Biosynthesis of photodynamically active rubellins and structure elucidation of new anthraquinone derivatives produced by Ramularia collo-cygni

Here we present the first isolation of the anthrachinone derivative rubellin A out of mycelium and culture filtrate of Ramularia collo-cygni. Furthermore, two compounds, rubellin E and 14-dehydro rubellin D were isolated and their structures elucidated. In comparison to the other rubellins, rubellin A shows increased photodynamic oxygen activation. By incorporating both 1-(13)C]-acetate and 2-(13)C]-acetate into the rubellins, we showed that such anthraquinone derivatives were biosynthesised via the polyketide pathway. The labelling pattern after being fed U-(13)C(6)]-glucose proved the existence of fungal folding mode of the poly-beta-keto chain. The ability to produce rubellins is not limited to R. collo-cygni in the anamorph genus Ramularia.