O-Benzylated thio sugars. Derivatives of 2,3,6-tri-O-benzyl-1-thio-d-galactopyranose suitable for use in oligosaccharide synthesis

The 4-O-benzoyl (15a) 4-O-p-nitrobenzoyl (15b) derivatives of 2,3, 6-tri-O-benzyl-1-thio-d-galactopyranose were synthesized from allyl 2,6-di-O-benzyl-α-d-galactopyranoside (1). In the first stage of the synthesis the 3-position of 1 was benzylated by an indirect route, and also by the direct reaction (preferred) of benzyl bromide with the 3,4-O-dibutylstannylene intermediate 7. The product 6 was sequentially isomerized (allyl → 1-propenyl), acylated at the 4-position, and hydrolyzed. The free sultars 11a and 11b were converted into the thio sugars by a standard sequence involving formation of the glycosyl halides 13a and 13b and the reaction of these with appropriate sulfur nucleophiles. A third derivative (29) of 2,3,6-tri-O-benzyl-1-thio-d-galactopyranose, having a 4-O-allyl protecting group, was similarly made from the corresponding normal sugar 25. The key intermediate 22, precursor to 25, was prepared by two routes from methyl 2,3,6-tri-O-benzoyl-α-d-galactopyranoside (17).     

Synthesis and characterization of propyl O-β-d-galactopyranosyl-(1→4)-O-β-d-galactopyranosyl-(1→4)-α-d-galactopyranoside

Allyl 4-O-(4-O-acetyl-2-O-benzoyl-3,6-di-O-benzyl-β-d-galactopyranosyl)-2-O-benzoyl-3,6-di-O-benzyl-α-d- galactopyranoside was O-deallylated to give the 1-hydroxy derivative, and this was converted into the corresponding 1-O-(N-phenylcarbamoyl) derivative, treatment of which with dry HCl produced the α-d-galactopyranosyl chloride. This was converted into the corresponding 2,2,2-trifluoroethanesulfonate, which was coupled to allyl 2-O-benzoyl-3,6-di-O-benzyl-α-d-galactopyranoside, to give crystalline allyl 4-O-[4-O-(4-O-acetyl-2-O-benzoyl-3,6-di-O-benzyl-β-d-galactopyranosyl)-2-O-benzoyl-3,6-di- O-benzyl-β-d-galactopyranosyl]-2-O-benzoyl-3,6-di-O-benzyl-α-d-galactopyranoside (15) in 85% yield, no trace of the α anomer being found. The trisaccharide derivative 15 was de-esterified with 2% KCN in 95% ethanol, and the product O-debenzylated with H₂-Pd, to give the unprotected trisaccharide. Alternative sequences are discussed.     

A synthesis of psi-cytidine

2-O-Benzoyl-3,6-di-O-benzyl-4-O-(chloroacetyl)-, 4-O-acetyl-2-O-benzoyl-3,6-di-O-benzyl-, and 2-O-benzoyl-3,4,6-tri-O-benzyl-α-d-galactopyranosyl chloride were converted into the corresponding 2,2,2-trifluoroethanesulfonates, and these were treated with allyl 2-O-benzoyl-3,6-di-O-benzyl-α-d-galactopyranoside, to give allyl 2-O-benzoyl-4-O-[2-O-benzoyl-3,6-di-O-benzyl-4-O-(chloroacetyl)-β-d-galactopyranosyl]-3,6-di-O-benzyl- α-d-galactopyranoside (26; 41% yield), allyl 4-O-(4-O-acetyl-2-O-benzoyl-3,6-di-O-benzyl-β-d-galactopyranosyl)-2-O-benzoyl-3,6-di-O-benzyl- α-d-galactopyranoside (27; 62% yield), and allyl 2-O-benzoyl-4-O-(2-O-benzoyl-3,4,6-tri-O-benzyl-β-d-galactopyranosyl)-3,6-di-O-benzyl-α-d-galactopyranoside (28; 65% yield). All disaccharides were free from their α anomers. Disaccharides 26 and 27 were found to be base-sensitive, and were de-esterified by KCN in aqueous ethanol, and debenzylated with H₂-Pd. Attempts to produce (1→4)-β-d-galactopyranosides from the coupling of a number of fully esterified d-galactopyranosyl sulfonates to allyl 2,3,6-tri-O-benzoyl-α-d-galactopyranoside were unsuccessful.     

