Panaxadiol and Panaxatriol Derivatives as Anti-Hepatitis B Virus Inhibitors

Hao Chen 0 1 Li-Jun Wang 0 1 Yun-Bao Ma 0 1 Xiao-Yan Huang 0 1 Chang-An Geng 0 1 Xue-Mei Zhang 0 1 Ji-Jun Chen 0 1 0 H. Chen University of Chinese Academy of Sciences , Beijing 100049, People's Republic of China 1 H. Chen L.-J. Wang Y.-B. Ma X.-Y. Huang C.-A. Geng X.-M. Zhang J.-J. Chen (&) State Key Laboratory of Phytochemistry and Plant Resources in West China, Kunming Institute of Botany, Chinese Academy of Sciences , Kunming 650201, People's Republic of China 28 Derivatives of panaxadiol (PD) and panaxatriol were synthesized and evaluated for their anti-HBV activity on HepG 2.2.15 cells, of which 17 derivatives inhibited HBV DNA replication. Compounds 4, 9, 10, 14, and 15 showed moderate activity against HBV DNA replication with IC50 values ranged from 7.27 to 28.21 lM compared with PD. In particular, 3-O-20-thenoyl panaxadiol (4) inhibited not only HBV DNA replication (IC50 = 16.5 lM, SI [ 115.7) but also HBsAg (IC50 = 30.8 lM, SI [ 62.0) and HBeAg (IC50 = 18.2 lM, SI [ 105.14) secretions. Their structure-activity relationships were discussed for guiding future research toward the discovery of new anti-HBV agents. 1 Introduction Hepatitis B virus (HBV) infection is a serious health problem all over the world. There are about 350 million chronically infected individuals with the risk of approaching liver cirrhosis and hepatocellular carcinoma [1]. The current therapies for HBV infection involve immunomodulators, interferon-a, polyethylene glycol interferon-a, and nucleoside drugs, and are unsatisfactory due to high recurrence, drug resistance and inevitable side effects including Electronic supplementary material The online version of this article (doi:10.1007/s13659-014-0018-2) contains supplementary material, which is available to authorized users. influenza-like illness, myalgia, headache, reduction of neutrophilic granulocyte and blood platelet, etc. [25]. Therefore, it is interesting to explore novel anti-HBV agents with novel antiviral targets and mechanisms. Natural products offer many opportunities to find lead compounds for drug discovery [610]. Dammarane triterpenes and their derivatives have antiviral and hepatoprotective potencies, as well as antitumor, hemolytic, antiplatelet, immunomodulatory, antioxidant and neuroprotective activities [11]. For example, chikusetsusaponin III reduced yield of herpes simplex virus type I with ID50 value of 29 lM [12]; panaxadiol (PD) derivatives incorporated with 2,2-dimethylsuccinyl group at C-3 and panaxatriol (PT) derivatives with same groups at C-3 and C-6, could inhibit HIV-1 protein proteases (IC50 = 2.7 4.3 to 5.4 3.8 lM) and HCV protein proteases (IC50 = 1.8 2.6 to 30.4 3.0 lM) [13]; furthermore, ginsenosides Rb3, Rc, Rd, XVII and notoginsenoside R1 from the flower buds of Panax notoginseng showed hepatoprotective activity against liver injury induced by D-galactosamine and lipopolysaccharide in mice [14]. Although derivatives of PD and PT (Fig. 1) exhibited antiviral and hepatoprotective effects, no report was concerned with their anti-HBV activity. As our Fig. 1 Panaxadiol (PD) and panaxatriol (PT) ongoing study for searching anti-HBV inhibitors from natural resources, PD and PT were revealed to be active against HBV DNA replication with IC50 values of 148.15 and 668.60 lM but low SI values of 6.2 and 3.6 in our random assay. In order to increase the activity and safety, PD and PT were hybridized with heteroaromatic rings based on our previous experience from the modification on caudatin and hemslecin A [15, 16]. Consequently, 28 panaxadiol and panaxatriol analogues were synthesized by modifying on rings A, B and C. Herein, we described the synthesis, in vitro anti-HBV activity and structureactivity relationships (SARs) of these derivatives (Scheme 1). 2 Results and Discussion 2.1 Chemistry The Steglich esterification condition was applied for synthesis of 3-O-substituted derivatives of PD and 3,6-Odisubstituted derivatives of PT in presence of 4-dimethylaminopyridine (DMAP), and N0,N0-dicyclohexylcarbodiimide (DCC). Derivatives (213, 2021) of PD and PT were also prepared with anhydrides under a catalytic amount of DMAP. There were no 12-O-substituted derivatives produced, of which the substituent position could be determined by the chemical shifts of derivatives at H-3 and H-12 in 1H NMR spectrum. For example, chemical shifts of H-3 and H-12 of PD appearred at dH 3.21 and 3.50 but at dH 4.42 and 3.52 of compound 1. Furthermore, the hydroxyl group at C-12 of 3-O-substituted derivatives (1, 4 and 14) were transformed as ketones by Jones reagent in order to disclose effects of hydroxyl groups. 2.2 Anti-HBV Activity PD, PT and their derivatives were evaluated for anti-HBV activities on HBsAg and HBeAg secretions, as well as HBV DNA replication on HepG 2.2.15 cells [9], and the results were summarized in Table 1. Accordingly, 4 active derivatives (4, 9, 10 and 11) inhibited HBsAg secretion with IC50 values ranged from 30.81 to 53.78 lM, a (...truncated)