L-Cystine

L-cystine D-cystine DL-cystine metbionine [56-893] [349-46-2] [923-32-0] [7005-18-7 J Met 2-arnino-4-rnetbyl-tbi obutanoic acid CH3SCH2CH2 CHCOOH 149.21... 

Bis-Af-ieri-butyloxycarbonyl-L-cystine, [10389-65-8] M 440.5, m 144.5-145 , [ot] -133.2 (c 1, MeOH), pKEst 2.9. Crystd from in EtOAc by adding hexane [Ferraro Biochem Prep 13 39 1971]. 

Cystamine dihydrochloride, S,5-(L,L)-Cystathionine, Cysteamine, Cysteamine hydrochloride, ( )-Cysteic acid, S-Cysteic acid (H2O), L-Cysteine hydrochloride (H2O), ( )-Cysteine hydrochloride and L-Cystine, Cytidine, see entries in Chapter 6. 

The presence of sparingly soluble components in human urine, such as calcium oxalate, calcium phosphate, magnesium ammonium phosphate, uric acid and l-cystine. Kidney stones are composed mainly of these compounds. 

Cyclohexyl chloride, 6, 24 Cyclohexylmagnesium bromide, 6, 20 Cyclohexylmagnesium chloride, 6, 24 3 Cyclohfxvi Propinf-i, 6, 26 Cyclopentanone, 5, 37 l Cystine, 5, 39... 

The synthesis commences with a straightforward acylation of the primary amino group of L-cystine dimethyl ester (13) with 5-hexy-noyl chloride (14) to give amide 12 in 90% yield (see Scheme 3). The action of zinc dust in acetic acid on intermediate 12 accom-... 

On several occasions the product isolated by the submitters was contaminated with L-cystine dihydrochloride, which was not easily removed by recrystallization. In this event the product was converted to the zwitterionic form and recrystallized in the following manner. The pH of a solution of the product in water was adjusted to 6 with aqueous 2.5N potassium hydroxide. The neutralized solution was evaporated to dryness under reduced pressure at ca. 40°. The residue was dissolved in a minimum amount of hot water, and two volumes of 95% ethanol were added to precipitate S-acetamidomethyl-L-cysteine monohydrate, dec. 187°, [a] 9 — 42.5° (c = 1, water). 

The first reductive kinetic resolution of racemic sulphoxides was reported by Balenovic and Bregant. They found that L-cysteine reacted with racemic sulphoxides to produce a mixture of L-cystine, sulphide and non-reduced optically active starting sulphoxide (equation 147). Mikojajczyk and Para reported that the reaction of optically active phosphonothioic acid 268 with racemic sulphoxides used in a 1 2 ratio gave the non-reduced optically active sulphoxides, however, with a low optical purity (equation 148). It is interesting to note that a clear relationship was found between the chirality of the reducing P-thioacid 268 and the recovered sulphoxide. Partial asymmetric reduction of racemic sulphoxides also occurs when a complex of LiAlH with chiral alcohols , as well as a mixture of formamidine sulphinic acid with chiral amines, are used as chiral reducing systems. ... 

Walsh et al. (2000) have reported the reduction of L-cystine hydrochloride to L-cysteine hydrochloride and have covered laboratory kinetics to process modelling for several m cells. 

In the case of the thiopurines the electrochemical processes do not appear to agree at all with the known biological oxidations. However, again in the case of 6-thiopurine not even a complete picture of the metabolites is available. The electrochemical data indicates that thiopurines are very readily oxidized to disulfides and hence to sulfinic or sulfonic acids. In view of well-known sulfide-disulfide transformations in biological situations (e.g., L-cy-steine to L-cystine), it is not unlikely that part of the metabolic degradation pathway for thiopurines might proceed via reactions of the sulfide moiety. 

A newer therapeutic approach is the administration of betaine (6-12 g daily), which lowers homocysteine levels by favoring remethylation [33], A theoretical hazard of betaine treatment is increasing the blood methionine, sometimes to an extravagant degree ( 1 mmol/1). Experience to date indicates that betaine administration is safe, with no major side effects except for a fishy odor to the urine. Other therapeutic approaches have included the administration of salicylate to ameliorate the thromboembolic diathesis. Patients also have been treated with dietary supplements of L-cystine, since the block of the transsulfura-tion pathway in theory could diminish the synthesis of this amino acid. 

Sanchez-Cano et al. have proposed paired synthesis for obtaining L-cysteic acid and L-cysteine from L-cystine which greatly improves the economical parameters [57], The global process-flow for the paired synthesis, with L-cystine and water as starting materials is shown in Fig. 3. Table 2 compares the results for the paired (B) and the individual syntheses (A, C). 

L-Cysteine is a high value a-amino acid used world-wide in a scale of 1200-15001 year-1 as additive in foodstuffs, cosmetics or as intermediate or active agent (as antidote to several snake venoms) in the pharmaceutical industry. Chemical routes generally lack the efficiency of electrochemical techniques, or they produce mixtures of l- and d- forms rather than the L-isomer. The most common electrochemical route is the cathodic reduction of L-Cystine in acid (usually HC1) solution to produce the stable hydrochloride. In Table 10, the charateristic data for a laboratory bench, laboratory pilot and a product pilot reaction using a DEM filter press are compared [13]. A production scale study was carried out in a filterpress reactor divided by a cation exchange membrane with a total area of 10.5 m2. The typical product inventory was 450 kg/24-hour batch time. For more details see Ref. [13]. 

M. Tomi, T. Funaki, H. Abukawa, K. Katayama, T. Kondo, S. Ohtsuki, M. Ueda, M. Obinata, T. Terasaki, and K. Hosoya. Expression and regulation of L-cystine transporter, system Z(T, in the newly developed rat retinal Muller cell line (TR-MUL). Glia 43 208-217 (2003). 

M. Tomi, K. Hosoya, H. Takanaga, S. Ohtsuki, and T. Terasaki. Induction of the xCT gene expression and L-cystine transport activity by diethyl maleate at the inner blood-retinal barrier. Invest. Ophthalmol. Vis. Sci. 43 774—779 (2002). 

Fig. 45. The structure of L-cystine dihydrobromide, seen down the crystallographic 2-fold axis. The disulfide is in a left-handed spiral conformation.

Optically active sulfoxides can also be obtained when a racemic sulfoxide is reduced with an insufficient amount of a chiral reagent. Balenovic and Bregant (65) found that L-cysteine reacted with racemic sulfoxides to produce a mixture of sulfide, L-cystine, and nonreduced optically active starting sulfoxide. Mikoikjczyk and Para... 

Bretti. C.. Crea. F.. Foti. C.. and Sammartano. S. Solnbility and acivity coefficients of acidic and basic nonelectrolytes in aqueous salt solutions. 1. Solnbility and activity coefficients o-phthalic and L-cystine in NaCl(aq). (CHsl NCUaq). and (C2Hs) NI(aq) at different ionic strengths and at t= 25 °C. Ind. Eng. Chem., 50(5) 1761-1767. 2005. 

Carta, R. and Tola, G. Solubilities of L-cystine, L-tyrosine, L-leucine, and glycine in aqueous solutions at various pHs and NaCl concentrations, J. Chem. Eng. Data, 41(3) 414-417, 1996. 

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