- Proton and Zinc(II) Complexes of 2-(Polyhydroxyalkyl)thiazolidine-4-carboxylic acid Derivatives
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The protonation and zinc-ion co-ordination equilibria of 2-(polyhydroxyalkyl)thiazolidine-4-carboxylic acid derivatives have been studied by potentiometric titration in the range pH 1.5-8.In most cases the formation of complexes with a metal-to-ligand ratio of 1:2 was demonstrated, but at above pH 6 mixed-ligand complexes involving hydroxide-ion co-ordination were also observed.The protonation and complex-formation constants were shown to depend on the structure of the polyhydroxy chains.In the case of the protonation constants this is due to the rearrangement of the intramolecular hydrogen-bonding network, while the complex-formation constants depend on the conformation of the OH groups on the first carbon atoms of the polyol chains.
- Gajda, Tamas,Nagy, Laszlo,Burger, Kalman
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p. 3155 - 3160
(2007/10/02)
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- Thiazolidine-4(R)-carboxylic acids derived from sugars: Part I, C2-epimerisation in aqueous solutions.
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Reactions of L-cysteine (1) with L-xylose, D-ribose, D-lyxose, D-arabnose, D-glucose, L-rhamnose, and-fucose in aqueoes ethanol yielded crystalline 2(S)-(polihydroxyalkyl)thiazolidine-4(R)-carboxylic acids.Likewise, glycolaldehyde and L-glyceraldehyde, D-xylose, L-arabinose, D-mannose, D-galactose, and D-fucose gave crystalline 2(R),4(R) epimers.The reaction of 1 and D-glycerinaldehyde gave a syrup mixture of 2(S),4(R) and 2(R),4(R) compounds.The same substrates, but with no ethanol present, gave the 2(S),4(R) epimers for glycolaldehyde, L-xylose, L-fucose, and L-arabinose, and the 2(R),4(R) epimers for D-lyxose, L-rhamnose, D-mannose, Dgalactose, and D-fucose.The reactions of D-ribose, D-arabinose, D-xylose, and D-glucose gave sirupy mixtures of epimers.The crystalline reaction products, when dissolved in water, undergo rapid epimerisation as reflected by mutarotation and changes in the 1H- and 13C-n.m.r. spectra.
- Radomski, Jan,Temeriusz, Andrzej
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p. 223 - 238
(2007/10/02)
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- Resolution of DL-Cysteine
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The diastereomeric 4-thiazolidinecarboxylic acids 3 and 4, obtained by condensation of DL-cysteine (DL-1) with D-(+)-galactose (2), can be separated by crystallization.Ring cleavage of 3 or 4 gives L-cysteine (L-1) or D-cysteine (D-1), respectively.Instead of D-(+)-galactose other chiral aldoses can be employed as resolution agents.
- Martens, Juergen,Drauz, Karlheinz
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p. 2073 - 2078
(2007/10/02)
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