Insecticides in Chinese Medicinal Plants:  Survey Leading to Jacaranone, A Neurotoxicant and Glutathione-Reactive Quinol

Sixty-two plant species from central China were purported to have insecticidal activity. Adult house fly (<i>Musca domestica</i>) toxicity assays were used to identify the two most active plants and guide the chromatographic isolation of the insecticidal components. The active ingredient of <i>Senecio palmatus </i>Pall. (Asteraceae) was characterized as methyl (1-hydroxy-4-oxocyclohexa-2,5-dien-1-yl)acetate (jacaranone) (<b>1</b>), previously known to have insect antifeedant activity. Mono- and bisglutathione (GSH) adducts are formed on incubation of <b>1 </b>with GSH and rat liver GSH <i>S</i>-transferase. The toxic action of <b>1</b> in mice (intraperitoneal LD<sub>50</sub> = 150−200 mg/kg) is associated with both neurological signs and GSH depletion in liver 90 min after treatment. <i>Paeonia suffruticosa</i> var. <i>papaveracea </i>(Andr.) Kerner (Paeoniaceae) was the other active plant found here to have 2‘-hydroxy-4‘-methoxyacetophenone (paeonol) (<b>2</b>) as an insecticidal ingredient in the root and in one case, for the whole plant, contaminated with <i>S</i>-<i>tert</i>-butylthiomethyl <i>O</i>,<i>O</i>-diethyl phosphorodithioate (terbufos) (<b>3</b>), a synthetic anticholinesterase insecticide. Keywords: Glutathione conjugates; insecticide; jacaranone; paeonol; terbufos