one-half percent overall yield of D-glucuronolactone from n-glucose. 37s An attempt t o oxidize directly the intermediate 3,5-boric acid ester doubtless was discouraged by the result obtained by v. VarghaS8in 1933, wherein potassium permanganate oxidation of the 3,5-monoborate of IJ-isopropylidene-D-glucofuranose in acetone solution had produced potassium 1,2-isopropylidene-~-xyluronaterather than the expected D-glucuronic acid derivative. In 1951 Ishidate and Okada39 prepared l12-cyclohexylidene-3,5benzylidene-D-glucuronic acid in eighty-eight percent yield from 1,2cyclohexylideize-3,5-benzylidene-~-glucoseby permanganate oxidation, Subsequently hydrolysis of the glucuronic acid derivative by a mixture of ethanol and hydrochloric acid produced D-glucuronolactone from D-glucose in an overall yield of approximately twenty-two percent. Acid hydrolysis under less stringent conditions, as well as catalytic reduction, in crystalgave the intermediate 1,2-cyclohexylidene-~-glucuronolactone line form, This compound appears to be identical with that prepared by Mehltretter40 by catalytic, air oxidation of 1,2-cyclohexylidene-cu-~glucofuranose. Protection of the hydroxyl groups in D-glucose in the preparation of D-glucuronic acid has also been effected by derivatives other than cyclic acetals. I n an earlier synthesis Stacey4I had prepared 1,2,3,4-tetraacetyl-6-trityl-~-ghlcose (X) from D-glucose by a modification of the procedure devised by Helferich, Moog and Junger. 42 Detritylation by the procedure of Helferich and Klein43yielded 1,2,3,4-tetraacetyl-j3-~glucose (XI), which upon oxidation in glacial acetic acid-acetone solution with permanganate gave 1,2,3,4-tetraacetyl-~-glucuronicacid (XII). (37a) For comparison of yields of D-glucuronolactone obtained by the methods which utilize 1,2-isopropylidene-a-D-glucofuranoseas an intermediate, all calculations are based on D-glucose with the assumption of a yield of sixty-nine percent, as obtained by Zervas and Sess1er,86for the preparation of l,%isopropylidene-a-D-gIucofuranose. (38) L,v. Vargha, Ber., 66,704 (1933). (39) M. Ishidate and M. Okada, J . Pharm. SOC.Japan, 71, 1163 (1951); Chem. Abstracfs, 46,4996 (1952). (40) C. L. Mehltretter, unpublished work. (41) M. Stacey, J. Chem. SOC.,1529 (1939). (42)L. Helferich, L. Moog and A. Jiinger, Ber., 68,872 (1925). (43) B. Helferich and J. Klein, Ann., 460,219 (1926).
CHEMICAL SYNTHESIS O F D-GLUCURONIC ACID
239
Deacetylation of the substituted glucuronic acid with aqueous barium hydroxide yielded barium D-glucuronate. After removal of barium with sulfuric acid, the aqueous solution of D-glucuronic acid was evaporated in vacuo to a sirup, which crystallized upon seeding with authentic D-glucuronolactone. An overall yield of D-glucuronolactone of twenty percent was obtained.
