Chiral-Phase Capillary Gas Chromatography and Mosquito Repellent Activity of Some Oxazolidine Derivatives of (+)- and (−)-Citronello1

Fourteen stereoisomeric mixtures of six oxazolidine heterocycles and one amino alcohol were obtained from commercial samples of (+)−, (−)−, or (±)-citronellol (2) and evaluated in a cloth test system as mosquito repellents. A technical sample of 3-acetyl-2-(2′, 6′-dimethyl-5′-heptenyl)oxazolidine (1), evaluated initially as a mixture of two pairs of enantiomers, was an effective repellent against two of the three species of mosquitoes. To study repellency-stereochemistry relationships, 1 was isolated as fractions G-1, G-2, I-1, and I-2, corresponding to representative samples of the four possible stereoisomers. The enantiomeric composition of 1, but not of the other derivatives, could be determined by chiral-phase capillary gas chromatography with Chirasil-Val. Two chiral phases showed that experimental samples of 1, and hence the commercial samples of 2, were composed of not more than 90% of one enantiomer. Differences in repellency of isomerically enriched samples were generally small. Fraction G, a mixture of diastereoisomers readily prepared from (+)−2, was considerably more effective than standard insect repellents in bioassays with three mosquito species.