Interactions between pairs of antimalarial drugs studied by experimental and ab initio (13)C NMR chemical shifts.

The interactions between the antimalarial drugs chloroquine (CQ) and amodiaquine (AQ), chloroquine and quinine (QN), and amodiaquine and quinine are studied by (13)C NMR. Experimental changes in chemical shift are compared to nucleus-independent chemical shifts to determine the best structure of the complex formed by each drug pair in solution. Structures of the CQ-AQ and CQ-QN complexes are found to be similar to those found previously for the drug dimers. On the other hand, the best solution structure for the AQ-QN complex suggests that the quinoline rings of the two drugs are at an angle with respect to each other.