Stereoselective Oxidation of α-Copaene, a Fire Ant Repellent Sesquiterpene from the Essential Oil of .

Imported fire ants are significant agricultural pests. Repellents can be used to prevent foraging fire ants from entering sensitive areas, including electrical equipment, nursing homes, and hospitals. Bioassay-guided fractionation of the essential oil extracted from gurjun balsam () resulted in the identification of (-)-α-copaene () as the repellent constituent with a minimum repellent effective dose (MRED) of 15.6 μg/g against both red imported fire ants () and hybrid imported fire ants ( × ). Stereoselective oxidation of via autoxidation and chemical methods produced (-)-5-hydroperoxy-α-copaene (), (+)-3-hydroperoxycopa-4-ene (), (-)-α-copaene oxide (), (+)-β-copaen-4α-ol (), copaenediol (), and copaene ketol (). Reduction of and with triphenylphosphine afforded (-)-5-hydroxy-α-copaene () and (+)-3-hydroxycopa-4-ene (), respectively, which led to the structural revision of copa-3-en-2α-ol and copa-2-en-4-ol as and , respectively. The configurational assignment of compound in the literature was also clarified by the detailed analysis of 2D NMR spectroscopic data. Compounds - showed repellency with MREDs ranging from 3.9 to 15.6 μg/g against hybrid and red imported fire ants, indicating that chemical modification can enhance the repellent effect of (-)-α-copaene.