Selective Oxygenation and Plant-Growth Regulatory Activity of Sesquiterpene Lactones

Presence of a hydroxyl group at the C-3 position in guaianolides and at the C-5 position in alantolides has been established in biologically active compounds that act as plant-growth regulators. Sesquiterpene lactones like dehydrocostus lactone and isoalantolactone were subjected to allylic oxidations with selenium dioxide (SeO2) in combination with urea hydrogen peroxide (UHP) replacing the common reagent tertbutyl hydroperoxide (TBHP) to form allylic alcohols. The reactions of dehydrocostus lactone and isoalantolactone with SeO2/UHP/polyethylene glycol-400(PEG-400) were more selective, and the yields were higher than reactions with SeO2/TBHP/ dichloromethane (CH2Cl2). The structures of all of the compounds were elucidated by spectroscopic techniques like infrared (IR) spectroscopy, proton nuclear magnetic resonance ( 1 H NMR) and Carbon 13 nuclear magnetic resonance ( 13 C NMR). All of the obtained compounds were subjected to biological evaluation as plant-growth regulators. The results were fairly good compared to the parent compounds.