5- Ethylcysteine

In cases in which both a serine and threonine residue are present in a peptide fragment that is phosphorylated, these can be distinguished by reaction of the peptide with ethanethiol in 5N NaOH, which converts phosphoserine to 5-ethylcysteine ... 

Kubec R, Svobodova M and Velisek J (2000), Distribution of 5-alk(en)ylcysteine sulfoxides in some Allium species. Identification of a new flavour precursor S-ethylcysteine sulfoxide (ethiin) , JAgric Food Chem, 48, 428-433. 

The lipophilic complex 99mTc(IV)-L,L-ECD (62) with a deprotonated L,L-ethylcysteine dimer as ligand, is clinically used as a cerebral perfusion imaging agent. It crosses the blood-brain barrier and... 

TABLE 13.4 Hydrogenolysis of A -Z-S-Ethylcysteine Derivatives with Addition of BF3-etherate... 

B(C2H5)2The tridentate ligand [HB pz-3,5-(CH3)2 2(SCgH4-4-CH3)]" was synthesized intentionally from ArSH and K[H2B pz-3,5-(CH3)2 2]- It was converted to L MSR complexes (M = Cu or Co SR = 0-ethylcysteine,p-nitrobenzenethiolate or pentafluorophenylthiolate). These compounds were studied as synthetic approximations of the proposed active sites in the blue copper proteins (plastocyanin, azurin)... 

All these enzymes have similar specificity and require the L-cysteine sulfoxide portion of the molecule. S-alkyl cysteines are not substrates 18, 24, 27, 39) neither are sulfoxides of N-substituted L-cysteine, / -di-methyl-L-cysteine, y8-thiopropionic acid 18), D-cysteine 19), and dl-methionine 18, 24, 39), nor do the enzymes act on L-cysteine itself 24, 27, 39), cysteic acid, cysteinesulfinic acid 24, 27), or cycloalliin 24, 39). There may be some action on S-ethylcysteine sulfone (42). 

One proposal to increase the visibility of the b and y sequence-specific ions and to provide complete sequence information is to derivatize phosphopeptides.106 Sequence analysis can also be improved by using the /3-elimination chemistry.102,107 As described above in this section, phosphoserine and phosphothreonine can be converted to S-ethylcysteine and 5-ethyl-/3-methylcysteine, respectively, upon the base-catalyzed /3-elimination of the phosphate group, followed by the reaction with ethanethiol. CID of the modified peptides results in more evenly distributed sequence-specific fragment ions. 

Meyer, H. E., Hoffmann-Posorske, E., and Heihneyer, L. M. G., Determination and location of phosphoserine in proteins and peptides by conversion to S-ethylcysteine, Meth. EnzymoL, 201, 169-185, 1991. 

DMSA dimercaptosuccinic acid, EDTA ethylenediaminetetraacetic acid, HMPAO hexamethyl propyl-eneamine oxime, DADS J yM-bis(mercaptoacetyl)ethylenediamine, DADT diaminodithiol, ECD ethylcysteinate dimer, MAG3 mercaptoacetyltriglycine, NOEt Et(OEt)NCS2, DTPA diethylene triamine pentaacetate, MDP methylenediphosphonate, HIDA N-(2,6-dimethylphenylcarbamoylmethyl) iminodiacetic acid, DMPE l,2-bis(dimethylphosphino) ethane, BATO boronic acid technetium oxime, MIBI methoxyisobutyl isocyanide... 

The ethylcysteinate dimer (ECD) belongs to the family of neutral, lipophilic tetradentate diaminedithiol ligands. The x-ray structure (Fig. 2.1.9) shows the functionalized ester dimer with a Tc(V)oxo core in a square pyramidal configuration (Watson et al. 1987). In fact, its high-performance liquid chromatography (HPLC) behavior is the same for the Tc and Tc-ECD complex (Edwards et al. 1990). 

CA cancer antigen, CD cluster of differentiation, MUC mucin, TAG tumor-associated glycoprotein, EGFR epidermal growth factor receptor, MAG mercaptoacetyltriglycine, EC ethylcysteinate, HYNIC hydrazine nicotinamide... 

Figure 19 Polarization pattern in the photoreaction of S-ethylcysteine Cys with 4-carboxybenzo-phenone at pH 77. Bottom trace spectrum in the dark top trace photo-CIDNP spectrum. The assignment of the resonances refers to the formula given at the top. The a proton is unpolarized, the p and y protons are polarized, so the radical cation is seen to be sulphur-centred. Further explanation, see text.

Previous studies reported that lipid-soluble DAS, DADS, and DATS (100 pM) were more effective in suppressing canine tumor cell proliferation than isomolar water-soluble SAC, S-ethylcysteine, and S-propylcysteine [119]. S-Al-lylmercaptocysteine, one of the more effective water-soluble allyl sulfur compounds, did not reduce the viability of human erythroleukemina cells until concentrations were about 100 pM [123]. While... 

Stereospecific S-oxidation to the sulphoxide has been observed in Allium cepa with S-methylcysteine, S-ethylcysteine, S-propylcysteine, S-trans-prop-enylcysteine, S-cis-propenylcysteine, and deoxycycloallinin as the sulphidic precursors. ... 

Arylhydroxylamines are readily converted into nitroso compounds with DAD at 0°C (eq 1). One example of the conversion of an A,A-dimethylhydrazone to a nitrile has been reported. Sulfur-containing amino acids like methionine and S-ethylcysteine can be oxidized to their sulfoxides in virtually quantitative yields, although another reaction pathway occurs with most other thioethers. Thioethers and ethers usually react with DAD to yield a-hydrazo derivatives by hydrogen abstraction. The initial ether/DAD adducts can be formed thermally at 100 °C or photochemically at much lower temperatures. ... 

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