2-Thiolhistidine
Title: 2-Thiolhistidine
CAS Registry Number: 13552-61-9
CAS Name: a-Amino-2,3-dihydro-2-thioxo-1H-imidazole-4-propanoic acid
Additional Names: 2-mercaptohistidine; a-amino-2-mercapto-4-imidazolepropionic acid
Molecular Formula: C6H9N3O2S
Molecular Weight: 187.22
Percent Composition: C 38.49%, H 4.85%, N 22.44%, O 17.09%, S 17.13%
Literature References: Prepn from histidine: Ashley, Harington, J. Chem. Soc. 1930, 2586; from aspartic acid: Harington, Overhoff, Biochem. J. 27, 338 (1933). Alternate procedures: Hegedüs, Helv. Chim. Acta 38, 22 (1955); Marei, Raphael, J. Chem. Soc. 1958, 2624. Review: J. P. Greenstein, M. Winitz, Chemistry of the Amino Acids vol. 3 (John Wiley, New York, 1961) pp 2671-2675.
 
Derivative Type: L-Form
Properties: Plates from water, darkens at 290°, not melted at 310°. [a]D20 -10° (c = 2 in N HCl). pK11 1.84; pK21 8.47; pK31 11.4. Readily sol in hot water, sparingly sol in water at room temp. Tends to form supersaturated solns. Practically insol in alcohol, other organic solvents.
pKa: pK11 1.84; pK21 8.47; pK31 11.4
Optical Rotation: [a]D20 -10° (c = 2 in N HCl)
 
Derivative Type: Dihydrochloride
Molecular Formula: C6H9N3O2.2HCl
Molecular Weight: 228.08
Percent Composition: C 31.60%, H 4.86%, N 18.42%, O 14.03%, Cl 31.09%
Properties: Large prisms, dec 197-199°. Freely sol in water, sparingly sol in alcohol.

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