The hex-5-enose degradation: zinc dust cleavage of 6-deoxy-6-iodo-a-D-galactopyranosidic linkages in methylated di- and trisaccharidesl

GERALD OLIVER ASPINALL,' DELPHI CHATTERJEE, A N D LEV KHONDO Department of Chernistry. York Universify, Downsview, Toronto, Ont., Canada M3J IP3

Received April 23, 1984

GERALD OLIVER ASPINALL, DELPHI CHATTERJEE, and LEV KHONDO. Can. J . Chem. 62, 2728 (1984). The Bernet-Vasella reaction of 6-deoxy-6-halohexopyranosides with zinc dust to give hex-5-enoses has been explored as

the basis for a new procedure for the selective cleavage of glycosidic linkages in complex oligo- and polysaccharides. The overall reaction sequence involves: (a) the generation of primary hydroxyl groups in otherwise fully methylated oligo- or polysaccharides; (b) the formation of 6-deoxy-6-iodohexopyranosides by iodide displacement of reactive sulfonate esters; and (c) treatment with zinc dust followed by the formation of suitable derivatives from the liberated hex-5-enoses. Oligosaccharides carrying P-D-xylopyranosyl substituents at the 2-0- (4), 3-0- (17), 4-0- (12), and both 3-0- and 4-0- (8) positions have been converted into otherwise fully methylated derivatives, each containing methyl 6-deoxy-6-iodo-a-D-galactopyranoside residues, to serve as model substrates for different structural environments. In each case the derived 5,6-dideoxy-hex-5-enoses formed on treatment with zinc dust have been characterized by conversion into the corresponding 1,2-dideoxy-hex-I-enitol acetates. During preparations of 6-deoxy-6-iodo-a-D-galactopyranosides from the corresponding 6-sulfonate esters, solvolytic side reactions have been observed which may include the formation of 3,6-anhydro-a-D-galactopyranosides with intramolecular participation of 3-0-methyl or 3-0-glycosyl substituents and subsequent loss of such substituents.

GERALD OLIVER ASPINALL, DELPHI CHATTERJEE et LEV KHONDO. Can. J. Chem. 62, 2728 (1984). On a examine la possibilitC d'utiliser la rkaction de Bernet-Vasella, qui permet de transformer des dCsoxy-6 halogCno-6

hexopyrannosides en hexkne-5 oses par action de la poudre de zinc, comme base d'une nouvelle mCthode pour cliver d'une faqon selective les liaisons glycosidiques d'oligo- et de polysaccharides complexes. Dans ['ensemble, la sCrie de rtactions implique: (a) qu'il faut gCnCrer des groupes hydroxyles primaires dans des oligo- et des polysaccharides qui sont par ailleurs complktement mCthylCs; (b) la formation de dCsoxy-6 iodo-6 hexopyrannosides grice a un dkplacement de sulfonates rtactifs par de I'iode et (c) un traitement par de la poudre de zinc qui est suivi par la formation de dCrivCs appropriCs des hexkne-5 oses libkres. On a pu transformer les oligosaccharides portant des substituants P-D-xylopyrannosyles en positions 2-0- (4), 3-0- (17), 4-0- (12) et 3-0- ainsi que 4-0- (8) en dCrivCs qui sont par ailleurs complktement mCthylks, qui contiennent chacun des rksidus dCsoxy-6 iodo-6 a-D-galactopyrannosides de mCthyle et qui peuvent servir de substrats modkles pour diffkrents environnements structuraux. Dans chaque cas, on a caractkrisC les didksoxy-5,6 hexkne-5 oses qui se forment par traitement avec de la poudre de zinc en les transformant en acetates des didksoxy- 1,2 hexkne- l itols correspondants. Lors de la prkparation des dksoxy-6 iodo-6 a-D-galactopyrannosides a partir des sulfonates-6 correspondants, on a observk des rkactions de solvolyses secondaires qui peuvent conduire a la formation des anhydro-3.6 a-D-galactopyrannosides par le biais d'une participation intramolkculaire des substituants 3-0-mtthyles ou 3-0-glycosyles et d'une perte subskquente de ces substituants.

[Traduit par le journal]

Bernet and Vasella (1) have shown that 6-deoxy-6-halo- glycosides react with zinc dust under mild conditions with glycoside cleavage and formation of hex-5-enoses. In order to

---0 F4 R-x., ---0 assess this reaction for the selective cleavage of glycosidic linkages in polysaccharide derivatives we have examined reac- tions of selected oligosaccharides. Methylated oligosaccharide glycosides, each of which contained a single primary hydroxyl group, were synthesized in standard reaction sequences. The reactions shown in Scheme 1 were studied, ( i ) the formation of - - - o y , ( I , , ) , x , 6-deoxy-6-iodohexopyranosides, and (ii) the zinc dust cleav- CHO .-- o age reaction followed by derivative formation suitable for the CYOAC

characterization of hex-5-en0se residues thus generated. The SCHEME 1. Generation of hex-5-enoses and formation of derivatives: oligosaccharides were all a-D-galactopyranosides, which were (i) sulfonylation, followed by displacement of sulfonate ester with chosen as models for different structural regions in carboxyl- Bu,N' I-; (ii) Zn dust; and (iii) NaBH4, followed by AczO/Pyr reduced methylated pectins and related a-D-galacturonans. (unchanged substituents are omitted). Since nucleophilic displacements at C-6 occur least readily in galactopyranosides'(2), it is likely that transformations which appeared the greatest chance for the intrO- proceed satisfactorily for these glycosides will take place with- duction of 6-halo substituents into sterically hindered galac- out difficulty for the corresponding gluco- and mannopyrano- topyranose residues in even less reactive environments in poly- sides. Two recent methods for halogenation at C-6 involve the saccharides where polymer chain may formation of highly reactive sulfonates followed by halide additional restrictions. Displacement by iodide ion was chosen displacement under mild conditions (3, 4). These reactions as the reaction least likely to be accompanied by competing

elimination (3, 4). ' Presented in part at the Canadian Institute of Chemistry Con-

ference, Montreal, Quebec, June 3-6, 1984, and at the 12th Oligosaccharide sy"theses International Symposium on Carbohydrate Chemistry, Utrecht, The The most readily accessible (1 + 2)-linked disaccharide Netherlands, July 2-6, 1984. glycoside (4) was synthesized without ambiguity as to linkage

'Author to whom correspondence should be addressed. type. Condensation of 2,3,4-tri-0-acetyl-a-~-xylopyranosyl

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ASPINALL ET AL

1 R , R f = C(CH3)?, R" = Ac, X = OBn 2 R = R' = R" = H, X = OBn 3 R = R' = R = Me, X = OBn 4 R = R' = R" = Me, X = OH

18 R = R' = R" = Me, X = 0-SOz-Irnidazolyl 1 9 R = R 1 = R = M e , X = I 29 R = R' = R" = Me, X = 0-CHO

5 R = Ac, X = OBn 6 R = H , X = OBn 7 R = Me, X = OBn 8 R = Me, X = OH

20 R = Me, X = I 30 R = Me, X = 0-CHO

bromide with methyl 6-0-benzyl-3,4-0-isopropylidene-a-D- galactopyranoside (5) afforded methyl 2-0-(2,3,4-tri-0-acetyl- P-D-xylopyranosy1)-6-0-benzyl-3 ,4-0-isopropylidene-a-D-ga- lactopyranoside ( I ) , which was successively treated with trifluoroacetic acid for de-isopropylidenation and sodium methoxide for de-0-acetylation to give crystalline methyl 6 -0 - benzyl-2-O-(~-~-xylopyranosyl)-a-~-galactopyranoside (2). The disaccharide benzyl ether (2) furnished a fully methylated derivative (3) which was hydrogenolyzed to give methyl 3,4-di-0-methyl-2-0-(2,3 ,4-tri-0-methyl-P-D-xylopyranosy1)- a-D-galactopyranoside (4).