-I
AcOCH
HbOAc
b
AcobH
H OAc
b-
AcO H HbOAc
+ ACOAK
b-
AcobH + b
H OAc
AcO H
HAoAc
HbOAc
Derivatives of D-glucose in which all the secondary hydroxyl groups are not blocked have been used chiefly in attempts to devise an economical process for the large-scale manufacture of D-glucuronic acid. Recent patents report methods for producing D-glucuronic acid by alkaline permanganate oxidation of soluble starch, 4 4 and of D-glucose derivatives in which the aldehyde function is protected. 4 6 Gallagher claimed t o have effected some degree of preferential oxidation of the primary alcohol group in both methyl a-D-glucopyranoside and 1,2-isopropylidene-a-D-glucofuranose under conditions of relatively high alkalinity and low temperature. Yields of methyl D-glucuronoside and of 1,2-isopropy~idene-~-g~ucuron~c acid were reported to be, respectively, sixty and thirty-four percent of theory as determined by colorimetric analysis of the reaction mixture by the naphthoresorcinol method. However, t.he claims are not convincing, since the products were not8 isolated and characterized. Furt,hermore, by-product uronic produced by oxidative degradation of the D-glucose derivatives at unshielded positions, are also capable of giving a positive naphthoresorcino1 test erroneously indicative of the presence of D-glucuronic acid. 2. Nitrogen Dioxide Maurer and ~ o w o r k e rfound s ~ ~ ~that ~ ~nitrogen dioxide in non-aqueous solution is capable of selectively oxidizing the primary alcohol group (44) T. Ohmori, Japanese Pat. 179,069 (1949); Chem. Abstracts, 46, 1585 (1952). (45) D. M, Gallagher, U. S. Pat. 2,592,266 (1952). (46) (a) K. Maurer and H. Reiff, J . Makromol. Chem., 1, 27 (1943); (b) K. Maurer and G. Drefahl, Ber., 80, 94 (1947).
240
C. L. MEHLTRETTER
of carbohydrates. Their initial experiment indicated that acetal formation, with the aldehyde function of glycolaldehyde, adequately protected that portion of the molecule from oxidation by nitrogen dioxide in chloroform or carbon tetrachloride solution. Accordingly, they oxidized methyl a-D-glucopyranoside,12 and upon hydrolysis of the reaction mixture presumed to have obtained barium D-glucuronate in sixty-seven percent yield. Their conclusion, however, was based solely on barium analyses of the salt, rather than on unequivocal proof by the isolation of crystalline D-glucuronolactone or some other suitable derivative of D-glucuronic acid. The oxidation of methyl a-~-galactopyranoside~~(~) in the same manner was more precise, in that the galacturonoside was recovered as amorphous calcium (methyl wga1actopyranosid)uronate in a yield of eighty percent and was obtained in crystalline form from the latter salt. In spite of numerous trials, Mehltretter4’ was unable to achieve the yield of barium n-glucuronate reported by Maurer and Drefahl.I2 Hardegger and spit^,^^ likewise, obtained only a small quantity of D-glucuronic acid as the lactone, through nitrogen dioxide oxidation of methyl a-D-glucopyranoside, and stated that the synthesis in its present form is not suitable as a preparative procedure. Considerably more oxidation occurred with the P-an~rner*~ but only small amounts of crystalline derivatives of methyl P-D-glucopyruronoside were isolated, while a seventy percent yield of organic acids was reported. A substantial portion of the latter was found t o be wglucosaccharic acid, which was not observed in the oxidation products from methyl a-D-ghcopyranoside. In 1950, two patents were issued to Peterman on methods for synthesizing D-glucuronic acid by nitrogen dioxide oxidation of glucosides. In one processlLoG) methyl D-ghcopyranoside was oxidized with a mixture of nitrogen dioxide gas and oxygen. The crude methyl D-glucuronoside obtained was hydrolyzed with one percent sulfuric acid at 90’ for one hour, to produce n-glucuronic acid. A theoretical yield of D-glucuronic acid was claimed. This is surprising, since it is known that approximately fourteen hours is required to hydrolyze completely the hemiacetal linkage in methyl a-D-hexuronosides with half-normal sulfuric acid at reflux temperature, 61 and that extensive degradation of the liberated uronic acid occurs during this period. The high yield of D-glucuronic (47) C. L. Mehltretter, unpublished work. (48) E. Hardegger and D. Spits, Helu. Chim. Aetca, 32, 2165 (1949). (49) E. Hardegger and D. Spite, Helu. Chim. Acta, 33, 337 (1950). (50) (a) E. A. Peterman, U. 5. Pat. 2,520,255 (1950);(b) U. S. Pat. 2,520,256 (1950). (51)F. Ehrlich and R. Guttmann, Ber., 66, 220 (1933).
