Concise synthesis of a pentasaccharide repeating unit corresponding to the O-antigen of Escherichia coli O102

An efficient synthetic strategy has been developed for the synthesis of a pentasaccharide repeating unit of the O-antigen of Escherichia coli O102 strain. The target pentasaccharide 1 has been synthesized using a [2+3] block glycosylation strategy. All glycosylation steps are highly stereoselective and high yielding. Concept of armed-disarmed and orthogonal glycosylation strategies has been applied during the synthesis. The target compound has been synthesized using the minimum number of steps.

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p-Methoxyphenyl 6-O-benzyl-2-deoxy-2-N-phthalimido-β-d-galactopyranosideC28H27NO8[α]D25=+6 (c 1.0, CHCl3)Source of chirality: d-Galactosamine

Ethyl 3-O-acetyl-6-O-benzoyl-2-deoxy-2-N-phthalimido-1-thio-β-d-galactopyranosideC25H25NO8S[α]D25=+29 (c 1.0, CHCl3)Source of chirality: d-Galactosamine

Ethyl (2,6-di-O-benzyl-3,4-O-isopropylidene-α-d-galactopyranosyl)-(1→6)-2,3,4-tri-O-benzoyl-1-thio-β-d-glucopyranosideC52H54O13S[α]D25=+30 (c 1.0, CHCl3)Source of chirality: d-Glucose, d-galactose

p-Methoxyphenyl (2,6-di-O-benzyl-3,4-O-isopropylidene-α-d-galactopyranosyl)-(1→6)-2,3,4-tri-O-benzoyl-β-d-glucopyranosideC78H75NO21[α]D25=+35 (c 1.0, CHCl3)Source of chirality: d-Galactose, d-glucose, d-galactosamine

p-Methoxyphenyl (2,6-di-O-benzyl-α-d-galactopyranosyl)-(1→6)-2,3,4-tri-O-benzoyl-β-d-glucopyranosyl)-(1→3)-4-O-acetyl-6-O-benzyl-2-deoxy-2-N-phthalimido-β-d-galactopyranosideC77H73NO22[α]D25=+12 (c 1.0, CHCl3)Source of chirality: d-Galactose, d-glucose, d-galactosamine

Ethyl (2,3,4-tri-O-benzyl-α-l-rhamnopyranosyl)-(1→4)-3-O-acetyl-6-O-benzoyl-2-deoxy-2-N-phthalimido-1-thio-β-d-galactopyranosideC52H53NO12S[α]D25=+10 (c 1.0, CHCl3)Source of chirality: l-Rhamnose, d-galactosamine

p-Methoxyphenyl (2,3,4-tri-O-benzyl-α-l-rhamnopyranosyl)-(1→4)-(3-O-acetyl-6-O-benzoyl-2-deoxy-2-N-phthalimido-β-d-galactopyranosyl)-(1→3)-(2,6-di-O-benzyl-α-d-galactopyranosyl)-(1→6)-(2,3,4-tri-O-benzoyl-β-d-glucopyranosyl)-(1→3)-4-O-acetyl-6-O-benzyl-2-deoxy-2-N-phthalimido-β-d-galactopyranosideC127H120N2O34[α]D25=+8 (c 1.0, CHCl3)Source of chirality: l-Rhamnose, d-galactosamine, d-galactose, d-glucose, d-galactosamine

p-Methoxyphenyl (α-l-rhamnopyranosyl)-(1→4)-(2-acetamido-2-deoxy-β-d-galactopyranosyl)-(1→3)-(α-d-galactopyranosyl)-(1→6)-(β-d-glucopyranosyl)-(1→3)-2-acetamido-2-deoxy-β-d-galactopyranosideC41H64N2O26[α]D25=+4 (c 1.0, CHCl3)Source of chirality: l-Rhamnose, d-galactosamine, d-galactose, d-glucose, d-galactosamine