Synthesis and properties of selected alpha amylase inhibitors

Abstract

A logical approach to the design of [alpha]-amylase inhibitors is developed from the known features of catalysis by glycosidases in general and [alpha]-amylases in particular. Four potential inhibitors of wheat a-amylase namely maltobiono-cf-lactone, maltal, N-D-glucosylbenzyl-amine and N-D-glucosylpiperidine have been synthesised and their structure established by a variety of physical methods. 1H NMR has shown maltal to exist either as an equilibrium system involving the and conformations, with the predominating, or possibly as a single conformation slightly distorted from the classical half chair. Both N-D-glucosylbenzylamine and N-D-glucosylpiperidine were shown to exist in the 3-form with the normal chair conformation of the sugar ring. The substituted piperidine ring undergoes rapid ring inversion at ambient temperature. For the inhibition studies, wheat g-amylase was extracted from a sample of malted Champlein wheat and obtained with a specific activity of 44 Units per mg of protein. Inhibition by maltobiono-s-lactone and maltal was examined at pH 5.0 by analysing for reducing sugar production using the alkaline ferricyanide method, Maltoiono-c-lactone was shown to be a non-competitive inhibitor with an inhibition constant of 2.5 mM. Maltal behaved as a slow-binding inhibitor, and atequilibrium (which was reached after about one hour undertest conditions) acted competitively with an inhibition constant of 4.4 mM. Inhibition by the N-glycosylamines was complicated by their significant hydrolysis at pH 5, and was examined at pH 6 using an iodine stain technique. N-D-glucosylbenylamine and N-D-glucosyl-t piperidine were moderate inhibitors of wheat a-amylase. Their inhibition behaviour was complex (non-linear), possibly because of concomitant hydrolysis.