The Structure and Synthesis of Some Minor Xanthones From the Lichen Rinodina thiomela

Abstract

The total synthesis of the xanthones 5,7-dichloro-8-hydroxy-2-methoxy-1,3-dimethyl-9H-xanthen-9-one(10),5,7-dichloro-2,8-dihydroxy-1,3-dimethyl-9H-xanthen-9-one(11),2-dechloro-8-O-methylthiomelin (6), 2-dechlorothiomelin (8), 4-dechloro-8-O-methylthiomelin (7), 4-dechlorothiomelin (5) and northiomelin (9) has been achieved. The compounds (5)-(7) and (10) were shown to be identical to the corresponding xanthones isolated from the lichen Rinodina thiomela, while chromatographic comparisons confirmed that the biosynthetically related xanthones (8), (9) and (11) were minor constituents of this species. This is the first reported natural occurrence of the xanthones (8) and (11).