Acta Crystallographica Section C

Crystal Structure Communications

Volume 68, Part 9 (September 2012)

organic compounds

eg3095 scheme

Acta Cryst. (2012). C68, o344-o350 [ doi:10.1107/S0108270112031691 ]

Pseudopolymorphs of chelidamic acid and its dimethyl ester

M. Tutughamiarso, T. Pisternick and E. Egert

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 pK_a values, 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-HO 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-HO hydrogen bonds, whereas an antiperiplanar arrangement is observed in the water-free structure. A database study and ab initio energy calculations help to compare the stabilities of the various ester conformations.

Formula: C₇H₅NO₅·CH₄O, C₂H₈N⁺·C₇H₄NO₅^-, C₇H₅NO₅·C₂H₆OS and C₉H₉NO₅·H₂O


	Chemical Markup Language (CML) file (3.9 kbytes) [ doi:10.1107/S0108270112031691/eg3095Iasup6.cml ] Supplementary material

	Chemical Markup Language (CML) file (4.4 kbytes) [ doi:10.1107/S0108270112031691/eg3095Ibsup7.cml ] Supplementary material

	Chemical Markup Language (CML) file (4.3 kbytes) [ doi:10.1107/S0108270112031691/eg3095Icsup8.cml ] Supplementary material

	Chemical Markup Language (CML) file (4.3 kbytes) [ doi:10.1107/S0108270112031691/eg3095IIasup9.cml ] Supplementary material

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