Synthesis and Biological Activity of New Melatonin Receptor Ligands

To discover analogues of melatonin with a longer half-life, novel non-indole analogues of the compound, in which the amide group of the side-chain has been reversed, have been prepared and evaluated in binding assays to determine their activity on melatonin receptors. The two most active compounds were those with the N-methylbutyramide side-chain. Butyramide and pentanoylamide side-chains resulted in similar affinities, irrespective of the skeleton tested whereas a propionamide side-chain led to loss of affinity. The biological actity of the molecules was more influenced by the length of the side-chain than by the nature of the skeleton, which had little effect. The results obtained show the relative importance of the length of the side-chain and of the nature of the skeleton in both the binding to and the activity on the melatonin receptor of the retroamide series.