Synthesis and Biological Evaluation of Novel Furozan-Based Nitric Oxide-Releasing Derivatives of 23-Hydroxy Betulinic Acid and 3-oxo-23-hydroxybetulinic acid as Potential Anti-Tumor Agents

1State Key Laboratory of Natural Medicines, China Pharmaceutical University, 24 Tong Jia Xiang, Nanjing 210009, PR China 2Department of Medicinal Chemistry, China Pharmaceutical University, 24 Tong Jia Xiang, Nanjing 210009, PR China 3Department of Organic Chemistry, China Pharmaceutical University, 24 Tong Jia Xiang, Nanjing, 210009, PR China 4Department of Microbiology, Immunology and Molecular Genetics, University of Kentucky College of Medicine, 800 Rose Street, Lexington, KY 40536, USA