Total synthesis of stevioside

TrtrdrrJtrw

t

Vol.

36,

pp.2Ml

to2648

Pcrgamon Press Ltd.. 1980. Pnntcd in Great Bntain

TOTAL SYNTHESIS OF STEVIOSIDE”*b TOMOYA OGAWA,*

MKHIO NOZAKI

and MASANAO MATSUI

The Inslitute of Physicaland Chemical Research, Wako-shi, Saitama, 351, Japan (Receiwd in Japan 28 January 1980)

Abstract-Steviol glycosidation.

2 was transformed

into stevioside I by applying the stereoselective methods of

Transformation

of steviol into steviolbiosidv

The eficieny and the stereochemical outcome of the

Chemical

degradation

of stevbside

into steviol

glycosidation at the teriary OH group was studied by using 3,4,6-tri-0-aoetyl-2-0-(2,3,4,6-tetra-0_~glucopyranosyl)-rx-D-glucopyran~yl bromide 7.’ ’ As a modeI alcohol, l-methyl cyclohexanol 8 was chosen. The glycosiclation of8 with 7 was studied in the presence of silver carbonate- celite,‘. I2 silver silver Willate - collidine13 or triflate-tetramethylurea.14 Deacetylation of each products afforded a-sophoroside 9, [r 1:’ + 36.7” (c = 0.48, MeOH ), in 18, 90 and 94 I’<, yield respectively. a-Stereochemistry of glycosidation was assigned by ‘H and 13C NMR data of 9. Thus, ‘H NMR in D 0 showed C, ,-H at 6 5.42 as a doublet, J = 3 Hz and 13C NMR showed C 1sat 6 94.2 ppm with ‘Ja = 168.4 Hz in good agreement with the empirical rule of Bock and Pedersen. I5 In these model experiments, /Gsomer of 9 could not be isolated from the mixture. However, the reaction of steviol methyl ester 6 and glycosyl bromide 7 in the presence of silver triflate and 2,4,6_collidine, deacetylation by sodium methoxide in methanol, and subsequent chromatography on the mlumn of silica gel afforded two isomers. The firstly eluted compound 10, R, 0.68 (chloroform: methanol: water = 30:20: 2), [Z 1:’ - 33.3” (c = 0.74, dioxane) was isolated in 3.1 I’,,yield. Secondly eluted compound 11, R, 0.64 (chloroform:methanol:water 30:20:2), [a:? + 31.2” (c = 0.73, dioxane) was obtained in 86”,, yield. The stereochemistry of the former and the latter compound was assigned as’/? and z respectively according to the ’ 3C NMR dataI [IO: 97.3 ppm, ‘J,” = 158 Hz for C,#. and 105.9 ppm, ‘J,, = 158 Hz for C,..; 11: 94.4 ppm, l.icH = 168Hz for C,. and 106.1ppm. ‘_I,” = 158Hz for C, ‘I;. Since the predominant formation of r-glycoside was observed in the above approach, a stepwise approach for the stereocon t rolled transformation of steviol methyl ester into steviolbioside methyl ester 10 was then studied. Orthoester method’ 6 was chosen for this purpose for two reasons. First, stereochemical outcome of glycosidation is established as 1,2-trans.’6 Secondly, the use of orthoester derivatives such as 12 is quite suitable for further glycosidation at C+H group of the product such as 14, having all other OH groups protected as benzyl ether. Glycosidation of 6 with 3.4.6-tri-o-benzyl- 1,2-O-( Imethoxy-ethylidene)-r-D-glucopyranoside 1217 in the presence of mercuric bromide “-I 8 at 90” during 5hr afforded 13. Saponification of 13 into I4 and 2641

TET

Vol . 36 Na.

113H

Total syntksis

P”

OR

of steviosicWb

&

!

‘OR

R

2643

=R’+‘=H

g

Ii =R'= H,

E

R=Bn

R@=Ac F?=Me

&

f?=: 6n

R’= H

z

R = d= &I

I$; Me

R’LMe

R-r &

25

R = R’= AC R”= H

g

R = R’= AC R”= SnE&

T. OGAWA et al.

Total synthesis of stevioside”*b

OAc

Scheme 1

24

stevioside but paves a way to prepare unnatural derivatives of stevioside, which shoulg be of interest from the view point of sweetness. For example, galactosyl derivative 30 of 1 could readily be synthesized by using 2,3,4,6-tetra-o-acetylz+galactopyranosyI bromide instead of 20 at the last step. In conclusion, the transformation of steviol into stevioside was executed in a stereocontrolled manner, which constitute the first total synthesis of stevioside in a formal sense.