In order to have available derivatives of linkage types likely to be encountered in tragacanthic acid (6) and related galac- turonan derivatives, syntheses were extended to the isomeric (1 - 3)- and (1-4)-linked disaccharide and the (1 - 3)- and (1 - 4)- linked branched trisaccharide series using generally similar reaction sequences. In each series of reactions all crys- talline compounds including end products (8, 12, and 17) were obtained in analytically pure form. The syrupy intermediates were isolated in chromatographically homogeneous form, gave nrnr spectra in accord with the structures shown, and were used directly for the next stages of the syntheses. Methyl 6-0-benzyl-2-0-methyl-a-D-galactopyranoside (7) was a con- venient starting material for each synthetic sequence. When 2,3,4-tri-0-acetyl-a-D-xylopyranosyl bromide was condensed with this compound, regardless of the molar ratios of glycosyl halide to aglycone, two products only, although in varying proportions, were observed on tlc and these were separated by preparative chromatography. The first product was methyl

9 R = H, R' = Ac, X = OBn 10 R = R' = H, X = OBn 11 R = R ' = Me, X = OBn 12 R = R' = Me, X = OH 21 R = R ' = Me. X = I

14 R' = Ac, R = Bz, X = OBn 15 R = R' = H, X = OBn 16 R = R' = Me, X = OBn 17 R = R' = Me, X = OH 22 R = R' = Me, X = I 31 R = R' = Me, X = 0-CHO 32 R = R' = Me, X = OAc

3,4-di-0-(2,3,4-tri-O-acetyl-~-~-xylopyran0sy1)-6-0-benzy1- 2-0-methyl-a-D-galactopyranoside (5), which on deacetyla- tion, methylation, and debenzylation afforded the trisaccharide derivative, methyl 2-0-methyl-3,4-di-0-(2,3,4-tri-0-methyl- P-D-xylopyranosy1)-a-D-galactopyranoside (8). Surprisingly, the second compound from mono-0-glycosylation was shown to be methyl 4-0-(2,3,4-tri-0-acetyl-P-D-xylopyranosy1)-6-0- benzyl-2-0-methyl-a-D-galactopyranoside (9), whose struc- ture was established by methylation-deacetylation, debenzyl- ation, remethylation, and methylated sugar analysis to give inter alia 2.,3,6-tri-0-methylgalactose, identified by glc-ms of the derived partially methylated alditol acetate. In contrast to the preferential glycosylation of equatorial 3-hydroxyl over 4-axial hydroxyl groups in a-D- (8) and P-D-galactopyrano- sides (9), the present observation provides an example of the opposite selectivity. 'The methylated disaccharide derivative (12) was then prepared in the same way as for the trisaccharide derivative (8). Entry was gained to the (1 - 3)-linked disac- charide series by reaction of methyl 6-0-benzyl-2-0-methyl- a-D-galactopyranoside (7) with trimethyl orthobenzoate fol- lowed by acid-catalyzed rearrangement to give the axial 4-benzoate (13) (10). Condensation of this compound with 2,3,4-tri-0-acetyl-a-D-xylopyranosyl bromide gave methyl 3-0-(2,3,4-tri-O-acetyl-~-~-xylopyranosyl)-4-O-benzoyl-6-0-

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2730 CAN. J . CHEM.

benzyl-2-0-methyl-a-D-galactopyranoside (14). The linkage position in this disaccharide was confirmed, as for the ( I -+

4)-linked disaccharide, by methylation analysis which gave 2,4,6-tri-0-methylgalactose from the galactose moiety. The disaccharide benzoate (14) was then converted into the methyl- ated derivative (17).

Preparation of 6-cleoxy-6-iodo oligosaccharides via sulfonate esters and competing 3,6-anhydrogalactopyranoside fortrzation

The 2-linked methylated disaccharide glycoside (4) was re- acted with sodium hydride and N,N1-sulfuryldiimidazole in oxolane, as described by Hanessian and Vatkle (4), and gave the crystalline imidazolylsulfonate (imidazylate) (18) which was quite stable provided that care was taken to minimize contact with polar solvents. The imidazylate was converted smoothly into methyl 6-deoxy-6-iodo-3,4-di-0-methyl-2-0- (2,3,4-tri-O-methyl-~-~xylopyranosyl)-a-~-ga1actopyranoside (19) on heating with tetrabutylammonium iodide in benzene. Alternatively, the iodo disaccharide derivative (19) was pre- pared in comparable yield by reaction of the methylated disac- charide glycoside (4) with triflic anhydride in pyridine (3) followed by direct iodide displacement. This procedure was adopted as the method of choice and was used for the con- version of trisaccharide 8 and disaccharides 12 and 17 into the respective 6-deoxy-6-iodo derivatives 20, 21, and 22 in good yield.

When an attempt was made to prepare the iododisaccharide (19) from the imidazylate (18) by activation on nitrogen by reaction with methyl iodide in N,N1-dimethylformamide (4), a second product was formed in almost equal amount. The for- mation of this compound, methyl 3,6-anhydro-4-0-methyl-2- 0-(2,3,4-tri-O-methy~-~-~-xylopyranosyl)-a-~-ga~actopyran- oside (23), was difficult to suppress entirely in any reaction

involving formation or further reaction of either reactive sul- fonate ester unless extreme precautions were taken to exclude moisture and avoid contact with polar solvents. The compound (23) was isolated as the major product when the imidazylate (18) was allowed to solvolyze in DMF at room temperature. Fragment ions observed in the mass spectrum and 'Hmr data showed loss of sulfonate ester and of a methoxyl group consis- tent with anhydride formation. 'The Cmr data showed a down- field shift for C-6 (6, 69.69) indicative of etherification, and the alteration in the signal for the anomeric carbon (ac 97.52, J l~c l . lk r l = 161.6 Hz) was consistent with change from the 4CI to a ,C' conformation for the a-D-galactopyranoside residue. In support of these assignments methyl 3,6-anhydro-2,4-di-0- methyl-a-D-galactopyranoside (24) showed signals for C-6 at gc 69.08 and for C-l at 6, 98.63 with J I ~ ~ , . ~ ~ , , = 161.1 HZ. Compound 23 may therefore be assigned the structure, methyl 3,6-anhydro-4-O-methyI-2-0-(2,3,4-tri-O-methyl-~-~-xylo- pyranosy1)-a-D-galactopyranoside. Supporting chemical evi- dence for the formation of the 3,6-anhydro derivative was obtained by glc-ms analysis of the products of methanolysis

SCHEME 2. Formation of 3.6-anhydro-a-D-galactopyranosides during solvolysis of 6-sulfonates with intramolecular participation and sub- sequent loss of 3-0-methyl or 3-0-glycosyl (R') substituent (other substituents are not specified).

