Isolation and Identification of Residues of 4‘‘-(epi-Methylamino)-4‘‘-deoxyavermectin B1a Benzoate from the Surface of Cabbage

Abstract

Cabbage was treated with a single application of [14C]-MK-0244, a semisynthetic avermectin analogue, at 0.3 lb/acre and harvested 1 day after application. The wrapper leaf and exterior head surface of the cabbage were rinsed with methanol, and 12 degradates were isolated from this rinse and identified by structural analysis. Ten of these residues can be accounted for by six previously reported transformations and two are apparently formed by novel transformations. This represents the first time that avermectin residues isolated from a plant have been unequivocally identified by direct methods. The cabbage residue profile bears a strong resemblance to that seen in the photodegradation of MK-0244 thin films on glass. Keywords: Avermectin; photodegradation; cabbage; surface residue; plant residue; pesticide