Ergocytochalasin A, a polycyclic merocytochalasan from an endophytic fungus Phoma multirostrata XJ-2-1

Ergocytochalasin A (1), an unprecedented merocytochalasan formed via Diels-Alder cycloaddition of a cytochalasin with an ergosterol, was isolated from an endophytic fungus Phoma multirostrata XJ-2-1. Compound 1 possessed a unique 5/6/14/6/5/6/6/6 fused octacyclic ring system and its structure was established by detailed NMR and HRESIMS spectroscopic analyses. The absolute configuration of 1 was determined by single-crystal X-ray diffraction. A plausible biogenetic pathway of 1 was postulated. Compound 1 was evaluated for its cytotoxicity against six cancer cell lines and showed inhibitory effects with IC_{50} values ranging from 6.92 to 26.63 μM. The in vitro immunosuppressive activity of 1 against ConA-induced T cell and LPS-induced B cell proliferation, as well as its antiviral activity against Human dengue virus type 3 (DV3), influenza A virus (H1N1) and respiratory syncytial virus (RSV), was also evaluated. Ergocytochalasin A is the first example of a merocytochalasan which consists of one cytochalasin moiety and one ergosterol moiety. Containing eighteen chiral centers, ergocytochalasin A owns a folded framework, which makes it extremely compact in space.