Cysteine-Derived Pleurotin Congeners from the Nematode-Trapping Basidiomycete Hohenbuehelia grisea

The discovery of a Hohenbuehelia grisea specimen during a field trip in Northern Thailand led to the isolation and identification of three novel sulfur-bearing derivatives of dihydropleurotinic acid (4). Thiopleurotinic acid A (1) was established by the interpretation of spectral data (HRESIMS, 2D-NMR) as a 2-hydroxy-3-mercaptopropanoic acid conjugate of dihydropleurotinic acid. Thiopleurotinic acid B (2) was shown to be the N-acetylcysteine conjugate of 4. A third compound (3) was established as a thiazole-containing derivative. Through feeding experiments with [U-¹³C₃, ¹⁵N]-l-cysteine the formation of all three metabolites was shown to involve cysteine condensation with 4. The decreased cytotoxicity and antimicrobial activities of the new derivatives 1-3, compared to the parent compound 4, indicate a possible detoxification pathway of filamentous fungi.