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FeCl3-Mediated Side Chain Modification of Aspartic Acid- and Glutamic Acid-Containing Peptides on a Solid Support

An efficient, convenient, and selective Lewis acid-based strategy for on-resin deprotection of the side chain tert-butyl-protected aspartic acid and glutamic acid of a peptide is achieved. The method is mild, cost-effective, and Fmoc chemistry compatible and allows on-resin incorporation of amides, esters, and thioesters in good yield. This method will find wide applicability in peptide and protein modification because it enriches the toolbox of orthogonal protection/deprotection techniques.