Malettinins B−D: New Polyketide Metabolites from an Unidentified Fungal Colonist of <i>Hypoxylon </i>Stromata (NRRL 29110)

Malettinins B−D (2−4), three new antimicrobial polyketide-derived metabolites related to the previously reported malettinin A (1), have been obtained from nonsporulating cultures of an isolate of Mycelia sterilia MYC-155 (= NRRL 29110) collected from colonies of Hypoxylon stromata. Malettinins B (2) and C (3) are partially reduced analogues of malettinin A and were identified by analysis of NMR and MS data. Malettinin D (4) is biogenetically similar, but possesses a new ring system, and the structure of 4 was established by single-crystal X-ray diffraction analysis.