Oxidative biotransformations by microorganisms: Production of chiral synthons by cyclopentanone monooxygenase from Pseudomonas sp NCIMB 9872

Cyclopentanone monooxygenase, an NADPH- plus FAD-dependent enzyme induced by the growth of Pseudomonas sp. NCIMB 9872 on cyclopentanol, has been utilised as a biocatalyst in Baeyer-Villiger oxidations. Washed whole-cell preparations of the microorganism oxidised 3-hexylcyclopentanone in a regio- but not enantioselective manner to give predominantly the racemic gamma-hexyl valerolactone. Similar preparations biotransformed 5-hexylcyclopent-2-enone exclusively by regio- plus enantioselective oxidation to the equivalent alpha,beta-unsaturated (S)-(+)-delta-hexyl valerolactone (ee = 78%), with no reductive biotransformations catalysed by either EC 1.1. x. x- or EC 1.3.x.x-type dehydrogenases. An equivalent biotransformation of 5-hexylcyclopent-2-enone was catalysed by highly-purified NADPH- plus FAD-dependent cyclopentanone monooxygenase from the bacterium. The regio- plus enantioselective biotransformation by the pure enzyme of 2-(2'-acetoxyethyl)cyclohexanone yielded optically-enriched (S)-(+)-7-(2'-acetoxyethyl)-2-oxepanone (ee = 72%). The same biotransformation when scaled up again provided optically-enriched (S)-(+)-epsilon-caprolactone which was converted, using methoxide, to (S)-(-)-methyl 6,8-dihydroxyoctanoate (ee = 42%), thereby providing a two-step access from the substituted cyclohexanone to this important chiron for the subsequent synthesis of (R-(+)-lipoic acid. Some characteristics of pure NADPH- plus FAD-dependent cyclopentanone monooxygenase were determined including the molecular weight of the monomeric subunit (50000) of this homotetrameric enzyme, and the N-terminal amino acid sequence up to residue 29, which includes a putative flavin nucleotide-binding site.