Hydroxychloroquine Isomer1 This drug is highly flexible and it is likely that a near complete identification of possible conformations was not made. Never-the-less, 265 unique conformations were optimized at the B97-D3(BJ)/cc-pVTZ theory level. In addition to the intramolecular hydrogen bond that is formed between the acyclic nitrogens (as found in chloroquine, see Figure and), this theory level predicts that the unique terminal hydroxyl group forms an intramolecular interaction with the conjugated rings system (e.g. conformer 1). Five conformations have relative energies below 2.0 kcal•mol -1 , with an additional ten conformation below 3.0 kcal•mol -1 .