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.
115 (base peak), 105. The diacetate 7, mp 112.5-114 °C, was prepared in the conventional manner and in high yield. The would also like to thank Syntex Laboratories, G. D. Searle and Company, and Ayerst Laboratories for generous gifts of hecogenin acetate.
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