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Chiral HPLC resolution of monoepoxides derived from 6,9-dienes and its application to stereochemistry assignment of fruit-piercing noctuid pheromone.

The resolution of insect pheromonal cis-monoepoxy racemates derived from (Z,Z)-6,9-dienes was examined employing chiral HPLC columns, and the results showed that a normal-phase column (Chiralpak AD) was suitable for both 6,7- and 9,10-epoxides with a C(17)-C(23) straight chain, as was a reversed-phase column (Chiralcel OJ-R) for the 6, 7-epoxides. To determine the absolute configuration of each separated enantiomer applying a modified Mosher's method, the epoxy ring was opened by methanolysis, and the (1)H-NMR data of (S)- and (R)-MTPA esters of the methoxyalcohols produced were analyzed. Further, the hydrogenated product of each enantiomer was chromatographed on the OJ-R column referring to the corresponding authentic chiral compounds with a saturated chain, which were prepared by a Sharpless epoxidation reaction. These analyses showed that the levorotatory 6,7- and 9,10-epoxides with shorter t(R)s possess 6S,7R and 9R,10S configuration, respectively, and the dextrorotatory enantiomers with longer t(R)s possess the opposite configuration. Utilizing this chiral HPLC, it was revealed that an abdominal tip extract of the fruit-piercing moth, Oraesia excavata Butler (Lepidoptera: Noctuidae), included (9S,10R)-(Z)-9, 10-epoxy-6-henicosene as a main sex pheromone component. The synthetic 9,10-epoxide with this configuration, which was separated from the racemate, exhibited stronger activity in electrophysiological and field tests against male moths than the enantiomer.