Fimbricalyx A, a novel phenanthrenone derivative having a rare 2H-benz[e]inden-2-one substructure

Fimbricalyx A (1), a novel phenanthrenone derivative having a rare 2H-benz[e]inden-2-one substructure, was isolated from the root extract of Strophioblachia fimbricalyx. The structure of 1 was elucidated on the basis of the NMR and MS data and confirmed by X-ray crystallography. This compound showed cytotoxicity against KB, MCF7 and NCI-H187 cancer cells with IC50 values of 38.4, 28.7 and 8.3 μg/mL, respectively. A possible biosynthesis of 1, via a ring-contracted p-quinone methide intermediate derived from a phenanthrenone precursor, is proposed.