Identification of 5-(1-methyl-5-(trifluoromethyl)-1H-pyrazol-3-yl)thiophene-2-Carboxamides as Novel and Selective Monoamine Oxidase B Inhibitors Used to Improve Memory and Cognition.

Initial work in Drosophila and mice demonstrated that the transcription factor cAMP (cyclic adenosine monophosphate) response element binding protein (CREB) is a master control gene for memory formation. The relationship between CREB and memory has also been found to be true in other species, including aplysia and rats. It is thus well established that CREB activation plays a central role in memory enhancement and that CREB is activated during memory formation. Based on these findings, a phenotypic high throughput screening campaign, which utilized a CRE-luciferase (CRE-Luci) SK-N-MC cell line, was performed to identify compounds that enhance transcriptional activation of the CRE promoter with a suboptimal dose of forskolin. A number of small-molecule hits of unknown mechanisms of action were identified in the screening campaign, including HT-0411. Follow-on studies suggested that the CREB activation by HT-0411 is attributed to its specific and selective inhibition of monoamine oxidase B (MAO-B). Further, HT-0411 was shown to improve 24-hour memory in rodents in a contextual fear conditioning model. This report describes the lead optimization of a series of 5-(1-methyl-5-(trifluoromethyl)-1H-pyrazol-3-yl) thiophene-2-carboxamides that were identified as novel, potent and selective inhibitors of MAO-B. Extensive SAR studies and in vivo behavioral evaluations of this and other related analog series identified a number of potential clinical development candidates; ultimately, compound 8f was identified as a candidate molecule with high selectivity towards MAO-B (29-56 nM) over MAO-A (no inhibition at 10 μM), an excellent profile against a panel of other enzymes and receptors, good pharmacokinetic properties in rodents and dogs, and efficacy in multiple rodent memory models.