Synthesis and biological evaluation of 5-substituted and 4,5-disubstituted-2-arylamino oxazole TRPV1 antagonists.

The synthesis and structure-activity relationships of a series of 5-monosubstituted and 4,5-disubstituted 2-arylaminooxazoles as novel antagonists of the transient receptor potential vanilloid 1 (TRPV1) receptor are described. The 7-hydroxy group of the tetrahydronaphthyl moiety on the 2-amino substituent of the oxazole ring was important for obtaining excellent in vitro potency at the human TRPV1 receptor, while a variety of alkyl and phenyl substituents at the 4- and 5-positions of the oxazole ring were well tolerated and yielded potent TRPV1 antagonists. Despite excellent in vitro potency, the 5-monosubstituted compounds suffered from poor pharmacokinetics. It was found that 4,5-disubstitution on the oxazole ring was critical to the improvement of the overall pharmacokinetic profile of these analogues, which led to the discovery of compound (R)-27, a novel TRPV1 antagonist with good oral activity in preclinical animal models of pain.