Page 28 - Tyrosine-Based Bioconjugations - Jorick Bruins

Chapter 1
Scheme 7. Generation and subsequent reactions of iminoquinones as reported by Francis et. al.
Iminoquinone conjugation in biomolecules has been realized by introducing p- aminophenylalanine on the external surface of genome-free MS2 capsids using amber stop codon suppression (not depicted).106 The incorporated aniline moieties could be modified by various o-aminophenol compounds after oxidation with NaIO4, including a cyclic penta-amino acid variant of RGD peptide. Comparable results were obtained when the iminoquinone was generated from o-azidophenols upon irradiation with 302 nm light.108 The applicability of this chemistry was not limited to bioconjugation strategies in solution, but was also applicable on surfaces (Scheme 8, top). For example, glass modification with aniline-bearing trimethoxysilane group coupled followed by selective surface patterning with in situ generated iminoquinone (by light irradiation of o-azidophenol) attached to a single stranded DNA. Subsequent binding of Saccharomyces cerevisiae, modified with the complementary DNA strand, allowed visualization of the photolithographic pattern.
Bioconjugation with iminoquinones was also employed to label high-molecular weight polyethyleneglycol 112 chains to the N-terminus of various proteins (not depicted).109 Using K3Fe(CN)6, a milder oxidant with less side-reactions than NaIO4,107 oxidation of o-aminophenols allowed for quick and selective modification of N-terminal residues, with proline having the highest degree of conjugation. This was applied to modify aniline-bearing glass surfaces with enzymes.113 Analogously to the light-induced patterning modification of glass, single stranded DNA was introduced by in situ generated iminoquinone via K3Fe(CN)6 oxidation. Next, a
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