Volume 4 of Advances in Medicinal Chemistry is comprised of six chapters on a wide range of topics in medicinal chemistry, including molecular modeling, structure-based drug design, organic synthesis, peptide conformational analysis, biological assessment, structure-activity correlation, and lead optimization. Chapter 1 presents an account about amino acid-based peptide mimetics corresponding to b-turn, loop, helical motifs in proteins as a probe of ligand-receptor and ligand-enzyme molecular interactions. Chapter 2 addresses new facets of the medicinal chemistry of the important anticancer dr.