N-acylaziridines as potential proinsecticides of carboxylic acids☆Part VI. Direct HPLC monitoring of the metabolism in insect tissues

Abstract

To determine the reversible masking potential of carboxylic acids afforded by the N-acyl structure in a proinsecticide perspective, the hydrolysis of monosubstituted N-acylaziridines and unsubstituted N-acylpyrrolidine was studied by reversed-phase high-performance liquid chromatography (HPLC) during in vitro assays conducted in the presence of insect tissues or of alpha-chymotrypsin. Chromatographic analysis of unextracted biological samples so-called "the direct injection approach" was simpler and more accurate than the "extraction approach" because it avoids problems associated with extraction. Thus, periodical injections of samples of biological insect tissues or of alpha-chymotrypsin incubated with N-acyl substrates were performed on packings allowing direct injection: a wide-pore column or a monolithic column. Moreover, to allow the simultaneous monitoring of the carboxylic acids and of the parent substrates, ion-pairing was used. In these conditions, it was shown that N-acylpyrrolidine is not hydrolyzed whatever the enzymatic conditions or the pH. On the other hand, the unmasking of the carboxylic acid is the preponderant mode of hydrolysis of N-acylaziridines in the presence of alpha-chymotrypsine and the exclusive one in the presence of locust fat-body, which establishes the convenience of this structure in our proinsecticide perspective. Due to the enzymatic character of the unmasking of the carboxylic acid during biological hydrolysis of N-acylaziridines, the research of possible chiral recognitions was undertaken. Thus, the enantiomeric composition of these substrates was analysed at the stage of their approximative half hydrolysis using a chiral alpha-AGP column. It appeared that locust fat-body hydrolyses preferentially the (R)-isomers of N-acylaziridines while the reverse is observed when alpha-chymotrypsine is used.