24 R = H, R' = OMe, R" = Me 25 R = R" = H , R' = OMe 26 R = H, R' = OMe, R" = Ac 27 R = OMe, R ' = H, R" = Ac

Unspecified substituents in formulae 23 and 33-36 are OMe

followed by acetylation which showed the formation inter alia of the same mixture of anomeric methyl glycoside acetates (26 and 27) and acetylated dimethyl acetal (28) that was obtained from synthetic methyl 3,6-anhydro-4-0-methyl-a-D-galacto- pyranoside (25) (1 1). The formation of 3,6-anhydro-D-galacto- pyranose derivatives by intramolecular displacement of 6-sulfonate esters with alkoxyl group participation was first shown by Brimacombe and Ching (12). Volkova et al. (13) have previously reported 3,6-anhydride formation during the reaction of benzy12,3,4-tri-O-benzyl-6-deoxy-6-tosyl-P-~-gal- actopyranoside with sodium iodide in both acetone and N, N-dimethylformamide.

Further examination of the solvolysis products from the imidazylate (18) showed the formation of a second compound (29). Although the anhydride (23) was still the major product, the second compound was formed in relatively greater yield when the triflate ester of disaccharide 4 was treated in the same way. Spectroscopic data, including the typical mass spectral fragment ions at m/z 293 and 233 for the galactosyl moiety, a characteristic one proton singlet in the 'Hmr spectrum at 6 8.15, and a carbonyl band in the ir spectrum at 1730 cm-I, coupled with characterization of otherwise unaltered sugar con- stituents on hydrolysis, showed that this second product was the disaccharide 6-formate (29). N,N-Dimethylformamide used as solvent has been observed to be the source of formylation as a side reaction in other transformations (14, 15).

In order to assess the extent to which variously substituted galactopyranoside 6-sulfonate esters were susceptible to sol- volytic side reactions, and in particular to see if 3,6-anhydride formation could occur with participation of a 3-0-glycosyl substituent and liberation of that substituent on collapse of an intermediate oxonium ion (Scheme 2), the solvolysis products

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LL ET AL. 273 1

from the triflate esters of disaccharides 12 and 17 and tri- saccharide 8 were examined. In the case of derivatives of disaccharide 12 and the branched trisaccharide 8, where par- ticipation by the 3-0-substituents might be expected to lead to the formation of the same 3,6-anhydro derivative, with libe- ration of 2,3,4-tri-0-methylxylose in the latter instance, no evidence was obtained for the formation of such a compound. The major product from the trisaccharide (8) was the corre- sponding 6-formate (30). Solvolysis of the triflate ester of disaccharide 17 also led to formation of the disaccharide 6-formate (31) as the major product. However, the occurrence of 3-0-glycosyl participation in 3,6-anhydride formation was clearly established. Direct examination of the solvolysis products by glc - mass spectrometry showed the formation of methyl 3,6-anhydro-2,4-di-0-methyl-D-galactopyranoside (24) (in 30% yield based on 1,6-anhydro-2,3,4-tri-0-methyl- P-D-galactopyranose as internal standard), together with the disaccharide 6-formate (31). When a portion of the solvolysis products was treated with sodium borohydride and then acetyl- ated, glc - mass spectrometry showed the presence of the anhydride (24), together with 2,3,4-tri-0-methylxylitol di- acetate from the liberated glycosyl substituent and a disaccha- ride derivative now converted into the 6-acetate (32).

Cleavage of 6-deoxy-6-iodo-oligosacchatkie glycosides with zinc dust and characterization of 5,6-clicleoxy-hex- 5-enoses

Each of the methylated 6-deoxy-6-iodo oligosaccharides was treated for short periods with freshly prepared activated zinc dust in boiling ethanol or 1-propanol and furnished the corre- sponding 5,6-dideoxy-hex-5-enose. In the case of the 4-linked 6-deoxy-6-iodo disaccharide glycoside (21), extended reaction time or the use of the higher-boiling solvent resulted in the liberation of 2,3,4-tri-0-methylxylose to a much greater extent than with the corresponding 2- and 3-linked disaccharide deriv- atives (19 and 22). It is possible that sufficient acidity, not otherwise detected, was generated from the basic zinc iodide formed in the reaction to cause hydrolysis of the resulting 5,6-dideoxy-hex-5-enose, proceeding by a mechanism in- volving 0-ally1 rather the normal glycosyl-oxygen cleavage during glycoside hydrolysis. Each 5,6-dideoxy-hex-5-enose- terminated oligosaccharide was conveniently characterized by reduction and acetylation to give the corresponding 1,2-dideoxy-hex- 1-enitol acetate (33-36). These derivatives in the di- and trisaccharide series were amenable to analysis by glc-ms as for the corresponding saturated oligosaccharide al- ditol derivatives (16). The accompanying structures for these derivatives show the most important fragment ions in the mass spectra, including those which clearly establish the substitution patterns of the methylated 1,2-dideoxy-hex- 1 -enitol acetate residues. In the case of the trisaccharide derivative (34) the V ion at m/z 215 pointed to the presence of vicinal glycosyl substituents (17). Additionally, the 'Hmr spectra of the oligo- saccharide derivatives showed characteristic signals for the ally1 group of 1,2-dideoxy-hex- 1 -enit01 residues. Furthermore, the oligosaccharide derivatives were hydrolyzed without de- tectable rearrangement of the 1,2-dideoxy-hex- 1-enitol resi- dues so that normal methylated sugar analysis by glc-ms of the partially methylated alditol acetates (18) could be performed. The various partially methylated 1,2-dideoxy-hex- 1 -enit01 acetates gave fragment ions indicative of substitution patterns.

These results clearly show that 5,6-dideoxy-hex-5-enose for- mation by zinc dust cleavage of 6-deoxy-6-iodo-a-D-galacto-

pyranosides, and presumably of other hexopyranose deriva- tives, may be used for the selective cleavage of glycosidic linkages. It is necessary that care should be exercised in the introduction of the halo substituent. In the examples studied to date, glycosyl substituents at all positions in the ring are re- tained in hexenose formation. An application of this non- hydrolytic degradative procedure to a polysaccharide substrate is described in the accompanying paper (6).

Experimental Evaporations were carried out under diminished pressure at tem-

peratures of 40°C or less. Optical rotations were measured with a Perkin-Elmer model 141 polarimeter at 20 * 2OC. 'The ir spectra were measured on a Unicam SP 200 spectrophotometer. The nmr spectra were recorded in deuteriochloroform with tetramethylsilane as internal standard with Varian EM 360 (for 'H), Varian CFT 80A (for "C), and Bruker WH 400 (for both 'H and I3C) spectrophotometers. Gas-liquid chromatography (glc) was performed on a Perkin-Elmer Sigma 3B chromatograph using (A) a packed column of 3% of silicone gum Silar 10 CP on Chromosorb W-HP (100/200 mesh) or (B) a S.C.O.T. column coated with silicone gum OV-225. For glc - mass spec- trometry, capillary columns of (C) silicone gum DB225-15N and (D) DB5-15N (permanently bonded OV-54) were attached by a jet sepa- rator to a VG Micromass 16F mass spectrometer operated with an inlet temperature of 250°C, an ionization potential of 70 eV, and an ion- source temperature of -250°C. Preparative tlc (thin-layer chromato- graphy) was performed on precoated silica gel plates (Baker tlc plate silica gel 60-F (250 km)). For column chromatography silica gel 60, 0.05-0.2 mm/70-270 mesh ASTM (Macherey Nagel), was used without activation. Zinc dust was activated by the procedure of Frank and Smith (19).

