Chemical synthesis of 6‴-α-maltotriosyl-maltohexaose as substrate for enzymes in starch biosynthesis and degradation

A branched nonasaccharide 6‴-α-maltotriosyl-maltohexaose was synthesised in 40 steps from d-glucose and maltose. Phenyl O-(2,3,4,6-tetra-O-benzyl-α-d-glucopyranosyl)-(1→4)-O-(2,3,6-tri-O-benzyl-α-d-glucopyranosyl)-(1→4)-2,3-di-O-benzyl-1-thio-β-d-glucopyranoside and O-(2,3,4,6-tetra-O-benzyl-α-d-glucopyranosyl)-(1→4)-O-(2,3,6-tri-O-benzyl-α-d-glucopyranosyl)-(1→4)-2,3,6-tri-O-benzyl-α,β-d-glucopyranosyl trichloroacetimidate were coupled by a general condensation reaction to form the per-O-benzylated branched hexasaccharide phenyl thioglycoside. The phenylthio group of this compound was converted into a trichloroacetimidate, which was coupled with phenyl O-(2,3,6-tri-O-benzyl-α-d-glucopyranosyl)-(1→4)-O-(2,3,6-tri-O-benzyl-α-d-glucopyranosyl)-(1→4)-2,3,6-tri-O-benzyl-1-thio-β-d-glucopyranoside to afford the per-O-benzylated branched nonasaccharide phenyl thioglycoside. Replacement of the phenylthio group with a free OH-group followed by hydrogenolysis gave the desired product. The synthons reported for this synthesis constitute a versatile tool for the chemical synthesis of other complex carbohydrates.