Sensitizing capacity of naturally occurring quinones. V. 2.6-dimethoxy-p-benzoquinone: occurrence and significance as a contact allergen.

2.6-dimethoxy-1,4-benzoquinone has already been discovered in more than 25 different plants and woods. Several authors have shown its strong bacteriostatic activity against micro-organisms. In 1972 a positive skin reaction to 2.6-dimethoxybenzoquinone was obtained in a patient allergic to Sucupira wood (Bowdichia nitida Benth.). This compound could be isolated from the wood. During the chemical investigations of other commercial woods which have been described as the cause of allergic contact dermatitis, 2.6-dimethoxybenzoquinone could be isolated from an additional 21 different species. In the case of Australian blackwood Acacia melanoxylan R.BR., its structure was elucidated by x-ray analysis. Sensitization of guinea pigs revealed that 2.6-dimethoxybenzoquinone is a relatively good sensitizer. In some of the woods investigated, quinones have never been discovered before, for example in Makoré, Australian blackwood, Wengé, White wood, Afrormosia and Afzelia. In 10 of them only this quinone was detectable. Besides its allergenic properties, 2.6-dimethoxybenzoquinone may be responsible for the high termite resistance of these woods. In all cases of contact dermatitis from these wood species in which quinoid allergens other than 2,6-dimethoxybenzoquinone could be detected, this quinone should be used for patch tests.