A New Harziane Diterpene, Harziaketal A, and a New Sterol, Trichosterol A, from the Marine‐Alga‐Epiphytic Trichoderma sp. Z43

Abstract

AbstractOne new diterpene, harziaketal A (1), and one new highly degraded sterol, trichosterol A (2), along with three known compounds, including one diterpene, harzianone (3), and two steroids, (22E,24R)‐5α,6α‐epoxy‐ergosta‐8(14),22‐dien‐3β,7α‐diol (4) and isoergokonin B (5), were isolated from the culture of the marine‐alga‐epiphytic fungus Trichoderma sp. Z43 by silica gel column chromatography (CC), Sephadex LH‐20 CC, and preparative thin‐layer chromatography (TLC). Their structures and relative configurations were assigned by nuclear magnetic resonance (NMR) and high resolution electrospray ionisation mass spectrometry (HR‐ESI‐MS) data, and the absolute configuration of 1 was established by X‐ray diffraction. Compound 1 features a hemiketal unit situated at the four‐membered ring of harziane‐type diterpenes for the first time, while 2 represents the rare occurrence of sterols with rings A and B being degraded. Compounds 1 and 2 displayed weak inhibition against the tested phytoplankton (Amphidinium carterae, Heterocapsa circularisquama, Heterosigma akashiwo, and Prorocentrum donghaiense) with half maximal inhibitory concentration (IC50) ranging from 14 to 53 μg/mL.