Of L-cystine

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-... 

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. 

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. 

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). 

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

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. 

Figure 10.24—Raman diffusion. Origin of emission bands cell geometry Raman spectrum of L-cystine.

Kunert, J. (1989c). Utilization of L-cystine as a source of carbon and nitrogen by various fungi. Acfa Univ. Palacki. Olomuc. Fac. Med. 123,351-364. 

Disulfides — A disulfide bond (R-S-S-R) is a strong covalent bond formed by the oxidation of two sulfhydryl groups (R-S-H). An amino acid that commonly forms S-S bonds in proteins is cysteine. When two cysteines are bonded by an S-S bond, the resulting molecule between the two protein chains is called cystine. The presence of disulfide bonds helps to maintain the tertiary structure of the protein. Industrial production of L-cysteine is based on the electrochemical - reduction of L-cystine in acidic - electrolytes using lead or silver -> cathodes. 

With the exception of L-cystine dimethyl ester (16), these results show the importance of the SH group in the interaction of silver with amino acids or... 

The hexagonal polymorph of L-cystine contains hydrogen-bonded layers which consist of 1 (16) hydrogen-bonded ring motifs, connected on one side by the disulfide bridges within the cystine molecules, and on the other by N-H O... 

The positive CD Cotton effect at 260 nm and the negative Cotton effect at 274 nm may be at least partly attributed to amino-acid residues. The side-chain residues of L-cystine, L-phenylalanine. L-tyrosine or L-tryptophan cause Cotton effects at 250—310 nm (101). However, copper complexes of simple amino acids show CD extremes at 245— 290 nm. Therefore, some contribution to the 260 nm band of erythro-... 

Numerous publications have been dedicated to the genesis of alkylthiazoles. A model reaction based on a mixture of cysteine/xylose/tributyrin was studied by Ledl and Severin (1973), who proposed the decarboxylation of cysteine into cysteamine (2-aminoethanethiol), followed by a condensation with sugar degradation products and a subsequent oxidation. Mulders (1973c) also proposed a model based on a system of cysteine/cystine/carbohydrates, with the formation of thiazolidines subsequently oxidized into thiazoles. The same pathway has been proposed by Flament (Firmenich, 1973), thiazolidines easily being formed by the reaction of cysteamine with aldehydes. Kato et al. (1973a) also found thiazoles in the volatile compounds produced by the reaction of L-cystine with carbonyl compounds. Similarly,... 

It could simply result from the degradation of the 2-mercaptoethylamine found among the pyrolysis products of L-cystine, as shown by Fujimaki et al. (1969). 

Human CGL displays an interesting substrate specificity with clear preference of C-S over S-S bond breakage L-cysteine and L-cystine are converted orders of magnitudes more slowly than the natural substrate L-cystathionine. The yeast enzyme attacks the C-/3-S bond of L-cystine or L-cysteine, whereas the streptomyces enzyme is quite active toward L-cystine. A CGL enzyme from Lactococcus lactis was reported to consist of at least six identical subunits and have a broad substrate specificity and relatively low specific activity toward L-cystathionine compared to bacterial CGL. In humans, L-cystathionine is split almost exclusively in... 

The chiroptical properties of the disulfide component of L-cystine have also been examined in the solid state in KBr disks (Imanishi and Isemura, 1969 Ito and Takagi, 1970) and in mulls (Kahn and Beychok, 1968b). The anomalous split CD spectrum of L-cystine is attributed to the proximity of the adjacent disulfide moieties in the crystal, which affords the possibility of exciton splitting. In the hydrochloride, no such effect occurs because of the interposition of chloride ions. The latter material exhibits a broad negative Cotton effect between 250 and 300 nm, which correlates with symmetry assignments made on the basis of solutions of molecules of conformationally restricted disulfide model compounds (Carmack and Neubert, 1967). 

Attempts have been made to correlate the chiroptical properties with the conformations of several sulfur-containing amino acids (Jung et al., 1973 Ottnad et al, 1975). Several reports describe conformations and chiroptical properties of L-cystine and its derivatives (Coleman and Blout, 1968 Casey and Martin, 1972 Strickland et al, 1974 Mattice, 1977). The CD data have been analyzed in terms of the chirality of the disulfide chromophore (Strickland et al, 1974) representing different conformer populations in solution. 

The CD spectra of L-cystine in potassium bromide disk (Ito and Takagi, 1970) and in mulls (Kahn and Beychok, 1968a) have been reported. 

Reaction 8, the direct cleavage of L-cystine to produce pyruvate and thiocysteine has been studied in much more detail. An enzyme has been found in a number of Brassica species which cattdyzes the production of pyruvate from L-cystine (Mazelis et al., 1%7). The specificity of this enzyme using six-fold purified B. napobrassica root preparations was limited to L-cystine and 5-methyl-L-cysteine sulfoxide of naturally occurring substrates. The enzyme was completely dependent on added pyridoxal 5 -phosphate. The for L-cystine was 1 vaM and 0.5 pM for pyridoxal phosphate. L-Cysteine was not a substrate but was a competitive inhibitor at low concentrations. This was due to the -SH function since glutathione had the same effect. The Aj for these compounds was 0.15 mM. 

A similar enzyme has recently been purified 277-fold from turnip (R. rapa) roots (Anderson and Thompson, 1979). The properties of this enzyme appear to be very similar to those of the rutabaga except the purified enzyme had some activity towards DL-cystathionine and several other substituted cysteines. Even though the activity towards cystathionine is only 22% that of L-cystine and the A , for cystathionine was 4 mM as compared to 0.94 mM for L-cystine, these authors consider that this may have a j8-cystathionase function in methionine biosynthesis. 

Scheme20 Synthesis of L-cystine-based hydrogelators 111, 112 and 113 (a) liq. NH3, -33°C (b) HCl/MeOH (c) 111 water, NaOAc, benzoyl chloride 112 EtsN, DMSO/CHCh.p-toluoyl chloride, 113 EtsN, DMSO/CHCI3, 2-naphthoyl chloride...

The electron density of L-cystine has been accurately measured. The deformation density distribution and AIM analysis clearly reveal disulfide bridge characteristics and sulfur lone pair electron regions in accord with high-level ab initio calculations. In terms of p s topology it is now known that SS bonds are weak single covalent bonds. The almost tetrahedral distribution of the VSCC of the sulfur atom is consistent with sp hybridization. 

Disulphides have also been studied. The final stable radical from a single crystal of L-cystine hydrochloride is an RS radical , but irradiation... 

As an example, the Stokes/anti-Stokes low-frequency Raman spectrum of L-cystine is shown in Figure L-Cystine is commonly used for testing the low-frequency capability of a Raman spectrometer. The 9.8 cm Raman bands are measurable in as short as 0.2 s fFig. 8.31. If the laser power is raised, faster measurements with 10 ms exposure time are possible. 

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