Synthesis, chemistry and conformational properties of piperazic acids

We review methods for the preparation of piperazic acids (“piz”) and significant aspects of their chemistry. Special attention is devoted to issues relating to acylation of these non-proteinogenic amino acids, given the importance of these operations for the synthesis of piz-containing oligopeptides. We also provide an account of the unique conformational properties of piperazic acids and discuss their behavior as rigid proline equivalents that should be quite useful for the creation and study of peptide turn mimics.