Discovery of a potent and selective prostaglandin D2 receptor antagonist, [(3R)-4-(4-chlorobenzyl)-7-fluoro-5-(methylsulfonyl)-1,2,3,4-tetrahydrocyclopenta[b]indol-3-yl]-acetic acid (MK-0524)

The discovery of the potent and selective prostaglandin D-2 (PGD(2)) receptor (DP) antagonist [(3R)-4-(4-chlorobenzyl)-7-fluoro-5-(methylsulfonyl)-1,2,3,4-tetrahydrocyclopenta[b]indol-3-yl]-acetic acid (13)is presented. Initial lead antagonists 6and 7were found to be potent and selective DP antagonists (DP K-i = 2.0 nM for each); however, they both suffered from poor pharmacokinetic profiles, short half-lives and high clearance rates in rats. Rat bile duct cannulation studies revealed that high concentrations of parent drug were present in the biliary fluid (C-max = 1100 mu M for 6and 3900 mu M for 7). This pharmacokinetic liability was circumvented by replacing the 7-methylsulfone substituent present in 6and 7with a fluorine atom resulting in antagonists with diminished propensity for biliary excretion and with superior pharmacokinetic profiles. Further optimization led to the discovery of the potent and selective DP antagonist 13.