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

C-alpha-Tetrasubstituted alpha-amino acids are widely used to design and prepare peptides and peptide mimics with constrained conformations. Subcategories of these compounds are cyclic C-alpha-tetrasubstituted alpha-amino acids, in which both alpha-substituents are covalently connected. This survey presents recent advances in the synthesis and application of cyclic C-alpha-tetrasubstituted alpha-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-alpha-tetrasubstituted alpha-amino acids and their use as conformation determining elements in peptides. (C) 2007 Wiley Periodicals, Inc.