Peptidomimetics are important drug design tools as substitutes for peptides in active sites of enzymes and receptors. The incorporation of some specific structure into biologically active peptides may lead to conformationally restricted peptidomimetics. Conformational restriction of peptidomimetics may significantly improve the pharmacodynamic properties and pharmacokinetic properties, including bioactivity, selectivity to receptors, stability of metabolism and absorption properties. To develop new approaches, allow rational design and synthesis of restricted peptidomimetics is of importance. Herein, we review two approaches to access conformationally restricted peptidomimetics, the local conformational restriction approach and the overall cyclization approach.

Contents
1 Introduction
2 Local conformational restriction of peptide
2.1 C^α-methylated amino acids
2.2 N-methylated amino acids
2.3 C^α,C^α-dialkyl amino acids
2.4 C^β,C^β-dialkyl amino acids
2.5 α,β-unsaturated amino acids
2.6 C-C cyclization of amino acids
2.7 C-N cyclization of amino acids
2.8 N-N cyclization of amino acids
3 The overall cyclization of peptides
3.1 The overall cyclization methods of peptides
3.2 Other cyclization methods expect lactam bond
4 Conclusion