Antitrypanosomal sesquiterpene lactones from Saussurea costus

In the course of a larger screen of 1800 plant and fungal extracts, the ethyl acetate extract of Saussurea costus roots potently inhibited the growth of Trypanosoma brucei rhodesiense. Subsequent HPLC based activity profiling led to the identification of the sesquiterpene lactones arbusculin B (1), α-cyclocostunolide (2), costunolide (3), and dehydrocostuslactone (4). They were tested for in vitro antitrypanosomal activities and cytotoxicity alongside the structurally related sesquiterpene lactones parthenolide (5), zaluzanin D (6), and eupatoriopicrin (7), and had IC(50)s between 0.8 and 22 μM. Cytotoxic IC(50)s were from 1.6 to 19 μM, and selectivity indices from 0.5 to 6.5.