Both L. major pteridine reductase and T. cruzi pteridine reductase had docking properties with Copaifera diterpenoids with comparable energies (average Edock = −93.8 and −96.8 kJ/mol, respectively) with the normal substrate dihydrobiopterin (Edock = −96.9 and −100.1 kJ/mol, respectively). Thus, Copaifera diterpenoids may compete with dihydrobiopterin for pteridine reductase.