Syntheses of model oligosaccharides of biological significance.Synthesis of methyl 3,6-DI-O-(α-d-mannopyranosyl)-α-d-mannopyranoside and the corresponding mannobiosides

Methyl 2-O-allyl-4,6-O-benzylidene-3-O-(2,3,4,6-tetra-O-acetyl-α-d-mannopyranosyl)-α-d-mannopyranoside(12) was prepared in 90 % yield by Helferich glycosylation of methyl 2-O-allyl-4,6-O-benzylidene-α-d-mannopyranoside (9) with tetra-O-acetyl-α-d-mannopyranosyl bromide (11). Removal of the benzylidene group and second Helferich glycosylation with 11 led to methyl 2-O-allyl-3,6-di-O-(2,3,4,6-tetra-O-acetyl-α-d-mannopyranosyl)-α-d-mannopyranoside (14) which, after deallylation and Zemplén deacetylation, gave the title compound 5. The disaccharides methyl 3-O-(α-d-mannopyranosyl)-α-d-mannopyranoside (7) and methyl 6-O-(α-d-mannopyranosyl)-α-d-mannopyranoside (6) have also been synthesized. Complete assignments of the ¹H-n.m.r. spectra of the compounds 5, 6, and 7 are given.     

Synthesis of 2-acetamido-2-deoxy-3-O-β-d-mannopyranosyl-d-glucose

Condensation of 4,6-di-O-acetyl-2,3-O-carbonyl-α-d-mannopyranosyl bromide with benzyl 2-acetamido-4,6-O-benzylidene-2-deoxy-α-d-glucopyranoside (2) gave an α-d-linked disaccharide, further transformed by removal of the carbonyl and benzylidene groups and acetylation into the previously reported benzyl 2-acetamido-4,6-O-benzylidene-2-deoxy-3-O-(2,3,4,6-tetra-O-acetyl-α-d-mannopyranosyl)-α-d-glucopyranoside. Condensation of 3,4,6-tri-O-benzyl-1,2-O-(1-ethoxyethylidene)-α-d-glucopyranose or 2-O-acetyl-3,4,6-tri-O-benzyl-α-d-glucopyranosyl bromide with 2 gave benzyl 2-acetamido-3-O-(2-O-acetyl-3,4,6-tri-O-benzyl-β-d-glucopyranosyl)-4,6-O-benzylidene-2-deoxy-α-d-glucopyranoside. Removal of the acetyl group at O-2, followed by oxidation with acetic anhydride-dimethyl sulfoxide, gave the β-d-arabino-hexosid-2-ulose 14. Reduction with sodium borohydride, and removal of the protective groups, gave 2-acetamido-2-deoxy-3-O-β-d-mannopyranosyl-d-glucose, which was characterized as the heptaacetate. The anomeric configuration of the glycosidic linkage was ascertained by comparison with the α-d-linked analog.     

Synthèse des l-fucose et l-(3-2H)fucose à partir du d-mannose

Oxidation with the dimethyl sulfoxide-acetic anhydride reagent of methyl 2-O-acetyl-4,6-O-benzylidene-α-d-mannopyranoside, obtained in quantitative yield from the corresponding 4,6-benzylidene acetal by stereoselective opening of a 2,3-orthoester, led in good yield to methyl 2-O-acetyl-4,6-O-benzylidene-α-d-arabino-hexopyranosid-3-ulose, which was reduced with either sodium borohydride or sodium borodeuteride into a methyl 4,6-O-benzylidene-α-d-altropyranoside or its 3-²H derivative. A sequence involving a C-6 halogenation-dehydrohalogenation followed by catalytic hydrogenation of the resulting methyl 6-deoxy-α-d-arabino-hex-5-enopyranoside gave methyl 6-deoxy-β-l-galactopyranoside (methyl β-l-fucopyranoside) and then α-l-fucose, with an overall yield of 24% with respect to the starting methyl α-d-mannopyranoside.     

Unambiguous syntheses of the 3,4-di- and 3,4,6-tri-methyl ethers of methyl α-d-mannopyranoside

The unambiguous syntheses of methyl 3,4,6-tri-O-methyl-α-d-mannopyranoside (6) and methyl 3,4-di-O-methyl-α-d-mannopyranoside (10) were performed by routes involving methyl 3-O-benzoyl-4,6-O-benzylidene-α-d-mannopyranoside (1) to form methyl 2-O-p-tolylsulfonyl-d-mannopyranoside (4). Compound 4 directly led to 6, and, via a 6-trityl derivative, to 10.     