EXPERIMENTAL

M.ps were determined with a Yanagimoto micro melting point apparatus and were uncorrected. Optical rotations

23

were determined with a Perkin-Elmer Model 141 polarimeter for solns in CHCl,, unless otherwise noted. IR spectra were recorded with an EPI-GZ Hitachi spectrophotometer, as KBr discs for the crystalline samples and as neat films for the liquid samples. ‘H NMR spectra were recorded with a Varian HA-100 NMR spectrometre, using TMS as the internal standard 23C NMR spectra were recorded with a JNM-FX100 FT NMR spectrometer operated at 25.05 MNr The values of 6, and S, are expressed in ppm downward from the internal standard. Column chromatography was performed on columns of Silica Gel Merck (7&230 mesh: E Merck, Darmstadt, Germany), Thin layer chromatography was perConned on precoated plates (layer thickness, 0.25mm: E. Merck, Darmstadt. Germany) of Silica Gel 60 F,,,. Steviol 2 (a) Stevioside (1,l g) and NaIO, (1.5 g)in H,O (75 ml) was stirred at room tcmp for 16 hr. Then KOH (7.5 g) was added

T,OGAWA et al.

2646

h

h

0

m

w

7 Y

d i

Y

A

x

U

x

TomJ synthesis of stcviosid@+b

and the mixture was refluxed for 1 hr. After cooling to room temp, the mixture was carefully acidified with A&H and extracted with ether, Organic layer was washed with water, dried (Magi) and ~n~t~~ in tt~cuo to give astir residue (300 mg, 75 %& Recrystallization (MeUH) gave 2 mp. 246”. The IR and NMR spectra were identical with those of the auth~tic sample.’ (h) Steviolbiosidc 5 (1OOmg)and IWO, (1Omg) in H,O (10x@ was stirred at room temp. for 16 hr. Then CaCO, ~~~rng~ was added and the rn~t~e was stirred at room temp. for 24hr. The mixture was acidified with A&H at 0” and extracted with ether. Organic layer was washed with water, dried ~Mg~~~~ and narrated in 111117~~ to give crystake residue (28mg, 56%). [g]r - 61.4” (c = 0.51). (Found: C, 71.81; H, 9.63. C,,H,,O,.CHSOH requires: C, 71.96; H, 9.78”$) 1-iWerhyicyclohexy1 pyranoside

2-O-~-D-glucopyran~syl-u~~-~i~c~-

9

(a) CH,ClCH,Cl (~rnl) containing 8 (114mg, l.OmM) and Fetiuln reagent “(3g) was distilled to the volume of 30 ml. To this mixture was added a so,in of 7 ( 1.4g, 20 mM) in CH,ClCH,Cl (10 ml) dropwise and the mixture stirred under reflux for 15min. After cooling to room temp. inorganic substance was filtered off. The filtrate was concr;ntrated in WGUO and ~rornat~~aph~ on silica gel (150 g). Elution with toluene-EtOAc (3:2) afforded an oil (130mg) which wa treated with 0.1 N NaOMe in MeOH (lOm1) at room temp overnight MeOH was evaporated and the residue was chromatographed on silica gel (log). Elution with CHCl,-MeOH-H,O (45:12:2) tiorded 9 flOOmg, 18% based on l~methyl~clohexanol). ~b)Toamixtureof8(456mg,4mM),silvertriflate(113mg, 0.51 mM) and 2,4,tkollidine (0.06m1, OS4mM) in ~H~~~~H~~l (Zml) was added dropwise a soln of 7 (138 mg, 0.3 mM) in CH,ClCH,Cl(2 ml) at 0”. The mixture was furtherstirred at 0” for 1 hr. Then themixture*wasdirectty appl~d to the cofumn of silica gel @Og). Elution with toluene-EtOAc (3: 2) afforded a crudeoil (130 mg) which was deacetylated and chromatographed on silica gel (10 g). Elution with CH~I~-M~H-~~~ i(45:12:2) afforded 9 (79 mg, 90‘%;). (~)Toamixtureof8(456mg,4mM),sikrtrifIate(ll3mg, 0.51 rnM~ and tetr~ethyl~a ~0.~7rn~ 0.59mM) in CH ,ClCH,Cl(2 ml) was added dropwise a soln of 7 (138 mg, 0.2 mM) in CHICICH,Cl (2 ml) at 0”. The mixture was further stirred at 0” for 1 hr and processed as described in (b) to give 9 (82mg, 94%). [a]? + 36.7” (c = 0.48, MeOH); Lj,,, (D@), 5.42 (1 H, d, J = 3 Hz), 4.02-3.02 (12H), 1.86-1.20 (10HX 1.22 13H, s): 6, (CD,OD), 94.2 (C,<, ‘J, = 168.4Hz), 106.0 (C,.., ‘3, = 16O.OHz). 82.5 (C& (Found: C, 52.26: H, 7.71. C,,H& I requires:C, 5205: H, 7.82?$)