The assembly of oligosaccharides from “standardized intermediates”: β-(1→3)-linked oligomers of d-galactose

Several 2-O-benzoyl-4,6-di-O-benzyl-3-O-R-α-d-galactopyranosyl chlorides, designed as general precursors of β-linked, interior d-galactopyranosyl residues in oligosaccharides, were tested in a sequential synthesis of the galactotriose β-d-Galp-(1→3)-β-d-Galp-(1→3)-d-Gal (19). The chlorides having R = tetrahydro-2-pyranyl and tert-butyldimethylsilyl gave excellent results whereas those having = 3-benzoylpropionyl and chloroacetyl were unsatisfactory. An activated disaccharide block (17), having R = 2,3-di-O-benzoyl-4,6-di-O-benzyl-β-d-galactopyranosyl, was also prepared and tested as a glycosyl donor. The coupling of 17 to 1-propenyl 2-O-benzoyl-4,6-di-O-benzyl-α-d-galactopyranoside (14), in the molar ratio 1.13:1, gave 64% of a trisaccharide derivative (18) that could be converted into 19. This latter synthesis of 19 is efficient because all three galactose units are derived from 14 or its immediate precursor.     

Synthetic mucin fragments. Methyl 6-O-(2-acetamido-2-deoxy-β-D-glycopyranosyl)-β-D-galactopyranoside,methyl 3,4-di-O-(2-acetamido-2-deoxy-β-D-glycopyranosyl)-β-D-galactopyranoside,and methyl O-(2-acetamido-2-deoxy-β-D-glucopyranosyl)-(1 å 3)-O-β-D-galactopyranosyl-(1 å 3)-O-(2-acetamido-2-deoxy-β- D-glucopyranosyl)-(1 å 3)-β-D-galactopyranoside

Condensation of methyl 2,6-di-O-benzyl-β-d-galactopyranoside with 2-methyl-(3,4,6-tri-O-acetyl-1,2-dideoxy-α-d-glucopyrano)-[2,1,-d]-2-oxazoline (1) in 1,2-dichloroethane, in the presence of p-toluenesulfonic acid, afforded a trisaccharide derivative which, on deacetylation, gave methyl 3,4-di-O-(2-acetamido-2-deoxy-β-d-glucopyranosyl)-2,6-di-O-benzyl-β-d- glactopyranoside (5). Hydrogenolysis of the benzyl groups of 5 furnished the title trisaccharide (6). A similar condensation of methyl 2,3-di-O-benzyl-β-d-galactopyranoside with 1 produced a partially-protected disacchraide derivative, which, on O-deacetylation followed by hydrogenolysis, gave methyl 6-O-(2-acetamido-2-deoxy-β-d-glucopyranosyl)-β-d-glactopyranoside (10). Condensation of methyl 3-O-(2-acetamido-4,6-O-benzylidene-2-deoxy-β-d-glucopyranosyl)-2,4,6-tri-O-benzyl-β-d- galactopyranoside with 3-O-(2-acetamido-3,4,6-tri-O-acetyl-2-deoxy-β-d-glucopyranosyl)-2,4,6-tri-O-acetyl-α-d-galactopyranosyl bromide in 1:1 benzene-nitromethane in the presence of powdered mercuric cyanide gave a fully-protected tetrasaccharide derivative, which was O-deacetylated and then subjected to catalytic hydrogenation to furnish methyl O-(2-acetamido-2-deoxy-β-d-glucopyranosyl)-(1→3)-O-β-d-galactopyranosyl-(1å3)-O-(2-acetamido-2-deoxy- β-d-glucopyranosyl)-(1å3)-β-d-galactopyranoside (15). The structures of 6, 10, and 15 were established by ¹³C-n.m.r. spectroscopy.     

Oligosaccharides from “standardized intermediates”. The 2-amino-2-deoxy- d-galactose analog of the blood-group O(H) determinant,type 2, and its precursors

The selectively benzylated glycoside allyl 2-acetamido-4,6-di-O-benzyl-2-deoxy-β- d-galactopyranoside ( 4) was prepared from the corresponding derivative of 2-acetamido-2-deoxy- d-glucose via the p-bromobenzenesulfonate and the benzoate. 2-O-Benzoyl-3,4,6-tri-O-benzyl-α- d-galactopyranosyl chloride ( 10) was obtained from allyl 6-O-benzyl-2-O-(2-butenyl)-α- d-galactopyranoside via known intermediates. To complete the sequence, the 1-propenyl 3,4,6-tri-O-benzyl galactoside was successively converted into the 2-benzoate, the free sugar, and the chloride 10. A fully protected form ( 11) of the trisaccharide α- l-Fucp-(1→2)-β- d-Galp-(1→4)- d-GalNAc was then synthesized by coupling 10 to 4, partially deblocking the disaccharide product, and l-fucosylating the resulting intermediate. Cleavage of the O-benzyl groups from 11, with concomitant saturation of the allyl group, gave the propyl β-glycoside of the unsubstituted trisaccharide.     

