Pyrido[2,3-b]pyrazines, discovery of TRPV1 antagonists with reduced potential for the formation of reactive metabolites.

The transient receptor potential cation channel, subfamily V, member 1 (TRPV1) is a non-selective cation channel that can be activated by a wide range of noxious stimuli, including capsaicin, acid, and heat. Blockade of TRPV1 activation by selective antagonists is under investigation in an attempt to identify novel agents for pain treatment. During pre-clinical development, the 1,8-naphthyridine 2 demonstrated unacceptably high levels of irreversible covalent binding.

Discovery of novel 6,6-heterocycles as transient receptor potential vanilloid (TRPV1) antagonists.

The transient receptor potential cation channel, subfamily V, member 1 (TRPV1) is a nonselective cation channel that can be activated by a wide range of noxious stimuli, including capsaicin, acid, and heat. Blockade of TRPV1 activation by selective antagonists is under investigation in an attempt to identify novel agents for pain treatment. The design and synthesis of a series of novel TRPV1 antagonists with a variety of different 6,6-heterocyclic cores is described, and an extensive evaluation of the pharmacological and pharmacokinetic properties of a number of these compounds is reported.

Aminoquinazolines as TRPV1 antagonists: modulation of drug-like properties through the exploration of 2-position substitution.

A focused SAR exploration of the lead 4-aminoquinazoline TRPV1 antagonist 2 led to the discovery of compound 18. In rats, compound 18 is readily absorbed following oral dosing and demonstrates excellent in vivo potency and efficacy in an acute inflammatory pain model.

From arylureas to biarylamides to aminoquinazolines: discovery of a novel, potent TRPV1 antagonist.

Bioisosteric replacement of piperazine with an aryl ring in lead VR1 antagonist 1 led to the biarylamide series. The development of B-ring SAR led to the conformationally constrained analog 70. The resulting aminoquinazoline 70 represents a novel VR1 antagonist with improved in vitro potency and oral bioavailability vs the analogous compounds from the lead series.

Activation of protein kinase C sensitizes human VR1 to capsaicin and to moderate decreases in pH at physiological temperatures in Xenopus oocytes.

The two-electrode voltage-clamp technique was used to evaluate the effect of protein kinase C (PKC) activation on ion current flow in Xenopus laevis oocytes injected with cRNA coding for the human vanilloid receptor (VR1). In the presence of 30 nM phorbol-12,13-dibutyrate (PDBu), current evoked by an effective concentration (EC(30)) of capsaicin (CAP) was potentiated by 638+/-117% (n=8). PDBu exhibited an EC(50) of about 17+/-3 nM for this effect (n=8).