CHEMICAL SYNTHESIS O F D-GLUCURONIC ACID
241
acid claimed by Peterman is in marked contrast to that found by previous investigator^.^^.^^ A second p r o c e ~ s describes ~ ~ ( ~ ) the oxidation of ethyl D-glucopyranoside by nitrogen dioxide in chloroform solution over a period of eight days at 20°C. When the reaction was completed the supernatant liquor was decanted and the residual gummy ethyl D-glucuronoside was dissolved in absolute alcohol. The solution was vacuum distilled to a dry product, which was claimed t'o be eighty to one hundred percent ethyl D-glucuronoside. Acid hydrolysis of the glucuronoside with one percent sulfuric acid at elevated temperature produced a mixture of D-glucuronic acid and furfural, the latter of which was removed by condensation with barbituric acid. A more recent patentb2 relates to the production of D-glucuronic acid by oxidation of methyl D-glucopyranoside with liquid nitrogen dioxide. An optimum yield of ~-glucuronicacid was obtained when the reaction was carried out at 20°C. for nine hours. The crude methyl D-glucuronoside was removed from aqueous solution by an anion-exchange resin. It was then eluted from the resin with dilute sulfuric acid, and the resulting solution was refluxed for sixteen hours t o produce D-glucuronic acid. After impurities were removed by extraction with l-butanol, the aqueous solution was concentrated to small volume and D-glucuronolactone crystallized by the addition of glacial acetic acid. From the data given, the yield of crystalline product was seventeen percent of theory. The use of nitrogen dioxide for the selective oxidation of polysaccharides to polyuronic acids was introduced by Kenyoii and his c ~ w o r k e r s ' ~ ~ ~ ~ in 1941. By this means extensive oxidation of the primary alcohol groups in cellulose was obtained, through the mechanism of preferential nitration followed by decomposition of the nitric acid ester with carboxyl format i ~ n . ~ ~ ( ' )Apparently *(~) some undissociated nitration products also were formed, since infrared absorption studies54 indicated the presence of nitrate radicals in the polyuronic acid. Side reactions produced carboxyl, (52) D. H. Couch and E. A. Cleveland, U. S.Pat. 2,592,249 (1952). (53) (a) E. C. Yackel and W. 0. Kenyon, J . Am. Cheni. SOC.,64, 121 (1942); (b) C. C. Unruh and W. 0. Kenyon, ibid., 64,127 (1942); ( c ) E. W. Taylor, W. F. Fowler, Jr., P. A. McGee and W. 0.Kenyon, ibid., 69, 342 (1947); (d) 1'. A. McGee, W. F. Fowler, Jr., and W. 0. Kenyon, ibid., 69, 347 (1947); (e) C. C. Unruh, P. A. McGee, W. F. Fowler, Jr., and W. 0. Kenyon, ibid., 69, 349 (1947); (f) P. A. McGee, W. F. Fowler, Jr., E. W. Taylor, C. C. Unruh and W. 0. Kenyon, ibid., 69, 355 (1947); ( 9 ) P. A. McGee, W. F. Fowler, Jr., C. C. Unruhand W. 0. Kenyon, ibid., 70,2700 (1948); (h) E. C. Yackel and W. 0. Kenyon, U. S. Pat. 2,448,892 (1948); (i) W. 0. Kenyon and W. F. Fowler, Jr., Abstracts Papers Am. Chem. SOC.,118, 4R (1950). (54) J. W. Rowen and E. K. Plyler, J . Research Nall. Bur. Standards, 44, 313 (1950).
