FACTORS AFFECTING THE LIPASE-CATALYZED TRANSESTERIFICATION REACTIONS OF 3-HYDROXY ESTERS IN ORGANIC-SOLVENTS

Chiral resolutions of racemic 3-hydroxy esters were performed in organ ic phases with lipases from Pseudomonas cepacia, Chromobacterium visco sum and Porcine pancreas. The reaction conditions have been optimized with 3-hydroxy octanoic acid methyl ester. Different organic solvents have been tested showing a tendentious correlation with the hydrophobi city of the solvents expressed as log P. The reaction time was shorten ed six fold by using irreversible acylating agents. We have found solv ent type, lipase type and acylating agent acting as tools for changing the enantioselectivity. Lipase from Pseudomonas cepacia was lyophiliz ed at different pH and the influence of the amount of water added was investigated, resulting in the highest activity at the pH optimum and a denaturation of the lipase above 1 % water (w/w(lipase). The water a ctivity was measured on-line with a humidity sensor. Water activities greater than 0.4 led to a decrease in enantioselectivity and reaction rate. In the optimized system the resolutions of other 3-hydroxy ester s were tested. Aliphatic compounds reacted with lower enantioselectivi ty, only the substrates could be isolated in high enantiomeric purity. In contrast, aromatic 3-hydroxy esters were acylated by lipases with high stereoselectivity. A model of the active site of lipase from Pseu domonas sp. explained these experimental observations.