KINETIC-STUDY OF CHEMOSELECTIVE ACYLATION OF AMINO-ALDITOL BY IMMOBILIZED LIPASE IN ORGANIC-SOLVENT - EFFECT OF SUBSTRATE IONIZATION

The kinetics of the lipase-catalyzed synthesis of oleoyl-N-methylgluca mide and 6-O-oleoyl-N-methylglucamine in organic systems were investig ated. We have shown that in apolar media, the ionic state of substrate s and the ionic state of enzyme microenvironment play an important rol e in immobilized Candida antarctica lipase activity and chemoselectivi ty of the reaction. In order to define the optimal conditions of the r eaction, to obtain the highest initial rate for amide formation, the i nfluence of acid/N-methylglucamine molar ratio is studied. This ratio determines the protonation states of substrates and of ionizable group s of catalytic site, on which the enzyme activity is dependent. To con firm our hypothesis, we have added to the medium a non-reactive base w hich is not a substrate of the enzyme. We observed that when the acid/ base ratio is higher than 1, the initial rate of ester synthesis incre ases whereas that of amide synthesis decreases. On the opposite, when the acid/base ratio is lower than i, the initial rate of amide synthes is becomes preponderant. (C) 1998 Elsevier Science B.V. All rights res erved.