Desymmetrization of cbz-serinol catalyzed by crude pig pancreatic lipase reveals action of lipases with opposite enantioselectivity

Lipase preparations from pig pancreas are widely used in industrial production of fine chemicals and pharmaceuticals. In our attempts to synthesize enantiopure building blocks for production of iminocyclitols, we used a crude preparation of pig pancreatic lipase in acetylation of carboxybenzyl-2-amino-1,3-propanediol (cbz-serinol) with vinyl acetate in tetrahydrofuran. The enantiomeric excess of the product monoester changed from (2S)-monoacetate to (2R)-monoacetate after prolonged reaction. By using vinyl acetate both as solvent and acyl donor only the (2R)-monoacetate was obtained. Purified enzyme preparation gave only the (2S)-monoacetate. It is likely that the crude enzyme preparation contains lipases with opposite stereoselectivity, acting at different rates in the desymmetrization reaction. The same enzyme preparation was used in hydrolysis of the diacetylated propanediol in phosphate buffer and acetonitrile as co-solvent. After 24 h the (2S)-monoacetate was obtained in high enantiomeric excess. Our results show that monitoring the progress of biocatalyzed reactions are of utmost importance, in particular when crude enzyme preparations are used as catalysts.