Guanacastane-type diterpenoids from the insect-associated fungus Verticillium dahliae

Four new guanacastane-type diterpenoids, namely dahlianes A (1), B (2), C (3), and D (4), were isolated from cultures of Verticillium dahliae. Their structures were elucidated on the basis of extensive spectroscopic data analysis. Their absolute configurations were determined by a combination of Mo₂(OAc)₄-induced electronic circular dichroism experiment and Mosher ester method. In cytotoxicity evaluation against human tumor cell lines, compounds 2 and 3 exhibited significant cytotoxicities against MCF-7 cell lines with IC₅₀ values of 3.35 and 4.72 μM, respectively.