New oxygenated himachalenes in male-specific odor of the Chinese windmill butterfly, Byasa alcinous alcinous

Abstract

Male adults of the Chinese windmill Byasa alcinous alcinous (Papilionidae) are well known to have a strong musk-like odor, in which two oxygenated himachalene compounds, together with six sesquiterpene hydrocarbons, were newly discovered. γ-Himachalen-4-yl acetate (1) was the predominant compound isolated from the solvent extract of the males. The structure of 1 was determined using MS and NMR, and its relative configuration was established as 1S*,4R*,6R* by NOE analysis with the help of quantum mechanical computation. Interestingly, the amount of 1 in males increased until 7 days after eclosion, suggesting that this compound is involved in sexual maturation for mating. Another new compound was identified as γ-himachalen-4-ol (2) by comparison with the retention time and mass spectrum of the hydrolysate of 1. Since males of other papilionid species have general volatiles omnipresent in plants and insects, the presence of species-specific volatiles in males is characteristic of B. alcinous alcinous.