chemoenzymatic Syntheses of Linear and Branched Hemithiomaltodextrins as Potential Inhibitors for Starch-Debranching Enzymes

摘要

Oligosaccharides embodying the S-maltosyl-6-thiomaltosl structure have been readily synthesised by using convergent chemoenzymatic approaches. The key steps for the preparation of these molecules involved: 1) transglycosylation reactions of maltosyl fluorides onto suitable acceptors catalysed by the bacterial transglycosylase, cyclodextrin glycosyltransferase (CGTase), and 2) the S_N2-type displacement of a 6-halide from acetylated acceptors by activated 1-thioglycoses. The target molecules, which were obtained in good overall yields, proved to be useful for investigating substrate binding in the active sites of several enzyme that act upon the #alpha#-1,6-linkage of pullulan and/or amylopectin. The compounds exhibit K_I values in the 2.5-1350 #mu#M range with the different enzymes, and the highest affinity found by using these molecules was seen for the pullulanase from Bacillus acidopullulyticus. Both barley-malt limit dextrinase and pullulanase type II from Thermococcus hydrothermalis only recognized the longest linear thiooligosaccharide, while a branched heptasaccharide was the strongest inhibitor of pullulanase from Klebsiella planticola.