Diazonium reaction with tyrosine

The synthesized CPMV-alkyne 42 was subjected to the CuAAC reaction with 38. Due to the strong fluorescence of the cycloaddition product 43 as low as 0.5 nM, it could be detected without the interference of starting materials. TMV was initially subjected to an electrophilic substitution reaction at the ortho-position of the phenol ring of tyrosine-139 residues with diazonium salts to insert the alkyne functionality, giving derivative 44 [100]. The sequential CuAAC reaction was achieved with greatest efficiency yielding compound 45, and it was found that the TMV remained intact and stable throughout the reaction. 

Diazotization of proteins with diazonium-l/f-tetrazole in previous work has been studied in terms of reaction with histidine and tyrosine residues (50, 51). When E. coli pyrophosphatase was incubated with this reagent, there was pseudo-first-order inactivation, but analysis of the... 

Much of Landsteiner s pioneer work was carried out with haptens that were aromatic amines. The compounds were converted to diazonium salts with nitrous acid and aUowed to react with proteins at alkaline pH (approximately 9). Reaction occurred primarily with histidine, tyrosine, and tryptophan residues of the protein carrier. For a representative procedure, see Kabat (p. 799 seq.). An interesting application of this procedure was the preparation of a chloramphenicol-protein conjugate which was used to elicit antibodies specific for chloramphenicol. In this case, a prior reduction of the nitro group of chloramphenicol to an amino group was required. As early as 1937, carcinogenic compounds were conjugated to protein carriers by means of their isocyanate derivatives which were prepared from amines. Immune sera were raised, and their properties were studied. - ... 

The site-selective conjugation at tyrosine residues of salmon calcitonin using diazonium salt 73 has recently been published (Equation 3.42) [257]. It has been indicated that the PEGylation reaction is reversible, and that the starting materials can be obtained by reaction with suitable reducing reagents. 

Figure 1.11 Tyrosine residues are subject to nucleophilic and electrophilic reactions. The unprotonated phe-nolate ion may be alkylated or acylated using a variety of bioconjugate reagents. Its aromatic ring also may undergo electrophilic addition using diazonium chemistry or Mannich condensation, or be halogenated with radioactive isotopes such as 12iI.

The phenolic group of tyrosine undergoes iodina-tion (Eq. 3-44), acylation, coupling with diazonium compounds, and other reactions. 

As standards for spectrophotometric measurements, Traylor and Singer (1967) prepared the monoazo derivatives of histidine and tyrosine with the various diazonium salts. The spectra of the products of reaction of N-acetyl histidine with the diazonium salt were obtained after reaction of a 100-fold excess of N-acetyl histidine with the diazonium salt in 0.1 M borate at pH 9.0. The spectral constants for the histidine and tyrosine derivatives are recorded in Table 5.1. 

The above studies emphasize the ability of diazonium-coupling reactions to modify proteins with extremely high efficiency, but one of the limitations of this method is the lack of selectivity that can be obtained when there are multiple tyrosines on the surface of a single protein. This has not been problematic for the viral capsids shown above, as only one tyrosine is accessible on each monomer, but many applications demand higher levels of selectivity than allowed by these coupling reactions. To address this need, and to increase the substrate scope for bioconjugation reactions in general, a versatile Mannich-type reaction has been developed for tyrosine modification, Fig. 10.3-5 [25]. In this reaction, aldehydes and anilines are mixed to form... 

H.G. Higgins, D. Fraser, The reaction of amino acids and proteins with diazonium compounds. 1. A spectrophotometric study of azo-derivatives of histidine and tyrosine, Australian J., Sci. Res. Ser. A Phys. Sciences 1952, 5, 736-753. 

It is interesting that when tyrosine is acylated with benzoyl chloride under this condition, it forms a dibenzoyl derivative that cannot react with the diazotized sulfanilic acid whereas histidine yields only a monobenzoyl derivative that can further react with diazonium acid. However, it has been found that when pyridine is added to scavenge the generated HCl, the reaction yield might be reduced." ... 

R. J. Barmett The diazonium salt probably combines with the phenolic group of tyrosine to give a light tan color which can be seen in the tissues which are negative for sulfhydryl, This doesn t interfere with the sulfhydryl color reaction which is red or blue, depending on the concentration of these groups. 

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