N- (4- chloro- 3- methyl- oxazol- 5- yl)- 2- [2- (6- methylbenzo[1,3]dioxol- 5- yl)acetyl]- thiophene- 3- sulfonamide

Sitaxsentan is a selective endothelin-A (ETA) receptor antagonist launched for the treatment of patients with pulmonary arterial hypertension (PAH), to improve exercise capacity. It is the second ET receptor antagonist to be marketed for this indication behind bosentan. PAH encompasses a heterogeneous group of disorders characterized by inappropriate overactivation of the endothelin system and is characterized by a progressive increase in pulmonary vascular resistance resulting from vascular remodeling, vasoconstriction, and cellular proliferation. Endothelin-1 (ET-1), a potent vasoconstrictor and smooth muscle mitogen, is a key contributor to the acceleration of the disease, and its effects are mediated through activation of ETA and ETB receptors. ETA receptors are found primarily on smooth muscle cells and, when activated, induce vasoconstriction and cellular proliferation. ETB receptors are expressed in both pulmonary vascular endothelial cells and smooth muscle cells, and their activation is associated with the renal and pulmonary clearance of ET.