The active site of TR consists of the residues involved in catalysis CYS53 and CYS58, HIS461 at the base of the site, also the residues GLU19, TYR111 and SER15 and a hydrophobic region formed by the amino acids LEU18, TRP22, TYR111, MET114 and MET113 . Table shows the results of the affinity energy of the molecules at the active site of TR, given by the Gibbs free energy (∆G, Kcal/mol); which considers negative energy values and indicates that the interaction process is spontaneous. We can see that trypanothione being its endogenous ligand has the highest binding energy value of -8.1 Kcal / mol, while that of nifurtimox is -6.7 Kcal / mol. Of the selected molecules that were coupled 4 have a better and greater energy affinity for the active site of TR, NF-279 is the one with the highest ∆G of binding -7.3 Kcal / mol, NF-150 -7.2 Kcal / mol and, NF-85 and 246 of -7.0 Kcal / mol, while NF-91 is the molecule with the lowest affinity energy of -6.5 Kcal / mol; which, is given by the interactions between the substituents of the ligands with the amino acid residues described in Table . Figure