Synthesis and biological activity of conformationally restricted tricyclic analogs of the hormone melatonin

A serie of rotationally restricted tricyclic naphthalenic and tetrahydronaphthalenic analogs of the hormone melatonin has been synthesized, the C-7 oxygen being incorporated in a pyran, furan or dioxan heterocyclic ring. The receptor binding profile of these compounds is a function of the directionality of the lone pairs electrons of this C-7 oxygen. In these two studied analogous series the agonist activity seems to be correlated with the existence of a naphthalene nucleus.