(E)-2-(4'-Methyl-3'-pentenylidene)-4-butanolide, Named β-Acariolide : A New Monoterpene Lactone from the Mold Mite, Tyrophagus putrescentiae (Acarina: Acaridae)

Abstract

Reinvestigation of the opisthonotal gland secretion of the mold mite, Tyrophagus putrescentiae, resulted in the isolation of a new monoterpene lactone, whose chemical structure was elucidated as (E)-2-(4'-methyl-3'-pentenylidene)-4-butanolide (3), to which we gave the trivial name β-acariolide in relation to β-acaridial {1, (E)-2-(4-methyl-3-pentenylidene)-butanedial}. The compound was synthesized by LiAlH₃(OEt) reduction of 1 and subsequent oxidation involving simultaneous cyclization by using Ag₂CO₃ on Celite. Both the E- and Z-isomers of β-acariolide (3 and 4) were also prepared by the reaction of α-ethoxaly-γ-butyrolactone (6) and 4-methyl-3-pentenal under basic conditions. Their NMR spectra were compared with each other, and the geometry of the pentenylidene double bond of the isolated compound was concluded as being E.