To a mixture of 6 (628mg, 1.9mM), silver triflate (214g, 9.7mM), and ~4,~~~~idi~ (1.3 ml, 9.9 mM) in CH,Cl, (7 ml) was added dropwise a soln of 7 (258g, 3.8 mM) in CH,Cl, (7 ml) at 0” under Ar. The mixture was further stirred at 0” for 1.5 hr and then astern The ~l~ate was narrate and chromatographed on silica gel (4OOg). Elution with toluene-EtOAc (3: 1) gave an oil (1.6g), which was treated with O.Of“/oNaOMe in MeUH ~2~rnl) at rmrn temp for 3 hr. The mixture was evaporated and chromatographed on silica gel (100 g). Elution with CHCl> -MeOH-)I,0 (45: 12:2) afforded 10 (38 mg, 3.1%), and 11 (1.072 g 86%). IO: R, 0.68 in CHCl,-MeOH-H,O (3(X20:2) [?T]: - 33.3” (c = 474, dioxsne). 6, (pyridine-d, at 6O*),97.3 (C,., ‘JR = 158.0Hz), 105.9 (C,.., IJ, = 158,0Hz), 83.9 (C,.). C NMR was identical with that ofthe authenticsample prepared from S by successive treatment with (i) Ac,O-pyridine, (ii) CH,N, in ether, and (iii) NaOMe in MeC?H. t 1: R, 0.64.[a]: + 31.2

2647

(c = 0.73, dioxane). S, (py~~n~d~ at 60”), 94.4 (C t ‘, *J, = ltXOHr), 106.1 (C,.+, 15&0Hz), 82.1 (C,.), 85.9 (C,,). (Found: C, 53.85; H, 7.43. C3,H,,0,,.2H,0 requires: C, 54.28; H, 7.43~~

Estc~ 6 (9%mg, 3mMX, 12 (7,Og, 14mM) and HgBr, (9oomg, 25mM) was stirred at 95” for 5 hr under vacuum (5 rn~g~. After cooling to room temp, the mature was chromatographed on a silica $tl (8oog). Elution with tolucne-EtOAc (20: 1) gave 13. [OL ]E - 7.46” (c = 0.67), R, 0~59 in toluc~-~t~Ac (9: 1) S, KDCI,), 2.00 13H, s), Treatment of t3 with 0.01% NaOMc in MeOH (1Sml) at room temp for 3 hr and s&sequent chromatography on silica crude 14 (24g); gel [3oOg, tol~ne-~t~Ae = 12: 1) gored R, 0.35 in tolueoe-EtOAc (9: 1). To a mixture of the crude 14 (232 g), silver triflate (3.40 g) and 2,4,6_coHidine (1.68 ml) in CH,Clt (22 ml) was added dropwise at 0” a soln of #) (5.5 g) in CH,Cl, (3Omf). The mixture was further stirred at 0” for 5 hr and filtered The filtrate was washed with water, dried over MgSO,, concentrated, and eht~mato~phed on silica gel (500g,toluene-EtOAc = 9:l)toaRordanoii(15,840m& 29% from 6). [at]25 - 19.6” (c = 0.81). 6, (CDCI,) 7.38-7.23 (lSH),5.33-3.33q25H), 233-0_67 (38 H), 3.60 (3H, s), 202 (~2H,bs),l.18(3H,s~0.88(3H,s).fFound:C,67.85:H,6.97. &H,*O,, requires: C, 67.88; H, 7.17%.)