The linkage of 4-O-methyl-L-galactose in the sulphated polysaccharide of Aeodes ulvoidea

Methyl 2-acetamido-5,6-di-O-benzyl-2-deoxy-β-d-glucofuranoside (11) was obtained in six steps from the known methyl 3-O-allyl-2-benzamido-2-deoxy-5,6-O-isopropylidene-β-d-glucofuranoside. Mild acid hydrolysis, followed by benzylation gave the 5,6-dibenzyl ether. The benzamido group was exchanged for an acetamido group by strong alkaline hydrolysis, followed by N-acetylation, and the allyl group was isomerized into a 1-propenyl group that was hydrolyzed with mercuric chloride. Treatment of 11 with l-α-chloropropionic acid and with diazomethabe gave methyl 2-acetamido-5,6-di-O-benzyl-2-deoxy-3-O-[d-1-(methoxycarbonyl)ethyl]-β-d-glucofuranoside which formed on mercaptolysis the internal ester 16, further converted into 2-acetamido-4-O-acetyl-5,6-di-O-benzyl-2-deoxy-3-O-[d-1-(methoxycarbonyl)ethyl]-d-glucose diethyl dithioacetal (18) by alkaline treatment followed by esterification with diazomethane and acetylation. Attempts to remove the O-acetyl group of the corresponding dimethyl acetal 20 with sodium methoxide in mild conditions were not successful.     

O-benzylated thio sugars: 2,3,4- and 2,4,6-tri-O-benzyl-1-thio-β-d-galactopyranose

The 2,3,4- (9) and 2,4,6-tribenzyl (19) ethers of 1-thio-β-d-galactopyranose were prepared from the corresponding O-benzylated normal (1-hydroxyl) sugars 4 and 15 via the sequence: normal sugar → diacetate → O-acetylglycosyl bromide → O-acetyl-glycosyl ethylxanthate → 1-thio sugar. 2,3,4-Tri-O-benzyl-α-d-galactopyranose (4) is most advantageously made from allyl 6-O-allyl-α-d-galactopyranoside (2) by a published synthesis. An improved synthesis of 2,4,6-tri-O-benzyl-d-galactopyranose (15) was devised; it involves the selective 3-O-benzoylation of allyl 2,6-di-O-benzyl-α-d-galactopyranoside (10).     

The stepwise synthesis of a methyl β-xylotetraoside related to branched xylans

3,4-Di-O-acetyl-2-O-benzyl-α-d-xylopyranosyl bromide (1) reacts with methyl 2,3-anhydro-α-d-ribopyranoside (2) to afford, in high yield, methyl 2,3-anhydro-4-O- (3,4-di-O-acetyl-2-O-benzyl-β-d-xylopyranosyl)-β-d-ribopyranoside (3). Deacetylation of 3 gave 4, which reacted with 2,3,4-tri-O-acetyl-α-d-xylopyranosyl bromide to give the branched tetrasaccharide derivative 5, which, in turn, was converted by a series or conventional reactions into methyl 4-O-[3,4-di-O-(β-d-xylopyranosyl)-β-d- xylopyranosyl]-β-d-xylopyranoside. The reaction of 1 with its hydrolysis product gave 3,4-di-O-acetyl-2-O-benzyl-α-d-xylopyranosyl 3,4-di-O-acetyl-2-O-benzyl-β-d-xylopyranoside, which was also isolated after the reaction of 1 with 2.     

Monomolar acetalations of methyl α-d-mannosides—synthesis of methyl α-d-talopyranoside

Methyl α-d-mannopyranoside (1 mole) reacts with 2,2-dimethoxypropane (1 mole), to give the 4,6-O-isopropylidene derivative (2) which rearranges to the 2,3-O-isopropylidene derivative (4). Compound4 can also be prepared by graded hydrolysis of methyl 2,3:4,6-di-O-isopropylidene-α-d-mannopyranoside. Successive benzoylation, oxidation, and reduction of4 provides a useful route to a number ofd-talopyranoside compounds. Methyl α-d-mannofuranoside (1 mole) reacts with 1–2 moles of 2,2-dimethoxypropane to give the 5,6-O-isopropylidene derivative (16) in 90% yield.     

