Synthesis Of Novel Lipophilic Ester Prodrugs Of 9-(2-phosphonylmethoxyethyl) Adenine(PMEA)

The Hepatitis B virus (HBV) is a DNA virus that can cause both acute and chronic liver disease in humans. Of the approximately two billion people who have been infected with HBV worldwide, an estimated 350–400 million are chronically infected, with 0.5–1.2 million deaths annually from the resulting cirrhosis, liver failure, and hepatocellular carcinoma[1].Though safe and effective HBV vaccine can be obtained, the trend of HBV spreading in the world can not be controled. Chronic infection with hepatitis B virus (HBV) creates significant econo- mic and social burdens globally.Only a few drugs are currently approved by the FDA for the treatment of chronic HBV infection. They include interferon, lamivudine, and adefovir dipivoxil. Interferon is be used to treat HBV in most of countries, but low efficiency (30-40%), high treatment expenditure and side effect limit its application. Lamivudine has a low sustained response rate, and drug resista- nce limits its efficacy.[2]Adefovir dipivoxil (Fig. 1), an ester prodrug of PMEA, has potent in vitro and in vivo activity against HBV. In particular, it has shown impressive ability to suppress replication of HBV resistance to lamivudine, emtricitabine, and famcicloir.[2] Unfortunately, PMEA displays unfavorable pharmacoki- netics, in that the drug accumulates primarily in the kidneys; only a limited amount is taken up by liver. The high kidney uptake of PMEA is likely to result in nephrotoxicity, as has been shown for related nucleoside phosphonate analogs. And doselimiting nephrotoxicity and its potential of releasing toxic formaldehyde and 2-Adenylacetic Acid are its primary limitations. [3,4]The oral bioavailability of PMEA is low in animals [5, 6] and humans[7], probably as a consequence of limited intestinal perm- eability of the phosphonate, which is ionized at physiological pH [8].In order to optimize cellular uptake and antiviral activity, and to reduce cytotoxicity of PMEA,several prodrugs such as bis(SATE)-PMEA[9], cyclo Sal-PMEA[10], and Hep-direct pro- drug remofovir[7](Fig. 1) have been reported. These new pro- drugs have improved the pharmacodynamics and pharmacoki- netics of PMEA,but their obvious weakness of instability and cytotoxicity[10,11] makes the development of newer and more effective prodrug strategies imperative.Thus we utilized several new prodrug strategies to design and synthesize a novel class of ester prodrugs of PMEA with potent activity and reduced toxicity.Objective: To enhance the therapeutic effects of PMEA in the liver and concomitantly reduce nephrotoxicity, we develop- ed several prodrug strategys for enhancing the therapeutic effects of PMEA to parenchymal liver cells.An active transporting mechanism has been applied in the designing of nucleoside L-amino acid ester prodrugs. These prodrugs significantly enhance oral bioavailability and antiviral activity of the parent drugs. When nucleoside L-amino acid ester prodrugs is metabolized in the body, it produces L-amino acid that can not bring cell toxicity. Because L-amino acid is endogenic substance, which has existed in human body.Cholesterol also is endogenic substance, and it has excellent liposolubility. When cholesterol was combined into nucleoside drugs, it could increase liposolubility of cholesterol ester prodrugs.Because benzyl has excellent liposolubility, small group size and high reacted activity, the prodrugs used benzyl as a decorated group is easy to get.Consequently we designed and synthesized a series of novel bis(L-amino acid), bis cholesterol and benzyl ester prodrugs of PMEA. The following was included:1. Bis(methyl L-threoninyl) PMEA;2. Bis(methyl L- serinyl) PMEA;3. Bis(methyl L- hydroxyprolineyl) PMEA;4. Bis[(N-Cbz-L-hydroxyprolinyl)carbonyloxymethyl] PMEA;5. Bis [(cholesterolyl)carbonyl oxymethyl]PMEA;6. Bis (benzyl) PMEA;7. Mono benzyl PME-N6-(benzyl) PMEA; 8. Bis benzyl PME-N6-(benzyl) PMEA.Methods: PMEA, 9-(2-Phosphonylmethoxyethyl)adenine, belongs to a new class of acyclic nucleoside phosphonate anal- ogs with strong and selective activity against a wide range of viruses.Synthesis of these novel compounds was carried out in a straightforward manner. Six PMEA ester prodrugs(1～6) were attained from the esterification of L-amino, cholesterol and benzylalcohol, which through the hydroxyl on the of PMEA. Mean while 6-NH2 of PMEA was decorated by benzyl, and compound 7 and 8 was furnished.Results: The series of novel bis(L-amino acid) ester pro- drugs of 9-[2-(phosphonomethoxy)ethyl] adenine (PMEA) was synthesized.Compound 1. ESI-MS: Calcd for C18H30N7O8P: 503.5. Found: 504.5(M+1)+; 526.6(M+Na)+;Compound 2. ESI-MS: Calcd for C16H26N7O8P: 475.4. Found: 476.6 (M+1)+ ; 498.8(M+Na)+.Compound 3. ESI-MS: Calcd for C20H30N7O8P: 527.5. Found: 528.6(M+1)+ ; 550.6(M+Na)+.Compound 4. ESI-MS: Calcd for C40H46N7O18P: 943.8. Found: 945.0(M+1)+; 978.6(M+Na)+.Compound 5. 1H-NMR(400 MHz, DMSO-d6 ,δ): 8.33(1H, s), 7.97(1H, s), 5.65(4H, d), 5.39(2H, s), 4.51(2H, m), 4.40(2H, t), 3.95(2H, t), 3.88(2H, d), 2.96(1H, s), 2.88(1H, s), 2.39(4H, m), 2.02-0.67(83H, m). ESI-MS: Calcd for C66H104N5O10P: 1158.5. Found: 1158.9, (M+1)+。Compound 6. ESI-MS: Calcd for C22H24N5O4P: 453.4. Found: 453.2,M+; 453.8(M+1)+; 476.2(M+Na)+; 907.3(2M+1)+; 929.4(2M+Na)+.Compound 7. 1H-NMR(400 MHz, DMSO-d6 ,δ): 9.65(2H, br.s), 8.79(1H, s), 8.69(1H, s), 7.34-7.24(10H, m), 5.58(2H, s), 4.68(2H, d), 4.39(2H, t), 3.88(2H, t), 3.46(2H, d).ESI-MS: Calcd for C22H24N5O4P: 453.4.Found:453.2, M+; 454.6 (M+1)+; 475.8(M+Na)+.Compound 8. ESI-MS: Calcd for C29H30N5O4P: 543.2.Found: 543.5, (M+1)+; 566.1(M+Na)+.Conclusion: Eight PMEA ester prodrugs(1～8) were successfully synthesized.