Two new ramulosin derivatives from the entomogenous fungus Truncatella angustata

Two new ramulosin derivatives, 7α-hydroxy-8-dihydroramulosin (1) and 7-ketoramulosin (2), along with three known metabolites, (+)-ramulosin (3), 6-hydroxyramulosin (4), and 8-dihydroramulosin (5), were isolated from the crude extract of Truncatella angustata, an entomogenous fungus isolated from the Septobasidium-infected insect Aspidiotus sp. The structures of 1 and 2 were elucidated by nuclear magnetic resonance experiments, and 1 was further confirmed by X-ray crystallography. The absolute configuration of 1 was assigned by single-crystal X-ray diffraction analysis using Cu Kα radiation, whereas that of 2 was determined by electronic circular dichroism (ECD) calculations. Compounds 1-5 were tested for cytotoxicity against four human carcinoma cell lines, HeLa, A549, MCF-7, and T24. Compound 4 showed weak cytotoxic effects against A549 and T24.