The synthesis and degradation of benzyl 4,6-O-benzylidene-2,3-dideoxy-3-C-ethyl-2-C-hydroxymethyl-α-d-glucopyranoside and -mannopyranoside

The use of carbohydrates for establishing, by synthesis, the absolute configuration of branched aliphatic alcohols is demonstrated by the synthesis and degradation of carbohydrate derivatives that contain two branch points. Benzyl 4,6-O-benzylidene-2,3-dideoxy-3-C-ethyl-2-C-hydroxymethyl-α-d-glucopyranoside (23) and -mannopyranoside (24) were formed from benzyl 2,3-anhydro-4,6-O-benzylidene-α-d-mannopyranoside (17) by a reaction sequence that involved ring-opening with ethylmagnesium chloride, oxidation, epimerisation, methylenation, and hydroboronation. The gluco isomer 23 was converted into (+)-(R)-2,3-bisacetoxymethylpentyl acetate (1) by sequential hydrogenolysis, borohydride reduction, periodate oxidation, borohydride reduction, and acetylation. The synthesis of 1 provides confirmatory evidence for the absolute configuration of the alkaloid pilocarpine (2). Unidentified products, and not the expected free-sugars, were obtained by acidic hydrolysis of methyl 4,6-O-benzylidene-2,3-dideoxy-3-C-ethyl-2-C-hydroxymethyl-α-d-glucopyranoside (8) and -mannopyranoside (9). Convenient syntheses of benzyl α-d-glucopyranoside derivatives are described.     

Synthesis of 8-(hydroxyalkyl)adenines

Treatment of methyl 4,6-O-benzylidene-2-O-p-tolylsulfonyl-α-D-ribo-hexopyranosid-3-ulose (1) with triethylamine-methanol at reflux temperature yields methyl 2,3-anhydro-4,6-O-benzylidene-3-methoxy-α-D-allopyranoside (2), a derivative (3) of 3-hydroxy-2-(hydroxymethyl)-4H-pyran-4-one, and methyl 4,6-O-benzylidene-α-D-ribo-hexopyranosid-3-ulose dimethyl acetal (4). The reaction of methyl 4,6-O benzylidene-3-O-p-tolylsulfonyl-α-D-arabino-hexopyranosid-2-ulose (12) with triethylamine-methanol afforded methyl 4,6-O-benzylidene-α-D-ribo-hexopyranosid-2-ulose dimethyl acetal (19) and methyl 2,3-anhydro-4,6-O-benzylidene-2-methoxy-α-D-allopyranoside (20); from the reaction of the β-D anomer (13) of 12, methyl 4,6-O-benzylidene-β-D-ribo-hexopyranosid-2-ulose dimethyl acetal (21) was isolated. Syntheses of the α-keto toluene-p-sulfonates 12 and 13 are described. Mechanisms for the formation of the compounds isolated from the reactions with triethylamine-methanol are proposed.     

Configurational assignments of C-nitromethyl-C-hydroxy branched-chain carbohydrate derivatives by use of a europium shift-reagent in 1 H-N.M.R. spectroscopy

Configurational assignments for the tertiary alcoholic centers of four branched-chain 3-C-nitromethylglycopyranosides, namely, methyl 2-benzamido-4,6-O-benzylidene-2-deoxy-3-C-nitromethyl-α-D-allopyranoside (1), benzyl 2-acetamido-4,6-O-benzylidene-2-deoxy-3-C-nitromethyl-α-D-glucopyranoside (4), benzyl 2-acetamido-4,6-O-benzylidene-2-deoxy-3-C-nitromethyl-α-D-allopyranoside (5), and methyl 4,6-O-benzylidene-3-C-nitromethyl-2-O-p-tolylsulfonyl-α-D-glucopyranoside (8), were made on the basis of the downfield chemical shifts of their identifiable protons per molar equivalent of added Eu(fod)₃, as compared with those of model compounds, of known configuration, having a close structural relationship. In some cases, the assignments were corroborated by the position of the acetyl resonances in the unshifted 60-MHz p.m.r. spectra of the corresponding O-acetyl derivatives.     

