Page 19 - Tyrosine-Based Bioconjugations - Jorick Bruins

Conjugation strategies utilizing less common and reactive amino acids are also available such as PTAD (4-phenyl-3H-1,2,4-triazoline-3,5(4H)-dione)-mediated modification of tyrosine (Scheme 1A),56 oxaziridine-based methionine conjugation Scheme 1B),57 or gold-catalyzed ethynylation of tryptophan (Scheme 1C).58 While these methods provide conjugates with high yield, the use of innate reactivity of an amino acid with multiple occurrences in a protein may not provide site- selectivity. This is clearly demonstrated with the PTAD-modification of tyrosine in human or bovine serum albumin (HSA, BSA),56 resulting in labeling of 3.9–8.3 tyrosine residues, depending on conditions.
Scheme 1. (A) Tyrosine (7) conjugation with PTAD (8), (B) Methionine (10) conjugation with oxaziridine (11), and (C) gold-catalyzed tryptophan (13) ethynylation.
General Introduction
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