<p><a>Pigments of mushrooms are a fertile
ground of inspiration: they spread across various chemical backbones,
absorption ranges, and bioactivities. While looking from a photochemical
perspective, we discovered a new bioactivity, i.e., photoactivity. We revealed
that singlet oxygen production is a common theme in one group of webcaps (i.e.,
dermocyboid Cortinarii, formerly called Dermocybe). This photoactivity was
explored by bioactivity-based molecular networking and photo-activity guided
isolation. As a result, three photosensitizers based on anthraquinone
structures were isolated. All three were photochemically characterized and
(photo)cytotoxically tested. For one of the three, i.e. (-)-7,7’-biphyscion (<b>1</b>),
a promising photoyield of </a>f<sub>D</sub>= 20 % (l<sub>exc</sub> = 455 nm) and an excellent
photocytotoxicity of approx. 64 nM against A549 lung cancer cell lines (l<sub>exc</sub> = 468 nm, 9.3 J/cm²) was found, while no effect was observed in the
dark. Several molecular biological methods proved the harmlessness of <b>1</b>
in the dark while showing that apoptosis is dose-dependent induced by <b>1</b>
under irradiation. Therewith, <b>1</b> is a promising candidate for
photodynamic therapy, while the photoactivity theme in the subgenus hints
towards a yet unthought bioactivity in fungi: photoactivated defense.</p>