Directed enzymatic synthesis of linear and branched gluco-oligosaccharides, using cyclodextrin-glucanosyltransferase

Cyclodextrin-glucanosyltransferase, in a kinetically controlled reaction, transfers one maltohexaosyl residue from cyclomaltohexaose (alpha CD) to HO-4 of an acceptor to form a linear or a branched gluco-oligosaccharide. The primary transfer product can be isolated in yields up to 45% and in high purity, if the reaction is stopped at an early stage. With increasing time of incubation, secondary and tertiary transfer products are formed by stepwise addition of maltohexaosyl units. At equilibrium, a mixture with almost equal proportions of oligosaccharides is obtained. Glucose and malto-oligosaccharides of any chain length carrying a free 4-hydroxyl group and with HO-1 free or substituted, and regardless of the configuration at C-1, may serve as acceptors. Substrates with galacto or manno configuration were not utilised by the enzyme. The selectivity of the enzyme with respect to the site of chain elongation in branched acceptor molecules has been investigated. The technique described here may be applied to prepare linear gluco-oligosaccharides of any chain length of branched oligosaccharides of the amylopectin type.