Preparative-scale kinetic resolutions catalysed by microbial lipases immobilised in AOT-stabilised microemulsion-based organogels: cryoenzymology as a tool for improving enantioselectivity

Abstract

Gelatin-containing microemulsion based organogels have been used as an immobilisation matrix for lipases from a number of different sources. Kinetic resolutions of octan-3-ol, 1-octen-3-ol and 1-octyn-3-ol by esterification with decanoic acid have been performed using Chromobacterium viscosum (CV) lipase. CV lipase is highly enantioselective in favour of the ( R)-(−) isomer of octan-3-ol, but the enantioselectivity is both reversed and decreased by the introduction of unsaturation at the 1-position. Marked improvements in enantioselectivity were achieved by carrying out the reaction at −15C, the enantiomeric excess of the ester product increasing from 47% ( E=3) to 73% ( E=8) in the case of 1-octen-3-ol, and from 17% ( E=1.4) to 38% ( E=2.5) in the case of l-octyn-3-ol. The enantiomeric excess was ≈85% ( E ≈15) for octan-3-ol, and there was no marked improvement in enantioselectivity, even at −15°C. Apparent activation energies for the esterification using decanoic acid of octan-3-ol, I-octen-3-ol and 1-octyn-3-ol by CV lipase were 32 kJ mol −1, 31 kJ mol −1 and 41 kJ mol −1, respectively. This compares to an activation energy of 21 kJ mol −1 for the esterification of octan-1-ol with decanoic acid using CV lipase under the same conditions. Lipases from Pseudomonas (Fluka), Pseudomonas (Genzyme) and lipoprotein lipase ex Microbial (Genzyme) also selectively esterified the ( R)-(−) isomer of racemic octan-3-ol, the two Pseudomonas preparations yielding product with an enantiomeric excess of 90%. Candida cylindracea lipase did not exhibit activity in gelatin-containing MBGs. Large-scale syntheses were performed in a 1 dm 3 batch reactor in which 200 cm 3 of pelleted MBG (containing 350 mg of CV lipase) was used repeatedly for the kinetic resolution of octan-3-ol.