Enzymatic Polymerization of α-D-Maltosyl Fluoride Utilizing α-Amylase as the Catalyst: A New Approach for the Synthesis of Maltooligosaccharides

Maltooligosaccharides have effectively been prepared by polycondensation of α-d-maltosyl fluoride (1) using α-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 ¹³C 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 a(1→4)-glycosidic bond is explained by a mechanism involving “double inversion” of the Cl carbon configuration of monomer 1. Other substrates such as d-maltose, α-D-maltosyl fluoride, and α-d-glucosyl fluoride gave no condensation products.