Crystal structures of (2R,4R)-2-(polyhydroxyalkyl)-1,3-thiazolidine-4-carboxylic acids: condensation products of l-cysteine with d-hexoses |
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Authors: | Miros?aw Tarnawski Katarzyna ?lepokura Tadeusz Lis |
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Affiliation: | aFaculty of Biotechnology, University of Wroc?aw, Przybyszewskiego 63/77, 51-148 Wroc?aw, Poland;bFaculty of Chemistry, University of Wroc?aw, Joliot-Curie 14, 50-383 Wroc?aw, Poland |
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Abstract: | We report herein the first crystal structures of (4-carboxy-1,3-thiazolidin-2-yl)pentitols [2-(polyhydroxyalkyl)thiazolidine-4-carboxylic acids], condensation products of l-cysteine with d-galactose and d-mannose: 2-(d-galacto-pentahydroxypentyl)thiazolidine-4-carboxylic acid hydrate, Gal-Cys·H2O (1), and 2-(d-manno-pentahydroxypentyl)thiazolidine-4-carboxylic acid hydrate, Man-Cys·H2O (2). In 1 and 2 the compounds crystallize as zwitterions, with the carboxylic groups deprotonated and the thiazolidine N atoms protonated. The sugar moiety and carboxylate group are in a cis configuration relative to the thiazolidinium ring, which adopts different conformation: twisted (T) on Cβ–S in 1, and S-puckered envelope (E) in 2. The carbon chain of the galactosyl/mannosyl moiety remains in an extended zig-zag conformation. The orientation of the sugar O2 atom with respect to the thiazolidinium S and N atoms is trans–gauche in 1 and gauche–gauche in 2. The molecular conformation is stabilized by the intramolecular N–H?OCys contacts in both 1 and 2 and by the additional N–H?OMan interaction in 2. The crystal packing of orthorhombic 1 and monoclinic 2 is determined mainly by N/O/C–H?O hydrogen bonds forming ribbons linked to each other by direct and water-mediated O/C–H?O/S contacts. |
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Keywords: | Cysteine Galactose Mannose X-ray crystal structure |
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