Facile synthesis of a pentasaccharide repeating unit corresponding to the common O-antigen of Salmonella enterica O57 and Escherichia coli O51

A concise chemical synthetic strategy has been developed for the synthesis of a pentasaccharide present in the O-antigen of Salmonella enterica O57 and Escherichia coli O51 strains. A sequential glycosylation strategy has been adopted for the synthesis of the target pentasaccharide. All intermediate steps are high yielding and the glycosylation steps are stereoselective. A number of recently developed methodologies have been used in the synthesis.

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Ethyl 3,4-di-O-benzyl-2-O-(p-methoxybenzyl)-1-thio-α-l-rhamnosideC30H36O5S[α]D25=-59 (c 1.2, CHCl3)Source of chirality: l-rhamnose

Phenyl 2,3,6-tri-O-benzoyl-1-thio-β-d-glucopyranosideC33H28O8S[α]D25=+56 (c 1.2, CHCl3)Source of chirality: d-glucose

Phenyl [3,4-di-O-benzyl-2-O-(p-methoxybenzyl)-α-l-rhamnopyranosyl]-(1→3)-2,3,6-tri-benzoyl-1-thio-β-d-glucopyranosideC61H58O13S[α]D25=-21 (c 1.2, CHCl3)Source of chirality: d-glucose, l-rhamnose

Phenyl [3,4-di-O-benzyl-2-O-(p-methoxybenzyl)-α-l-rhamnopyranosyl]-(1→3)-2,3,6-tri-benzyl-1-thio-β-d-glucopyranosideC61H64O10S[α]D25=-29 (c 1.2, CHCl3)Source of chirality: d-glucose, l-rhamnose

2-(p-Methoxyphenoxy) ethyl (3,4-di-O-benzyl-α-l-rhamnopyranosyl)-(1→4)-(2,3,6-tri-O-benzyl-α-d-glucopyranosyl)-(1→3)-2-azido-4,6-O-benzylidene-2-deoxy-β-d-galactopyranosideC69H75N3O16[α]D25=-16 (c 1.2, CHCl3)Source of chirality: d-galactose, d-glucose, l-rhamnose

2-(p-Methoxyphenoxy) ethyl (2-O-acetyl-3,4-di-O-benzyl-α-l-rhamnopyranosyl)-(1→2)-(3,4-di-O-benzyl-α-l-rhamnopyranosyl)-(1→4)-(2,3,6-tri-O-benzyl-α-d-glucopyranosyl)-(1→3)-2-azido-4,6-O-benzylidene-2-deoxy-β-d-galactopyranosideC91H99N3O21[α]D25=-4 (c 1.2, CHCl3)Source of chirality: d-galactose, d-glucose, l-rhamnose

2-(p-Methoxyphenoxy) ethyl (3,4-di-O-benzyl-α-l-rhamnopyranosyl)-(1→2)-(3,4-di-O-benzyl-α-l-rhamnopyranosyl)-(1→4)-(2,3,6-tri-O-benzyl-α-d-glucopyranosyl)-(1→3)-2-azido-4,6-O-benzylidene-2-deoxy-β-d-galactopyranosideC89H97N3O20[α]D25=-10 (c 1.2, CHCl3)Source of chirality: d-galactose, d-glucose, l-rhamnose

2-(p-Methoxyphenoxy) ethyl (3-O-acetyl-4,6-O-benzylidene-2-deoxy-2-N-phthalimido-β-d-glucopyranosyl)-(1→2)-(3,4-di-O-benzyl-α-l-rhamnopyranosyl)-(1→2)-(3,4-di-O-benzyl-α-l-rhamnopyranosyl)-(1→4)-(2,3,6-tri-O-benzyl-α-d-glucopyranosyl)-(1→3)-2-azido-4,6-O-benzylidene-2-deoxy-β-d-galactopyranosideC112H116N4O27[α]D25=-11 (c 1.2, CHCl3)Source of chirality: d-galactose, d-glucose, l-rhamnose, d-glucosamine

2-(p-Methoxyphenoxy) ethyl (2-acetamido-2-deoxy-β-d-glucopyranosyl)-(1→2)-(α-l-rhamnopyranosyl)-(1→2)-(α-l-rhamnopyranosyl)-(1→4)-(α-d-glucopyranosyl)-(1→3)-2-acetamido-2-deoxy-β-d-galactopyranosideC43H68N2O26[α]D25=-1 (c 1.2, CHCl3)Source of chirality: d-galactose, d-glucose, l-rhamnose, d-glucosamine