Lactones 44. Microbial lactonization of γ-ketoacids

Abstract 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 (+)-(4 S ,5 R )- 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.