Structures and absolute configurations of phomalones from the coral-associated fungus Parengyodontium album sp. SCSIO 40430

Abstract

Coral-associated microorganisms are likely to play an important role in host defense by the production of antimicrobials. Six new chromanones, namely, phomalichenones H-M (5, 6, and 8–11), and ten known analogues (1–4, 7, and 12–16) were isolated from the coral-associated fungus Parengyodontium album sp. SCSIO 40430. Their structures were elucidated by comprehensive spectroscopic analyses. In addition, the structure of 8 was confirmed by X-ray crystallographic analysis. Resolution using a chiral column showed that each of the compounds 1–8 was an enantiomeric mixture with variable enantiomeric excess (ee) values. Their absolute configurations were determined by a comparison of the experimental and calculated ECD data and by a modified Mosher's method. A plausible biosynthetic scheme was proposed for the production of 1–16. Compounds 2, 3, 13, and 14 were found to be active against Mycobacterium tuberculosis H37Ra with MIC values of 16–64 μg mL⁻¹.