Chemoprophylactic agents in schistosomiasis: eremanthine, costunolide, -cyclocostunolide and bisabolol

The wood oils of the trees Eremanthus elaeagnus Sch.-Bip., Vanillosmopsis erythropappa Sch.-Bip. and Moquinea velutina Bong. inhibit penetration of cercariae of the trematode Schistosoma mansoni. The effect is due to the presence of α,β-unsaturated sesquiterpene lactones of which three, eremanthine (I), costunolide (III) and α-cyclocostunolide (V), have been characterized. The sesquiterpene alcohol (-)-bisabolol (II) present in two of the oils is weakly active while dihydro-β-cyclocostunolide (VI) which lacks the unsaturated lactone function is inactive. I and V react with the sulphydryl group of cysteine, and their activity may be related to inhibition of sulphydryl groups in cercarial enzymes.