Compounds reaction with cysteine

Amino acids containing other reactive functional groups react with pyridoxal to form heterocycUc compounds. Reaction with cysteine during sterilisation of milk gives a thiazoUdine derivative... 

Maleic acid imides (maleimides) are derivatives of the reaction of maleic anhydride and ammonia or primary amine compounds. The double bond of a maleimide may undergo an alkylation reaction with a sulfhydryl group to form a stable thioether bond (Chapter 2, Section 2.2). Maleic anhydride may presumably undergo the same reaction with cysteine residues and other sulfhydryl compounds. 

This means that gold(I) compounds can undergo associative ligand exchange reactions with cysteine-rich peptides and proteins such as glutathione, metallothionein and albumin28,29, particularly where the p/fsH is low, e.g. the Cys-34 of albumin30. 

Adrenochrome was observed to react readily with primary thiols to form varying mixtures of the above mentioned compounds [243], With cysteine and glutathione (free acid) all three types of product were formed the same was true with homocysteine and glutathione (monosodium salt) except that in these cases significantly greater amounts of the addition products were formed [239, 240, 243]. When the reaction was carried out with neutral primary thiols, e.g. 1-propanethiol, 1,2-propanedithiol, 1,3-propanedithiol and 2,3-dimercaptopropanol (B.A.L.) only the addition product (122) and 5,6-dihydroxy-iV-methylindole (44) were detected [243]. No reaction took place between adrenochrome and secondary or tertiary thiols, such as... 

Peptides typically are prepared for this ligation process using a-alkyl thioesters, because they are simple to make at the time of peptide synthesis. However, due to the relatively slow reaction kinetics of alkyl thioesters, most native chemical ligation processes have been catalyzed through the use of thiol compound additives, such as benzyl mercaptan or thiophenol (Dawson et al., 1997). These compounds react with the initial a-alkyl thioester to form another intermediate, an aryl thioester, which is more reactive toward the N-terminal cysteine on the other peptide to be coupled. A study... 

Using this type of cysteine-uptake assay, it is possible to determine the percentage of maleimides that reacted over time. Thus, an indication of the reaction efficiency of a sulfhydryl-containing compound coupling with a maleimide-activated protein may be determined. Figure 19.21 shows the reaction rate for the coupling of cysteine to maleimide-activated BSA. Note that maximal coupling is obtained in less than 2 hours, and over 80 percent yield is achieved in less than 30 minutes. 

Direct evidence of the reaction of PAN with sulfhydryl compounds has since been obtained (PAN at 115 ppm for 1-10 min). - In the reaction with glutathione, the major products are oxidized glutathione (disulfide) and 5-acetylglutathione. Other sulfhydryl compounds (e.g., coenzyme A, lipoic acid, and cysteine) yield only oxidation products, with no evidence of 5-acetylation. However, acetylation reactions have been observed with alcohols and amines. Sulfur compounds other than thiols can undergo oxidation by PAN methionine is converted to methionine sulfoxide, and oxidized lipoic acid (disulfide) is converted to sulfoxide. 

The reaction of cysteine and related compounds with penicillins and cephalosporins. Journal of Antibiotics,... 

Fluoromethyl ketones are one of the most widely used classes of peptidyl a-fluoroalkyl ketones, second only to trifluoromethyl ketones. Peptidyl fluoromethyl ketones are very effective as irreversible inhibitors of cysteine proteases the first reported use of a fluoromethyl ketone compound was the use of Z-Phe-Ala-CH2F as an irreversible inhibitor of cathepsin BJ2,31 Today, many lysine and arginine derivatives have been synthesized as potential inhibitors for trypsin and trypsin-like enzymesJ3 There are four basic methods for the synthesis of peptide fluoromethyl ketones (1) the reaction of HF with peptide diazomethyl ketones (Section 15.1.4.1.1), (2) a halogen-exchange reaction with a chloro-, bromo-, or iodomethyl ketone (Section 15.1.4.1.2), (3) a Henry nitro-aldol condensation reaction (Section 15.1.4.1.3), and (4) a modified Dakin-West acylation reaction (Section 15.1.4.1.4). 

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