Novel bioactive cube insecticide constituents: Isolation and preparation of 13-homo-13-oxa-6a,12a-dehydrorotenoids

Two novel rotenoid-like compounds isolated from cube resin, used as an insecticide and piscicide, have an unprecedented skeleton consisting of a 1,5-benzodioxepin (A and B rings) and a chromone (C and D rings). Their structures are assigned as (-)-13-homo-13-oxa-6a,12a-dehydrorotenone (5) and 13-homo-13-oxa-6a,12a-dehydrodeguelin (6) based on H-1 and C-13 NMR, MS, UV, and optical rotation, X-ray structure determination confirmed the assignment of 5 and revealed that the 1-methylethenyl group is disordered into two sets of atoms. Compound 5 from cube resin was identical with a product previously reported as being formed by reaction of rotenone (1) with acetyl chloride and DMF and misassigned as ''6a, 12a-epoxyrotenone'' (7). A modified procedure was developed for preparation of the new oxarotenoid component of the commercial insecticide, The cube resin from which 5 and 6 were isolated in equal amounts contains B and deguelin (2) in a > 10:1 ratio; this large difference in ratio indicates that 5 and Fi are not artifacts formed from 1 and 2, respectively, Rotenoid 5 acts as a respiratory inhibitor with 50% inhibition of NADH:ubiquinone oxidoreductase activity at O.11 mu M, of goldfish survival at 1 ppm, and of the viability of three cell lines at 4-8 mu M.