Epiquinine is a stereoisomer of quinine, antimalarial alkoloid from the bark of a cinchona tree. Quinine was over 100 times more active than epiquinine against chloroquine-sensitive Plasmodium falciparum and over 10 times more active against chloroquine-resistant P. falciparum. Intra-erythrocytically active anti-malarial quinine acts by binding to haematin, blocking beta-haematin formation (while the anti-malarially inactive epiquinine had no effect on the reaction, however as quinine epiquinine was reported to bind ferriprotoporphyrin IX) and leaving toxic haematin in the parasite food vacuoles. Distinguishing features of the weakly active epiquinine include a higher dipole moment, a different direction of the electric field, a greater intrinsic nucleophilicity, lower acidity of the hydroxyl proton, a lesser electron affinity of the lowest unoccupied molecular orbitals, and a higher proton affinity than the active cinchona alkaloids. Epiquinine has little inhibitory effect toward peroxidative destruction of haem.