Antifeedant and Phytotoxic Activity of Cacalolides and Eremophilanolides

The antifeedant effect of six cacalolides and six eremophilanolides was tested against the herbivorous insects Spodoptera littoralis, Leptinotarsa decemlineata, and Myzus persicae. The test compounds included several natural products isolated from Senecio madagascariensis (14-isovaleryloxy-1,2-dehydrocacalol methyl ether, 4), S. barba-johannis (13-hydroxy-14-oxocacalohastine, 5; 13-acetyloxy-14-oxocacalohastine, 6) and S. toluccanus [6-hydroxyeuryopsin, 7; 1(10)-epoxy-6-hydroxyeuryopsin, 9; toluccanolide A, 11] and the derivatives cacalol methyl ether (1); cacalol acetate (2); 1-acetyloxy-2-methyloxy-1,2,3,4-tetradehydrocacalol acetate (3); 6-acetyloxyeuryopsin (8); 6-acetyloxy-1(10)-epoxyeuryopsin (10), and toluccanolide A acetate (12). Compound 11 and its derivative 12 exhibited moderate antifeedant activity against S. littoralis; 2, 7D10, and 12 showed strong activity against L. decemlineata, while the aphid M. persicae was moderately deterred in the presence of compounds 1, 4, 8, 10, and 12. The phytotoxic activity of 1D12 on Lactuca sativa was also evaluated. Compounds 2 and 4D 12 moderately inhibited seed germination at 24 h, while compounds 1D4, 6, 9, and 10 had a significant inhibition effect on L. sativa radicle length (over 50%).