242
C. L. MEHLTRETTER
aldehyde, and ketone groups from the secondary hydroxyl positions of the polysaccharide.6a(g)t66 Although the uronic acid content of cellulose oxidized by nitrogen dioxide was found to be high,6s(a),(d),(n),66,66(a),(b) satisfactory acid hydrolysis to D-glucuronic acid has not yet been achieved. Starch also has been oxidized with nitrogen dioxide.67 As expected, the product obtained by oxidation with nitrogen dioxide in carbon tetrachloride at room temperature gave a qualitative naphthoresorcinol test for D-glucuronic acid. No quantitative data are available, however, on the hydrolysis of such polyglucuronosides to D-glucuronic acid. A wider variety of oxidation products can be anticipated from corn starch, since it is composed of a linear or amylose fraction, present to the extent of about twenty-five percent and containing predominantly a-ll4-glucosidic linkages, and a branched or amylopectin fraction whose branches are considered to be formed mostly through a-1,6-glucosidic linkages. Kerr6’cd)has shown that amylose oxidized with gaseous nitrogen dioxide has significantly more anhydroglucuronic acid units than amylopectin that had been similarly treated. Whole starch, oxidized in the same manner, gave an amount of uronic acid intermediate between those obtained with the two fractions. From a practical point of view, nitrogen dioxide is not a satisfactory oxidant for the preparation of D-glucuronic acid. Anhydrous conditions of reaction are generally necessary and the oxidation progresses slowly. Periods of a t least nine hours are required for completion of an oxidation when liquid nitrogen dioxide is used. Reactions with nitrogen dioxide in chloroform solution or in the gaseous state take a number of days. Side reactions occur to some extent, and lower the yield of the main product. 3. Catalytic Oxidation by Oxygen The oxidation of aliphatic aldehydes and primary alcohols t o acids by use of oxygen in the presence of noble-metal catalysts, has long been known.68 Its application, however, to the preferential oxidation of aldehyde and primary alcohol groups in carbohydrates is quite recent. In 1941 B u s ~ hquantitatively ~~ converted D-glucose to D-gluconic acid with air, using a palladium-impregnated, calcium carbonate catalyst and (55) T. P. Nevell, J . Textile I d . , 43, T91 (1951). (56) (a) A. S. Perlin, Can. J . Chem., SO, 278 (1952); (b) P. Hirsch, Rec. truu. chim., 71, 999 (1952). (57) (a) W. 0.Kenyon and C. C. Unruh, U. S. Pat. 2,472,590 (1949); (b) J. W. Mench and E. F. Degering, Proc. Indiana Acad. Sci., 66, 69 (1945); (c) J. E. Pierce and E. F. Degering, Abstracts Papers Am. Chem. Soc., 113, 17D (1947); (d) R. Kerr, J . Am. Chem. Soc., 73, 816 (1950). (58) J. Houben, “Die Methoden der Organischen Chemie,” 3rd ed., 1952, p. 22. (59) M. Busch, German Pat. 702,729 (1941).
CHEMICAL SYNTHESIS O F D-GLUCURONIC ACID
243
the theoretical amount of alkali for neutralization of the acid. Somewhat later, Heyns and Heinemannso prepared D-gluconic acid in analogous manner with a platinized-carbon catalyst. With this more active catalyst, Dalmer and Heynsll*slwere able to oxidize L-sorbose, under neutral or slightly alkaline conditions, to 2-keto-~-gulonic acid for the production of ascorbic acid. Similarly, Trenners2 converted 2,3-isopropylidene-L-sorbose in aqueous solution to 2,3-isopropylidene-2-ketoL-gulosaccharic acid. The oxidation of D-glucose to D-glucosaccharic acid in fifty-four percent yield also has been carried out with this catalyst,68although Heyns and HeinemannG0were unable to detect D-glucosaccharic acid as an oxidation product of D-glucose in their experiments. Mehltretter, Alexander, Mellies and Rist l 4 then prepared D-glucuronic acid through catalytic oxidation of 1,2-isopropy~idene-a-~-glucofuranose (XIII). The intermediate 1,2-isopropylidene-~-glucuronic acid (XIV), obtained in fifty to sixty percent yield, was hydrolyzed quantitatively to D-glucuronic acid, which was isolated as the crystalline lactone. An overall yield of t,hirty percent of D-glucuronolactone, based on D-glucose, has consistently been realized by these investigators. A similar study reported at approximately the same time by Col6n and his associatesa4 7
-
I
HCOH
I CHzOH XI11
1
I
I
HCOH
bOOH XIV
Direct hydrolysis attained only half' this amount of D-glucuronolactone. of the oxidation mixture, after the removal of cations by ion exchange, produced a sirup from which an overall yield of approximately fifteen percent of crystalline D-glucuronolactone, based on D-glucose, was obtained. (60) (61) (62) (63)
K. Heyns and R. Heinemann, Ann., 668, 187 (1947). K. Heyns, Ann., 668, 177 (1947). N. R. Trenner, U. S. Pat. 2,428,438 (1947); 2,483,251 (1949). C. L. Mehltretter, C. E. Rist and B. H. Alexander, U. S. Pat. 2,472,168
(1949). (64) R. Fernandez-Garcia, L. Amoroa, Hilda Blay, E. Santiago, Hilda SolteroDiaz and A. A. Col6n, El Crisol, 4, 40 (1960).
