Enantiodifferentiation of four γ-lactones produced by Penicillium roqueforti

Abstract

Identification and enantiodifferentiation of γ-lactones produced during the bioconversion of soy bean fatty acids by Penicillium roqueforti spores in the presence of an exogenous lipase was performed using gas chromatography- mass spectrometry (GC-MS) in selected ion monitoring (SIM) mode. It was shown that 4-dodecanolide and 4-hexanolide were first produced with an enantiomeric excess (99%) in favor of the (R) form, whereas an enantiomeric excess in favor of the (S) form (94%) is found for (6Z)-dodecen-4-olide, the major lactone produced by the fungus. If incubation was continued, mixtures of both enantiomers were found, more particularly for 4-decanolide (R/S:40/60), which was produced only after 120 hr of incubation. The results obtained can be explained by the stereoselective hydroxylation by a 10-hydratase and/or a 10- lipoxygenase of the unsaturated fatty acid precursors, oleic and linoleic acids, and by competition between different pathways. The results point out the limitations of chiral GC analysis as a criterion for the natural origin of relevant lactones, and the complexity of mechanisms involved in γ- lactone formation by microorganisms.