SynthesisandBiologicalEvaluationofHeterocyclicRingFusedBetulinicAcidDerivativesasNovelInhibitorsofOsteoclastDifferentiationandBoneResorption,徐军,李珍惜,Aseriesofbetulinicacid(BA)derivativesweresynthesizedbyintroducingvariousfusedheterocyclicringsatC-2andC-3positions