Uredinorubellins and Caeruleoramularin, Photodynamically Active Anthraquinone Derivatives Produced by Two Species of the Genus Ramularia

Both the phytopathogenic fungus Ramularia collo-cygni and the hyperparasite R. uredinicola biosynthesize a number of red and yellow anthraquinone derivatives called rubellins. The new compounds uredinorubellins I and II, which were isolated from R. uredinicola, contribute to understanding the biosynthesis pathway that leads from simple anthraquinones to the rubellins. In addition, we isolated for the first time such simple compounds as chrysophanol and helminthsporin from both Ramularia species. A blue compound isolated from the mycelium of R. collo-cygni was revealed to be a unique 9,4-anthracenedione derivative. Structure elucidation by 1H and 13C NMR of the new but unstable compound caeruleoramularin was possible only by feeding the fungus different labeled 13C acetates. The photodynamic activity of the uredinorubellins was comparable to rubellin D, whereas chrysophanol and caeruleoramularin did not display such activity.