Synthesis of compounds as melatonin agonists and antagonists

The functions of melatonin, the hormone of the pineal gland, are of considerable current interest. Synthetic melatonin analogues as agonists and antagonists have been explored in some detail and the molecule can be considered as consisting of an indole core, acting mainly as a spacer, and the 5-methoxyl and 3-amidoethyl side chains acting as the functional components, as originally proposed by Heward and Hadley. This review focuses on the synthetic routes to these melatonin analogues, first of the core, then of the substituents that have been attached to the core, and finally those compounds with restricted conformations and those that are chiral. The importance of the various factors involved in the activity of the compounds as agonist or antagonists is indicated, as is the difference in activity of enantiomers.