Tyrosine reactivity

Figure 4.21 Tyrosine reactive probes. Nitration of tyrosine by reaction with tetranitromethane, followed by reduction with sodium dithionite, to yield an o-aminotyrosine.

Several flaoraza reagents shown in Tables 3a and 3b (B, C, E, F, J, and K) are reactive enough to fluorinate an aromatic ring (Table 1). The ortho isomer predominates in the o/mlp mixture Reagent K has been used to prepare fluorinated derivatives of tyrosine and estradiol [77 (equation 35) (Table 1, entry 10)... 

Using the general synthetic concepts described in Sec. II, we employed tyrosine dipeptides as the monomeric starting material. After protection of the N and C termini, the reactivity of a fully protected tyrosine dipeptide (structure 2) could be expected to resemble the... 

In an attempt to identify more biocompatible diphenols for the design of degradable biomaterials, we studied derivatives of tyrosine dipeptide as potential monomers. After protection of the amino terminus and the carboxylic acid terminus, the reactivity of tyrosine dipeptide (Figure 1) could be expected to be similar to the reactivity of industrial diphenols. Thus, derivatives of tyrosine dipeptide could be suitable replacements for BPA in the synthesis of a variety of new polymers that had heretofore not been accessible as biomaterials due to the lack of diphenolic monomers with good biocompatibility. 

Figure 1. Molecular structures of Bisphenol A and fully protected tyrosine dipeptide. The amino and carboxylic acid groups of the dipeptide are rendered unreactive by protecting groups (schematically represented by X and Y). This leaves the phenolic hydroxyl groups as the only reactive sites of the molecule.

Figure 4. DDC (A), serotonin (B), and tyrosine hydroxylase (C) immunore-activity in the posterior region of a wild-type Drosophila ventral ganglion. Tyrosine hydroxylase (TH) encodes the rate-limiting step in dopamine biosynthesis and is a marker for dopamine cells. B and C are the same CNS assayed for both serotonin and TH. M, medial dopamine neurons VL, ventrolateral serotonin neurons DL, dorsolateral dopamine neurons. Short unmarked arrows in C show vacuolated cells that do not contain DDC immunoreactivity. The immunoreactivity in these cells may represent a nonspecific cross-reactivity of the rat TH antibody. The length bar in A is 50 pM. The images are confocal projections generated on a Molecular Dynamics-2000 confocal laser scanning microscope.

In dilute aqueous solution, formaldehyde can react with a variety of amino acids. However, the primary initial targets are lysine and cysteine. The primary amine moiety of lysine can accept two methylol adducts. Other amino acids with which formaldehyde reacts include arginine and tyrosine, which are particularly reactive, as well as histidine, serine, tryptophan, glutamine, and asparagine.2 ... 

Maleic acid is a linear four carbon molecule with carboxylate groups on both ends and a double bond between the central carbon atoms. The anhydride of maleic acid is a cyclic molecule containing five atoms. Although the reactivity of maleic anhydride is similar to other cyclic anhydrides, the products of maleylation are much more unstable toward hydrolysis, and the site of unsaturation lends itself to additional side reactions. Acylation products of amino groups with maleic anhydride are stable at neutral pH and above, but they readily hydrolyze at acid pH values around pH 3.5 (Butler et al., 1967). Maleylation of sulfhydryls and the phe-nolate of tyrosine are even more sensitive to hydrolysis. Thus, maleic anhydride is an excellent reversible blocker of amino groups to temporarily mask them from reactivity while another... 

Figure 12.3 The strong oxidant chloramine-T can react with iodide anion in aqueous solution to form a highly reactive mixed halogen species. 125IC1 then can modify tyrosine and histidine groups in proteins to form radiolabeled products.

Figure 12.5 IODO-GEN is a water-insoluble oxidizing agent that can react with 1251 - to form a highly reactive mixed halogen species, 125IC1. This intermediate can add radioactive iodine atoms to tyrosine or histidine side chain rings.

Figure 12.6 The immobilized glucose oxidase/lactoperoxidase system radioiodinates proteins through the intermediate formation of hydrogen peroxide from the oxidation of glucose. H2O2 then reacts with iodide anions to form reactive iodine (I2). This efficiently drives the formation of the highly reactive H2OI+ species that is capable of iodinating tyrosine or histidine residues (see Figure 12.2).

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