Studies on the optical isomers of EPN and EPNO

Abstract

The optical isomers of EPN ( O-ethyl O-p-nitrophenyl phenylphosphonothionate) and EPNO ( O-ethyl O-p-nitrophenyl phenylphosphonate) have been synthesized. No significant difference in the rate of alkaline hydrolysis of the isomers at the two pH's evaluated was observed. The (+)-isomers of EPN and EPNO were more toxic to house flies than the corresponding (−)-isomers, while the (+)- and (−)-isomers, as well as the racemic mixture of EPN, were almost equally toxic to mice. The (+)-EPNO is more toxic to mice than the corresponding (−)-isomer. Cholinesterase inhibition studies demonstrated that (+)-EPNO has a higher bimolecular rate constant, ( k i ) than the corresponding (−)-isomer. This higher inhibitory power was due to a higher affinity ( K a ) of the (+)-isomer.