Synthèse de trithioorthocarbonates de pyranosides par thermolyse de bis(dithiocarbonates)

The thermal decomposition of methyl 4,6-O-benzylidene-2,3-di-O-[(methylthio)-thiocarbonyl]-α-d-glucopyranoside afforded methyl 4,6-O-benzylidene-2-thio-α-d-mannopyranoside 3-O,2-S-(S,S-dimethyl trithioorthocarbonate) and methyl 4,6-O-benzylidene-3-thio-α-d-allopyranoside 2-O,3-S-(S,S-dimethyl trithioorthocarbonate) in good yield. This decomposition can be generalized to 1,3-diols derived from sugars. Thus methyl 2,3-di-O-methyl-4,6-di-O-[(methylthio)thiocarbonyl]-α-d-glucopyranoside afforded in the same way the corresponding trithioorthocarbonates, following a regioselective process. The structures of these trithioorthocarbonates are confirmed by spectral and chemical proofs.     

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.     

Studies on the structure of a polysaccharide from Epidermophyton floccosum and approach to a synthesis of the basic trisaccharide repeating units

An alkali-soluble polysaccharide, designated as S-Iawe, has been isolated from the maycelia of Epidermophyton floccosum. Methylation, periodate oxidation, and acetolysis studies suggested that S-lawe is composed of (1→6)-Oα-d-mannopyranosyl-(1→6)-O-[α-d-mannopyranosyl-(1→2)]-O-α-d-mannopyranosyl repeating units. Condensation of 2,3,4,6-tetra-O-acetyl-α-d-mannopyranosyl bromide with methyl 3-O-benzyl-4,6-O-benzylidene-α-d-mannopyranoside in the presence of mercuric cyanide gave in 70% yield methyl 3-O-benzyl-4,6-O-benzylidene-2-O-(2,3,4,6-tetra-O-acetyl-α-d-mannopyranosyl)-α-d-mannopyranoside. Condensation of the debenzylidenated disaccharide with 2,3,4,6-tetra-O-acctyl-α-d-mannopyranosyl bromide afforded the corresponding trisaccharide repeating unit.     

Synthesis and 13C-N.M.R. spectroscopy of 2-O- and 6-O-acetyl-3-O-α-l-rhamnopyranosyl-d-galactose,constituents of bacterial cell-wall polysaccharides

Benzyl 2-O-acetyl-4,6-O-benzylidene-3-O-(2,3,4-tri-O-acetyl-α-l-rhamnopyranosyl)-β-d-galactopyranoside (11) has been synthesised by two routes. Partial deacetylation of 11 and then acid hydrolysis yielded benzyl 2-O-acetyl-3-O-α-l-rhamnopyranosyl-β-d-galactopyranoside, catalytic hydrogenolysis of which gave the first title compound in excellent yield. Benzyl 4,6-O-benzylidene-3-O-α-l-rhamnopyranosyl-β-d-galactopyranoside was benzylated, and hydrogenolysis (LiAlH₄-AlCl₃) of the product gave the disaccharide derivative 16 with only HO-6 unsubstituted. Acetylation of 16 followed by catalytic hydrogenolysis gave the crystalline, second title compound. As model compounds for comparative n.m.r. studies, 2-O-, 3-O-, and 6-O-acetyl-d-galactose were also synthesised.     

Synthesis of 2-acetamido-2-deoxy-4-O-β-d-galactopyranosyl-3-O-methyl-d-glucopyranose (N-acetyl-3-O-methyllactosamine) and its benzyl α-glycoside

