Phragmalin-type limonoid orthoesters from Chukrasia tabularis var. velutina

Nine new phragmalin-type limonoid orthoesters, tabulalides F-N (1-9), together with three known compounds, tabulalides C and D, and tabularisin N (10-12), were isolated from the stem bark of Chukrasia tabularis var. velutina. Extensive spectroscopic technologies were applied to elucidate the structures of these new compounds, including the application of circular dichroism (CD) exciton chirality method for the determination of the absolute configurations of 1 and 2. Tabulalide F (1) has a rare orthoisobutylate moiety in phragmalin-type limonoid orthoesters. These compounds were evaluated for cytotoxic activity against five human cancer cell lines in vitro. Tabulalide G (2) exhibits moderate cytotoxic activity against MCF-7 with IC(50) value of 20.4 μmol/l, and other compounds have weak inhibitory effects on the growth of tested tumor cells.