Cysteine ninhydrine reaction

Accordingly, as the first step, the interaction of qinghaosu and cysteine in the presence of a catalytic amount of Fe(lFlll) was studied. From the reaction mixture, a water-soluble compound was isolated. This compound could be visualized with ninhydrin on TLC, and it showed a formula of C16H27NO6S H2O. Treatment of this compound with acetic anhydride yielded a cyclic thioether 165, which in turn undoubtedly showed the formation of adduct 166 of 1 and cysteine through a a bond between C-3 and sulfur. A stable adduct 167 of cysteine and 170 was then isolated in 33% yield with the same reaction protocol. As mentioned, both adducts of cysteine with primary and secondary free radical derived from arte-mether were also identified recently, albeit in low yield (Structure 5-25). More... 

Although ninhydrin is typically used as an indicator for terminal amines, it has been used for the protection of A-terminal cysteine peptides. The derivative is readily formed under aqueous conditions at neutral to acidic pH. It is cleaved by reaction with an excess of cysteine using the mass action principle, 3-mercaptopropiosulfonic acid at pH 7.7, or Zn in 10% aqueous TFA. ... 

Reaction with thiols. The reagent reacts specifically with the thiol group of an amino acid or protein to give a derivative (2) which is colored or develops color with ninhydrin. Thus the sulfhydryl group of cysteine adds to the activated double bond to give a yellow neutral compound (2). This compound, which gives a purple color with ninhydrin, rearranges even in neutral solution to the carboxylic acid (3).1... 

In the case of amino acid analysis, the quantification of cysteine can be difficult because it is oxidized to cystine during acid hydrolysis. To circumvent this problem, cysteine can be oxidized to cysteic acid with performic acid prior to analysis. Alternatively, cysteine can be converted to the pyridyl ethyl derivative and subsequently detected by postcolumn reaction with ninhydrin. Still another method involves the production of carboxymethyl cysteine following alkylation with iodoacetic acid. All of these cysteine derivatives can be separated by either reversed-phase precolumn or ion-exchange postcoT umn methods. 

Another structural revision is concerned with the repqrted " formation of the thiazine system (127) in the reaction of ninhydrin with cysteine. The chemical and spectroscopic properties of the condensation product are in... 

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