Benzyl 2-acetamido-2-deoxy-3-O-methyl-α-d-glucopyranoside (3) was obtained by deacetalation of its 4,6-O-benzylidene derivative (2). Compound 2 was prepared by methylation of benzyl 2-acetamido-4,6-O-benzylidene-2-deoxy-α-d-glucopyranoside with methyl iodide-silver oxide in N,N-dimethylformamide. Diol 3 was selectively benzoylated and p-toluenesulfonylated, to give the 6-benzoic and 6-p-toluenesulfonic esters (4 and 5, respectively). Displacement of the sulfonyl group of 5 with sodium benzoxide in benzyl alcohol afforded the 6-O-benzyl derivative (6). Glycosylation of 4 with 2,3,4,6-tetra-O-acetyl-α-d-galactopyranosyl bromide (7) in dichloromethane, in the presence of 1,1,3,3-tetramethylurea, furnished the disaccharide derivative 8. Similar glycosylation of compound 6 with bromide 7 gave the disaccharide derivative 10. O-Deacetylation of 8 and 10 afforded disaccharides 9 and 11. The structure of compound 9 was established by ¹³C-n.m.r. spectroscopy. Hydrogenolysis of the benzyl groups of 11 furnished the disaccharide 2-acetamido-2-deoxy-4-O-β-d-galactopyranosyl-3-O-methyl-d-glucopyranose (N-acetyl-3-O-methyllactosamine).     

Synthesis and biological activity of O-(N-acetyl-β-muramoyl-l-alanyl-d-isoglutamine)-(1→6)-2-acylamino-2-deoxy-d-glucoses

Benzoylation of benzyl 2-acetamido-2-deoxy-4,6-O-isopropylidene-α-d-glucopyranoside, benzyl 2-deoxy-2-(dl-3-hydroxytetradecanoylamino)-4,6-O-isopropylidene-α-d-glucopyranoside, and benzyl 2-deoxy-4,6-O-isopropylidene-2-octadecanoylamino-β-d-glucopyranoside, with subsequent hydrolysis of the 4,6-O-isopropylidene group, gave the corresponding 3-O-benzoyl derivatives (4, 5, and 7). Hydrogenation of benzyl 2-acetamido-4,6-di-O-acetyl-2-deoxy-3-O-[d-1-(methoxycarbonyl)ethyl]-α-d-glucopyranoside, followed by chlorination, gave a product that was treated with mercuric actate to yield 2-acetamido-1,4,6-tri-O-acetyl-2-deoxy-3-O-[d-1-(methoxycarbonyl)ethyl]-β-d-glucopyranose (11). Treatment of 11 with ferric chloride afforded the oxazoline derivative, which was condensed with 4, 5, and 7 to give the (1→6)-β-linked disaccharide derivatives 13, 15, and 17. Hydrolysis of the methyl ester group in the compounds derived from 13, 15, and 17 by 4-O-acetylation gave the corresponding free acids, which were coupled with l-alanyl-d-isoglutamine benzyl ester, to yield the dipeptide derivatives 19–21 in excellent yields. Hydrolysis of 19–21, followed by hydrogenation, gave the respective O-(N-acetyl-β-muramoyl-l-alanyl-d-isoglutamine)-(1→6)-2-acylamino-2-deoxy-d-glucoses in good yields. The immunoadjuvant activity of these compounds was examined in guinea-pigs.     

Reaktionen von kohlenhydraten mit dichlormethylendimethylammoniumchlorid: ein neuer weg zu 2-chlor-2-desoxy-, und 3-chlor-3-desoxyhexose-, und 3-chlor-3-desoxypentosederivaten

Treatment of methyl 4,6-O-benzylidene-α-D-mannopyranoside with dichloromethylenedimethylammonium chloride gave methyl 4,6-O-benzylidene-3-chloro-3-deoxy-2-(N,N-dimethylcarbamoyl)-α-D-altropyranoside and methyl 4,6-O-benzy]idene-2-chloro-2-deoxy-3-(N,N-dimethylcarbamoyl)-α-D-glucopyranoside. Methyl 4,6-O-benzylidene-α-D-allopyranoside gave under analogous conditions the corresponding 2-chloro-3-(N,N-dimethylcarbamoyl)-α-D-altrose and 3-chloro-2-(N,N-dimethylcarbamoyl)-α-D-glucose derivatives. Methyl 5-O-benzyl-α,β-D-ribofuranoside and methyl 5-O-methyl-β-D-ribofuranoside gave only the corresponding methyl 3-chloro-2-(N,N-dimethylcarbamoyl)-α-D-xylofuranoside derivatives.     