244
C. L. MDHLTRETTER
Because the synthesis by catalytic oxidation represents the most satisfactory preparative method t o date for D-glucuronolactone, it will be described more elaborately than the previously mentioned procedures. The oxidation of 60 grams of 1,2-isopropy~idene-a-n-glucofuranose in 900 milliliters of water was carried out in the presence of 6.8 grams of platinum-activated carbon catalyst which contained 13 percent of platinum by weight. After being heated to 50°C., the mixture was vigorously stirred at about 3,500 r.p.m., while introducing air at the rate of 112 liters per hour. A volume of 10 percent sodium hydroxide solution, which represented the theoretical quantity of alkali for the complete conversion of 1,2-isopropy~idene-a-~-glucofuranose t o sodium 1,2-isopropylidene-~glucuronate, was immediately added dropwise to maintain the pH of the reaction mixture at 8-9 throughout the addition. All of the alkali generally was introduced in one to two hours, after which the pH of the oxidation mixture was allowed to decrease to 7. The reaction was then stopped, the light-brown solution filtered from catalyst, and the latter washed with hot dilute sodium chloride solution to prevent colloid formation and loss of platinum. The combined filtrate and washings were concentrated in vucuo t o approximately 200 milliliters and oxalate ions were precipitated by the addition of 2 grams of calcium chloride. The addition to the filtered mixture of 13 grams of calcium chloride in concentrated aqueous solution caused almost immediate crystallization of calcium 1,2-isopropylidene-~-glucuronate.After filtration, the product was washed with 50 percent ethanol and air dried, t o yield 41.8 grams hydrate. . (fifty-three percent) of calcium 1,2-isopropylidene-~-glucuronate The fairly pure calcium salt was treated with the theoretical quantity of oxalic acid to precipitate calcium oxalate and liberate 1,24sopropylideneD-glucuronic acid. Hydrolysis of the filtered solution at 90-100" for two hours gave D-glucuronic acid quantitatively, as determined by the reducing power of the solution. The nearly colorless hydrolyzate was concentrated on the steam bath to crystallization of D-glucuronolactone in eighty percent yield. Slightly more D-glucuronic acid was obtained when barium 1,2-isopropylidene-~-glucuronatewas precipitated from the oxidation mixture in lieu of the calcium salt. were Calcium, barium and sodium 1,2-isopropylidene-~-glucuronates prepared from authentic 1,2-isopropylidene-~-glucuronicacid. The crystalline calcium salt contained 5.5 molecules of water and had [a],z6 - 1-54" ( 6 , 1.97, water), while the barium salt was a monohydrate insoluble in water. The anhydrous sodium salt had [aIDz6-2.58' (c, 10.74, water). Catalytic oxidation of 1,2-cyclohexylidene-~-glucofuranoae~~ in an (65) R. C. Hockett, R. E. Miller and A. Scattergood, J . Am. Chem. Soc., 71,3072 (1949).
