Lead discovery, chemistry optimization, and biological evaluation studies of novel biamide derivatives as CB₂ receptor inverse agonists and osteoclast inhibitors

N,N′-((4-(Dimethylamino)phenyl)methylene)bis(2-phenylacetamide) was discovered by using 3D pharmacophore database searches and was biologically confirmed as a new class of CB₂ inverse agonists. Subsequently, 52 derivatives were designed and synthesized through lead chemistry optimization by modifying the rings A-C and the core structure in further SAR studies. Five compounds were developed and also confirmed as CB₂ inverse agonists with the highest CB₂ binding affinity (CB₂K_i of 22-85 nM, EC₅₀ of 4-28 nM) and best selectivity (CB ₁/CB₂ of 235- to 909-fold). Furthermore, osteoclastogenesis bioassay indicated that PAM compounds showed great inhibition of osteoclast formation. Especially, compound 26 showed 72% inhibition activity even at the low concentration of 0.1 μM. The cytotoxicity assay suggested that the inhibition of PAM compounds on osteoclastogenesis did not result from its cytotoxicity. Therefore, these PAM derivatives could be used as potential leads for the development of a new type of antiosteoporosis agent.