Lipase-catalyzed chemoselective N-acylation of amino-sugar derivatives in hydrophobic solvent: Acid-amine ion-pair effects.

Enzymatic N-acylation of N-methyl-glucamine (1-deoxy-1-methylamino-D-glucitol) in hexane using lipase from Rhizomucor miehei (Lipozyme(R)) is described. N-methyl-glucamine was solubilized by oleic acid addition which resulted in the formation of an ion-pair between acid and amine function. This ion-pair, identified by Infra-Red spectroscopy, is essential for amide or ester synthesis. Its stability in hexane was also found to be the limiting factor of reaction yield which never exceeded 50% of acid conversion. The chemoselectivity of the reaction between oleic acid and N-methyl-glucamine towards amide or ester synthesis nas under the control of acid/amine ratio. This is the first report showing the key role of substrate ionic state when operating enzyme catalysis in non-conventional media. (C) 1997 Elsevier Science Ltd.