Chaetoglobosin U, a Cytochalasan Alkaloid from Endophytic Chaetomium globosum IFB-E019

A new cytotoxic cytochalasan-based alkaloid named chaetoglobosin U (1), along with four known analogues, chaetoglobosins C (2), F (3), and E (5) and penochalasin A (4), has been characterized from the EtOAc extract of a solid culture of Chaetomium globosum IFB-E019, an endophytic fungus residing inside the stem of healthy Imperata cylindrica. The structure of chaetoglobosin U was determined through correlative analyses of its UV, IR, CD, MS, and 1D (1H and13C NMR and DEPT) and 2D NMR (COSY, NOESY, HMQC, and HMBC) data. Chaetoglobosin U (1) exhibited cytotoxic activity against the human nasopharyngeal epidermoid tumor KB cell line with an IC50 value of 16.0 μM, comparable to that (14.0 μM) of 5-fluorouracil co-assayed as a positive reference. The known analogues 2−5 were moderately active to the cell line, with IC50 values of 34.0, 52.0, 48.0, and 40.0 μM, respectively.