IDENTIFICATION OF THE SECONDARY DEGRADATES OF L-648,548 IN AN ANIMAL HEALTH FORMULATION

L-648,548 is a semisynthetic analog of avermectin. During stability in vestigations of this compound in an animal health formulation, two new degradates were discovered. These degradates (L-648,548 phenol and it s 8,9-Z isomer) were identified as the reaction products of 5-oxo-L-64 8,548 formed by oxidation of L-648,548. Addition of base to the reacti on medium containing 5-oxo-L-648,548 was found to catalyze the formati on of L-648,548 phenol via a postulated dehydration by an E(1cb) elimi nation followed by the rapid tautomerization of the C5 carbonyl. Photo lysis of L-648,548 phenol with visible light (including ambient labora tory lighting) was found to readily produce 8,9-Z-L-648,548 phenol. Th is transformation was confirmed to be exclusively a photoinduced proce ss.