The anthraquinones of Heterodermia obscurata

Three anthraquinones, two bianthrones and a phenanthroperylenequinone were isolated from the lichen Heterodermia obscurata (Nyl.) Trevis. (Physciaceae). The structures were inferred from their spectra (UV, mass, 1H and 13C NMR): emodin, 7-chloroemodin, 5,7-dichloroemodin, flavoobscurin A, flavoobscurin B and 7,7′-dichlorohypericin, with the latter being recently discovered as a lichen anthraquinone. 7-Chloroemodin and 5,7-dichloroemodin were synthesized by a new method, and characterized spectroscopically. The synthetic and natural products were found to be identical in all respects.