Flavichalasines A-M, cytochalasan alkaloids from Aspergillus flavipes

Two new tetracyclic cytochalasans, flavichalasines A and B (1 and 2), three new pentacyclic cytochalasans, flavichalasines C-E (3-5), and eight new tricyclic cytochalasans, flavichalasines F-M (6-13), together with eight known analogues (14-21), were isolated from the solid culture of Aspergillus flavipes. Structures of these new compounds were elucidated on the basis of extensive spectroscopic analyses including 1D, 2D NMR and HRESIMS data. Their absolute configurations were determined by comparison of their experimental ECD with either computed ECD or experimental ECD spectrum of known compound. The structure and absolute configuration of 2 were further determined by X-ray crystallographic diffraction. Flavichalasine A (1) represents the first example of cytochalasan with a terminal double bond at the macrocyclic ring and flavichalasine E (5) is the only cytochalasan with an α-oriented oxygen-bridge in D ring. These new compounds were evaluated for their cytotoxic activities against seven human cancer cell lines, of which, 6 and 14 displayed moderate inhibitory activities against tested cell lines. In addition, compounds 6 and 14 induced apoptosis of HL60 cells by activation of caspase-3 and degradation of PARP.