Optimization of Insecticidal Triterpene Derivatives by Biomimetic Oxidations with Hydrogen Peroxide and Iodosobenzene Catalyzed by Mn ^III and Fe ^III Porphyrin Complexes

Abstract Semisynthetic functionalized triterpenes (4 α ,14‐dimethyl‐5 α ,8 α ‐8,9‐epoxycholestan‐3 β ‐yl acetate; 4 α ,14‐dimethyl‐5 α ‐cholest‐8‐ene‐3,7,11‐trione; 4 α ,14‐dimethyl‐5 α ‐cholesta‐7,9(11)‐dien‐3‐one and 4 α ,14‐dimethyl‐5 α ‐cholest‐8‐en‐3 β ‐yl acetate), previously prepared from 31‐norlanostenol, a natural insecticide isolated from the latex of Euphorbia officinarum , have been subjected to oxidation with hydrogen peroxide (H 2 O 2 ) and iodosobenzene (PhIO) catalyzed by porphyrin complexes (cytochrome P‐450 models) in order to obtain optimized derivatives with high regioselectivity. The main transformations were epoxidation of the double bonds and hydroxylations of non‐activated C–H groups and the reaction products were 25‐hydroxy‐4 α ,14‐dimethyl‐5 α ‐cholesta‐7,9(11)‐dien‐3 β ‐yl acetate (59 %), 25‐hydroxy‐4 α ,14‐dimethyl‐5 α ‐cholest‐8‐ene‐3,7,11‐trione (60 %), 4 α ,14‐dimethyl‐5 α ,7 β ‐7,8‐epoxycholest‐9(11)‐en‐3‐one (22 %), 8‐hydroxy‐4 α ,14‐dimethyl‐5 α ‐cholest‐9(11)‐ene‐3,7‐dione (16 %), 12 α ‐hydroxy‐4 α ,14‐dimethyl‐5 α ,7 β ‐7,8‐epoxycholest‐9(11)‐en‐3‐one (16 %), and 4 α ,14‐dimethyl‐5 α ,8 α ‐8,9‐epoxycholestan‐3 β ‐yl acetate (26 %), respectively. We also investigated the insect ( Myzus persicae , Rhopalosiphum padi and Spodoptera littoralis ) antifeedant and postingestive effects of these terpenoid derivatives. None of the compounds tested had significant antifeedant effects, however, all were more effective postingestive toxicants on S. littoralis larvae than the natural compound 31‐norlanostenol, with 4 α ,14‐dimethyl‐5 α ,8 α ‐8,9‐epoxycholestan‐3 β ‐yl acetate being the most active. The study of their structure–activity relationships points out at the importance of C3 and C7 substituents.