Synthesis and Biological Evaluation of Heterocycle-Fused Pyxinol Derivatives as Anti-osteoporosis Agents

A series of novel heterocycle-fused pyxinol compounds
was designed
and synthesized through structure–activity relationship (SAR)-guided
optimization to develop potent inhibitors of RANKL-induced osteoclastogenesis.
Among the synthesized derivatives, compound 36 (SH543)
demonstrated the most potent inhibitory activity with an IC50 value of 3.3 nM, representing an approximately 848-fold increase
in potency compared to the hit compound pyxinol (IC50 =
2.8 μM). Mechanistic investigations revealed that SH543 effectively
downregulated key osteoclastogenesis-related marker genes (Atp6v0d2, Trap, Ctsk, Mmp9) and proteins (TRAP, CTSK, and MMP9). Furthermore,
SH543 directly bound to KEAP1, activated the Nrf2-HO-1 antioxidant
pathway, reduced ROS levels, and inhibited PI3K-AKT and MAPK signaling
pathways. In ovariectomized mice, SH543 administration significantly
attenuated pathological bone loss by preserving trabecular microarchitecture
and improving biomechanical strength. These results establish SH543
as a promising lead compound for the development of novel antiosteoporosis
agents, acting through multiple mechanisms.