Compound 15 ~l~rn~ 0.09 mM) was treated with 0.01% NaOMe in M&H (1Oml) at room temp for 3 hr. MeOH was evaporated in wcuo, To the residue in DMF (5 ml) was added NaH (42 mg, 60%) at room tcmp and the mixture was stirred for 3Omin. To the mixture was added dropwise benzyl bromide (175 mg) in DMF (Zml) at 0” and the mixture was stirred at room temp for 3 hr. MeOH (1 ml) was added and the soln was concentrated in uacw. The residue was dissolved in ether and ether layer was washed with water, dried (MgSO,), evaporated, and chromatographed on silica gel (log, toluen~-~t~Ac = 20: 1) to aRord an oil (17, 91 mg, f;%r [al:: - 4.3” (c = 0.46). S, (CIXl, at 60”). 961 (C,,, = 158 Hz), 1023 (C,.., ‘J, = 158 Hz), 86.7 (C,,j. (Funds C, 74.62; H, 7.18. C,,H,,0,3 requires: C, 74.85; H, 7.360/,) ~fev~~~~si~ 5. To a soln of 17 (248 mg) in TH F (5 ml) and liq. NH3 (10ml) was added Na metal (5Omg) piece by piece. The mixture was stirred at - 30” for 3 hr. MeOH was added to the mixture and the solvent was maporated The residue was chromatographed on silica gel (10 g). Elution with CHCl,-MeOH-H,O (45: 12:2) afforded 5 (55mg, 45%) [al:: - 32.7” (c = 0.46, MeUH). (Found: C, 58.07: H, 7.64. C,2H,oO,,.H,Ortquires:C,58.l7;H,7.93%r6,(pyridined, at 60”): 106.1 (C,,., lJcx = 158Hz), 97.6 (C,., ‘J, = 156 Hz), 86.2 CC,,), 84.1 (C,.). The general procedure for the synthesis of 2,3,4,6-tetra-Oucetvl-8-D-ltfuco~,~~syE esters qkifmxyiic acids, Z&-2&. ~is~&~-n-butyltin~ oxide (29.8 R,0.05 M) and carboxylic acid (0.1 M) in benzene (lOOmI) was refluxed for 15hr with continuous -tropic removal of water. Evaporation of benzene gave t~butyltin ester of carboxylic acid which is enough pure for the next step. 23,4,6_TetraGacetyl+B glucopyranosyl bromide (822 mg, 2 mM) and tributyltin ester of =boxylic acid (2mM) in CH2CXH,Cl (l~ml) was stirred at 80” in the presence of tetrabutylammonium bromide (322mg,, 1 mM). The mixture was evaporated in BXW. The rkduc was chromato~aph~ on silica gel (100 g) to give the product (Table 1). StevkWde 1 and its QBUW 29. Compound 25 (25g, 28 mM), bis~~buty~tin~xide (850 mg, 1.4 mM) in toluene (#ml) was r&luxed for 15 hr with continuous azottopic removal of water. Toluene was evaporated to afford t~bu~ltin ester of 26, v,, 2920,1740,1640 cm - ! Com~und

