Prenylated Phenols that Cause Contact Dermatitis from Trichomes of Phacelia ixodes.

The principal phenolic constituents were isolated from the exudate of the glandular trichomes of PHACELIA IXODES K ELLOGG (Hydrophyllaceae), a Mexican plant that causes allergic contact dermatitis. These are, in decreasing order of the amount in the trichomes: geranylhydroquinone (I), 3-geranyl-2,5-dihydroxyphenyl acetate (II), geranylbenzoquinone (III), 2-geranyl-6-hydroxy-4-methoxyphenyl acetate (IV), 2-geranyl-4-hydroxyphenyl acetate (V), 6-hydroxy-2-methyl-2-(4-methyl-3-pentenyl)-chromene (VI), and 6,7-dimethoxyapigenin. Compounds II, IV, and V are new natural products. Geranylbenzoquinone was the principal contact allergen in testing with guinea pigs.