Effect of the azetidine and azocine rings of okaramine B on insecticidal activity

Four degraded okaramine B (2) products, 4',5'-dihydrookaramine B (3), two azetidine ring-opened compounds (4 and 5) and 1',2',4',5'-tetrahydrookaramine B (6), were prepared and their insecticidal activity was examined. Neither compounds 4 nor 5 showed such activity against silkworms, indicating that the azetidine ring moiety played an important role in the insecticidal activity. Moreover, both compounds 3 and 6 exhibited lower activity than 2, which means that the azocine ring moiety was indispensable to form the active conformation.