Structural characterization of selenium and selenium-diiodine analogues of the antithyroid drug 6-n-propyl-2-thiouracil and its alkyl derivatives

Abstract

The structures of four selenium analogues of the antithyroid drug 6-n-propyl-2-thiouracil [systematic name: 2,3-dihydro-6-n-propyl-2-thioxopyrimidin-4(1H)-one], namely 6-methyl-2-selenouracil, C5H6N2OSe (1), 6-ethyl-2-selenouracil, C6H8N2OSe (2), 6-n-propyl-2-selenouracil, C7H10N2OSe (3), and 6-isopropyl-2-selenouracil, C7H10N2OSe (4), are described, along with that of the dichloromethane monosolvate of 6-isopropyl-2-selenouracil, C7H10N2OSe·CH2Cl2 (4·CH2Cl2). The extended structure of (1) is a two-dimensional sheet of topology 63 with a brick-wall architecture. The extended structures of (2) and (4) are analogous, being based on a chain of eight-membered R 8 6(32) hydrogen-bonded rings. In (3) and (4·CH2Cl2), R 2 2(8) hydrogen bonding links molecules into chains. 6-n-Propyl-2-selenouracil·I2, C7H10N2OSe·I2 (7), is a charge-transfer complex with a `spoke' structure, the extended structure of which is based on a linear chain formed principally by intermolecular N—H...O hydrogen bonds. Re-crystallization of 6-ethyl-2-selenouracil or (7) from acetone gave crystals of the diselenides [N-(6′-ethyl-4′-pyrimidone)(6-ethyl-2-selenouracil)2(Se—Se)]·2H2O (9·2H2O) or [N-(6′-n-propyl-4′-pyrimidone)(6-n-propyl-2-selenouracil)2(Se—Se)] (10), respectively: these have similar extended chain structures formed via N—H...O and C—H...O hydrogen bonds, stacked to give two-dimensional sheets. Re-crystallization of (7) from methanol/acetonitrile led via deselenation to the formation of crystals of 6-n-propyl-2-uracil (11), in which six symmetry-related molecules combine to form a six-membered R 6 6(24) hydrogen-bonded ring, with each pair of molecules linked by an R 2 2(8) motif.