CHIRAL GAMMA-LACTONES FROM FUSARIUM-POAE - ENANTIOMERIC RATIOS AND SENSORY DIFFERENTIATION OF CIS-6-GAMMA-DODECENOLACTONE ENANTIOMERS

The cis-6-gamma-dodecenolactone is the major monounsaturated gamma-lactone produced by a filamentous fungus, Fusarium poae. The two enantiomeric forms of this compound were successfully separated by column gas chromatography, on a fused silica capillary column coated with a modified alpha-cyclodextrin or beta-cyclodextrin phase, and by HPLC, on a Chiraspher column. Elucidation of the configuration of each enantiomer was realized by the interpretation of the H-1-NMR spectra of the Moshers' esters formed with the corresponding 4-hydroxyalkenoic acid esters of this lactone. An analysis of an extract obtained from a culture of F. poae in a liquid malt broth showed that the (R)-enantiomer was highly predominant (> 99%). The odour of each pure enantiomer was assessed by sniffing the column effluent: the detection threshold calculated for the (S)-enantiomer is 2-3 times lower than that of the (R)-form (3 and 7 pg, respectively, of injected compound). This result was confirmed by a sensory analysis of each enantiomer diluted in water at a level of 1.3-mu-g/ml. The odour of the (S)-enantiomer was significantly described as more intense than that of the (R)-form, but no sensory difference was found in the odour quality, which was described as flowery, fruity, coconut-, peach- and apricot-like.