Synthesis of 2-Phenylthiazolidine Derivatives as Cardiotonic Agents. IV. Modification of the Phenylpiperazino Moiety of 2- (Phenylpiperazino-alkoxyphenyl) thiazolidine-3-carbothioamides and the Corresponding Carboxamides

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Examination of the structure-activity relationships of 2- (phenylpiperazinoalkoxyphenyl) -thiazolidine-3-carbothioamides and the corresponding carboxamides (1) as new cardiotonic agents was extended by the chemical modification of the phenylpiperazino moiety. The 4-phenylpiperidine (13), 4-phenyltetrahydropyridines (17), and related derivatives were prepared from the chlorides (10) through several intermediates (12, 14, and 16) and tested for cardiotonic activity. Generally, both the 4-phenylpiperidine (13) and 4-phenyltetrahydropyridine (17) derivatives exhibited potent positive inotropic activity comparable to that of 1. The N-phenylpiperidines (9) and amide derivatives (22, 25, and 28) exhibited no significant positive inotropy. This is also the case for the phenylpropylamines (29) and the ethylenediamines (30), which are pseudo-ring analogues of 1 with respect to the piperazine moiety. The activity of the homopiperazine derivative (23) was approximately one-thirtieth of that of the corresponding piperazine derivative (1). Thus, the presence of the six-membered, basic azacycloalkane ring (piperidine or piperazine) with a 4-phenyl group at the end of the alkoxy side chain appears to be essential for the appearance of potent positive inotropic activity in this series of compounds.