CHEMOENZYMATIC SYNTHESIS OF D-GLUCOPYRANOSYL-6-OMEGA-THIOMALTOOLIGOSACCHARIDES - THEIR BINDING TO ASPERGILLUS-NIGER GLUCOAMYLASE G1 AND ITSSTARCH-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 o f 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 a ctivated form of 6-tetra-O-acetyl-1-S-acetyl-1-thio-alpha-D-glucose (4 ) afforded peracetylated I)-S-alpha-D-glucopyranosyl-6(III)-thiomaltot riose (5) and -S-alpha-D-gluco-pyranosyl-6(IV)-thiomaltotetraose (6) i n 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 differe nce spectroscopy. It was found that the starch-binding domain has high er affinity for 7 and 8 than for maltotetraose and maltopentaose.