Methyl 6-O-benzyl-2-O-(~-~-xylopyranos)~l)-a-~-galactopyranosicle ( 2 )

Drierite (pre-dried, 25 g) was added to methyl 6-0-benzyl-3,4- 0-isopropylidene-a-D-galactopyranoside (5) (6.8 g, 20.9 mmol) in dry benzene and nitromethane (500 mL, I : 1) and solvent (200 mL) was removed by distillation with exclusion of moisture. Mercuric cyanide (6 g, 23.7 mmol) was added to the reaction flask at room temperature, followed by 2.3,4-tri-0-acetyl-a-D-xylopyranosyl bro- mide (8 g, 23.5 mmol). The reaction mixture was stirred for 12 h, further quantities of mercuric cyanide (1.5 g, 2.5 mmol) and glycosyl bromide (2.1 g, 2.5 mmol) were added, and the mixture was stirred for another 8 h. The filtrate from the reaction mixture was diluted with dichloromethane, extracted with M potassium bromide solution (2 x 50 mL) and water (3 X 50 mL), dried, and concentrated to a syrup (I4 g). The syrup was chromatographed on silica gel in chloroform-ether ( I : 1) to give methyl 2-0-(2,3,4-tri-O-acetyl-P-~-xylopyranosyI)-6- O-benzyl-3,4-O-isopropylidene-a-~-galactopyranoside (1) (9 g, 77%) as a syrup, R, 0.5 1 ; [a], f21.3" (c, 1.37 in chloroform); nmr 6: 7.25-7.37 (m, 5H, Ph), 3.39 (s, 3H, COzCH3), 2.07 (s, 3H, OAc), 2.05 (s, 6H, 2 X OAc), 1.33 and 1.50 (2s, 2 X 3H, MeZC); Sc: 101.6 ( J , , . z . 165.4 HZ (C-l')), 99.1 ( J l . 2 169.5 HZ (C-I)).

This isopropylidene compound 1 (3.1 g) was kept in trifluoroacetic acid (30 mL, 90%) for 1 h , the solution was diluted with water, concentrated, and repeatedly concentrated after further addition of water to ensure removal of trifluoracetic acid. The crude product was treated with 0. I M methanolic sodium methoxide. When de- acetylation was complete the solution was treated with Amberlite IR-120 (H) resin to remove sodium ions, and thc filtrate was concen- trated to a crystalline residue which was recrystallized from ethanol and then chloroform-methanol (10: 1 ) to give the disaccharide gly- coside 2 (1.8 g, SO%), mp 180- 182°C; [a],, f53" (c, 4.3 in meth- anol). Anal. calcd. for C19HZ"OIO: C 54.80. H 6.73; found: C 54.60, H 6.55. Methyl 3,4-di-0-methyl-2-0-(2,~?,4-tri-O-tnetl1y1-~-~-~y10pyrat10~y1)-

a-D-galactopyrattosicle (4) Sodium hydride (0.93 g, 38.7 mmol) was added to disaccharide

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glycoside 2 (1.2 g, 2.9 mmol) in dry oxolane (50 mL), the mixture was stirred for 4 h at room temperature, cooled to O°C, methyl iodide (4 mL) was added, and the mixture was stirred overnight. Excess of sodium hydride was destroyed by the addition of methanol (0.3 mL), solvent was removed, and the residue was partitioned between water and chloroform. The dried organic layer was concentrated to a syrup which was chrornatographed on silica gel in chloroform-ether (1 : I) to give methyl 6-0-benzyl-3,4-di-O-methyl-2-0-(2,3,4-tri-O-methyl- P-D-xylopyranosy1)-a-D-galactopyranoside (3) (0.9 g, 65%), mp 68-71°C; nrnr 6: 4.85 (d, IH, J1.2 3.7 HZ, H-I), 4.41 (d, IH, Jl.,z, 6.9 Hz, H-1'); 6,: 105.92 (C-If), 100.08 (C-I). Anal. calcd. for C24H3XOIO: C 59.24, H 7.87; found: C 58.74, H 8.00. The fully etherified disaccharide glycoside 3 (0.587 g) in ethanol (50 mL) was hydrogenolyzed over 10% palladium-on-charcoal (0.17 g) for 16 h, the solution was filtered, and the filtrate was concentrated to a residue which was crystallized from ether-hexane to give the disaccharide glycoside 4 (0.458 g, 96%), mp 125-126°C. Anal. calcd. for C17H3201~: C 51.51, H 8.14; found: C 51.41, H 8.21.

Methyl 3,4-di-0-(2,3,4-tri-O-ace~l-~-~-xylopyranosyl)-6-O-benzyl- 2-0-methyl-a-D-galactopyranoside (5) and methyl 4-0-(2,3,4- tri-O-aceQl-P-~-xylopyranosyl-6-O-benzyl-2-O-methyl-a-~- galactopyratloside (9)

Powdered Drierite ( I5 g) and mercuric cyanide (4.72 g, 18.7 mmol) were added to methyl 6-0-benzyl-2-0-methyl-a-D-galactopyranoside (7) (4.3 g, 14.4 mmol) in benzene-nitromethane (350 mL, I : I) and solvent (100 mL) was removed by distillation at atmospheric pressure to remove moisture. 2,3,4-Tri-0-acetyl-a-D-xylopyranosyl bromide (5.58 g, 18.7 mmol) was added and the mixture was stirred at room temperature for 3 h; tlc (chloroform-acetone, 5: 1) showed the for- mation of two products, R f 0.75 and 0.48, together with some starting material, R , 0.25. Further portions of acetobromoxylose (3.0 g, 10.1 mmol) and mercuric cyanide (2.55 g, 10.1 mmol) were added, and the mixture was stirred for 2 h, at which time tlc showed complete disap- pearance of starting material. The reaction mixture was filtered through Celite and the filtrate was concentrated to a residue which was extracted with chloroform. The extract was washed with M potassium bromide solution and water alone, dried, and concentrated to a syrup which was chromatographed on silica gel in benzene - ethyl acetate (2: I) to give (i) trisaccharide glycoside 5 (5.3 g, 45%) as a syrup, R , 0.75, [a], -0.3" (c, 1.0 in chloroform); nrnr 6: 7.34 (s, 5H, Ph), 4.85 (d, IH, J1.2 3.57 Hz, H-I), 4.70 (d, IH, J I ~ . 2 ~ 7.62 Hz, H-l 'or H-I"), 4.55, 4.5 1 (ABq, 2H, JAB 1 1.7 Hz, CH2-Ph), 3.4 1, 3.40 (s, each 3H, 2 x OMe), 2.07, 2.05, 2.02 (s, each 3H, 3 x OAc); 6,: 102.4 (C-I", 4-linked), 100.0 (C-l', 3-linked), 97.4 (C-I); and (ii) disaccharide glycoside 9 (2.65 g, 33%), mp 128- 129°C (from ether), Rf 0.48; [a], +9. lo (c, l .O in chloroform); nmr 6: 7.38 (s, 5H, Ph), 4.60 (s, 2H, CH,-Ph), 3.53, 3.45 (s, each 3H, 2 X OMe), 2.10 (m, 9H, 3 x OAc); 6,: 103.2 (C-l'), 98.2 (C-I). Anal. calcd. for C26H3601): C 56. l I , H 6.52; found: C 55.84, H 6.07. A sample of the disaccharide glycoside 9 was subjected to the following series of reactions: debenzylation, deacetylation, methylation, hydrolysis, reduction (NaBD,), and acetylation. The derived partially methylated alditol acetates were characterized by glc-ms on column C (180°C) as formed from 2,3,4-tri-0-methylxylitol and 2,3,6-tri-0-methylgalactitol (fragment ions at m/z 233, 173, 162, 131, 118, and 102).

