ENZYMATIC POLYMERIZATION OF ALPHA-D-MALTOSYL FLUORIDE UTILIZING ALPHA-AMYLASE AS THE CATALYST - A NEW APPROACH FOR THE SYNTHESIS OF MALTOOLIGOSACCHARIDES

Maltooligosaccharides have effectively been prepared by polycondensation Of alpha-D-maltosyl fluoride (1) using alpha-amylase as the catalyst in a mixed solvent of methanol-phosphate buffer (pH 7) (enzymatic polymerization). The structure of the resulting oligomers was confirmed by means of C-13 NMR spectroscopy as well as by an enzymatic hydrolysis experiment. The most appropriate reaction conditions for the production of the higher oligomers were to use methanol/buffer = 2/1 as solvent and to employ an amylase enzyme from Aspergillus oryzae as the catalyst. The stereo- and regioselective formation of an alpha(1 --> 4)-glycosidic bond is explained by a mechanism involving "double inversion" of the C1 carbon configuration of monomer 1. Other substrates such as D-maltose, beta-D-maltosyl fluoride, and alpha-D-glucosyl fluoride gave no condensation products.