A series of 7, 6-and 7, 5-fused bicyclic thiazepinones and oxazepinones were generated and incorporated as conformationally restricted dipeptide surrogates in mercaptoacyl dipeptides. These compounds are potent inhibitors of angiotensin-converting enzyme (ACE) and neutral endopeptidase (NEP) both in vitro and in vivo. Compound 1a, a 7, 6-fused bicyclic thiazepinone, demonstrated excellent blood pressure lowering in a variety of ...