Convergent synthesis of a pentasaccharide repeating unit corresponding to the cell wall O-antigen of Salmonella enterica O44

A convergent synthetic strategy has been developed for the synthesis of a pentasaccharide fragment corresponding to the O-antigen of Salmonella enterica O44 strain. An intermediate tetrasaccharide derivative was prepared by a [2+2] block glycosylation of two disaccharide derivatives. The p-methoxybenzyl (PMB) group has been used as the in situ temporary protecting group minimizing the number of functional group manipulation steps. The application of the armed–disarmed glycosylation concept reduced the number of steps in the synthetic strategy. The glycosylation steps were highly stereoselective and high yielding.

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Ethyl 2,4,6-tri-O-benzyl-3-O-p-methoxybenzyl-1-thio-β-d-galactopyranosideC37H42O6S[α]D25=+19 (c 1.0, CHCl3)Source of chirality: d-galactose

2-Azidoethyl (3-O-benzyl-4,6-O-benzylidene-α-d-glucopyranosyl)-(1→6)-2,3,4-tri-O-benzyl-α-d-glucopyranosideC49H53N3O11[α]D25=+33 (c 1.0, CHCl3)Source of chirality: d-glucose

Ethyl (2,4,6-tri-O-benzyl-3-O-p-methoxybenzyl-α-d-galactopyranosyl)-(1→3)-4,6-O-benzylidene-2-deoxy-2-N-phthalimido-1-thio-β-d-glucopyranosideC58H59NO12S[α]D25=+25 (c 1.0, CHCl3)Source of chirality: d-galactose, d-glucosamine

2-Azidoethyl (2,4,6-tri-O-benzyl-α-d-galactopyranosyl)-(1→3)-(4,6-O-benzylidene-2-deoxy-2-N-phthalimido-β-d-glucopyranosyl)-(1→2)-(3-O-benzyl-4,6-O-benzylidene-α-d-glucopyranosyl)-(1→6)-2,3,4-tri-O-benzyl-α-d-glucopyranosideC97H98N4O22[α]D25=+28 (c 1.0, CHCl3)Source of chirality: d-galactose, d-glucosamine, d-glucose

2-Azidoethyl (3,4,6-tri-O-acetyl-2-deoxy-2-N-phthalimido-β-d-glucopyranosyl)-(1→3)-(2,4,6-tri-O-benzyl-α-d-galactopyranosyl)-(1→3)-(4,6-O-benzylidene-2-deoxy-2-N-phthalimido-β-d-glucopyranosyl)-(1→2)-(3-O-benzyl-4,6-O-benzylidene-α-d-glucopyranosyl)-(1→6)-2,3,4-tri-O-benzyl-α-d-glucopyranosideC117H117N5O31[α]D25=+18 (c 1.0, CHCl3)Source of chirality: d-galactose, d-glucosamine, d-glucose

2-Aminoethyl (2-acetamido-2-deoxy-β-d-glucopyranosyl)-(1→3)-(α-d-galactopyranosyl)-(1→3)-(2-acetamido-2-deoxy-β-d-glucopyranosyl)-(1→2)-(α-d-glucopyranosyl)-(1→6)-α-d-glucopyranosideC36H63N3O26[α]D25=+8 (c 1.0, H2O)Source of chirality: d-galactose, d-glucosamine, d-glucose