Methyl 2 - 0 - m e t h y l - 3 , 4 - d i - ( 2 , 3 , 4 - t r i - O - m e t h y l - P 1 ) - a-D-galactopyranoside (8)

Acetylated trisaccharide glycoside 5 (4.9 g, 6.0 mmol) in methanol (50 mL) was treated with a catalytic quantity of sodium methoxide for I h. Sodium ions were removed by treatment with Dowex 50W-X8 (H') resin and the filtrate was concentrated to syrupy methyl 6-0- benzyl-2-O-methyl-3,4-di-O-~-~-xylopyranosyl-a-~-ga~actopyrano- side (6) (2.91 g, 86%), [a], +44.5" (c, 1.0 in methanol). Sodium hydride (0.5 1 g, 21 mmol) was added to the trisaccharide glycoside 6 (1.97 g, 3.5 mmol) in oxolane (60 mL). The mixture was stirred at room temperature for 2 h, cooled to WC, and, after addition of methyl iodide, stirred at room temperature overnight. Excess sodium hydride

was destroyed by careful addition of methanol to a stirred pre-cooled solution, the solution was concentrated, and the residue was extracted with chloroform. The extract was washed with water, dried, and concentrated to a syrup which was chrornatographed on silica gel in chloroform-ether (3: 1) to give methyl 6-0-benzyl-2-0-methyl-3,4- di-0-(2,3,4-tri-0-methyl-~-~-xylopyranosyl)-a-~-galactopyranoside (7) as a syrup (1.67 g, 74%), [a], + 10.6" (c, 1.6 in chloroform); nmr 6:7.33(~,5H,Ph),4.91 (d, lH,J1.23.61 Hz,H-l),4.71 (d, lH,JI,.z. 7.36 HZ, H-l'), 4.59,4.52 (ABq, 2H, J A B 11.8 HZ), 4.52 (d, IH, JI.,,z.. 7.52 Hz, H-1"). 3.44-3.62 (8s, each 3H, 8 x OMe); 6,: 104.4 (C-If, 3-linked), 103.4 (C- I", 4-linked), 97.9 (C- I). Trisaccharide glycoside 7 (1.62 g, 2.5 mmol) in ethanol (25 mL) was hydrogenolyzed over 10% palladium-on-charcoal ( I . l g) for 2 h at 505 kPa. The filtered solution was concentrated to a syrup which was crystallized from isopropyl ether to give trisaccharide glycoside 8 ( I . 15, 83%), mp 129- 130°C, [a], +20.5" (c, 1 .O in chloroform); nrnr 6: 4.86 (d, IH, JI,, 3.10 HZ, H-I), 4.67 (d, IH, J1..2. 7.53 HZ, H-l'), 4.51 (d, IH, J,.,,? 7.51 Hz, H-I"), 3.42-3.62 (8s, each 3H, 8 x OMe); 6,: 104.7 (C-1', 3-linked), 104.4 (C-1", 4-linked), 98.1 (C-I). Anal. calcd. for CZ4H++OI4: C 51.79, H 7.97; found: C 52.01, H 8.14.

Methyl 2,3-di-0-methyl-4-0-(2,3,4-tri-0-~hyl-~-~-xylopyratzos~l)- a-D-galactopyranoside (12)

Acetylated disaccharide glycoside 9 (2.5 g, 4.5 mmol) was de-0- acetylated as described for compound 5 and crystallization of the product from chloroform-methanol gave methyl 6-0-benzyl-2-0- methy~-4-O-~-~-xylopyranosyl-a-~-galactopyranoside (10) (1.76 g, 91%), mp 172-173"; [a], +75.5" (c, 0.6 in methanol). Anal. calcd. for C2oH3oOlo: C 55.80, H 7.03; found: C 55.84, H 7.05. Compound 10 was methylated as described for compound 6 and column chro- matography afforded methyl 6-0-benzyl-2,3-di-0-methyl-4-0- (2,3,4-tri-0-methyl-~-~-xylopyranosyl)-a-~-gaactopyranoside (11) (1.53 g, 90%) as a syrup, [a], +29.0° (c, I . 1 in chloroform); nrnr 6: 7.34 (s, 5H, Ph), 4.89 (d, lH, J1.2 3.62 HZ, H-I), 4.65 (d, IH, J1..2, 7.23 HZ, H-l'), 4.59, 4.53 (ABq, 2H, J A B 11.7 HZ, CHZPh), 3.62-3.46 (6s. each 3H, 6 x OMe); 6,: 103.2 (C-l'), 98.1 (C-I). The foregoing disaccharide glycoside 11 (1.46 g, 3 mmol) was hydro- genolyzed as described for compound 7 and recrystallization of the solid product from isopropyl ether furnished disaccharide glycoside 12 ( 1.07 g, 90%), mp 69-70°C; [a], +47.5" (c, 1.0 in chloroform); nmr 6: 4.83 (d, IH, 51.2 2.81 HZ, H-I), 4.55 (d, IH, JI.,?s 7.41 HZ, H-l'), 3.63-3.39 (6s, each 3H, 6 x OMe); 6,: 104.2 (C-1'), 98.3 (C-I). Anal. calcd. f 0 r C ~ ~ H ~ ~ 0 ~ 0 : C 51.51, H 8.14; found: C 51.30, H 7.95.

Methyl 4-O-benzoyl-6-O-betzzyl-2-O-tnethyl-a-~-galactopyranoside (13)

Methyl 6-0-benzyl-2-0-methyl-a-D-galactopyranode (2.0 g, 6.7 mmol), trimethyl orthobenzoate (2.3 mL, 13.4 mmol) and toluene-p- sulfonic acid (15 mg) were dissolved in dry benzene and solvent was removed under diminished pressure. Thin-layer chromatography (chloroform-ether, 1 : I) showed disappearance of starting material and formation of a new compound of R , 0.72. The residue was kept in 80% acetic acid (10 mL) for 0.5 h at room teperature and tlc showed disappearence of the compound of R, 0.72 and formation of a new compound, Rr 0.50. The solution was concentrated several times with toluene to a residue which was chromatographed on silica gel in hexane - ethyl acetate (I : I) and recrystallized from isopropyl ether to give the 0-benzoyl glycoside 13 (1.99 g, 74%). mp 75"; [a], +66.3" (c, l .O in chloroform); nmr 6: 8.08-7.25 (m, IOH, 2 x Ph), 5.68 (m, IH, H-4), 5.05 (d, IH, J1.2 3.52 HZ, H-I), 4.52, 4.42 (ABq, 2H, J A B

11.8 Hz, CH2Ph), 3.52, 3.48 (s, 3H each, 2 x OMe); 6,: 97.4 (C- I). Anal. calcd. for C22H2607: C 65.66, H 6.51; found: C 65.45, H 6.59.

