Structure elucidation and synthesis of dioxolanes emitted by two Triatoma species (Hemiptera: Reduviidae).

Volatiles from the metasternal glands of two species of true bugs of the Triatominae subfamily, Triatoma brasiliensis and Triatoma infestans, were analyzed by SPME-GC/MS. Two sets of new natural products were found: (4S,5S)- and (4R,5R)-2,2,4-triethyl-5-methyl-1,3-dioxolane (1) (major component) and (4S*,5S*)-2,4-diethyl-2,5-dimethyl-1,3-dioxolane (2) (trace component), (2R/S,4S,5S)- as well as (2R/S,4R,5R)-4-ethyl-5-methyl-2-(1-methylethyl)-1,3-dioxolane (3) (minor component), (2R/S,4S*,5S*)-4-ethyl-5-methyl-2-(1-methylpropyl)-1,3-dioxolane (4) (trace component), and (2R/S,4S*,5S*)-4-ethyl-5-methyl-2-(2-methylpropyl)-1,3-dioxolane (5) (trace component). Syntheses of optically active 1 and 3 were carried out by reacting pure enantiomers of 2,3-pentanediol with 3-pentanone or 2-methylpropanal. The preparation of pure stereoisomers of 2,3-pentanediol involved a novel key step for the synthesis of secondary alcohols: the reduction of a carboxylic ester by means of DIBAH and in situ alkylation of the intermediate by Grignard reaction at low temperature. Starting from the pure enantiomers of methyl lactate, all four stereoisomers of 2,3-pentanediol were synthesized and transformed to the corresponding isomers of 1 and 2. Relative configurations of the natural products and enantiomeric compositions of naturally occurring 1 and 2 were determined by comparison of their mass spectra and gas chromatographic retention times (co-injection) with those of authentic reference samples.