Chemistry of Fruit Flies. Composition of the Rectal Gland Secretion of (Male) Dacus cucumis (Cucumber Fly) and Dacus halfordiae: Characterization of (Z,Z)-2,8-Dimethyl-l,7-dioxaspiro[5: 5]undecane

Abstract

Combined gas chromatography-mass spectrometry and synthesis have established that the major components of the rectal gland secretion of adult male cucumber flies (Dacus cucumis) are the E,E, E,Z, and Z,Z diastereomers of 2,8-dimethyl-l,7-dioxaspiro[5.5]undecane, which have been synthesized utilizing organomercury chemistry from l,10-undecadien-6-one. The thermodynamically least stable Z,Z diastereomer has been characterized for the first time, by1H and13C NMR measurements and mass spectrometry. Minor amounts of 3-hydroxy-2,8-dimethyl-l,7-dioxaspiro[5.5]undecane and various derivatives of the l,6-dioxaspiro[4.5]decane and 1,7-dioxaspiro[5.6]dodecane systems are also present. 1,3-Nonanediol occurs in significant amounts, and both enantiomers have been acquired by Sharpless asymmetric epoxidation of (E)-2-nonen-l-ol followed by Red-Al (Aldrich) reduction of the chiral epoxy alcohols. Chiral gas chromatographic analysis of the diols (as their cyclic carbonates) has demonstrated that the natural material is the R-(-) enantiomer. Natural (E,Z)-2,8-dimethyl-l,7-dioxaspiro-[5.5]undecane is shown to be racemic, whereas the more abundant E,E diastereomer is enantiomerically highly pure, possessing the 2S,6R,8S configuration. The major volatile component of the rectal gland secretion of male Dacus halfordiae (Tryon) is also (E,E)-2,8-dimethyl-l,7-dioxaspiro[5.5]undecane, with no detectable levels of the E,Z or Z,Z isomers. Other spiroacetals present were 2-ethyl-7-methyl-l,6-dioxaspiro[4.5)decane and the unusual even carbon-numbered (E,E)-2-ethyl-8-methyl-l,7-dioxaspiro[5.5]undecane. 6-Oxo-l-nonanol, diethyl succinate, and 2-methyl-6-pentyl-3,4-dihydro-2H-pyran were also identified.