Site-Selective Synthesis of Insulin Azides and Bioconjugates

A synthetic method to access novel azido-insulin analogs directly from recombinant human insulin (RHI) was developed via diazo-transfer chemistry using imidazole-1-sulfonyl azide. Systematic optimization of reaction conditions led to site-selective azidation of amino acids B1-phenylalanine and B29-lysine present in RHI. Subsequently, the azido-insulin analogs were used in azide–alkyne [3 + 2] cycloaddition reactions to synthesize a diverse array of triazole-based RHI bioconjugates that were found to be potent human insulin receptor binders. The utility of this method was further demonstrated by the concise and controlled synthesis of a heterotrisubstituted insulin conjugate.