Post-Assembly Modification of Head-to-Tail Cyclic Peptides by Methionine-Directed β-C(sp 3 )-H Arylation.

Peptide modification by C(sp ³ )-H functionalization of internal residues remains a major challenge due to the inhibitory effect of peptide bonds. In this work, we developed a methionine-directed β-C(sp ³ )-H arylation method for internal alanine functionalization. By tuning the σ _C-C bond rotation of internal Ala through head-to-tail cyclization, we overcame the inhibitory effect and functionalized a wide range of head-to-tail cyclic peptides with aryl iodides with excellent position selectivity.