Synthesis of N1-phenethyl substituted indole derivatives as new melatoninergic agonists and antagonists.

The potency of new indolic N1-phenethyl substituted melatoninergic ligands with and without methyl groups in the alpha and beta position of the alkanamidoethyl side chain was examined using the pigment aggregation response in a clonal line of Xenopus laevis melanophores. The non 5-OMe substituted compounds, 8a--e, are all weak antagonists while introduction of the 5-OMe group, 9a--e, increases both agonist and antagonist activity except for 9c (R=C3H7), which is only an agonist and 9e (R=c-C4H7), which is only an antagonist. Introduction of an alpha-methyl group into the 5-OMe derivatives, 14a-e, reduces the agonist potency while introduction of a beta-methyl group has only a small effect on either the agonist or antagonist potency. Double beta-methyl substitution of the 5-OMe derivatives, 20a--e, generally increases the agonist potential (20c, R=C3H7 is the most potent agonist of the compounds described) and decreases the antagonist potency, except for 20a (R=CH3), which is the most potent antagonist of this series of compounds.