CHEMICAL SYNTHESIS O F D-GLUCURONIC ACID
245
analogous manner yielded the sodium salt of 1,2-cyclohexylidene-~glucuronic acid in solution. Addition of calcium chloride to the filtered and concentrated oxidation mixture precipitated relatively insoluble crystalline calcium 1,2-cyclohexylidene-~-glucuronate.Removal of calcium with sulfuric acid and concentration of the solution to dryness gave a sirup, which was extracted with hot ethanol. On cooling the extract, 1,2-cyclohexylidene-~-glucuronolactonec r y ~ t a l l i z e d . ~D-Glucuronolac~ tone was prepared from this substance by hydrolysis and evaporation to crystallization. Oxidation of the anomers of methyl D-glucopyranoside, D-galactopyranoside, D-mannopyranoside,6E(8)~(”) Z-menthyl ~-glucopyranoside,~’ and of 2-naphthyl P-D-g1ucopyranosidee8to their corresponding D-glycuronosides has also been readily achieved by this method. Acid hydrolysis of the glucuronosides, however, left much to be desired, and produced D-glucuronolactone in relatively low yield. In Mehltretter’s synthesis66(8) the oxidation mixture containing the sodium salt of methyl a-D-glucuronoside was adjusted to pH 2 with sulfuric acid and concentrated in vacuo to dryness. The crude methyl a-D-ghcuronoside was separated from sodium sulfate by extraction with hot methanol. After removal of solvent, the glucuronoside was hydrolyzed with N sulfuric acid at 95-100” for fifteen hours to yield a relatively small quantity of n-glucuronic acid. Sulfuric acid was removed as barium sulfate and the crude D-glucuronic acid solution was neutralized wit.h sodium hydroxide and concentrat.ed in vacuo to small volume. An alcohol solution of aniline was then introduced and the mixture adjusted to approximately pH 4 with acetic acid to enhance crystallization of the sodium salt! of aniline D-glucuronoside. The salt in dilute acetic acid solution was heated to generate aniline, which was removed by solvent extraction or steam distillation. The aniline also could be eliminated by Schiff-base formation with benzaldehyde, followed by ether extraction of the benzalaniline. The resulting aqueous soIution was concentrated, and sodium D-glucuronate monohydrate was conveniently crystallized by the addition of ethanol, a yield of fourteen percent, based on methyl D-glucopyranoside, being obtained. Neutralization with potassium or ammonium hydroxide instead of sodium hydroxide, before reaction with aniline, resulted in the precipitation of potassium6g or ammonium salts of aniline D-ghcuronoside. (66) (a) C. L. Mehltretter, U. S. Pat. 2,562,200 (1951); (b) S. A. Barker, E. J. Bourne and M. Stacey, Chemistry & Industry, 970 (1951). (67) C. A. Marsh, Nature, 168, 602 (1951); J. Chern. SOC.,1578 (1952). (68) K. C. Tsou and A. M. Seligman, J . Am. Chem. SOC.,74, 5605 (1952). (69) H. Thierfelder, 2.physiol. Chem., lS, 275 (1889).
246
C. L. MEEILTRETTER
Recently Smith and William~'~described a p-toluidine-ammonium D-glucuronate complex, containing one mole of toluidine and one mole of the toluidide of ammonium D-glucuronate, which might have utility in the recovery of D-glucuronic acid from glucuronoside hydrolyzates. Little is known about the configuration and properties of the salts of arylamine D-glucuronosides, and investigations paralleling those of Howard, Kenner, Lythgoe and Todd7' with amine glycosides would appear t o be desirable. The catalytic oxidation of methyl- a-D-glucopyranoside by Barker, Bourne and Staceys6ch)yielded eighty-seven percent of the glucuronoside, which upon hydrolysis gave an overall yield of sixteen percent of D-glucuronolactone. Methyl p-D-glucopyranoside upon oxidation produced glucuronoside to the extent of sixty-eight percent of theory. Formic acid hydrolysis of the latter subst,ance gave an overall yield of D-glucuronolactone of fifteen percent. Only a small amount of D-glucuronolactone was obtained by hydrolysis of the glucuronate secured through oxidation of dipotassium a-D-glucose 1-phosphate. The weak link in any synthesis of D-glucuronic acid which employs methyl a-D-glucopyranoside is the degradation of D-glucuronic acid which takes place during the hydrolysis step. To obtain a more efficient hydrolysis, Barker, Bourne and Stacey66(b)have suggested oxidation of the more easily cleaved methyl D-ghcofuranosides, or enzymic splitting of a salt of D-glucuronic acid 1-phosphate. p-D-Glucuronidase has been utilized for the hydrolysis of phenolphthalein p-D-glucuronoside,T2 I - m e n t h ~ l ~and ~ ( ~phenyl ) & ~ - g h c u r o n o s i d e s , and ~ ~ ~2-naphthyl ~) 8-D-glucopyranuronoside. 