The acid hydrolysis of glycosides X. Hydrolysis of 2-O-(4-O-methyl-α-D -glucopyranosyluronic acid)-D -xylose and related disaccharides

488

CARBOHYDRATE RESEARCH

Notes The acid hydrolysis

of glycosides X. Hydrolysis of Z-O-(4-O-methyl-a-D-glucopyranosyluronic xylose and related disaccharides

acid)-D-

The great resistance to hydrolysis of the 4-O-methyl-p_glucuronic acid residues in (4-O-methylgiucurono)xylans is well known. It has been found that, under conditions of hydrolysis that cause cleavage of all xylopyranosidic bonds, two-thirds of the 4- O-methyl-D-glucopyranuronide linkages remain intactil’. Several investigators have tried to determine the rate of hydrolysis of the acid side-chains in various xylans 3*4, but the rest& do not agree, even after application of correction factors5. Whistler and Richards3 found that 2-0-(4-O-methyl-a-D-glucopyranosyl)-D-xylitol is hydrolyzed at the same rate as maltose, and 18 to I9 times as fast as 2-0-(4-Umethyl-a-D-glucopyranosyluronic acid)-D-xylose. The rate coefficients, however, decreased notably during the course of the hydrolysis. It was the object of the present investigation to adduce more-exact information on this point. RESULTS AND DISCUSSION

2-0-(4-O-Methyl-a-D-glucopyranosyluronic acid)-D-xylose (1) was obtained by partial, acid hydrolysis of an aspen (4-U-methylglucurono)xylan, as described previouslyg. Reduction of peracetylated 1 with diborane afforded6 2-0-(4O-methyl-a-Dglucopyranosyl)-D-xylose (2). When treated with borohydride, compound 1 gave 2-0-(4-O-methyl-a-D-glucopyranosyluronic acid)-D-xylitol (3). Kinetic data for the three disaccharides were determined as described earlier’ -g_ The results are presented in Table I, together with values for maltose’ and for 2-0(/I-D-glucopyranosyluronic acid)-D-glucose* TABLE KINETIC

(4).

I DATA

FOR

THE

HYDROLYSIS

OF DISACCHARIDES

Compound

k x 106, se& 60”

70”

80”

E.

Asx

kd.

at 60” Cal. deg.-l mole&

nwfe-1

2-0-(4-0-Methyl-a-D-glucopyranosyluronic acid)D-xylose (1) 2-0-(4-O-Methyl-a-D-glucopyranosyl)-D-xylose (2) 2-0-(4-0-Methyl-a-D-glucopyrnosyluronic acid)D-ZCylitOl (3) Xylobiose7 Maltose7 2-O-@-D-Giucopyranosyturonic acid)-D-glucose* (4) Carbohyd. Res., 6 (1968) 488-490

0,062

0.275

1.22

32.4

+ 4.6

3.62

14.1

59.5

33.0

+ 14.0

19.0 5.56 0.12

69.8 23.6 0.52

6.95 274 91.0 1.98

32.7 32.7 32.2

+16.5 + 14.0 f 5.1

489

NOTES

Despite its a--p_glycosidic bond, compound 1 is hydrolyzed half as fast as 4, possibly owing to its C-4 methoxyl group. The pronounced influence of the carboxyl group on the rate of hydrolysis is shown by the fact that compound 2 is hydrolyzed 60 times as fast as 1.The largest ratio so far reported between the rates of hydrolysis of an aldobiouronic acid and the corresponding, neutral disaccharide is” 37, recorded for cellobiouronic acid and cellobiose”. Maltose is hydrolyzed 90 times as fast as 1. The factor of 19 previously reported3 is probably incorrect. Compound 3 is hydrolyzed almost 6 times as fast as 1,presumably because of the greater mobility of the acyclic xylitol end-group present in 3. Both isomaltose’2 and maltose13, on the other hand, have been reported to be hydrolyzed at a somewhat lower rate than isomaltitol and maltitol, respectively. Obviously, care has to be exercised when comparison is made between rates of hydrolysis of aldose residues and those of alditol residues, a fact not always realized by previous investigators3. Xylobiose is hydrolyzed 250 to 300 times as fast as compound 1.Even when allowance is made for the fact that the two linkages on either side of the branch point are somewhat more stableg, the overall difference in rate of hydrolysis of the glucuronide and the xyloside linkages in (4-O-methylgh.~curono)xylans is very large, thus confirming previous, qualitative observations1*2. EXPERIhfENTAL

General experimental conditions were the same as in previous investigations’-‘. Preparation and characterization sf disaccharides. - Compound 1 had [u)h5 +110.6” (c 2, water) and gave D-xylose and 4-U-methyl-D-glucuronic acid on hydrolysis. The latter had [01]g +45” (c 2, water); the derived amide14 had m.p. 231-232” and [c&’ + 135” (c 2, water). Compound I was reduced to 2 as described previously6. For preparation of 3, compound 1 (380 mg) was reduced in the usual way with potassium borohydride (800 mg), giving a product which was purified by preparative, paper chromatography to give 3 (205 mg, 54%), [a]“,” + 82.9” (c 2, water). Anal. Calc. for C12HZ201,: OCH,, 9.10. Found: OCH,, 10.0. ACKNOWLEDGMENT

This investigation was supported by National Science Foundation Research Grant GB-1081 and by U. S. Public Health Service Research Grant No. ROl AM07193, which are hereby gratefully acknowledged. Cellulose Research Institute and Department of Forest Chemistry, State Uhir;ersiiy College oj’ Forestry, Syracuse, X. Y. 13210 (U. S. A.)

NIKMOLENDU

ROY*

T. E. TIMELL

*Present address: National Institutes of Health, Bethesda, Maryland 20014, U.S.A. C’arbohyd. Res., 6 (1968) 488490

NOTES

490 REFERENCES 1 2 3 4 5

6 7 8 9 10 II 12 13 14

H. M. R. A. A.

AND K. C. B. WILKIE, Ho/=forschung, 13 (1959) 177. ZINBO AND T. E. TIMELL, Svensk Papperstid., 68 (1965) 647. . L. WHI~R AND G. N. RICAARDS, J. Amer. Chem. Sot., 80 (1958) 4888. ROUDIER AND H. GILLFT,Assoc. Tech. Ind. PapetiPre Ball., 17 (1963) 145. MELLER, J. Polym. Sci., Part A-I, 5 (1967) i443. N. ROY AND T. E. TIMELL, Carbobyd. Res., 3 (1966) 246. T. E. TIMELL, Can. J. Gem., 42 (1964) 1456. N. ROY AND T. E. TIMELL, Carbohyd. Res. 6 (1968) 475. N-. ROY AND T. E. TIhlELL, Carbohyd. Res. 6 (1968) 482. K. K. DE AND T. E. TIMELL, Carbohyd. Res., 4 (1967) 177. I. JOHANSSON, B. LINNDBERG, AND 0. THEANDER, Acta Chem. Saud., 17 (1963) 20 19. R. W. Jo=, R. J. DIMLER, AND C. E. RIST,J. Amer. Chem. Sot., 77 (1955) 1659. J. N. BEMILLER AND R. K. MANN, Carbohyd. Res., 2 (1966) 70. F. Smm, J. Chem. Sot., (1951) 2646.

M&R

(Received January 13th, 1968) Carbohyd. Res., 6 (1968) 48-90