Insecticidal meliacarpins (C-seco limonoids) from Melia azedarach

Three new meliacarpin derivatives. namely 1,3-dicinnamoyl-11-hydroxymeliacarpin. 1-cinnamoyl-3-methacryl-11-hydroxymeliacarpin and 1-cinnamoyl-3-acetyl-11-hydroxymeliacarpin, were isolated as the principal insecticidal and growth disrupting constituents of Melia azedarach leaves. Their structures were unambiguously established on the bads of MS spectrometric and NMR spectroscopic data (H-1,C-13. COSY. H-1-detected direct and long-range C-13-H-1 correlations) and by comparison with known compounds. The insecticidal properties of the new meliacarpin derivatives were examined using larvae of the polyphagous pest insect Spodoptera litroralis. When incorporated into artificial diet and offered to lan ae in a chronic feeding bioassay, 1-cinnamoyl-3-acetyl-11-hydroxymeliacarpin exhibited an EC50 of 0.27 ppm and a LC50 of 0.48 ppm and is thus comparable with regard to insecticidal activity to the well known natural insecticide azadirachtin. Further-more. all three meliacarpin derivatives had a pronounced detrimental influence on larval metamorphosis. (C) 1999 Elsevier Science Ltd.;lll rights reserved.