Discovery of a Potent and Selective Prostaglandin D sub(2) Receptor Antagonist, [(3R)-4-(4-Chloro- benzyl)-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 sub(2) (PGD sub(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 6 and 7 were found to be potent and selective DP antagonists (DP K sub(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 sub(max) = 1100 mu M for 6 and 3900 mu M for 7). This pharmacokinetic liability was circumvented by replacing the 7-methylsulfone substituent present in 6 and 7 with 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.