Table . Properties with a significant correlation with the observed inhibitory effect on T. brucei for compounds in the merged series calculated with QikProp. The properties are defined as in Table . Values shown in bold face are within 90% of the previously determined top value or exceeded the previously obtained range for the reference compounds and compounds in the N10-, PABA-and Tail-modified series, see Table . The activity against T. brucei brucei Lister 427 bloodstream form at 10 µM compound concentration (%inhibition) is given. For the most promising compounds, 5d, 5e and 5f, in addition, measured EC50 values, CC50 interval estimation and selectivity indices are reported and compared to pentamidine, a reference compound with activity against T. brucei. EC50 represents the arithmetic average of at least two independent measurements done in triplicate. CC50 estimation was done by at least three independent cytotoxicity assessments on THP-1-derived macrophages by a colorimetric MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide) assay, as previously reported. The selectivity index is determined as the CC50 or lower CC50 interval estimation divided by EC50. N.D.: Not determined.