Design, synthesis, and biological evaluation of AT1 angiotensin II receptor antagonists based on the pyrazolo[3,4-b]pyridine and related heteroaromatic bicyclic systems

Novel AT(1) receptor antagonists bearing the pyrazolo[3,4-b]pyridine bicyclic heteroaromatic system (or structurally related moieties) were designed and synthesized as the final step of a large program devoted to the development of new anti hypertensive agents and to the understanding of the molecular basis of their pharmacodynamic and pharmacokinetic properties. The preliminary pharmacological characterization revealed nanomolar AT(1) receptor affinity for several compounds of the series and a potent antagonistic activity in isolated rabbit aortic strip functional assay for 7c and 8a. These results stimulated the study of the biopharmaceutical properties of some selected compounds, which were found to be characterized by a permeability from medium to high. Remarkably, the least permeable 7c showed both permeability and oral bioavailability (80%) higher than losartan, but its terminal half-life was shorter. These results suggest that the permeability is not a limiting factor in the pharmacokinetics of these AT(1) receptor antagonists.