Analogues of captopril, enalaprilat, and the phosphinic acid [hydroxy(4-phenylbutyl)phosphinyl]acetyl]-L-proline incorporating 4-substituted proline derivatives have been synthesized and evaluated as inhibitors of angiotensin-converting enzyme (ACE) in vitro and in vivo. The 4-substituted prolines, incorporating alkyl, aryl, alkoxy, aryloxy, alkylthio, and arylthio substituents were prepared from derivatives of 4-hydroxy- and 4-ketoproline. In general, analogues of all three classes of inhibitors with hydrophobic substituents on proline were more potent in vitro than the corresponding unsubstituted proline compounds. 4-Substituted analogues of captopril showed greater potency and duration of action than the parent compound as inhibitors of the angiotensin I induced pressor response in normotensive rats. The S-benzoyl derivative of cis-4-(phenylthio)captopril, zofenopril, was found to be one of the most potent compounds of this class and is now being evaluated clinically as an antihypertensive agent. In the phosphinic acid series, the 4-ethylenethioketal and trans-4-cyclohexyl derivatives were found to be the most potent compounds in vitro and in vivo. A prodrug of the latter compound, fosinopril, is also being evaluated in clinical trials.

As part of a program to discover potent antihypertensive analogues of diltiazem (3a), we prepared 1-benzazepin-2-ones (4). Benzazepinones competitively displace radiolabeled diltiazem, and show the same absolute stereochemical preferences at the calcium channel receptor protein. Derivatives of 4 containing a trifluoromethyl substituent in the fused aromatic ring show potent and long-acting antihypertensive activity. Studies of the metabolism of 4 lead to the metabolically stable antihypertensive calcium channel blockers 5a and 5c. Benzazepinone 5a is a longer acting and more potent antihypertensive agent than the second generation diltiazem analogue TA-3090 (3e).

The synthesis and CNS activity of a series of 34 substituted bicyclic pyrazolines are described. Ten of these compounds were also screened for antiinflammatory activity. One of the compounds (15) exhibited significant antiinflammatory activity in the carrageenan-induced edema test.

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