Secondary mould metabolites. Part 15. Structure elucidation of rubellins A and B, two novel anthraquinone metabolites from Mycosphaerella rubella

The structure of rubellins A (1) and B (2), two novel anthraquinone metabolites isolated from Mycosphaerella rubella, have been assigned by detailed analysis of their 1H and 13C n.m.r. spectra and chemical evidence. Their relative configuration and conformation were deduced from the observed 1H–{1H} nuclear Overhauser effects (n.O.e.s) and the value of 1H–1H coupling constants.