Lactones 44. Microbial lactonization of γ-ketoacids

Enantiomerically pure γ-lactones ((+)-4a, (−)-5a, (+)-4b) have been obtained from the corresponding γ-ketoacids (3a and 3b) by their biotransformations with the three fungal strains: Rhodotorula glutinis AM242, Saccharomyces cerevisiae AM464 and Chaetomium sp. KCh6670. Microbial lactonization of 3,7-dimethyl-4-oxooctanoic acid (3a) with R. glutinis AM242 afforded the (+)-(4S,5R)-trans-γ-lactone (4a) with 99% ee, while Chaetomium sp. KCh6670 proved to be the best biocatalyst for the bioreduction and following lactonization of γ-ketoacid (3a), which afforded (−)-cis-γ-lactone (5a) with 99% ee. Biotransformation of 3,7,7-trimethyl-4-oxooctanoid acid (3b) in the culture of S. cerevisiae AM464 gave the corresponding (+)-trans-γ-lactone (4b) with 99% ee. The odours of the racemic γ-lactones ((±)-4a, (±)-5a, (±)-4b and (±)-5b) and optically pure isomers ((+)-4a, (−)-5a, (+)-4b) were evaluated.