Pyranonigrin A (CAS: 773855-65-5)

Pyranonigrin A is a tetramic acid-derived fungal secondary metabolite produced by Aspergillus niger and related species. Its structure was reassigned based on spectroscopic and computational analysis, confirming a fused γ-pyrone-pyrrole core with defined absolute configuration. Biologically, pyranonigrin A exhibits antioxidant activity comparable to ferulic acid and contributes to UV resistance in fungal isolates, including strains recovered from the International Space Station. Biosynthetic studies have elucidated its gene cluster and key enzymatic steps responsible for γ-pyrone formation and exo-methylene installation. Computational analyses further suggest potential inhibitory interactions with SARS-CoV-2 main protease (Mpro), expanding its relevance to antiviral screening research.