Syntheses of 3-O-(2-acetamido-2-deoxy-β-d-glucopyranosyl)-α-d-galactopyranose (“lacto-N-biose II”) and 3,4-di-O-(2-acetamido-2-deoxy-β-d-glucopyranosyl)-d-galactopyranose

3- O-(2-Acetamido-2-deoxy-β-d-glucopyranosyl)-α-d-galactopyranose (10, “Lacto-N-biose II”) was synthesized by treatment of benzyl 6-O-allyl-2,4-di-O-benzyl-β-d-galactopyranoside with 2-methyl-(3,4,6-tri-O-acetyl-1,2-dideoxy-α-d-glucopyrano)[2,1-d]-2-oxazoline (5), followed by selective O-deallylation, O-deacetylation, and catalytic hydrogenolysis. Condensation of 5 with benzyl 6-O-allyl-2-O-benzyl-α-d-galactopyranoside, followed by removal of the protecting groups, gave 10 and a new, branched trisaccharide, 3,4-di-O-(2-acetamido-2-deoxy-β-d-glucopyranosyl)-d-galactopyranose (27).     

Synthesis of 3,6-dideoxy-3-(methylamino)hexoses for G.L.C.-M.S. identification of Rhizobium lipopolysaccharide components

A direct synthetic route from methyl α-d-glucopyranoside to 3,6-dideoxy-3-(methylamino)hexoses having the d-gluco, d-galacto, and d-manno configurations has been developed. Methyl α-d-glucoside was converted into the 4,6- <O-benzylidene-2,3,-di-O-tosyl derivative, which has then transformed into the 4-O-benzyl-6-deoxy 2,3-ditosylate (5) by successive reductive cleavage of the acetal ring, iodination, and reduction. The intermediate 5 was readily converted into the allo 2,3-epoxide, which yielded the pivotal intermediate methyl 4-O-benzyl-3,6-dideoxy-3-(methylamino)-α-d-glucopyranoside (7) by cleavage of the oxirane ring with methylamine. The amino compound 7 can be directly converted into the derivatized galacto and manno derivatives for mass-spectrometric identification by selective inversion at C-4 and C-2, respectively, followed by hydrolysis, reduction, and acetylation.     

Conversion of allyl 2-acetamido-2-deoxy-β-d-glucopyranoside into 2-methyl-(3,4,6-tri-O-benzoyl-1,2-dideoxy-α-d- galactopyrano)-[2′,1′:4,5]-2-oxazoline

2-Methyl-(3,4,6-tri-O-benzoyl-1,2-dideoxy-α-d-galactopyrano)-[2′,1′:4,5]-2-oxazoline (7) was prepared from 1-propenyl 2-acetamido-3,4,6-tri-O-benzoyl-2- deoxy-β-d-galactopyranoside (6). The latter was prepared from allyl 2-acetamido-2-deoxy-β-d-glucopyranoside (1) through selective benzoylation at O-3 and O-6, conversion into the 4-p-bromobenzenesulfonate 4, inversion of configuration at C-4 to afford allyl 2-acetamido-3,4,6-tri-O-benzoyl-β-d-galactopyranoside (5), and subsequent isomerization with palladium-charcoal to give 6.     

Highly stereoselective C-α-d-ribofuranosylation. Reactions of d-ribofuranosyl fluoride derivatives with enol trimethylsilyl ethers and with allyltrimethylsilane

2,3,5-Tri-O-methyl-d-ribofuranosyl flouride (6), 2,3-di-O-benzyl-5-O-methyl-d-ribofuranosyl fluoride (7), and 5-O-benzyl-2,3-di-O-methyl-d-ribofuranosyl fluoride (8) were obtained in 57 (6α, 15; and 6β, 42), 87 (7α, 22; and 7β, 65), and 85.5 (8α, 35.5; and 8β, 50%) yields, respectively, from the corresponding OH-1 derivatives by the reaction with N,N-diethyl-1,1,2,3,3,3-hexafluoropropylamine, adduct of hexafluoropropene with diethylamine. These fluorides and 2,3,5-tri-O-benzyl-d-ribofuranosyl fluoride (5) reacted with isopropenyl trimethylsilyl ether, (Z)-1-ethyl-1-propenyl trimethylsilyl ether, and allyltrimethylsilane, in the presence of boron trifluoride·diethyl etherate to give the corresponding 1-d-ribofuranosyl-2-propanones, 2-d-ribofuranosyl-3-pentanones, and 3-d-ribofuranosyl-1-propenes in good yields. C-Acetonylation was confirmed to afford the α-d anomer as the initial product, and the α-d anomer was isomerized into the corresponding β-d anomer to give a mixture. The C-allylation reaction gave only the α-d anomer. C-Pentanonylation, however, gave a mixture of diastereoisomers that could not be isolated. All reactions afforded almost the same results starting with either α- or β-d-ribofuranosyl fluoride. No reaction of the β anomer of 5 with 1-isopropyl-2-methyl-1-propenyl trimethylsilyl ether took place.     

