Discovery of 1,2,3,4-tetrahydropyrimido[1,2-a]benzimidazoles as novel class of corticotropin releasing factor 1 receptor antagonists

Publication date: 15 May 2018
Source:Bioorganic & Medicinal Chemistry, Volume 26, Issue 9
Author(s): Takuto Kojima, Michiyo Mochizuki, Takafumi Takai, Yasutaka Hoashi, Sachie Morimoto, Masaki Seto, Minoru Nakamura, Katsumi Kobayashi, Yuu Sako, Maiko Tanaka, Naoyuki Kanzaki, Yohei Kosugi, Takahiko Yano, Kazuyoshi Aso
A new class of corticotropin releasing factor 1 (CRF1) receptor antagonists characterized by a tricyclic core ring was designed and synthesized. Novel tricyclic derivatives 2a–e were designed as CRF1 receptor antagonists based on conformation analysis of our original 2-anilinobenzimidazole CRF1 receptor antagonist. The synthesized tricyclic derivatives 2a–e showed CRF1 receptor binding activity with IC50 values of less than 400 nM, and the 1,2,3,4-tetrahydropyrimido-[1,2-a]benzimidazole derivative 2e was selected as a lead compound with potent in vitro CRF1 receptor binding activity (IC50 = 7.1 nM). To optimize the pharmacokinetic profiles of lead compound 2e, we explored suitable substituents on the 1-position and 6-position, leading to the identification of compound 42c-R, which exhibited potent CRF1 receptor binding activity (IC50 = 58 nM) with good oral bioavailability (F = 68% in rats). Compound 42c-R exhibited dose-dependent inhibition of [¹²⁵I]-CRF binding in the frontal cortex (5 and 10 mg/kg, p.o.) as well as suppression of locomotor activation induced by intracerebroventricular administration of CRF in rats (10 mg/kg, p.o.). These results suggest that compound 42c-R successfully binds CRF1 receptors in the brain and exhibits the potential to be further examined for clinical studies.

Graphical abstract

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