To explore further derivatives of the studied pteridines, we next designed a merged compound library as follows. The pteridine core scaffold was retained and the studied compounds were decomposed into fragments of their N10, PABA and Tail regions and recombined in silico in Table . Descriptors with significant correlations with the observed inhibitory effect on T. brucei for the reference compounds and pteridines of the N10-, PABA-and Tail-modified series calculated with QikProp. QPlogKp: Predicted skin permeability, log Kp; QPlogPo/w: Predicted octanol/water partition coefficient. QPlogKhsa: Prediction of binding to human serum albumin. Cohesive index: Index of cohesive interaction in solids, (no. of hydrogen bond acceptors x no. of hydrogen bond donors x 0.5 / surface area) ; CIQPlogS: Conformationindependent predicted aqueous solubility, log S with S in mol dm -3 being the concentration of the solute in a saturated solution that is in equilibrium with the crystalline solid. R (Pearson correlation) and R 2 were calculated using the percentage of inhibition of the T. brucei brucei Lister 427 bloodstream form at 10 µM compound concentration as defined in the SI. Only descriptors with at least a Pearson correlation/anti-correlation of 0.40/-0.40 and two-tailed P-values lower than the chosen significance level α of 0.05 are reported. Covered range: property values obtained for the studied compounds. Recommended range: values the properties take for typical drug-like molecules. Resampling recovery rate indicates in how many cases (expressed as percentage) the same property was identified when leaving a single compound out of the data set. The optimization direction indicates whether higher or lower values would putatively lead to improved anti-parasitic effects.