2,4-Dinitrophenyl group

The cycloaddition between a nitrilimine 319 and an aroyl substituted heterocyclic ketene aminal 318 has been found to be stepwise, involving an initial nucleophilic addition of 318 to 319 followed by intramolecular cyclocondensation of the intermediate 320 providing fully substituted pyrazole 321 (Eq. 36) [92]. When Ar was the 2,4-dinitrophenyl group, the intermediate 320 was isolable and required forcing conditions (xylene, reflux, 10 h) to undergo cyclization ... 

M Mammen, FA Gomez, GM Whitesides. Determination of the binding of ligands containing the lV-2,4-dinitrophenyl group to bivalent monoclonal rat antibody using affinity capillary electrophoresis. Anal Chem 67 3526—3535, 1995. 

Insulin was reacted with Sanger s reagent and then completely hydrolyzed. Two amino acids, a glycine and a phenylalanine, were found to be labeled with the 2,4-dinitrophenyl group. 

Oxidation and reduction procedures have little effect on 1-aryl substituents which are also very difficult to remove. When, however, there are strongly electron-withdrawing groups present in the benzene ring, nucleophiles are effective in promoting dearylation. Thus, a 2,4-dinitrophenyl group at N-1 of histidine is cleaved by alkaline hydrolysis, aminolysis or hydrazinolysis. On the other hand, l-(2-pyridyl)imidazole is cleaved neither by 2M sodium hydroxide nor by 2M hydrochloric acid. 

A detailed study of the specific rates of solvolysis of N,N,N, N -tetra-methyldiamidophosphorochloridate (80) (TMDAPC) with analysis in terms of the extended Grunwald-Winstein equation has been reported (Scheme 19). The stereochemistry of nucleophilic attack at tetracoordinate phosphorus was also discussed." The initial reaction of bis (2,4-dinitrophenyl) phosphate (BDNPP) (81) with hydroxylamine involves release of 1 mol 2,4-dinitrophen-oxide ion and formation of a phosphorylated hydroxylamine (82), which reacts readily with further NH2OH, giving the monoester (83). The intermediate (82) also breaks down by two other independent reactions one involves intramolecular displacement of aryloxide ion (83) and the other involves migration of the 2,4-dinitrophenyl group from O to N and formation of phosphorylated 2,4-dinitrophenylhydroxylamine (84) (Scheme 20)." ... 

The 2,4-dinitrophenyl group is cleaved by thiols, for instance 2-mercapto-ethanol, under mildly basic conditions. 

Another method for sequence analysis is the Sanger N-terminal analysis, based on the use of 2,4-dinitrofluorobenzene (DNFB). When a polypeptide is treated with DNFB in mildly basic solution, a nucleophilic aromatic substitution reaction (SnAt, Section 21.1 lA) takes place involving the free amino group of the N-terminal residue. Subsequent hydrolysis of the polypeptide gives a mixture of amino acids in which the N-terminal amino acid is labeled with a 2,4-dinitrophenyl group. After separating this amino acid from the mixture, it can be identified by comparison with known standards. 

Dinitrofluorobenzene will react with any free amino group in a polypeptide, including the e-amino group of lysine, and this fact complicates Sanger analyses. Only the N-terminal amino acid residue of a peptide will bear the 2,4-dinitrophenyl group at its a-amino group, however. Nevertheless, the Edman method of N-terminal analysis is much more widely used. ... 

The electron-withdrawing property of the 2,4-dinitrophenyl group makes separation of the labeled amino acid very easy. Surest how this is done. PRACTICE PROBLEM 24.5... 

A suspension of l-(2,4-dinitrophenyl)-3-phenyl-4,5-cyclotetramethylenepyrazole in ethanol refluxed 3-4 min. with 85%-hydrazine hydrate 3-phenyl-4,5-cyclo-tetramethylenepyrazole. Y 84%.—Removal of the 2,4-dinitrophenyl group by formation of the scarcely soluble, easily removed 2,4-dinitrophenylhydrazine circumvents more drastic alkali cleavage and permits a convenient prepn. of certain pyrazoles, 1,2,3-triazoles, and tetrazoles without N-substituents. F. e. s. S. Rossi, S. Maiorana, and G. Bianchetti, G. 94, 210 (1964) for 1,2,3-triazoles and tetrazoles s. G. 94, 340. 

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