Synthesis of 2-O-benzyl- and 2,3- and 2,6-di-O-benzyl-D-galactose

The following ethers, of potential value for the synthesis of α-D-galactopyranosides, were prepared: 2-O-benzyl-D-galactose, 2,6-di-O-benzyl-D-galactose, and 2,3-di-O-benzyl-D-galactose. Isopropylidenation of methyl α-D-galactopyranoside in the presence of phosphorus pentaoxide gave its 3,4-, and 4,6-O-isopropylidene derivatives. Treatment of the 3,4-acetal with trityl chloride in pyridine produced the 6-trityl ether, which was benzylated with benzyl chloride and sodium hydride in N,N-dimethylformamide to yield the 2-benzyl ether. Acid hydrolysis of this product gave 2-O-benzyl-D-galactose. Benzylation of methyl 3,4-O-isopropylidene-α-D-galactopyranoside, followed by hydrolysis, gave 2,6-di-O-benzyl-D-galactose. Similarly, 2,3-di-O-benzyl-D-galactose was obtained by acid hydrolysis of methyl 2,3-di-O-benzyl-4,6-O-isopropylidene-α-D-galactopyranoside and of methyl 2,3-di-O-benzyl-4,6-O-benzylidene-β-D-galactopyranoside.     

The synthesis of racemic purpurosamine B

Starting from methyl 4,6-dichloro-4,6-dideoxy-α-D-galactopyranoside (1), D-chalcose (4,6-dideoxy-3-O-methyl-D-xcylo-hexopyranose) (5) was prepared by dechlorination with tributyltin hydride, selective benzoylation with benzoyl cyanide at O-2, methylation at O-3, and acid hydrolysis. D-Chalcose (5) was obtained as well by direct methylation of 1 with diazomethane at O-3, reduction with tin hydride, and hydrolysis. Chalcosyl bromide prepared from 5 was not very suitable for β-glycoside synthesis under Koenigs-Knorr conditions, and better results were obtained with 2- O-acetyl-4,6-dichloro-4,6-dideoxy-3-O-methyl-α-D-galactopyranosyl bromide, which gave β-glycosides with methanol, cyclohexanol, benzyl alcohol, 1,2:3,4-di-O-isopropylidene-α-D-galactopyranose, and methyl 2,3-di-O-benzyl-6-deoxy-α-D-glucopyranoside. After dechlorination with tributyltin hydride, the corresponding β-glycosides of D-chalcose were obtained in good yield.     

Oligosaccharides from “standardized intermediates”. Synthesis of a branched tetrasaccharide glycoside isomeric with the blood-group B,type 2 determinant

Building-block derivatives of the component monosaccharides were used to construct the tetrasaccharide glycoside 15, in which an α- d-Galp-(1→4)- d-Gal linkage replaces the α-(1→3) linkage of the human blood-group B, type 2, determinant structure. The initial coupling of 2-O-benzoyl-3,6-di-O-benzyl-4-O-(tetrahydropyran-2-yl)-α- d-galactopyranosyl chloride to allyl 2-acetamido-3,6-di-O-benzyl-2-deoxy-β- d-glucopyranoside was followed by selective deprotection of the disaccharide product, either at O-4′ (to give 8) or O-2′ (to give 3). The conversion of 8 into 15 involved successive coupling with tetra-O-benzyl-α- d-galactopyranosyl bromide ( 8 → 11), O-debenzoylation at O-2′ ( 11 → 12), coupling with tri-O-benzyl-α- l-fucopyranosyl bromide ( 12 → 14), and O-debenzylation by hydrogenolysis ( 14 → 15). Alternatively, 3 was α- l-fucosylated to give 6, and 6 was selectively deprotected at O-4′ to give 7. However, attempts to α- d-galactosylate 7 were unsuccessful. The unsubstituted forms of the intermediate disaccharide ( 8) and trisaccharide ( 12) glycosides were obtained by appropriate deblocking procedures.     

