Structure-activity relationships of tricyclic antidepressants, with special reference to tianeptine

Structure-activity relationships in the classical antidepressant (imipramine-like) series show a relative lack of specificities: Compounds should simply have a nucleus consisting of two phenyl rings and a third, seven-member central ring. This central ring may have one, several, or no heteroatoms, and it may or may not be saturated. The side chain may be attached to any one of the atoms of the central ring, but it must be short (two or three carbon atoms), and have a terminal amine group (secondary, tertiary, or included in a ring). We investigated the structure-activity relationships of 22 new tricyclic tianeptine derivatives exhibiting reserpine-induced ptosis reversal potency in the mouse. Tianeptine is an antidepressant characterized by a 3-chlorodibenzothiazepin nucleus and an aminoheptanoic side chain. Our results indicate highly specific structural requirements for the tianeptine-like series. In order to be active, compounds must have an aminocarboxylic chain (with an optimal length of six methylene links), a tricyclic system with an electron-donor heteroatom in position 5, and an aromatic substitution with a moderate electron-acceptor atom in position 3. These specificities in the tianeptine series are in sharp contrast with the lack of specific requirements that characterize the classical tricyclic series.