Synthesis of the hexasaccharide repeating unit corresponding to the cell wall lipopolysaccharide of Azospirillum irakense KBC1

A convenient chemical synthesis of the hexasaccharide repeating unit of the cell wall lipopolysaccharide of Azospirillum irakense KBC1 has been successfully achieved. A stereo- and regioselective [4 + 2] block glycosylation strategy has been used to obtain the target hexasaccharide as its octyl glycoside. All synthetic intermediates have been prepared in high yields from commercially available reducing sugars following a series of protection–deprotection reactions. An oxidation–reduction methodology has been applied to convert β-d-glucosidic unit to a β-d-mannosidic moiety.

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Octyl [2-O-acetyl-4-O-benzyl-3-O-(4-methoxybenzyl)-α-l-rhamnopyranosyl]-(1→3)-4-O-acetyl-2,6-di-O-benzyl-β-d-galactopyranosideC53H68O13[α]D25=+1.1 (c 1.2, CHCl3)Source of chirality: d-galactose, l-rhamnose

Octyl [2,4-di-O-benzyl-3-O-(4-methoxybenzyl)-α-l-rhamnopyranosyl]-(1→3)-2,4,6-tri-O-benzyl-β-d-galactopyranosideC63H76O11[α]D25=-7 (c 1.2, CHCl3)Source of chirality: d-galactose, l-rhamnose

Octyl [2,4-di-O-benzyl-3-O-(4-methoxybenzyl)-α-l-rhamnopyranosyl]-(1→3)-2,4,6-tri-O-benzyl-β-d-galactopyranosideC55H68O10[α]D25=-1.4 (c 1.2, CHCl3)Source of chirality: d-galactose, l-rhamnose

Octyl (2-O-acetyl-3,4-di-O-benzyl-α-l-rhamnopyranosyl)-(1→3)-(2,4-di-O-benzyl-α-l-rhamnopyranosyl)-(1→3)-2,4,6-tri-O-benzyl-β-d-galactopyranosideC77H92O15[α]D25=-5.9 (c 1.2, CHCl3)Source of chirality: d-galactose, l-rhamnose

Octyl (3,4-di-O-benzyl-α-l-rhamnopyranosyl)-(1→3)-(2,4-di-O-benzyl-α-l-rhamnopyranosyl)-(1→3)-2,4,6-tri-O-benzyl-β-d-galactopyranosideC75H90O14[α]D25=-15.1 (c 1.2, CHCl3)Source of chirality: d-galactose, l-rhamnose

Octyl (2,3-di-O-acetyl-4,6-O-benzylidene-β-d-glucopyranosyl)-(1→2)-(3,4-di-O-benzyl-α-l-rhamnopyranosyl)-(1→3)-(2,4-di-O-benzyl-α-l-rhamnopyranosyl)-(1→3)-2,4,6-tri-O-benzyl-β-d-galactopyranosideC92H108O21[α]D25=-16 (c 1.2, CHCl3)Source of chirality: d-galactose, l-rhamnose, d-glucose

Octyl (4,6-O-benzylidene-β-d-glucopyranosyl)-(1→2)-(3,4-di-O-benzyl-α-l-rhamnopyranosyl)-(1→3)-(2,4-di-O-benzyl-α-l-rhamnopyranosyl)-(1→3)-2,4,6-tri-O-benzyl-β-d-galactopyranosideC88H104O19[α]D25=-9 (c 1.0, CHCl3)Source of chirality: d-galactose, l-rhamnose, d-glucose

Ethyl (2,3,5,6-tetra-O-benzyl-α-d-galactofuranosyl)-(1→2)-3,4-di-O-benzyl-1-thio-α-l-rhamnopyranosideC56H62O9S[α]D25=+16 (c 1.2, CHCl3)Source of chirality: d-galactose, l-rhamnose

Octyl (2,3,5,6-tetra-O-benzyl-α-d-galactofuranosyl)-(1→2)-(3,4-di-O-benzyl-α-l-rhamnopyranosyl)-(1→3)-(4,6-O-benzylidene-β-d-glucopyranosyl)-(1→2)-(3,4-di-O-benzyl-α-l-rhamnopyranosyl)-(1→3)-(2,4-di-O-benzyl-α-l-rhamnopyranosyl)-(1→3)-2,4,6-tri-O-benzyl-β-d-galactopyranosideC142H160O28[α]D25=-7.2 (c 1.2, CHCl3)Source of chirality: d-galactose, l-rhamnose, d-glucose, d-galactose

Octyl (α-d-galactofuranosyl)-(1→2)-(α-l-rhamnopyranosyl)-(1→3)-(β-d-mannopyranosyl)-(1→2)-(α-l-rhamnopyranosyl)-(1→3)-(α-l-rhamnopyranosyl)-(1→3)-β-d-galactopyranosideC44H78O28[α]D25=-27 (c 1.0, CH3OH)Source of chirality: d-galactose, l-rhamnose, d-glucose, d-galactose