26 (l&g, 1.2mM), 20 (SlOmg, 1.2mM), and tetrabutylammonium bromide (289 mg, 0.9 mM) in tolucnr (20 ml) was refluxed for 65 hr. The soln was evaporated in uamo. The residue was chromatographed on a column of silica gel (2OOg).Elution with toluene-EtOAc (3: 1) gave a mixture of 27 and 28. This mixture was stirred in 0.1 N NaOMe in MeOH (15 ml) at rmrn temp for 3 hr and the solvent was evaporated in vucuo. The residue was chromatographed on silica gel (1oOg). Elution with CHCl,-MeOH-H,O (45:12:2) afi’orded 1 (610mg, 61%) and its a-anomer 29 [23Omg, 23%). 1: R, 0.43 in CHCI,! MeOH: H,O = 30:20:4. [a 1;’ - 30.9” (c = 0.56, pyndine). Y,, 3390, 2930. 1730, 108Ocm’ ‘. S, (pyridined, at 60”): 95.6 (C,,.., 0.35 in IJ,, = 163.2 Hz), 176.7 (C,,). 29: R CHCI,:MeOH:H,O = 30:20:4. [ol]:’ + 7.6” (c = 0.61, pyridine). v, 3390,2930,1730,1080cm- ‘. 6, (pyridinsd, at 60”) 93.2 (C,.,,, ‘J, = 172.1Hz), 176.5 (C,,). (Found: C, 53.85; H, 7.48. C,,H,,O,,.ZH,O requires: C, 54.28; H, 7.43:/;. ) 13-o- [2-0-(~-GItrcop~rano.s~~I-fl-D-~I~cop)lransyI]steuiol-~-D-galoctopyranosyl ester 30. A soln of 26 (897 mg, 0.76 mM ), acetobromogalactose (698 mg, 1.7 mM), and tetrabutylammonium bromide (250 mg, 0.77 mM) in toluene (IOml) was refluxed for 70 hr. Toluene was evaporated in vacua. The residue was chromatographed on silica gel (200 8). Elution with toluene-EtOAc (1: 1) afforded a crude oil (958 mg), which was treated with 0.1 N NaOMe in MeOH (10 ml) at room temp for 3 hr. MeOH was evaporated and the residue was chromatographed on silica gel (5Og). Elution with CHCI,--MeOH-H,O = 45:12:2 afforded 30 (224mg 36?/;). [a)i5 - 16.6” (c = 0.58, MeOH). S, (pyridined, at 60”): 96.1 (C,..,, ‘J,, = 16OHz), 176.8 (C,,). (Found: C, 54.43: H, 7.29. C3gH6001s.2H20 requires: C, 54.28; H, 7.43(:/k) Acknowledgements -We thank Dr. H, Homma and his staff for the elemental analyses, and Dr. J. Uzawa and Mrs T. Chijimatsu for recording and measuring the NMR spectra. Generous gifts of stevioside by Takasago Perfumery Co., Ltd., and by Tama Biochmical Co., Ltd., are greatly appreciated We also thank ProE K. Mori, University of Tokyo, for his discussion and encouragement.

REFERENCES

Bride1 and R. Labieille, Bull. Sot. Chim Biol. 13, 636 (1931): J. Pharm Chim. 14,99. 154 (1931). ‘F. Dolder, H. Lichti, E. Mosettig and P. Quitt, J. Am Chem Sot. 82 246 (1960): E. Mosettig,, P. Quitt, U. Beglinger, J. A. Waters, H. Vorbriigtgwen and C. Djerassi, Ibid. 83, 3163 (1961); C. Djerassi, P. Quitt, E Mosettig, R. C. Cambie, P. S. Rutledge and L. U. Briggs, Ibid 83, 3720 (1961): E. Mosettig, H. Beglinger, F. Dolder, H. Lichti, P. Quitt and J. A. Waters, Ibid. 85, 2305 (1963). 3H B. Wood, Jr., R. Allerton, H. W. Diehl and H. G. Fletcher Jr:, 1. Org. Chent. 20,875 (1955); H. B. Wood Jr. and H. G. Fletcher Jr., J. Am Chem Sot. 78,207 (1956); E. Vis and H. G. Fletcher Jr., Itrid 78, 4709 (1956). 4K, Yamasaki, H. Kohda, T. Kobayashi, R, Kasai and 0. Tanaka, Tetrahedron Lett. 1005 (1976).

