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 tert- butyl 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 ( 1H NMR) and Carbon 13 nuclear magnetic resonance (13C 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.