In Silico Prediction and Experimental Evaluation of Furanoheliangolide Sesquiterpene Lactones as Potent Agents against Trypanosoma brucei rhodesiense

As a continuation of our earlier study on the in vitro antiprotozoal activity of 40 natural sesquiterpene lactones (STLs), we extended the set of tested compounds from our laboratories to 59. On the basis of this extended data set, further enriched by literature data for 10 compounds tested under the same conditions, our quantitative structure-activity relationship (QSAR) analyses for activity against T. brucei rhodesiense (etiologic agent of human African trypanosomiasis, or sleeping sickness) were continued, and the QSAR model thus obtained with 69 structures was used to predict the activity of a virtual library of 1,750 STL structures. As a major result from these calculations, furanoheliangolide-type compounds, a subclass of STLs hitherto untested against T. brucei rhodesiense, were predicted to have an exceptionally high level of in vitro activity. Four representative compounds of this type, goyazensolide, 4,5-dihydro-2',3'-epoxy-15-deoxygoyazensolide, budlein A, and 4,15-isoatriplicolide tiglate, were therefore tested. They displayed 50% inhibitory concentrations (IC50s) of 0.07, 0.20, 0.07, and 0.015 μM, respectively, so that the in silico prediction was experimentally confirmed. 4,15-Isoatriplicolide tiglate is the most potent STL against T. b. rhodesiense found. Furanoheliangolide STLs were thus identified as interesting leads against this parasite which deserve more detailed investigations.