CHEMOENZYMATIC SYNTHESIS OF GALACTOSYLMALTOOLIGOSACCHARIDONOLACTONE AS A SUBSTRATE-ANALOG INHIBITOR FOR MAMMALIAN ALPHA-AMYLASE

We performed chemo-enzymatic transformation of maltooligosaccharides i nto both end-modified oligosaccharidonolactones of potential use as su bstrate analogue inhibitors for mammalian alpha-amylases, Enzymatic mo dification of the non-reducing end glucosyl residue of the maltooligos accharide was first performed by transglycosylation with beta-D-galact osidase from Bacillus circulans, When maltotriose and maltotetraose we re the accepters, the enzyme regioselectively synthesized 4(3)-O-beta- D-galactosyl maltotriose (LG3) and 4(4)-O-beta-D-galactosyl maltotetra ose (LG4) from lactose as a donor, LG4 was further selectively hydroly zed with a specific alpha-amylase to afford 4(2)-O-beta-D-galactosyl m altose (LG2), The anomer hydroxyl groups of LG2 and LG3 were chemicall y oxidized to give the corresponding lactones, 4(2)-O-beta-D-galactosy l maltobionolactone (LG2O) and 4(3)-O-beta-D-galactosyl maltotrionolac tone (LG3O), respectively, LG2O and LG3O, which are competitive inhibi tors for mammalian alpha-amylases, exhibited K-1 values of the order o f 2.8-18.0 mu M, With p-nitrophenyl alpha-maltopentaoside (G5P) as the substrate, On H-1-NMR analysis, these oligosaccharidonolactones were shown to be transformed into the corresponding aldonic acid forms with time in an aqueous solution, In this case, the lactone form was essen tial for the occurrence of the alpha-amylase inhibitor.