68 The successful application of catalytic oxidation by air or oxygen t o the preparation of uronic acids depends on a number of factors which are discussed below. (1) The activity of the platinum-carbon catalyst is of prime concern in obtaining maximum yields of product in a minimum of time. It was found by Mehltretter and his associatesI4that a modification of Trenner's procedures2consistently produced an effective catalyst. In the modified method, platinum from an aqueouR solution of chloroplatinic acid was deposited on acid-washed Darco (2-60brand of activated carbon by means of formaldehyde and sodium carbonate. To maintain high activ(70) J. N. Smith and R. T. Williams, Biochem. J., 44, 250 (1949). (71) G. A. Howard, G. W. Kenner, B. Lythgoe and A. R. Todd, J . Chem. SOC.,855
(1946). (72) P. Talalay, W. A. Fishman and C. Huggins, J . Biol. Chem., 166, 757 (1946). (73) (a) G. A. Levvy, Biochem. J., 42,2 (1948); (b) L. M. H. Kerr, A. F. Graham and G. A. Lewy, Biochem. J . , 42, 191 (1948).
CHEMICAL SYNTHESIS O F D-GLUCURONIC ACID
247
ity of the catalyst the reactants in the oxidation must be extremely pure. Mehltretter has used the same catalyst for at least five oxidations of 1,2-isopropy~idene-a-~-glucofuranose before it became sufficiently inactive to require replacement. Poisoning of the catalyst was relatively insignificant in repeated oxidations of recrystallized methyl a-D-glucopyranoside. (2) Heterogeneous reactions of this type require vigorous agitation t o obtain increased contact of the catalyst with the aerated aqueous solution of the carbohydrate. The use of creased flasks and high-speed stirring enabled oxidations to be carried out efficiently in small-scale experiments. For the oxidation of several liters of solution, however, the employment of 8 turbo-mixer was more practical. In such cases the heat of reaction was great enough to require cooling of the mixture t o maintain a constant temperature of 50-60” throughout the oxidation. Satisfactory oxidations were obtained with stirrer speeds of 3,500 r.p.m. but doubtless the rate of reaction can be increased significantly by even greater a g i t a t i ~ n . ’ ~Other ways to enhance the reaction rate are t80 increase (a) the ratio of catalyst t,o t.he subst,ance being oxidized, (b) the air flow or air pressure during the reaction, and (c) the temperature of the reaction. The extent of their use, however, is limited by such factors as cost, design of equipment, and the occurrence of majorside reactions. 4. Use of Other Oxidants
Early methods for preparing D-glucuronic acid from D-glucose or D-glucosides utilized hydrogen peroxide or the halogens as oxidizing agents, in neutral or alkaline solution. The syntheses developed, however, proved to be unsat,isfactory because of the low yields obtained in both the oxidation and hydrolysis stages. One of the first attempts to use hydrogen peroxide in such a synthesis was made by J01les.’~ A two-percent solut,ion of D-glucose was oxidized over an extended period of time but only an insignificant quantity, if any, of D-glucuronic acid was detected in the oxidation mixture. I n 1924 Smolenski7Bdevised a procedure in which a twenty to thirty percent yield of methyl a-D-glucuronoside was obtained by hydrogen peroxide oxidation of methyl a-D-glucopyranoside. Fifteen years elapsed before the use of hydrogen peroxide was again reported for the preparation of D-glucuronic acid. By means of hydrogen peroxide generated at, the cathode of an electrolytic cell, Leutgoeb and Heinrich7I converted (74) (75) (76) (77)
A. W. Hixson, Ind. Eng. Chern., 36,488 (1944). A. Jolles, Biochem. Z., 34, 243 (1911). K. Smolenski, Roczniki Chemji, 3, 153 (1924); Chem. Abstracts, 19,41 (1925). R. A. Leutgoeb and H. Heinrich, J . A m . Chem. Soc., 61, 870 (1939).
