Chemical synthesis of a dual branched malto-decaose:: A potential substrate for α-amylases

A convergent block strategy for general use in efficient synthesis of complex alpha-(1 -> 4)- and alpha-(1 -> 6)-malto-oligosaccharides is demonstrated with the first chemical synthesis of a malto-oligosaccharide, the decasoccharide 6,6""-bis(alpha-maltosyl)-maltohexaose, with two branch points. Using this chemically defined branched oligosaccharide as a substrate, the cleavage pattern of seven different alpha-amylases were investigated. alpha-Amylases from human saliva, porcine pancreas, barley alpha-amylose 2 and recombinant barley alpha-amylase 1 all hydrolysed the decasaccharide selectively. This resulted in a branched hexasaccharide and a branched tetrasoccharide. alpha-Amylases from Asperagillus oryzae, Bacillus licheniformis and Bacillus sp. cleaved the decasoccharide at two distinct sites, either producing two branched pentasoccharides, or a branched hexasoccharide and a branched tetrasaccharide. In addition, the enzymes were tested on the single branched octasoccharide 6-alpha-maltosyl-maltohexaose, which was prepared from 6,6""-bis(alpha-maltosyl)-maltohexoose by treatment with malt limit dextrinose. A similar cleavage pattern to that found for the corresponding linear malto-oligosaccharide substrate was observed.