Tyrosine bioconjugation

N.S. Joshi, L.R. Whitaker, M.B. Francis, A three-component Mannich-type reaction for selective tyrosine bioconjugation, J. Am. Chem. Soc. 2004, 126,15942-15943. 

Ban H, Gavrilyuk J, Barbas CF (2010) Tyrosine bioconjugation through aqueous ene-type reactions a click-like reaction for tyrosine. J Am Chem Soc 132 1523-1525... 

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.

Although the chemical modification of tyrosine residues has enjoyed a long history, this residue remains an underused target for bioconjugation reactions. It is typically modified through electrophilic aromatic substitutions (EAS), which makes its reactivity distinct from other amino acid side chains. This reaction... 

Tyrosine residues are underutilized targets for bioconjugate preparation. As it is displayed with intermediate frequency on protein surfaces, tyrosine can often be modified with greater selectivity than other residues. In contrast to charged amino acids, tyrosine residues are often partially buried in the surface of the proteins owing to the amphipathic nature of the phenolic group, Fig. 10.3-3(a-d). This close association with the topography of protein... 

Fig. 10.3-3 Tyrosine residues as targets for bioconjugation, (a) In contrast to charged amino acid side chains, tyrosine residues (yellow) are more closely associated with the protein surface. The reactive 3- and 5-positions of the phenolic ring (indicated...

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... 

M.W Jones, G. Mantovani, C.A. Blindauer, S.M. Ryan, X. Wang, D.J. Brayden, D.M. Haddleton, Direct peptide bioconjugation/PEGylation at tyrosine with linear and branched polymeric diazonium salts. /. Am. Chem. Soc., 134 (17) 1406-1413, 2012. 

For the covalent approach, standard protocols include bioconjugation techniques that have been routinely used in protein derivatization (Ma et al., 2012). The most widely used reactions include the reactive side chains of lysine (Lys), cysteine (Cys), aspartic acid (Asp), glutamic acid (Glu), and tyrosine (lyr) residues, which are available to form biocompatible covalent bonds (Fig. 15.5A). Lysine residues and N-termini provide reactive moieties in primary amines form (R-NH ) that have been mainly targeted with A-hydroxysuccinimidyl-esters (NHS-esters) or NHS-ester sulfate derivatives (Smith et al., 2013). 

---