Antifeedant activity of neo-clerodane diterpenes from Baccharis flabellata Hook & Arn var. flabellata toward Tribolium castaneum Herbst: structure-activity relationships.

In order to establish structure-activity relationships, nine neo-clerodane diterpenes isolated from the acetone extract of aerial parts of Baccharis flabellata Hook & Arn var. fabellata were assayed for antifeedant activity against Tribolium castaneum (Coleoptera: Tenebrionidae). Compounds exhibiting maximal antifeedant activities showed an alpha,beta-unsaturated carbonyl group on the decalin portion and a furan ring at the side chain. Stereoelectronic studies indicate that the distance between the furan heteroatom and the more electrophilic carbon of the decaline moiety, as well as the electrostatic charge on that atom, were important features for antifeedant activity. Compounds possesing an alpha,beta,gamma,delta-unsaturated carbonyl group or an acetoxyl group at C-2, were inactive. Theoretical calculations were performed in order to find some structure-activity relationships.