Structure of the anti-malarial drug primaquine diphosphate

8-(4-Amino-1-methylbutylamino)-6-methoxyquinoline bis(dihydrogenphosphate), C15H23N3O2+.2(H2PO4)-, Mr = 455.35, triclinic, P1, Z = 2, a = 7.389 (6), b = 8.862 (4), c = 16.055 (10) A, alpha = 97.57 (2), beta = 100.21 (3), gamma = 77.01 (2) degrees, V = 1003.6 (5) A3, Dm = 1.495 (by flotation), Dx = 1.507 g cm-3, lambda (Cu K alpha) = 1.5418 A, mu(Cu K alpha) = 24.48 cm-1, F(000) = 480, room temperature, R = 0.068 for 3448 observed reflections. The above working cell is related to the reduced cell with angles alpha = 82.43, beta = 79.79 and gamma = 77.01 degrees by the transformation (-100/0 -10/001). Primaquine diphosphate was crystallized in the dicationic form with protonation on the quinoline ring nitrogen atom and on the terminal amino group. One dihydrogenphosphate anion is chelated by the quinoline ring and the butylamino side chain. The other dihydrogenphosphate anion is hydrogen bonded to the terminal amino group. The C(14) atom is nearly in the plane of the quinoline ring with a C(9)-C(8)-N(13)-C(14) torsion angle of 169 degrees. The butyl-diamino side chain is kinked by rotation about the C(14)-C(16) bond with a N(13)-C(14)-C(16)-C(17) torsion angle of -59 degrees. The C(15) methyl substituent is in line with the rest of the butyl chain. The terminal amino group N(19) is hydrogen bonded to three symmetry-related phosphate groups while N(1) and N(13) are 'chelated' to a fourth phosphate group.