The yellow pigments named eumitrins A_1, A_2, and B were islelated from the lichen, Usnea bayleyi (Stirt.)Zahlbr. The modified bixanthone structures of these compounds were deduced mainly from their spectral data, and their absolute structures (XII, XIV, XV) were established on the basis of X-ray crystallographic analysis of a transformed product(XVIII) of tribromoeumitrin B (XVI).
