Onydecalins, Fungal Polyketides with Anti-Histoplasma and Anti-TRP Activity

We report an unusual 3-substituted pyridine polyketide, onydecalin A (1), which was obtained along with 2 as a major constituent from the fungus Aioliomyces pyridodomos (order: Onygenales) following a two-month fermentation. Feeding studies demonstrated that the pyridine subunit originates via an unprecedented biosynthetic process in comparison to other polyketide-linked pyridines or derivatives such as pyridones. The slow growth of the fungus led us to perform a one-year fermentation, leading to production of compounds 2–4 as the major constituents. These compounds showed modest but selective inhibition against a variety of transient receptor potential channels, as well as against the human pathogenic fungus Histoplasma capsulatum.