Discovery and Synthesis of (S)-3-[2-(3,4-Dimethoxyphenyl)ethoxy]-2- (4,6-dimethylpyrimidin-2-yloxy)-3,3-diphenylpropionic Acid (LU 302872), a Novel Orally Active Mixed ETA/ETB Receptor Antagonist

Structural variation of the endothelin A-selective antagonist (S)-3-methoxy-2-(4,6-dimethoxypyrimidin-2-yloxy)-3,3-diphenylpropionic acid (LU 135252) led to analogues which retain ETA affinity but exhibit substantial ETB affinity as well. The most active derivative obtained is (S)-3-[2-(3,4-dimethoxyphenyl)ethoxy]-2-(4,6-dimethylpyrimidin-2-yloxy)-3,3-diphenylpropionic acid (LU 302872), which can be prepared in enantiomerically pure form in eight steps via an acid-catalyzed transetherification. It has a Ki = 2.15 nM for binding to the ETA receptor and a Ki = 4.75 nM for binding to the ETB receptor, is orally available, and antagonizes the big ET-induced blood pressure increase in rats and the big ET-induced bronchospasm in guinea pigs each time at a dose of 10 mg/kg.