Design, synthesis, and physicochemical properties of a novel, conformationally restricted 2,3-dihydro-1,3,4-thiadiazole-containing angiotensin converting enzyme inhibitor which is preferentially eliminated by the biliary route in rats

J Med Chem. 1991 Jan;34(1):439-47. doi: 10.1021/jm00105a066.


Two novel series of dihydrothiadiazole ring containing inhibitors of angiotensin converting enzyme have been designed and synthesized. The compounds are highly potent enzyme inhibitors and, as a consequence of conformational restriction, chemically stable with respect to undesirable cyclization reactions. The most interesting compound from this series, 5a (FPL 63547), is the monoethyl ester prodrug of the highly potent "aminocarboxy" inhibitor 5b (FPL 63674). It produces an antihypertensive effect of long duration in animal models after oral dosing. Unlike other ACE inhibitors, 5b is eliminated almost entirely by biliary clearance in the rat. The favorable pharmacological properties of 5a and 5b are rationalized in terms of their unique physicochemical profiles. The clear preference for biliary clearance seen with 5b is consistent with its lipophilicity and its high degree of net ionization at physiological pH, which results from the very low pKa of the C-terminus carboxylic acid function. FPL 63547 is presently undergoing clinical investigation in man.

Publication types

  • Comparative Study

MeSH terms

  • Angiotensin-Converting Enzyme Inhibitors / chemical synthesis*
  • Animals
  • Antihypertensive Agents / chemical synthesis*
  • Bile / metabolism*
  • Drug Design
  • Indicators and Reagents
  • Male
  • Metabolic Clearance Rate
  • Models, Molecular
  • Molecular Conformation
  • Molecular Structure
  • Rats
  • Structure-Activity Relationship
  • Thiadiazoles / chemical synthesis*
  • Thiadiazoles / chemistry
  • Thiadiazoles / metabolism
  • Thiadiazoles / pharmacology
  • X-Ray Diffraction


  • Angiotensin-Converting Enzyme Inhibitors
  • Antihypertensive Agents
  • Indicators and Reagents
  • Thiadiazoles