Chemical synthesis of 6"'-alpha-maltotriosyl-maltohexaose as substrate for enzymes in starch biosynthesis and degradation.

A branched nonasaccharide 6"'-alpha-maltotriosyl-maltohexaose was synthesised in 40 steps from D-glucose and maltose. Phenyl O-(2,3,4,6-tetra-O-benzyl-alpha-D-glucopyranosyl)-(1-->4)-O- (2,3,6-tri-O-benzyl-alpha-D-glucopyranosyl)-(1-->4)-2,3-di-O-benzyl-1-th io- beta-D-glucopyranoside and O-(2,3,4,6-tetra-O-benzyl-alpha-D-glucopyranosyl)-(1-->4)-O-(2,3,6-tri- O-benzyl-alpha-D-glucopyranosyl)-(1-->4)-2,3,6-tri-O-benzyl-alpha, beta-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-alpha-D-glucopyranosyl)-(1-->4)-O-(2,3,6-tri-O- benzyl-alpha-D-glucopyranosyl)-(1-->4)-2,3,6-tri-O-benzyl-1-thio-beta-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.