Debenzylation of carbohydrate benzyl ethers and benzyl glycosides via free-radical bromination

The dealkylation of benzylated carbohydrates by free-radical bromination and hydrolysis has been further examined. Free-radical bromination of methyl 2,3,4,6-tetra-O-benzyl-α-D-glucopyranoside (1) methyl 2,3-di-O-benzyl-α-D-glucopyranoside (2) 6-O-benzyl-3,5-O-benzylidene-1,2-O-isopropylidene-α-D-glucofuranose (4) and 6-O-benzyl-D-glucose (3) appears to be quantitative. Spectroscopic evidence of a CBr bond indicates that an α-bromobenzyl ether is the product. Alkaline hydrolysis yielded methyl α-D-glucopyranoside from 1 and 2 and D-glucose from 3 and 4. A benzyl group present as an aglycon could be removed in the same way. Reaction of benzyl α-D-glucopyranoside tetraacetate (6) with bromine and chlorine under free-radical conditions and examination of the products by t.l.c. and i.r. spectrophotometry indicated that the first product was an α-halobenzyl glycoside and that the aglycon could be displaced by Br^- or Cl^- to form the tetra-O-acetyl-D-glucopyranosyl halide, undoubtedly with anomerization. Treatment of the mixture of products with moist ether and silver carbonate yielded only 2,3,4,6-tetra-O-acetyl-D-glucopyranose.     

Synthesis of 3- and 2′-fucosyl-lactose and 3,2′-difucosyl-lactose from partially benzylated lactose derivatives

O-β-d-Galactopyranosyl-(1→4)-O-[α-l-fucopyranosyl-(1→3)]-d-glucose has been synthesised by reaction of benzyl 2,6-di-O-benzyl-4-O-(2,3,4,6-tetra-O-benzyl-β-d-galactopyranosyl)-β-d-glucopyranoside with 2,3,4-tri-O-benzyl-α-l-fucopyranosyl bromide in the presence of mercuric bromide, followed by hydrogenolysis. Benzylation of benzyl 3′,4′-O-isopropylidene-β-lactoside, via tributylstannylation, in the presence of tetrabutylammonium bromide or N-methylimidazole, gave benzyl 2,6-di-O-benzyl-4-O-(6-O-benzyl-3,4-O-isopropylidene-β-d-galactopyranosyl)-β-d-glucopyranoside (6). α-Fucosylation of 6 in the presence of tetraethylammonium bromide provided either benzyl 2,6-di-O-benzyl-4-O-[6-O-benzyl-3,4-O-isopropylidene-2-O-(2,3,4-tri-O-benzyl-α-l-fucopyransoyl)-β-d- galactopyranosyl]-β-d-glucopyranoside (13, 73%) or a mixture of 13 (42%) and benzyl 2,6-di-O-benzyl-4-O-[6-O-benzyl-3,4,-O-isopropylidene-2-O-(2,3,4-tri-O-benzyl-α-l-fucopyranosyl)-β-d- galactopyranosyl-3-O-(2,3,4-tri-O-benzyl-α-l-fucopyranosyl)-β-d-glucopyranoside (16, 34%). α-Fucosylation of 13 in the presence of mercuric bromide and 2,6-di-tert-butyl-4-methylpyridine gave 16 (73%). Hydrogenolysis and acid hydrolysis of 13 and 16 afforded O-α-l-fucopyranosyl-(1→2)-O-β-d-galactopyranosyl-(1→4)-d-glucose and O-α-l-fucopyranosyl-(1→2)-O-β-d-galactopyranosyl-(1→4)-O-[α-l-fucopyranosyl-(1→3)]-d-glucose, respectively.     

Synthesis of p-isothiocyanatophenyl 3-O-(3,5-dideoxy-α-d-ribo-hexopyranosyl)-α-d-mannopyranoside

The synthesis of the title disaccharide derivative (1C), corresponding to the Salmonella O-factor 2¹, is described. Treatment of 2-O-benzyl-4-O-p-nitrobenzoyl-α-paratosyl bromide (5) with p-nitrophenyl 2-O-benzyl-4,6-O-benzylidene-α-d-mannoside in dichloromethane, in the presence of mercuric cyanide, gave the α- and β-linked disaccharide derivatives (6a and 6b) in yields of 34 and 5%, respectively. The disaccharide derivative 10 can react with free amino groups in proteins to produce artificial antigens useful in studies on Salmonella immunology.