‘M

‘IL Mori, Y. Nakahara and M. Mat& Ibid 2411 (1970); Tetrahedron 2%’3217 (1972) 28. 61. F. Cook and J. R. Knox, Tetrahedron ktt. 4091(1970): Y. Nakahara, M. Mori and M. Matsui, Agr. Bill Chem 35, 9 18 (1971);F. E. Ziegler and T. A. Klock, Tetrahedron 33, 375 (1977). ‘E. Mosettig and W. R. Nes, J. Org. Chem. 20,884 (1955); R, D. Bennett, E. R. Lieber and H. Heftmann, Phytochem 6, 1107 (1967); 1. Yosioka, S. Saijoh, J. A. Waters and 1. Kitagawa, Chem Pham Bull. a,2500 (1972); H. Kohda and 0. Tanaka, Yukugukuzasshi 95,246 (1975). ‘T Takamoto and S. Hanessian, Tetrahedron Lett. 4009 (39741 9G. Sneider. 0. Mirsch and H. W. Liebish, Ibid., 405 (1977): G. Sneider, ci. Sembdner and K. Schreiber, Tetrahedron 33,

1391 (1977). ‘OP.J. Keay, J. S. Moffatt and T. P. C. Mulholland, J. Chem Sot. 1605 (1965); K. Schreiber, J. Wieland and G. Sembdner, Tetrahedron 2.5, 5541 (1969); K Hiraga, H. Yamane and N. Takahashi, Phytochem 13, 2371 (1974). *lB. Coxon and H. G. Fletcher, Jr., J. Org. Chm 26, 2892 (1961). ’ 2M. Fetizon and M. Golfier, C. R ‘Acud Sci, Paris 267,900 (1968). 13R U. Lemieux, T. Takeda and B. Y. Chung, Synthetic Methodsfor Carbohydrates, ACS Smp. Series3!3,91 (1976). ’ 4S. Hanessian and J. Banoub, Catbohydr. R&s. 53, Cl 3 (1977). ’ 5K. Buck, I. Lundt and C. Pedersen, Tetrahedron Lett. 1037 (1973); K Bock and C. Pedersen, J. Chem Sot. Perkin Trans. 2, 293 (1974): Acta Chem Stand Ser. B 29, 258 (1975). ‘6N. K. Kochetkov, A. Ya Khorlin and A. F. Bochkov, Tetrahedron 23, 693 (1967): S. E. Zurabyan, M. M. Tikhomirov, V. A. Nesmeyanov and A. Ya Khorlin. Carbohydt. Res. 26, 117 (1973); A. F. Bochkov and Y. V.

Voznyi, Ibid. 32, 1 (1974).

1‘H. B. Boren, G. Ekborg, K_ Eklind, P. J. Garregg, A. Pilotti and C. G. Swahn, Acta Chem Stand Ser. B 27,2639 (1973); N. K. Kochetkov, B. A. Dmetriev, N. N. Malysheva, A. Ya Chernyak, E. M. Klimov, N. E. Bairamova and V. I. Torgov, Carbohydr. Res. 45, 283 (1975). “T. Ogawa, K. Katano and M. Matsui, Ibid. 70, 37 (1979). ‘9R. Bugianesi and T. Y. Shen, Ibid 19, 179 (1971); A. Komhauser and D. Keglevib, Ibid. 11, 407 ( 1969): C. Pedersen and H. G. Fletcher, Jr., J. Am Chem Sot. 82,3215 (1960); H. G. Fletcher, Jr., Methods Carbohydr. Chem 2, 23 l(1963); N. K. Kochetkov, E. M. Klimov, S. A. Pogosjan and V. A Derevitskaya, Izu. Akud. Nauk SSSR Ser. Khim 1657 (1972); D. Keglevi& 5. ValetekoviC, G. RogliC, D. Gold and F. Plaitsi Carbohydr. Rex 29, 25 (1973): P. E Pfeffer, G. G. Moore, P. D. HoagIand and E. S. Rothman, Synthetic Methods for Carbohydrates, ACS Symp. Ser. 3% 155 (19761.

2*Preliminary communication. T. Ogawa, M. Nozaki and M. Matsui, Carbohydr. Res. 60, C7 ( 1978). 2iR. H. Lemicux and J. Hayarni, Can. J. Chem. 43, 2162 (1965); IT.Ishikawa and H. G. Fletcher, Jr., J. Org. Chem. 34,563 (1969): R. U. L-emieux, K. B. Hendriks, .R. V. Stick and K. James, J. Am. Chem Sot. 97,456 (1975). 22G, Wulff, H. Schroder and W. Schmidt, Ang. Chem Int. Ed. Engl. 18, 309 (1979).