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The synthesis of chiral 1,5-benzothiazepines 2a-c, 14a-c, 15c, and 16a prepared from cysteine is described. In vitro inhibition of angiotensin converting enzyme (ACE) is reported for each compound. Compound 2c was the most potent in vitro having an IC50 of 2.95 nM. The ester of 2c, i.e. 14c, was found to inhibit the AI pressor response by 75% at a dose of 0.05 mg/kg iv and by 39% at 1.0 mg/kg po. Additionally, 14c lowered blood pressure in the spontaneous hypertensive rat (SHR) by 35 mmHg, at a dose of 10 mg/kg po.

Investigation of tricyclic heterocycles related to the 2-arylpyrazolo[4,3-c]quinolin-3(5H)-ones, structures with high affinity for the benzodiazepine (BZ) receptor, led to the synthesis of 2-phenyl-[1,2,4]triazolo[1,5-c]quinazolin-5(6H)-one, a compound with 4 nM binding affinity to the BZ receptor. Analogues were prepared to assess the importance of the 2-substituent and ring substitution in modifying activity. Several novel synthetic routes were designed to prepare the target compounds, including a two-step synthesis beginning with an anthranilonitrile and a hydrazide. Of the 34 compounds screened in this series, three compounds were found to be potent BZ antagonists in rat models. The leading compound, 9-chloro-2-(2-fluorophenyl) [1,2,4]triazolo[1,5- c]quinazolin-5(6H)-one (CGS 16228), showed activity comparable to that of CGS 8216 from the pyrazolo[4,3-c]quinoline series.

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