Photoredox C-H functionalization leads the site-selective phenylalanine bioconjugation

Site-selectively chemical bioconjugation of peptides and proteins can improve the therapeutic exploration of modified protein drugs. Only 3.8% natural abundance of phenylalanine in protein and nearly 90% of proteins contain at least one phenylalanine residue in their sequenced, showing the potential in biopharmaceutical utility of the phenylalanine bioconjugation. However, the covalent bioconjugation of native phenylalanine is one of the most challenging problems in protein modification. Herein, an approach to protein modification is described that relies on a photoredox method for the site-selective bioconjugation of phenylalanine. This methodology has been validated on peptides as well as protein insulin using a straightforward and mild condition. In addition, based on characterization by near-UV CD spectroscopy and small angle X-ray scattering (SAXS), this pyrazole labeling approach permitted the insulin hexamer to completely dissociate into the monomeric form, thus making it a potential candidate for use as rapid-acting insulin for the treatment of diabetes.

Automated summary

Site-selective chemical bioconjugation of peptides and proteins, particularly phenylalanine bioconjugation, has great potential in improving the therapeutic effectiveness of modified protein drugs. However, covalent bioconjugation of native phenylalanine remains a challenging problem in protein modification. In this study, a photoredox method for site-selective bioconjugation of phenylalanine is described, which has been successfully validated on peptides and protein insulin under straightforward and mild conditions. The pyrazole labeling approach used in this study allows the complete dissociation of insulin hexamer into the monomeric form, making it a potential candidate for rapid-acting insulin in diabetes treatment.