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Photodegradation of 4"-(epimethylamino)-4"-deoxyavermectin Bu 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 Bu (a geometric isomer), delta 2,3-4"-(epimethylamino)-4"-deoxyavermectin Bu (a positional isomer), avermectin Bu monosaccharide, 4"-epiamino-4"-deoxyavermectin Bu, 4"-N-formyl-4"-deoxyavermectin Bu, and 4"-iV-methyl-N-formyl-4,,-deoxyavermectin Bu. The secondary degradates formed, both geometric isomers of two primary degradates, were 8,9-Z-4"-epiamino-4"deoxyavermectin Bu and 8,9-Z-4"-JV-formyl-4"-deoxyavermectin Bu. The substitution of the epi-iVmethylamino group for the hydroxyl group at the 4" position of avermectin Bu profoundly affected the formation of photodegradates in thin films reported in earlier studies.

Photodegradation of avermectin B1, thin films under artificial light (above 260 nm) for short periods of time (greater than 60% of parent compound remaining) resulted in the formation of at least 10 primary degradates including two geometric isomers, 7 monooxygenated derivatives, and 1 dealkylated derivative. Prolonged photolysis of avermectin B1, thin films (no parent compound remaining) resulted in a polar residue which appeared to consist of a complex mixture of degradates with few characteristics of the parent molecule.

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