Three previously undescribed azepino-indole alkaloids, named purpurascenines A–C (1–3), together with the new-to-nature 7-hydroxytryptophan (4) as well as two known compounds, adenosine (5) and riboflavin (6), were isolated from fruiting bodies of Cortinarius purpurascens Fr. (Cortinariaceae). The structures of 1–3 were elucidated based on spectroscopic analyses and ECD calculations. Furthermore, the biosynthesis of purpurascenine A (1) was investigated by in vivo experiments using 13C-labeled sodium pyruvate, alanine, and sodium acetate incubated with fruiting bodies of C. purpurascens. The incorporation of 13C into 1 was analyzed using 1D NMR and HRESIMS methods. With [3-13C]-pyruvate, a dramatic enrichment of 13C was observed, and hence a biosynthetic route via a direct Pictet–Spengler reaction between α-keto acids and 7-hydroxytryptophan (4) is suggested for the biosynthesis of purpurascenines A–C (1–3). Compound 1 exhibits no antiproliferative or cytotoxic effects against human prostate (PC-3), colorectal (HCT-116), and breast (MCF-7) cancer cells. An in silico docking study confirmed the hypothesis that purpurascenine A (1) could bind to the 5-HT2A serotonin receptor’s active site. A new functional 5-HT2A receptor activation assay showed no functional agonistic but some antagonistic effects of 1 against the 5-HT-dependent 5-HT2A activation and likely antagonistic effects on putative constitutive activity of the 5-HT2A receptor.

Five fungal secondary metabolites named 1,2,4,5-tetrachloro-3,6-dimethoxybenzene (1); ergosterol (2); ergosterol peroxide (3); (E)- 4-(3,4-dihydroxyphenyl)but-3-en-2-one (4) and [Bi-1,4-cyclohexandien-1-yl]-3,3’,6,6’-tetrone, 4, 4’-dihydroxyl-2,2’,5,5’-tetramethyl (5) were purified from ethyl acetate extract of the fruit bodies of Phellinus gilvus collected at Pu Mat national park, Nghe An province. Their structures were charaterized by 1D, 2D NMR and GC-MS spectroscopies. Especially, the structure of compound 1 was confirmed by X-ray crystallographic analysis. The antimicrobial and cytotoxicity activities of compounds 1 were also evaluated. This is the first report on the chemical constituents of Vietnamese Phellinus gilvus.