Synthesis and Biological Evaluation of Heterocyclic Ring-Fused Betulinic Acid Derivatives as Novel Inhibitors of Osteoclast Differentiation and Bone Resorption
A series of betulinic acid (BA) derivatives were designed and synthesized by introducing various fused heterocyclic rings at C-2 and C-3 positions. Their inhibitory effects of RANKL-inducedosteoclastogenesis were evaluated by using a cell-based tartrate-resistant acid phosphatase (TRAP) activity assay. To our delight, most of these compounds exhibited a dramatic increase in inhibitory potency, compared
and to investigate their cytotoxic activities. Some of those heterocycles were previously known in the oleanane (allobetulin) group; however, to our knowledge the syntheses and biological activities of lupane heterocycles have not been reported before. Starting from betulin (1) and betulinic acid (2), we prepared 3-oxo compounds and 2-bromo-3-oxo compounds 3–10, 2-hydroxymethylene-3-oxo compounds 11–13