Bisbenzylisoquinoline alkaloids from the roots of cyclea tonkinensis.

Cissampentine A (1), an enantiomer of cissampentin, three new cycleatjehenine-type bisbenzylisoquinoline alkaloids, cissampentine B-D (2-4), and five known alkaloids were isolated from the roots of Cyclea tonkinensis. Their structures were established by interpretation of NMR, high-resolution ESI-MS data, and CD spectra. In vitro studies indicated that compounds 1 and 4 exhibited cytotoxicity against the HCT-8 tumor cell line (IC50 values of 8.97 and 9.73 µM, respectively), and compound 4 was also active against the Bel-7402 tumor cell line (IC50 value of 5.36 µM).