Acyl substitution at the ortho position of anilides enhances oral bioavailability of thiophene sulfonamides:: TBC3214, an ETA selective endothelin antagonist

Sitaxsentan (3, TBC11251) (Wu et al. J. Med. Chem. 1997, 40, 1690) is an orally active ETA selective endothelin antagonist that attenuates pulmonary vascular hypertension and cardiac hypertrophy in rats (Tilton et al. Pulm. Pharmacol. Ther. 2000, 13, 87). It has demonstrated efficacy in a phase II clinical trial for congestive heart failure (Givertz et al. Circulation 2000, 101, 2922). During the discovery of 3, we observed several structure-oral bioavailability relationships. To investigate whether there is any generality in these trends, we synthesized some similar pairs of compounds in the latest series (Wu et al. J. Med. Chem. 1999, 42, 4485) and evaluated their oral properties. In both series, an acyl group at the 2-position of the anilide of these thiophene sulfonamides improved oral bioavailability. As a result of this exercise, TBC3214 (17) was identified as a sitaxsentan follow-on candidate. It is very potent (IC50 for ETA = 40 pM) and highly selective for ETA vs ETB receptors (400 000-fold), with a half-life of >4 h and oral bioavailability of 25% in rats, 42% in cats, and 70% in dogs.