Discovery of a Novel 5-HT3 Antagonist/5-HT1A Agonist 3-Amino-5,6,7,8-tetrahydro-2-{4-[4-(quinolin-2-yl)piperazin-1-yl]butyl}quinazolin-4(3H)-one (TZB-30878) as an Orally Bioavailable Agent for Irritable Bowel Syndrome

We have prepared a series of quinazolinone derivatives linked with piperazinylquinoline for the treatment of irritable bowel syndrome (IBS). Using pharmacophore analysis, we designed and synthesized compounds which bind to both serotonin receptor subtype 1A (5-HT1A) and subtype 3 (5-HT3). Quinazolinone derivatives with a sulfur atom in the linker showed high affinity in in vitro assays, but low in vivo activity. Focusing on the linker to improve the pharmacokinetic profile, the sulfur atom in the linker was replaced with a methylene group. Further optimization led to the discovery of compound 17m (TZB-30878) (J. Pharmacol. Exp. Ther. 2007, 322, 1315-1323, Patent WO2005082887 (A1), 2005), a novel 5-HT1A agonist/5-HT3 antagonist in the 3-aminoquinazolinone series. In in vivo functional assays, 17m dose dependently inhibited the Bezold-Jarisch reflex and induced 5-HT1A-mediated behaviors, and in an IBS animal model, 17m significantly inhibited stress-induced defecation. Pretreatment by WAY-100635 (5-HT1A antagonist) significantly attenuated but did not abolish the inhibitory effects of 17m. These results suggested that 17m exerted inhibitory effects via both 5-HT1A agonistic and 5-HT3 antagonistic activities and that 17m would be useful as a therapeutic agent for IBS.