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Tutughamiarso M, Pisternick T, Egert E. Pseudopolymorphs of chelidamic acid and its dimethyl ester. Acta Crystallogr C 2012; 68:o344-50. [PMID: 22935501 DOI: 10.1107/s0108270112031691] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2012] [Accepted: 07/11/2012] [Indexed: 11/10/2022] Open
Abstract
Different tautomeric and zwitterionic forms of chelidamic acid (4-hydroxypyridine-2,6-dicarboxylic acid) are present in the crystal structures of chelidamic acid methanol monosolvate, C7H5NO5·CH4O, (Ia), dimethylammonium chelidamate (dimethylammonium 6-carboxy-4-hydroxypyridine-2-carboxylate), C2H8N+·C7H4NO5−, (Ib), and chelidamic acid dimethyl sulfoxide monosolvate, C7H5NO5·C2H6OS, (Ic). While the zwitterionic pyridinium carboxylate in (Ia) can be explained from the pKavalues, a (partially) deprotonated hydroxy group in the presence of a neutral carboxy group, as observed in (Ib) and (Ic), is unexpected. In (Ib), there are two formula units in the asymmetric unit with the chelidamic acid entities connected by a symmetric O—H...O hydrogen bond. Also, crystals of chelidamic acid dimethyl ester (dimethyl 4-hydroxypyridine-2,6-dicarboxylate) were obtained as a monohydrate, C9H9NO5·H2O, (IIa), and as a solvent-free modification, in which both ester molecules adopt the hydroxypyridine form. In (IIa), the solvent water molecule stabilizes the synperiplanar conformation of both carbonyl O atoms with respect to the pyridine N atom by two O—H...O hydrogen bonds, whereas an antiperiplanar arrangement is observed in the water-free structure. A database study andab initioenergy calculations help to compare the stabilities of the various ester conformations.
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