Design, synthesis and evaluation of 1,3,6-trisubstituted-4-oxo-1,4-dihydroquinoline-2-carboxylic acid derivatives as ETA receptor selective antagonists using FRET assay

The endothelin axis and in particular the two receptor subtypes, ETA and ETB, are under investigation for the treatment of various diseases such as pulmonary arterial hypertension, fibrosis, renal failure and cancer. Previous work in our lab has shown that 1,3,6-trisubstituted-4-oxo-1,4-dihydroquinoline-2-carboxylic acid derivatives exhibit noteworthy endothelin receptor antagonist activity. A series of analogues with modifications centered around position 6 of the heterocyclic quinolone core and replacement of the aryl carboxylic acid group with an isosteric tetrazole ring was designed and synthesized to further optimize the structure activity relationship. The endothelin receptor antagonist activity was determined by in vitro Förster resonance energy transfer (FRET) using GeneBLAzer® assay technology. The most potent member of this series exhibited ETA receptor antagonist activity in the subnanomolar range with an IC50 value of 0.8nM, and was 1000-fold selective for the ETA receptor compared to the ETB receptor. Its activity and selectivity profile resembles that of the most recently approved drug, macitentan.