Methyl 2,4-di-0-methyl-3-0-(2,3,4-tri-0-metI1y1-~-~-~y1opyrano~~l)- a-D-galactopyranoside (17)

Powdered Drierite (5 g) and mercuric cyanide (1.35 g, 5.3 mmol) were added to the foregoing galactoside 13 (1.65 g, 4.1 mrnol) in benzene-nitromethane (150 mL, I : 1) and solvent (50 mL) was re- moved by distillation. 2,3,4-Tri-0-acetyl-a-D-xylopyranosyl bromide (1.81 g, 5.3 mmol) was added and the mixture was stirred at room temperature for 4 h. The filtrate from the reaction mixture was concen-

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-L ET AL. 2733

trated to a residue which was dissolved in chloroform, and the extract was washed with M potassium bromide solution and water alone, dried, and concentrated to a syrup. 'The syrup was chromatographed on silica gel in chloroform-ether (3: 1) to give syrupy methyl 3-0-(2,3,4-tri-O-acetyl-~-~-xylopyranosyl)-4-0-benzoyl-6-O-benzyl- 2-0-methyl-a-D-galactopyranoside (14) (1.97 g, 73%); [a], +35.8" (c, l .O in chloroform); nmr 6: 8.08-7.29 (m, IOH, 2 X Ph), 5.72 (m, 1 H, H-4), 4.53, 4.48 (ABq, 2H, J A B 1 1.8 HZ, CHZPh), 3.53, 3.50 (s, each 3H, 2 X OMe), 2.07, 1.97, 1.77 (s, each 3H, 3 x OAc); ijc: 100.9 (C-l'), 97.7 (C-I). The linkage type in compound 14 was confirmed as described for disaccharide glycoside 9, by methylation analysis which furnished inter alia 2,4,6-tri-0-methylgalactitol tri- acetate which was characterized by glc-ms on column C (180°C) with fragment ions at m/z 277, 245, 234, 203, 202, 174, 161, 129, 118, and 101. Acetylated disaccharide glycoside 14 (1.92 g, 2.9 mmol) was de-0-acylated with sodium methoxide for 48 h and chromatography on silica gel by elution with a chloroform-methanol gradient afforded syrupy methyl 6-0-benzyl-2-0-methyl-3-0-P-D-xylopyranosyl-a-D- galactopyranoside (15) (1.15 g, 92%), [a], +76" (c, 1.4 in methanol). Disaccharide glycoside 15 (1.08 g, 2.5 mmol) was methylated as described for compound 6 and chromatography on silica gel in chloroform-ether (4: 1) afforded methyl 6-0-benzyl-2,4-di-0-meth- y~-3-0-(2,3,4-tri-0-methy~-~-~-xy~opyranosy~)-a-~-ga~actopyrano- side (16) (0.95 g, 78%), [a], +34.0° (c, 1.0 in chloroform); nmr 6: 7.34 (s, 5H, Ph), 4.88 (d, IH, JI,Z 3.60 HZ, H- I), 4.60, 4.52 (ABq, 2H, J , \ B 11.8 HZ, CHzPh), 4.56 (d, IH, JI.,2. 7.42 HZ, H-l ') , 3.61-3.42 (6s, each 3H, 7 x OMe); ijc: 104.4 (C-l'), 97.8 (C-I). Disaccharide glycoside 16 (0.90 g, 1.85 mmol) in ethanol (15 mL) was hydrogenolyzed as described for compound 7 and re- crystallization of the solid product from isopropyl ether furnished disaccharide glycoside 17 (0.58 g, 79%), mp 83-84°C; [a], +40.8" (c, 0 .9 in chloroform); nmr 6: 4.93 (d, IH, JI.? 3.63 Hz, H-I), 4.54 (d, lH , J1,.2, 7.43 Hz, H-l ') , 3.61 -3.43 (6s, each 3H, 6 X OMe); tic: 104.5 (C-1'), 97.9 (C-I). Anal. calcd. for C17H32OI0: C 51.51, H 8.14; found: C 51.81, H 8.32.

Methyl 6-deoxy-6-iodo-3,4-di-0-methyl-2-0-(2,3,4-tri-O-methyl- P-D-xylopyranosyl)-a+-galactopyranoside (19)

A. Synthesis via imidazoiyl.sulfonate (18) Sodium hydride (0.048 g, 2 mmol) was added to methylated disac-

charide glycoside 4 (0.397 g, 1 mmol) in freshly distilled dry oxolane (10 mL) at O°C, the suspension was stirred for 2 h, cooled to -40°C, and N,N1-sulfuryldiimidazole (0.619 g, 3 mmol) in oxolane (5 mL) was added. The reaction mixture was kept at -40°C for 20 min and then stirred at room temperature for 2 h. Thin-layer chromatography showed complete disappearance of starting material and formation of a single product, and excess of sodium hydride was destroyed by the addition of dry methanol (0.2 mL) to the reaction mixture at O°C. The reaction mixture was diluted with dichloromethane (15 mL), and the solution was extracted with water until the aqueous extracts were neutral (pH 6.5). The dried organic extract was concentrated to a syrup which crystallized on storage at O°C and was recrystallized from ether to give methyl 6-O-imidazolysulfony1-3,4-di-O-methyl-2-0-(2,3,4- tri-0-methyl-~-~-xylopyranosyl)-a-~-galactopyranoside (18) (0.500 g, 95%), mp 95-99°C. Anal. calcd. for CmH3,N2012S: C 45.60, H 6.46, N 5.32, S 6.08; found: C 45.63, H 6.43, N 5.18, S 6.16.

The imidazylate 18 (0.229 g, 0.435 mmol) was heated in boiling benzene ( I 0 mL) with tetrabutylammonium iodide (0.5 g, 1.35 mmol) for 25 min. Solvent was removed, the residue was diluted with dichlo- romethane, and the organic solution was extracted with aqueous sodi- um thiosulfate, washed with water, dried, and concentrated to a crys- talline residue. Purification by chromatography on silica gel in chloroform-ether (I : 1) afforded the iododisaccharide 19 (0.179 g, 81%), mp 120- 121°C. The mass spectrum showed prominent frag- ment ions at m/z 415, 375, 315, 175, and 143. Anal. calcd. for C,7H,1091:C40.31, H6.12,125.O;found: C40.26, H6.39, 125.0.

B . Synthesis via tr$uoromethanesulfonnte (with V. Puvanesarajah)

Trifluoromethanesulfonic anhydride (50 pL) in dichloromethane

(0.5 mL) was added dropwise with stirring to dry pyridine (25 pL) in dichloromethane (0.5 mL) at - 10°C. Methylated disaccharide gly- coside 4 (50 mg) in dichloromethane ( 1 mL) was added dropwise and the mixture was stirred at - 10°C for 2 h. Thin-layer chromatography (dichloromethane-acetone, 10: 1) showed complete disappearance of starting material. The reaction mixture was poured into ice-water, and the combined separated organic layer and dichloromethane extracts were washed with aqueous sodium hydrogen carbonate and then with water until free from pyridine, dried, and concentrated to a syrup which showed strong absorption at 1420 cm-' (sulfonate) but none at 3400 cm-' (OH). The triflate ester was heated in boiling benzene (4 mL) with tetrabutylammonium iodide ( I00 mg) for 2 h. After removal of solvent the residue was chromatographed on silica gel in dichloromethane-acetone (10: I) to yield iododisaccharide 19 (45 mg, 70%) which was identical (mp and glc - mass spectrometry) to the previous sample. A polar component (-2 mg) was also isolated from the column and shown to be indistinguishable (glc - mass spec- trometry) from the anhydro disaccharide 23.

C. Synthesis from imidazolylsulfonate (18) in N,N-dimethylformamide

Imidazylate 18 in N,N-dimethylformamide containing imidazole (0.5 equiv.) was treated with methyl iodide and kept for 24 h at room temperature. Thin-layer chromatography showed complete disap- pearance of starting material with formation of iododisaccharide 19 as the major product with a second component, later identified as the anhydrodisaccharide 23. The mixture was chromatographed on silica gel in chloroform-acetone (4: 1 ) to give crystalline iododisaccharide 1 9 (65%), which was identical to the previously isolated sample, and syrupy anhydrodisaccharide 23 (20%). The latter compound gave a single peak on glc on column B (210°C) and the mass spectrum showed fragment ions at m/z 233, 175, 173, and 143.