248
C.
L. MEHLTRETTER
methyl a-D-glucopyranoside to the corresponding wglucuronoside. PGlucuronic acid was recovered as its cinchonine salt in low yield after hydrolysis of the glucuronoside. The preparation of D-glucuronic acid by hydrogen peroxide oxidation of soluble has also been investigated. Hydrolysis of the polyuronide with sulfuric or oxalic acid gave D-glucuronic acid, which was isolated as the crystalline lactone. The preparation of glucuronosides by halogen oxidation of D-glucosides was first reported by Bergmann and Wolff ,78 Menthyl a-D-glucopyranoside in pyridine solution was subjected to the action of sodium hypobromite in dilute aqueous alkali, and gave only a low yield of the glucuronoside. When methyl a-D-glucopyranoside was treated with proportionately more barium hypobromite in aqueous barium hydroxide solution, the hydrolyzed reaction mixture gave a high reducing value and a pronounced naphthoresorcinol test for D-glucuronic acid, However, only the crystalline benzylphenylhydrazone of glyoxylic acid could be isolated from the hydrolyzate. The following year, Sm0lenski7~claimed the preparation of methyl D-ghcuronoside in nearly thirty percent yield by alkaline hypobromite oxidation of methyl a-D-glucopyranoside. Further illustration of the inadequacy of hypobromite oxidation for the conversion of glycosides to uronides is the work of Jackson and Hudson.79 Only a twelve percent yield of the brucine salt of methyl a-D-mannuronoside was obtained because of oxidative cleavage of the carbon chain of methyl a-D-mannopyranoside. A number of workers have investigated the oxidation of dextrinssO and starchs1 with halogens in neutral and alkaline solutions and have reported the presence of significant amounts of anhydroglucuronic acid units in the products obtained, as determined by furfural formation. No attempt has been made, however, to develop a practical synthesis of wglucuronic acid by this means. Sowden82recently has prepared n-glucuronic acid isotopically labeled a t carbon atom 6 for certain chemical and biochemical studies. In this novel synthesis, 5-aldehydo-1,2-isopropylidene-~-xylofuranose** (XVI), prepared by periodate cleavage of 1,2-isopropy~idene-a-~-glucofuranose (XV), was condensed with V4-1abeled sodium cyanide. Alkaline (78) M.Bergmann and W. Wolff, Ber., 66, 1060 (1923). (79)E.L. Jackson and C. S. Hudson, J . Am. Chem. Soc., 69,994 (1937). (80) W.Syniewski, Ann., 441, 277 (1925). (81) G. Felton, F. F. Farley and R. M. Hixon, Cereal Chem., 16, 678 (1938); F. F. Farley and R. M. Hixon, I d . Ens. Chem., 34, 677 (1942);C. Dumazert and H. Lehr, Trav. membres. soc. chim. biol., 23, 1284 (1941), B i d . Abatrmts, 21, 2373 (24202)(1947). (82)J. C. Sowden, J . Ana. Chem. Soc., 74,4377 (1952). (83) K.Iwadare, BUZZ. Chem. SOC.Japan, 16, 40 (1941).
CHEMICAL SYNTHESIS O F D-GLUCURONIC
ACID
249
hydrolysis of the cyanohydrin (XVII) gave sodium 1,2-isopropylidene-~glucofuranuronate (XVIII). Ion exchange of this salt to remove sodium ions produced the free acid, which was lactonized to 1,2-isopropylidene-~glucofuranurono-y-lactone (XIX). Isolation of XIX in high yield indi-
HCOH I
CHO
I
k*N
~H,OH
xv
XVI
XVII
I
1 y\
H c o l/CH3 I
HO~H
I
HCO-O&H
HCO
I HCO.
HLOH
H~OH
I
C*OONa XVIII
I
I
-c*o
XIX
CHs
I--*
HC HboH
I -c*o xx
cated that only a minor quantity of the diastereoisomeric nitrile was formed during the cyanohydrin reaction. Hydrolysis and lactonization of X I X gave, quantitatively, ~-glucuronolactone-6-C'4 ( x x ) .