Diversity-Oriented Approaches to Unusual α-Amino Acids and Peptides: Step Economy, Atom Economy, Redox Economy, and Beyond

Here we describe several useful strategies to a variety of unusual a-amino acid derivatives and peptides based on building block approach. These building blocks are suitable for modification at an amino acid as well as at a peptide level. Moreover, these methods have embedded several points for diversification and are capable of producing a library of modified amino acids and peptides. We have employed highly atom-economic processes such as the Diels-Alder reaction, [2 + 2 + 2] cycloaddition, Suzuki-Miyaura cross-coupling, and olefin metathesis as key steps to assemble various unnatural amino acid derivatives and peptides. In some instances, we have used rongalite to generate Diels-Alder precursors.