Stereochemical effects in an insect repellent.

Racemic 1-[3-cyclohexen-1-ylcarbonyl]-2-methylpiperidine repels blood-feeding arthropods such as mosquitoes, chiggers, and ticks. The compound contains two asymmetric carbon atoms and the racemate consists of four stereoisomers. Quantitative mosquito bioassays using Aedes aegypti (L.) showed that (1S,2'S) and (1R,2'S) configurations were 2.8-3.1 and 1.6-1.8 times more effective, respectively, than the other two stereoisomers in reducing mosquito bites. (1S,2'S) was 2.5 more repellent than the racemate. Biological data show that an interaction of the (2'S)-2-methylpiperidine configuration with a repellent receptor system in A. aegypti is apparently important to repellent activity. Nuclear magnetic resonance spectra and molecular mechanics calculations for the stereoisomers provided insight into the conformation of the (2'S)-group. Results indicate that enhanced repellent effects can be realized through formulation of the most active stereoisomers of the compound.