Scheme 7. Enzyme-mediated strategies for tyrosine bioconjugation. (a) Strategies relying on the enzyme tyrosinase. The catechol generated via this enzyme can be O-alkylated or reacted with boronate esters. If oxidation is allowed to progress to the o-quinones, these can be reacted with bicyclononynes in a strain-promoted cycloaddition or with N or S nucleophiles. (b) Strategy relying on incorporation of unnatural tyrosine residues via the enzyme tubulin tyrosine ligase.
