Antimicrobial Terpenoids and Polyketides from the Algicolous Fungus Byssochlamys spectabilis RR-dl-2-13.

Abstract

Four new carotane sesquiterpenoids, byssocarotins A-D (1-4), two new nor-sesquiterpenoids, byssofarnesin (5) and byssosesquicarin (6), and three new polyketides, byssoketides A and B (7 and 8) and (8R)-paecilocin A (9a), were obtained from a macroalga-associated strain (RR-dl-2-13) of the fungus Byssochlamys spectabilis. These isolates were identified by a combination of spectroscopic methods, including mass spectroscopy, nuclear magnetic resonance, electronic circular dichroism, and X-ray diffraction. Compounds 1-4 greatly contribute to the diversity of rarely occurring 2,15-epoxycarotane sesquiterpenoids, while 5 and 6 are degradation products of farnesane and sesquicarane precursors, respectively. Compound 7 is a structurally unique furan fatty acid derivative that possesses an aldehyde group and a large conjugated unit, and 8 features a hemiketal group. During antimicrobial assays, 8 showed antagonism against the phytopathogenic fungi Glomerella cingulata, Fusarium oxysporum f. sp. cucumerium, and F. oxysporum f. sp. cubense and the marine-derived bacteria Vibrio parahaemolyticus and V. harveyi with MIC values of 13 to 50 μg/mL.