Enantio- and diastereoselective syntheses of cyclic Ca-tetrasubstituted a-amino acids and their use to induce stable conformations in short peptides

C-Tetrasubstituted -amino acids are widely used to design and prepare peptides and peptide mimics with constrained conformations. Subcategories of these compounds are cyclic C-tetrasubstituted -amino acids, in which both -substituents are covalently connected. This survey presents recent advances in the synthesis and application of cyclic C-tetrasubstituted -amino acids in a systematic order beginning with cyclopropane amino acids, continuing with four, five, six membered rings, and ring structures larger than six-membered. We discuss synthetic routes to the cyclic C-tetrasubstituted -amino acids and their use as conformation determining elements in peptides.