Delta(2)-oxazolines-1,3 and N-acylaziridines as potential proinsecticides of carboxylic acids - V. Direct thin-layer chromatography monitoring of themetabolism in locust tissues

Modern thin-layer chromatography (TLC) was used for the evaluation of Delta (2) -oxazolines-1,3 I and N-acylaziridine VII structures, as potential pro insecticides of carboxylic acids III. Thus the unmasking(2) of the active p rinciples III from Delta (2) -oxazolines-1,3 Ia-c and N-acylaziridine VIIc was monitored by spotting aliquots directly onto RP-18 TLC plates, without any sample pretreatment during in vitro assays performed in concentrated lo cust tissues. To achieve a good separation of carboxylate IIIa from endogen ous components of the tissues, a short preliminary development with methano l or ion-pairing was necessary. From UV-TLC chromatograms (densitograms) it appeared that in a phosphate buffer at pH 7.4, the oxazoline Ia with a C-2 substituent devoid of alpha -ramification or alpha,beta -in saturation hyd rolysed slowly into the corresponding beta -hydroxylamide VIa and intermedi ate aminoester Va. Significantly, locust mesenteron (or fat body) efficient ly triggered the unmasking of IIIa, a transformation which corresponds to t he expected proinsecticide behavior of Ia. Conducting TLC monitoring in the same locust tissues also revealed that the oxazolines Ib and Ic with an al pha -ramification and an alpha,beta -insaturation, respectively, cannot be considered as proinsecticides of the corresponding carboxylic acids IIIb an d IIIc. In contrast, the N-acylaziridine VIIc appeared as a convenient proi nsecticide structure for masking the carboxylic acid IIIc. (C) 2001 Elsevie r Science B.V. All rights reserved.