Antileishmanial activity of natural diterpenes from Cistus sp. and semisynthetic derivatives thereof.

Eleven cis-clerodane diterpenes, seven labdane type diterpenes and one triterpene isolated from Cistus monspeliensis and the resin "Ladano" of Cistus creticus subsp. creticus were evaluated against Leishmania donovani promastigotes, the causative agent for visceral leishmaniasis. In addition, eleven semisynthetic manoyl oxide, seventeen labdane type derivatives and a triterpene were also evaluated for their antileishmanial activity. 18-Acetoxy-cis-clerod-3-en-15-ol, 15,18-diacetoxy-cis-clerod-3-ene and 13-(E)-8a-hydroxylabd-13-en-15-ol 2-chloroethylcarbamate exhibited the most potent and selective leishmanicidal activity with IC50 values of 3.3 microg/ml, 3.4 microg/ml and 3.5 microg/ml, respectively.