Discovery of potent, orally available vanilloid receptor-1 antagonists.: Structure-activity relationship of N-aryl cinnamides

The vanilloid receptor-1 (TRPV1 or VR1) is a member of the transient receptor potential (TRP) family of ion channels and plays a role in regulating the function of sensory nerves. A growing body of evidence demonstrates the therapeutic potential of TRPV1 modulators: particularly in the management of pain. As a result of our screening efforts, we identified (E)-3-(4-tert-butylphenyl)-N-(2,3-dihydrobenzo[b][1,4]dioxin-6-yl)acrylamide (1): an antagonist that blocks the capsaicin-induced and pH-induced uptake of Ca-45(2+) in TRPV1-expressing Chinese hamster ovary cells with IC50 values of 17 +/- 5 and 150 +/- 80 nM, respectively. In this report.. we describe the synthesis and structure-activity relationship of a series of N-aryl cinnamides, the most potent of which (49a and 49b) exhibit good oral bioavailability in rats (F-oral = 39% and 17%. respectively).