New syntheses of methyl 4,6-O-benzylidene-2-deoxy-3-C-methyl-α-d-arabino-hexopyranoside and its conversion into d-evermicose

Methyl 4,6-O-benzylidene-2-deoxy-3-C-methyl-α-d-arabino-hexopyranoside (4) was prepared from methyl 4,6-O-benzylidene-2,3-dideoxy-3-C-methylene-α-d-erythro-hexopyranoside (1b) and from methyl 4,6-O-benzylidetic-3 C-methyl-α-d-gluco-hexopyranoside (6a) by two different methods. Synthesis of d-evermicose3 (10 (2,6-dideoxy-3-C-methyl-d-arabino-hexose) was then achieved in four steps from 4.     

Synthesis of benzyl 2-acetamido-2-deoxy-3-O-β-d-fucopyranosyl-α-d-galactopyranoside and benzyl 2-acetamido-6-O-(2-acetamido-2-deoxy-β-d-glucopyranosyl)-2-deoxy-3-O-β-d-fucopyranosyl-α-d-galactopyranoside

Condensation of benzyl 2-acetamido-4,6-O-benzylidene-2-deoxy-α-d-galactopyranoside with 2,3,4-tri-O-acetyl-α-d-fucopyranosyl bromide in 1:1 nitromethane-benzene, in the presence of powdered mercuric cyanide, afforded benzyl 2-acetamido-4,6-O-benzylidene-2-deoxy-3-O-(2,3,4-tri-O-acetyl-β-d-fucopyranosyl)-α-d-galactopyranoside (3). Cleavage of the benzylidene group of 3 with hot, 60% aqueous acetic acid afforded diol 4, which, on deacetylation, furnished the disaccharide 5. Condensation of diol 4 with 2-methyl-(3,4,6-tri-O-acetyl-1,2-di-deoxy-α-d-glucopyrano)-[2,1-d]-2-oxazoline in 1,2-dichloroethane afforded the trisaccharide derivative (7). Deacetylation of 7 with Amberlyst A-26 (OH^?) anion-exchange resin in methanol gave the title trisaccharide (8). The structures of 5 and 8 were confirmed by ¹³C-n.m.r. spectroscopy.     

Desulfonyloxylations of some secondary p-toluenesulfonates of glycosides by lithium triethylborohydride; a high-yielding route to 2- and 3-deoxy sugars

Lithium triethylborohydride (LTBH) reacts readily with p-toluenesulfonates of methyl 4,6-O-benzylidene-α-d-glucopyranoside (4) to give deoxyglycosides in > 90% yield. Thus, the 2,3-ditosylate (1) and the 3-monotosylate (2) thereof afford methyl 4,6-O-benzylidene-2-deoxy-α-d-ribo-hexopyranoside (7) in highly regio- and stereo-selective reactions that proceed via methyl 2,3-anhydro-4,6-O-benzylidene-α-d-allopyranoside (6), and the 2-monotosylate (8) of 4 gives the 3-deoxy-α-d-arabino isomer (12) of 7via the corresponding 2,3-anhydro-α-d-mannopyranoside 11. In the series of the corresponding β anomers, the 3-monotosylate 14 and the 2-monotosylate 16 are similarly desulfonyloxylated, with equal ease, but furnish mixtures of regioisomeric deoxyglycosides, namely, the 3- and 2-deoxy-β-d-ribo derivatives 20 and 21, and 2- and 3-deoxy-β-d-arabino derivatives 22 and 23, respectively. It could be shown that this difference is due to the failure of the intermediary, β-glycosidic epoxides 18 and 19 (the anomers of 6 and 11) to obey the Fürst-Plattner rule in their reductive ring-opening with LTBH. The β-glycosidic 2,3-ditosylate 15 reacts less readily, and gives 20–23, with 20 preponderating. The 2-O-methyl-3-O-tosyl-β-d-glucopyranoside 24 is partly desulfonylated and partly desulfonyloxylated, whereas its 3-O-methyl-2-O-tosyl isomer 27 undergoes desulfonylation exclusively. The reductions of 1, 2, and 8 by LTBH are compared with those previously effected by lithium aluminum hydride, which are slower, involve considerable desulfonylation, and afford lower yields of deoxyglycosides, with the main products differing from those obtained by the action of LTBH. Mechanistic differences associated with the two reductants are discussed.     

