PHOTODEGRADATION OF 4''-(EPIMETHYLAMINO)-4''-DEOXYAVERMECTIN-B1A THIN-FILMS ON GLASS

Photodegradation of 4"-(epimethylamino)-4"-deoxyavermectin B1a as thin films on glass, using artificial light, resulted in the formation of multiple photodegradates. Six primary degradates and two secondary degradates were identified. The primary degradates formed were 8,9-Z-4"-(epimethylamino)-4"-deoxyavermectin B1a (a geometric isomer), delta 2,3-4"-(epimethylamino)-4"-deoxyavermectin B1a (a positional isomer), avermectin B1a monosaccharide, 4"-epiamino-4"-deoxyavermectin B1a, 4"-N-formyl-4"-deoxyavermectin B1a, and 4"-N-methyl-N-formyl-4"-deoxyavermectin B1a. The secondary degradates formed, both geometric isomers of two primary degradates, were 8,9-Z-4"-epiamino-4"-deoxyavermectin B1a. and 8,9-Z-4"-N-formyl-4"-deoxyavermectin B1a. The substitution of the epi-N-methylamino group for the hydroxyl group at the 4" position of avermectin B1a profoundly affected the formation of photodegradates in thin films reported in earlier studies.