Trichorenins A–C, Algicidal Tetracyclic Metabolites from the Marine-Alga-Epiphytic Fungus <i>Trichoderma virens</i> Y13‑3

Three novel polyketide-like metabolites, trichorenins A–C (<b>1</b>–<b>3</b>), with a unique tetracyclic carbon skeleton were obtained from the culture of <i>Trichoderma virens</i> Y13-3, an epiphyte of the marine red alga <i>Gracilaria vermiculophylla</i>. Their structures and relative configurations were established by analysis of 1D/2D NMR and MS data, and their absolute configurations were unequivocally assigned by X-ray diffraction and ECD spectra aided by quantum chemical calculations. Compounds <b>1</b>–<b>3</b> exhibited potent inhibition against two marine phytoplankton species, <i>Chattonella marina</i> and <i>Karlodinium veneficum