Mannich condensation with tyrosine

Figure 16.3 Conceptual illustration of two peptides before (left) and after (right) a chemical reaction with formaldehyde. The amino acids are represented as circles. In this particular peptide, a tyrosine (Y) is located within the epitope (shaded circles). An arginine (R) is located elsewhere in the peptide. Formaldehyde results in the formation of a covalent bond between the two residues, due to a Mannich condensation reaction, as shown on the right. The new configuration prevents antibodies from binding to the epitope on the left. 

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.

Fig. 10.3-5 Tyrosine modification using a when proteins are treated alone with either three component Mannich-type reaction. component, (b) The reaction conversion is (a) Aldehydes and anilines condense to listed for a number of anilines and aliphatic form imines in situ, which react with tyrosine amines using a-chymotrypsinogen A as the residues through an electrophilic aromatic substrate and formaldehyde as the aldehyde substitution reaction. No reaction occurs component.

Simple tetrahydroisoquinoline alkaloids are obtained upon condensation of phenylethylamines and catecholamines with carbonyl compounds. In a subsequent Mannich-hke reaction, the biosynthetic equivalent to a Pictet-Spengler reaction, the heterocyclic ring system is established. Numerous examples of simple tetrahydroisoquinoline alkaloids have been isolated from different plant sources. Several of these tyrosine-derived secondary metabolites exhibit intriguing biological and physiological properties, due to their structural relationship to catecholamines and phenylethylamines. 

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