Studies on the stereoselective synthesis of a protected α-d-Gal-(1→2)-d-Glc fragment

A novel 1,2-cis stereoselective synthesis of protected α-d-Gal-(1→2)-d-Glc fragments was developed. Methyl 2-O-acetyl-3-O-allyl-4,6-O-benzylidene-α-d-galactopyranosyl-(1→2)-3-O-benzoyl-4,6-O-benzylidene-α-d-glucopyranoside (13), methyl 2-O-acetyl-3-O-allyl-4,6-O-benzylidene-α-d-galactopyranosyl-(1→2)-3,4,6-tri-O-benzoyl-α-d-glucopyranoside (15), methyl 2-O-acetyl-3-O-allyl-4,6-O-benzylidene-α-d-galactopyranosyl-(1→2)-3-O-benzoyl-4,6-O-benzylidene-β-d-glucopyranoside (17), and methyl 2-O-acetyl-3-O-allyl-4,6-O-benzylidene-α-d-galactopyranosyl-(1→2)-3,4,6-tri-O-benzoyl-β-d-glucopyranoside (19) were favorably obtained by coupling a new donor, isopropyl 2-O-acetyl-3-O-allyl-4,6-O-benzylidene-1-thio-β-d-galactopyranoside (2), with acceptors, methyl 3-O-benzoyl-4,6-O-benzylidene-α-d-glucopyranoside (4), methyl 3,4,6-tri-O-benzoyl-α-d-glucopyranoside (5), methyl 3-O-benzoyl-4,6-O-benzylidene-β-d-glucopyranoside (8), and methyl 3,4,6-tri-O-benzoyl-β-d-glucopyranoside (12), respectively. By virtue of the concerted 1,2-cis α-directing action induced by the 3-O-allyl and 4,6-O-benzylidene groups in donor 2 with a C-2 acetyl group capable of neighboring-group participation, the couplings were achieved with a high degree of α selectivity. In particular, higher α/β stereoselective galactosylation (5.0:1.0) was noted in the case of the coupling of donor 2 with acceptor 12 having a β-CH₃ at C-1 and benzoyl groups at C-4 and C-6.     

Synthesis of p-nitrophenyl 6-O-(2-acetamido-2-deoxy-β-d-glucopyranosyl)-α-d-mannopyranoside

The reaction of p-nitrophenyl 2,3-O-isopropylidene-α-d-mannopyranoside and 2-methyl-(3,4,6-tri-O-acetyl-1,2-dideoxy-α-d-glucopyrano)-[2,1-d]-2-oxazoline gave a crystalline, 6-O-substituted disaccharide derivative which, on de-isopropylidenation followed by saponification, produced the disaccharide p-nitrophenyl 6-O-(2-acetamido-2-deoxy-β-d-glucopyranosyl)-α-d-mannopyranoside. Synthesis of methyl 6-O-(2-acetamido-2-deoxy-β-d-glucopyranosyl)-α-d-mannopyranoside was also accomplished by a similar reaction-sequence. The structures of these disaccharides have been established by ¹³C-n.m.r. spectroscopy.     

Synthesis of a tetrasaccharide donor corresponding to the O-specific polysaccharide of Shigella dysenteriae type 1

O-(2,4-Di-O-chloroacetyl-α-l-rhamnopyranosyl)-(1 → 2)-O-(3,4,6-tri-O-benzoyl-α-d-galactopyranosyl)-(1 → 3)-O-(2-acetamido-4,6-di-O-acetyl-2-deoxy-α-d-glycopyranosyl)-(1 → 3)-2,4-di-O-benzoyl-α-l-rhamnopyranosyl trichloroacetimidate (1) was synthesized in a stepwise manner, using the following monosaccharide units: 2-(trimethylsilyl)ethyl 2,4-di-O-benzoyl-α-l-rhamnopyranoside, 2-azido-4,6-O-benzylidene-3-O-chloroacetyl-2-deoxy-β-d-glycopyranosyl chloride, methyl 3,4,6-tri-O-benzoyl-2-O-(4-methoxybenzyl)-1-thio-β-d-galactopyranoside, and 2,4-di-O-benzoyl-3-O-chloroacetyl-α-l-rhamnopyranosyl chloride. Compound 1 corresponds to a complete tetrasaccharide repeating unit of the O-specific polysaccharide of the lipopolysaccharide of Shigella dysenteriae type 1.