Cysteine hydrochloride hydrate

Various crystalline states of cysteine, cysteine hydrochloride, and cysteine hydrochloride hydrate have been tested for solid-state reactivity. Thus, (R)-352 and (i )-352-HCl-H20 were also reactive in the solid-state. This was verified by quantitative solid-solid reactions with paraformaldehyde (354) in stoichiometric ball-milling experiments at room temperature giving 100% yield of R)-355 [12] or (J )-355-HCl [10] after drying. 

Potassium tetrabromoaurate(l-) (0.3005 g, 0.541mmole)6 is placed in a 100-mL beaker containing a magnetic stirring bar. To this is added 20 mL HBr solution (0.1 M). L-Cysteine hydrochloride hydrate (available from Aldrich Chemical Co., Milwaukee, WI) (0.3120 g, 1.78mmole) is dissolved in a separate 100-mL beaker with 20 mL HBr (0.1 M). (The acid concentration is important. Use of 1 M HBr leads to a different product.) The CySH HCl H20 solution is rapidly added to the [AuBr4]" solution with constant stirring. 

A slurry of diammonium isopentenyl phosphate, s-cysteine hydrochloride hydrate, and pyridine warmed 20 hrs. at 50° in vacuo over KOH, dissolved in water, and passed through Dowex-50-H s-felinine phosphate (startg. m.f. 10). Y 76%. H. Eggerer, A. 657, 212 (1962). 

Aminothiophenol (236t) reacts quantitatively to give the five-membered compound 350 [5] (Scheme 56). On the other hand, d- and rac-penicillamine hydrochloride (43-HCl) (but not the free bases) give the d- and rac-thiazolidine hydrochloride hydrates (351) with 100% yield if acetone (316) vapors are applied to them. The same is true for L-cysteine hydrochloride (352-HCl) giving the thiazolidine L-353-HC1-H20 [5]. 

Cysteine hydrochloride 1-hydrate in lx MMR (titrate to pH 8.0 with NaOH). Make up freshly. 

Other amino-acids which have been studied include L-cysteic acid mono-hydrate,which is conformationally similar to L-cysteine and taurine, and (—)-2-aA o-amino-norbornane-2-carboxyllc acid hydrobromide which has been shown to have the absolute configuration (li , 2R, AS). DL-Tryptophan formate exhibits an anti conformation about the C -Cp bond, in contrast to the gauche arrangement observed in the hydrochloride. 

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