An efficient preparation of the pseudopeptide endothelin-B receptor selective antagonist BQ-788

The endothelins are a family of bicyclic 21 amino acid peptides that are potent and prolonged vasoconstrictors. BQ-788 is a modified tripeptide that is the only known highly potent and selective antagonist for the endothelin-B (ET(B)) receptor subtype discovered to date. Previous preparations of BQ-788 (N-(cis-2,6-dimethylpiperidinocarbonyl)-gamma-methylleucyl-D-1-(methoxycarbonyl)tryptophanyl-D-norleucine sodium salt) have suffered from several synthetic difficulties, including formation of the sterically hindered N-(cis-2,6-dimethylpiperidinocarbonyl)-gamma-methylleucine, racemization of tryptophan during carbamination, and the facile reduction of the indole ring of tryptophan during catalytic hydrogenation. In order to prepare sufficient quantities of BQ-788 for in vitro and in vivo evaluations of the physiological significance of the ET(B) receptor, we have developed an efficient solution phase multiple-gram synthetic strategy.