Traceless reductive ligation at a tryptophan site: a facile access to β-hydroxytryptophan appended peptides

An efficient methodology for cysteine-free ligation at a tryptophan (Trp) site is described. A chemically active scaffold, β-hydroxy-α-azidotryptophan, has been synthesized and explored towards the synthesis of a series of β-hydroxytryptophan appended native peptides in good yields via one-pot reductive traceless ligation of β-O-peptidyl-α-azidotryptophan involving an O → N peptidyl transfer strategy. Pre-organized conformational analysis and reaction energy pathway based theoretical studies further supported the experimental findings on the chemical structure stability of ligated products.