Cytotoxic cochlioquinone derivatives from the endophytic fungus Bipolaris sorokiniana derived from Pogostemon cablin.

Chemical investigation of the liquid culture of the endophytic fungus Bipolaris sorokiniana A606, which was isolated from the medicinal plant Pogostemon cablin resulted in the isolation of four new cytotoxic compounds, named isocochlioquinones D-E (1-2) and cochlioquinones G-H (3-4), along with five known cochlioquinone analogues (5-9). Their structures were determined on the basis of extensive spectroscopic analysis. Isocochlioquinone D (1) possessed a rare benzothiazin-3-one moiety and cochlioquinone G (3) was the first example of cochlioquinones bearing an indole-4,7-dione fragment. All of the isolates (1-9) were evaluated for their cytotoxic activities against MCF-7, NCI-H460, SF-268 and HepG-2 tumor cell lines by the sulforhodamine B (SRB) assay. Compounds 4 and 6-9, featuring a cochlioquinone core, exhibited potent cytotoxicities in vitro against the four tumor cell lines, and a preliminary structure-activity relationship of these compounds was also discussed.