Potential proinsecticides of fluorinated carboxylic acids and beta-ethanolamines IV. Evaluation of the Delta(2)-oxazoline-1,3 structure by F-19 NMR monitoring of the in vitro metabolism in locust tissues

The enzymatic effect of locust tissues upon hydrolysis of the fluorinated D elta (2)-oxazoline-1,3 Ia was elucidated using F-19[H-1] NMR monitoring. In a phosphate buffer at pH = 7.4 (mean physiological pH of locust tissues) , the substrate Ia hydrolyses slowly into the corresponding fluorinated hyd roxylamide VIa. If diluted, locust haemolymph (12.5% in phosphate buffer) catalyses slightl y this hydrolytic pathway, it overall triggers the unmasking of carboxylate IIIa, corresponding to the expected proinsecticide behaviour of Ia. This b ehaviour is spectacularly almost the unique reaction observed during in vit ro assays in concentrated fat body and mesenteron. Inasmuch as beta -hydrox ylamide VIa is not hydrolysed into carboxylate IIIa during such conditions, it must be concluded that carboxylate formation exclusively results from h ydration and hydrolysis of substrate Ia via the aminoester Va. The formatio n of this intermediate aminoester is demonstrated by complementary assays. The enzymes supposed to intervene are of the alpha -chymotrypsine type for the first step (hydration) and of the esterase type for subsequent hydrolys is of intermediate aminoester Va. Thus, this work constitutes the first example of a Delta (2)-oxazoline-1,3 structure exploited for elaborating proinsecticides of carboxylates III and /or beta -ethanolamines II based on enzymatic activation in insects. (C) 20 01 Elsevier Science B.V. All rights reserved.