An Atom-Economic Inverse Solid-Phase Peptide Synthesis Using Bn or BcM Esters of Amino Acids

An atom-economic N-to-C-directed solid-phase peptide synthesis is reported that uses benzyl (Bn) or (benzhydryl-carbamoyl)-methyl (BcM) esters of amino acids as the building blocks, which facilitate efficient hydrazinolysis, convenient conversion to acyl azide, and robust amidation with the next amino acid ester. This method is free of coupling reagents and free of protection on the side-chain OH, CO2H, CONH2, etc., therefore exhibiting a significantly improved atom economy compared to those of BOC- or Fmoc-based C-to-N-directed approaches.