Chapter 15: Cyclic Peptides as Privileged Structures

There is increasing interest in the use of peptide drugs as therapeutics. In comparison to small molecules, peptides can be more specific, less toxic and do not accumulate in organs. Cyclic peptides are often more beneficial than their linear counterparts due to conformational rigidity. They are also often more stable to exopeptidases and even endopeptidases because of flexible cyclic backbone. Literature encompasses several cyclic peptides that show diverse biological activities. Out of these, we have selected the so-called “privileged structures” among cyclic peptides, viz. diketopiperazines, benzodiazepines and cyclotides, for our discussion in this chapter, with a summary of their structure, function and therapeutic activities.