Solvolysis of imidazolylsulfonate (18) in N,N-dimethylformamide Imidazylate 18 (36 mg) was kept in dry N,N-dimethylformamide (2

mL) for 36 h. The acidic solution was neutralized with sodium hydro- gen carbonate, diluted with water, and extracted with chloroform. Examination of the chloroform extract by glc - mass spectrometry (column C, 170°C, 1 min, 170 + 200°C, 6"/min) showed anhy- drodisaccharide 23 as the major component with a second minor component, later identified as methylated disaccharide 6-formate 29, which showed fragment ions at m/z 293,233,201, 175, and 143. The extract was chromatographed on silica gel in chloroform-acetone (4: 1) to give syrupy methyl 3,6-anhydro-4-0-methyl-2-0-(2,3,4-tri- O-methyl-~-~-xylopyranosyl)-a-~-galactopyranoside (23) (16 mg); nmr 6: 4.84 (d, IH, J I . ? 2.85 HZ, H-I), 3.46-3.70 (5s, each 3H, 5 x OMe); 6c: 102.84 ( J l ) C l . . l ~ , . 160.5 HZ, (C-I))), 97.52 ( ~ ~ ~ C I . ~ H I 16 1.1 Hz (C- I)), 69.69 (C-6). A sample was boiled under reflux with methanolic 2% hydrogen chloride for 2 h, and the cooled solution was neutralized and concentrated to a syrup which was treated with acetic anhydride in pyridine. Examination of the products by glc on column B (150 + 180°C, SO/min, hold) showed the presence of methyl glycosides of 2,3,4-tri-0-methylxylose together with three com- ponents which were identical (glc - mass spectrometry on column C) to those (26-28) similarly formed from methyl 3,6-anhydro-4-0- methyl-a-D-galactopyranoside (25).

Solvolysis of tr~fluoromethanesulfonate esters of methylated oligo- saccharides (4, 8, and 17) in N,N-dimethylformamide

Samples (-20 mg) of methylated oligosaccharides were converted into triflate esters using procedure B, and the esters were kept in dry N,N-dimethylformamide (1 mL) for I h at which time tlc (benzene- methanol, 5 : 1) showed complete disappearance of starting material. Solutions were diluted with dichloromethane (10 mL), washed several times with water, dried, and concentrated.

Examination of the solvolysis products from the triflate ester of methylated disaccharide 4 by glc - mass spectrometry (as above) showed the formation of anhydro disaccharide 23 and methylated disaccharide 6-formate (29) in the molar ratio of 1.3 : 1. A sample of compound 29 was isolated by preparative tlc; v,,,, 1730 cm-'; nmr 6: 8.15 (s, IH, -0-CHO). Hjrdrolysis of the disaccharide derivative,

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2734 CAN. I . CHEM. VOL. 62 . 1984

followed by reduction and acetylation, afforded acetates of 2,3,4-tri-0-methylxylitol and 3,4-di-0-methylgalactitol which were characterized by glc-ms on column C and shown to be identical to derivatives formed similarly from methylated disaccharide 4.

The solvolysis products from the triflate ester of methylated disac- charide 17 were formed in the presence of I ,6-anhydro-2,3,4-tri- 0-methyl-P-D-galactopyranose as-an internal standard. The glc anal- ysis of the products on column B (130 + 180°C, 4"/min, hold) showed the formation of methyl 3,6-anhydro-2,4-di-0-methyl-a-D- galactopyranoside (24) in 30% yield. The identity of the latter com- pound was confirmed by glc - mass spectrometry on column C (180 -, 200°C. 6"/min, hold) with fragment ions at m/z 173, 113, 10l ,71 as for a synthetic sample. The major reaction product had a high retention time and fragment ions at m/z 293, 175, 143, 101, and 88 were consistent with those of the 6-formate (31) of the methylated disaccharide 17. A sample of the 6-formate 31 was isolated by prep- arative tlc and methylated sugar analysis gave the same products as from the parent disaccharide 17. A sample of the solvolysis mixture was treated with sodium borohydride and then with acetic anhydride in pyridine. Analysis of the products by glc - mass spectrometry as for the solvolysis mixture showed the presence of 2,3,4-tri-0-methyl- xylitol diacetate, anhydro derivative 24, and a disaccharide derivative identical to a synthetic sample of the 6-acetate of methylated disaccha- ride 17 (fragment ions at m/z 307, 187, 175, 143, 127).

The reaction mixture from solvolysis of the triflate ester of methyl- ated trisaccharide 8 afforded a single major product, a sample of which was isolated by preparative tlc. The 'Hmr spectrum of this compound (30) showed signals at 6 8.08 (s, IH, -0-CHO), 4.90 (d, IH, J,,? 3.56 HZ, H-I), 4.65 (d, IH, J,,,,, 7.39 HZ, H-It), 4.51 (d, lH, J1".2.. 7.37 Hz, H-I") and the mass spectrum (direct insertion) showed frag- ment ions at m/z 453, 393, 247, 175, 143 which were consistent with its formulation as the 6-formate of methylated trisaccharide (12).

Methyl 6-deoxy-6-iodo-2-O-tnethyl-3,4-di-0-(2,3,4-tri-O-methyl- P-D-qlopyranosy1)-m-gnlactopyratlosie (20)

The iodo trisaccharide (20) was synthesized in 73% yield from methylated trisaccharide glycoside 8 by method B as described for compound 19, and had [a], + 19.6" (c, 0.7 in chloroform); nmr 104.6 (C-If , 3-linked), 103.6 (C-1", 4-linked), 98.0 (C-I), 4.8 (C-6); m/z: 535, 475, 329, 269, 253, 175, 143.

Methyl 6-deo.~y-6-iodo-2,3-di-0-methyl-4-0-(2.3,4-tri-O-methyl- ~-~-xy~opyra12osy~)-a-o-ga~acropyralloside (21)

The iodo disaccharide (21) was synthesized in 74% yield from methylated disaccharide glycoside 12 by method B as described for compound 19, and after recrystallization from hexane had mp 115- 116°C; [a],, +55.3" (c, 0.8 in chloroform); nmr tic: 103.4 (C-1'), 98.2 (C-I), 4.6 (C-6). Anal. calcd. for CI7H3,OP1: C 40.32, H 6.17, 125.06; found: C 40.33, H 6.37, 124.91.

Methyl 6-deoxy-6-iodo-2,4-di-O-methyl-3-O-(2,3,4-tri-O-methyl- P-D-xy/opyranosyl)-cx-D-galactopyratzo.sid (22)

The iododisaccharide (22) was synthesized in 75% yield from methylated disaccharide glycoside 17 by method B as described for compound 19, and after recrystallization from hexane had mp 111-112"C;[a], +41.I0(c, 1.6inchloroform);nmr6: 4.86(d, IH, J1.2 3.65 HZ, H-I), 4.56 (d, IH, J1.,2, 7.54 HZ, H-1'), 3.47-3.65 ( 6 ~ , each 3H, 6 X OMe); 104.4 (C-1'), 97.9 (C-1), 2.6 (C-6); tn/z: 375, 315, 255, 223, 195, 175, 143. Anal. calcd. for CI7H3,O9I: C 40.32, H 6.17, 125.06; found: C 40.15, H 6.05, 124.51.

