CHEMOENZYMATIC SYNTHESIS OF 6-OMEGA-S-ALPHA-D-GLUCOPYRANOSYL-6-OMEGA-THIOMALTOOLIGOSACCHARIDES - THEIR BINDING TO ASPERGILLUS-NIGER GLUCOAMYLASE G1 AND ITS STARCH-BINDING DOMAIN

A coupling reaction of cyclodextrin glucosyltransferase (CGTase) with glucose and 6-deoxy-6-iodo-cyclomaltoheptaose (1), in the presence of glucoamylase, followed by acetylation, led to a convenient synthesis of acetylated 6(III)-deoxy-6(III)-iodo-maltotriose (2) and 6(IV)-deoxy-6(IV)-iodo-maltotetraose (3). Nucleophilic displacement of the iodine atom of these protected maltotriose and maltotetraose analogs by the activated form of 2,3,4,6-tetra-O-acetyl-1-S-acetyl-1-thio-alpha-D-glucose (4) afforded peracetylated 6(III)-S-alpha-D-glucopyranosyl-6(III)-thiomaltotriose (5) and 6(IV)-S-alpha-D-gluco-pyranosyl-6(IV)-thiomaltotetraose (6) in high yield. The interaction of OH-free tetra- and penta-saccharides (7 and 8) with both glucoamylase G1 from Aspergillus niger as well as its isolated starch-binding domain fragment were studied by UV difference spectroscopy. It was found that the starch-binding domain has higher affinity for 7 and 8 than for maltotetraose and maltopentaose.