1 , 2 - D i d e o x y - 3 , 4 - d i - 0 - m e t h y 1 - 5 - 0 - ( 2 , 3 , 4 - ~ 1 - ~ - ~ - xylopyranosy1)-L-lyxo-hex-1-enitol acetate (33)

Methylated iododisaccharide 19 (169 mg, 0.33 mmol) in I-propanol- water (5 mL, 14: I) was boiled under reflux with freshly activated zinc dust (0.4 g, 6.1 mmol). After 1 h tlc showed formation of a single product and complete disappearance of starting material. The cooled mixture was filtered through Celite, the filtrate was con- centrated, and the residue in oxolane-water (2: 1) was treated with sodium borohydride for 4 h at room temperature. The reaction mixture was worked up in the usual way, and the product was acetylated with

acetic anhydride in pyridine. The resulting acetylated derivative (33) was chromatographed on silica gel in chloroform-ether (I : 1) to give the title compound as a syrup (90 mg, 69%); nmr 6: 5.85 (ddd, IH, Js,s(,,,,,.,) 17 HZ, JS.~,,,,, 10.3, J 4 . ~ 7.9 Hz, -CH=CH2), 5.50 (m, 2H, -CH=CH2), 4.28 (d, IH, JI,,2. 7.3 HZ, H-If) , 3.60-3.20 (5s, each 3H, 5 x OMe), 2.10 (s, 3H, OAc). Examination by glc-ms on column D (140°C, 1 min, 140 + 200°C, SO/min, hold) showed a single peak with fragment ions at the m/z values shown in structure 33. Anal. calcd. for CIxH3,09: C 55.10, H 8.16; found: C 55.24, H 8.15. A portion of the unsaturated disaccharide alditol was hydrolyzed as in methylation analysis, reduced, and acetylated to give two com- pounds which were characterized by glc-ms on column C as 2,3,4-tri-0-methylxylitol diacetate and 1,2-dideoxy-3,4-di-0-di-0- methyl-L-lyxo-hex-1-enitol diacetate (fragment ions at m/z 189, 129, 115, 87, and 71).

1,2-Dideoxy-5-O-methyl-3,4-di-0-(2,3,4-tri-O-tnethyl-P-~- qlopyranosy1)-L-lyxo-hex-1 -enit01 acetate (34)

Methylated iodotrisaccharide 20 (67 mg, 0. I mmol) was reacted with zinc dust in 1-propanol- water as above for 30 min. Thin-layer chromatography indicated a single product which was reduced with sodium borohydride and then acetylated to give the trisaccharide hex- I-enitol acetate 34; nmr 6: 5.98 (ddd, lH, J5.6(,r0,,s) 17.3 HZ, J5.6'(r;s) 10.7 HZ, 54.5 6.1 HZ, H-5), 5.32 (d, IH, J s . ~ ( , ~ ~ , , ~ ) 17.26 HZ, H-6), 5.17 (d, lH, Js.h~(crs) 10.66 HZ, H-67, 3.60 (s, 6H, 2 X OMe), 3.58-3.45 (5s, each 3H, 5 X OMe), 2.07 (s, 3H, OAc). Analysis by glc-ms on column D (180°C. 2 min, 180 + 230°C, 4'/min, hold) showed a single peak with fragment ions at the m/z values shown with structure

34. Hydrolysis etc. as described for compound 33 gave 2,3,4-tri- 0-methylxylitol diacetate and 1 ,2-dideoxy-5-0-methyl-L-lyxo-hex-1- enitol 3,4,6-triacetate (fragment ions at m/z 215, 189, 155, 129, and 99).

1,2-Dideoxy-4,5-di-O-methyl-3-0-(2,3,4-tri-O-tnethyl-~-~- xylopyranoxy1)-L-lyxo-hex-1-enitol acetate (35)

Methylated iododisaccharide 21 was treated with zinc dust in ethanol-water (14: 1) at a bath temperature of 85°C for 30 min. Under these conditions essentially a single product was observed and reduc- tion followed by acetylation afforded the disaccharide hex-I-enitol acetate 35 which was analyzed by glc-ms on column C (180°C, 1 min, 180 + 200°C, 4'/min, hold). Hydrolysis etc. as described for compound 33 gave 2,3,4-tri-0-methylxylitol diacetate and 1.2-

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ASPINALL ET AL. 2735

dideoxy-4,5-di-0-methyl-L-lyxo-hex- I -enitol diacetate (fragment ions at m/z 16 1, 143, 127, 1 17, 101, and 99). When the zinc dust treatment was performed in I-propanol for longer periods a second product was detected by tlc and was shown to be 2,3,4-tri-0-methylxylose by conversion into the corresponding partially methylated alditol acetate.

1,2-Dideoxy-3,5-di-O-methyl-4-0-(2,3,4-tri-O-tnethyl-~- xylopyranosyl)-L-lyxo-hex-1-enitol acetate (36)

Methylated iododisaccharide 22 was treated with zinc dust in I-propanol - water as described for compound 19 to give a single product which was reduced and acetylated to furnish the disaccharide 1,2-dideoxy-hex-I-enitol acetate 36 whose structure was confirmed by glc-ms on column C (10O0C, 2 min, 100 + 200°C, 8"/min, hold). Hydrolysis etc. for compositional analysis afforded 2,3,4-tri-0- methylxylitol diacetate and 1 ,2-dideoxy-3,5-di-0-methyl-L-lyxo- hex- l -enit01 diacetate (fragment ions at m/z 189, 187, 129, 127, 1 17, and 71.

Derivutives of methyl 3,6-a11l1ydro-a-~-galactopyranoside Samples of the 2,4-di-0-methyl (24) and 4-0-methyl (25) deriva-

tives of methyl 3,6-anhydro-a-D-galactopyranoside were prepared by incomplete methylation as described by Anderson et a/. (I 1) . The I3C nmr spectrum of 24 included signals at tjc 98.63 ( J I ~ ~ , . lrll 161 Hz) and 69.08 (C-6). The acetylated derivative (26) of compound 25 when examined by glc - mass spectrometry on column C showed fragment ions at m/z 201 (M - OCH,), 129, 1 16, 103, and 71. A sample of glycoside 25 was treated with boiling methanolic 2% hydrogen chlo- ride for 2 h and the products were acetylated; glc - mass spectrometry

showed the presence of 3 components, the first indistinguishable from 26, the second well separated but giving a similar mass spectrum (presumably the P-D-glycoside 27), and a third and major component for which the acetylated dimethylacetal structure (28) may be pro- posed in the light of prominent fragment ions at tnlz values shown (compare Chizhov et a/. (20)).

Acknowledgements The authors are grateful to the Natural Sciences and En-

gineering Research Council of Canada for financial support. They also thank Dr. V. Puvanesarajah for performing the ex- periment cited, Drs. B. H. Khouw and K. R. Sharma for recording the mass spectra and some of the I3C nmr spectra, and the Southwestern Ontario NMR Centre at the University of Guelph for recording high field "C and 'H nmr spectra.

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13. L. V. VOLKOVA, M. G. LUCHINSKAYA, N. G. MOROZOVA, N. B. ROZANOVA, and R. P. EVSTIGNEEVA. J. Gen. Chem. (U.S.S.R.) 42, 2101 (1972).

14. V. POZSGAY and P. NANASI. Carbohydr. Res. 68, 157 (1979). 15. L. HOUGH and A. W. LEWIS. Carbohydr. Res. 42, 173 (1975). 16. J. LONNGREN and S. SVENSSON. Adv. Carbohydr. Chem. Bio-

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