Synthesis and anti-HIV activity of some novel arylphosphate and H-phosphonate derivatives of 3'-azido-2',3'-dideoxythymidine and 2',3'-didehydro-2',3'-dideoxythymidine.

Phosphate and H-phosphonate derivatives of anti-HIV nucleoside analogues (AZT and d4T) were prepared as potential prodrugs of the bio-active free nucleotide and they were evaluated for their inhibitory effects on the replication of HIV-1 in several cell culture systems. One compound exhibited an important anti-HIV-1 activity and proved to be significantly more efficient than the parent nucleoside.     

Synthesis and antiretrovirus properties of 5'-isocyano-5'-deoxythymidine, 5'-isocyano-2',5'-dideoxyuridine, 3'-azido-5'-isocyano-3',5'-dideoxythymidine, and 3'-azido-5'-isocyano-2',3',5'-trideoxyuridine

The 5'-azidonucleosides 3 and 4 were obtained by treating thymidine and 2'-deoxyuridine with TPP/DEAD/HN3. The 3'-O-silylated 5'-azido-5'-deoxythymidine 5 and the corresponding 2'-deoxyuridine derivative 6 were transformed to the formamides (7 and 8, respectively) and dehydrated to the protected 5'-isocyano derivatives 9 and 10; deblocking gave 5'-isocyano-5'-deoxythymidine (11) and 5'-isocyano-2',5'-dideoxyuridine (12). 2,3'-Anhydro-5'-formamido derivatives of thymidine and 2'-deoxyuridine (19 and 20, respectively) were prepared by three different ways. In the most direct synthesis 3 and 4 were transformed to the 2,3'-anhydro-5'- azidonucleosides 17 and 18 by using TPP/DEAD; following the reaction with TPP/HCO2COCH3 gave 19 and 20. Nucleophilic opening reaction with LiN3 yielded the 3'-azido-5'-formylamino derivatives 21 and 22. Dehydration to 3'-azido-5'-isocyano-3',5'-dideoxythymidine (23) and 3'-azido-5'-isocyano-2',3',5'-trideoxyuridine (24) was achieved with tosyl chloride/pyridine. In contrast with 3'-azido-3'-deoxythymidine, compounds 11, 12, 23, and 24 were devoid of any marked inhibitory effect against DNA and RNA viruses including human immunodeficiency virus type I (HIV).     

Synthesis and biological activities of 5-trifluoromethyl-5'-azido-2',5'-dideoxyuridine and 5-trifluoromethyl-5'-amino-2',5'-dideoxyuridine.

5-Trifluoromethyl-2'-deoxyuridine (1) was tosylated with p-toluenesulfonyl chloride in dry pyridine at 3 degrees to give 5-trifluoromethyl-5'-O-(p-tolylsulfonyl)-2'-deoxyuridine (2), which was converted to 5-trifluoromethyl-5'-azido-2',5'-dideoxyuridine (3) by reacting with lithium azide in N,N-dimethylformamide at 85-90 degrees for 2 h. Compound 3 was then hydrogenated in ethanol-water (1:1, v/v) at room temperature and 35 psi of hydrogen pressure, using 10% palladium on charcoal as cstalyst, to yield 5-trifluoromethyl-5'-amino-2',5'-dideoxyuridine (4). Compound 4 is about fourfold less potent than compound 1 as an antiviral agent but is about 40-fold less toxic to the host Vero cells. Thus the therapeutic index of compound 1 has been improved by a factor of 10 by replacement of the 5'-hydroxyl with an amino group. Compound 1, however, is more than 100-fold more inhibitory to Sarcoma 180 cells in culture relative to compound 4. Compound 3 is markedly less potent than compound 1 or 4 as either an antiviral or an antineoplastic compound.     

Brain targeting of anti-HIV nucleosides: synthesis and in vitro and in vivo studies of dihydropyridine derivatives of 3'-azido-2',3'-dideoxyuridine and 3'-azido-3'-deoxythymidine

A significant number of patients with AIDS and AIDS-related complex develop neurological complications. Therefore, it is critical that anti-HIV agents penetrate the blood-brain barrier and suppress viral replication in the brain. In an effort to increase the brain delivery of anti-HIV nucleosides, in vitro and in vivo pharmacokinetics of dihydropyridine derivatives of 3'-azido-2',3'-dideoxyuridine (AzddU, AZDU, or CS-87) and 3'-azido-3'-deoxythymidine (AZT, Zidovudine) have been studied. In vitro studies of the prodrugs (AzddU-DHP and AZT-DHP) in human serum, mouse serum, and mouse brain homogenate indicated that the rates of serum conversion from prodrugs to parent drugs are species dependent: mouse brain homogenate greater than mouse serum greater than human serum. Half-lives in human serum, mouse serum, and mouse brain homogenate are 4.33, 0.56, 0.17 h, respectively, for AzddU and 7.70, 1.40, and 0.18 h, respectively, for AZT. In vivo studies of AzddU-DHP and AZT-DHP showed that the prodrugs have areas under the serum concentration-time curves (AUC) similar to those of the parent drugs. The AUC in serum for AzddU following prodrug administration is 25.79 micrograms h/mL, which is similar to the value of 25.83 micrograms h/mL when AzddU was administered. Analogously, the serum AUCs for AZT when AZT-DHP and AZT were administered are 25.38 and 26.64 micrograms h/mL, respectively. However, the brain AUCs for both AzddU and AZT derived from prodrugs, being 11.43 and 11.28 micrograms h/mL, respectively, are greater than the brain AUCs for AzddU (2.09 micrograms h/mL) and AZT (1.21 micrograms h/mL) when the parent drugs were administered. Thus, the relative brain exposure (re) for AzddU (5.47) and AZT (9.32) indicate a significant increase in exposure to the anti-HIV nucleosides following prodrug administrations. The results of extended half-lives of the synthesized prodrugs in human serum along with the higher re values in vivo warrant studies in larger animals to determine the potential usefulness of the prodrugs in humans.     

Single dose and multiple dose pharmacokinetics of 2'-fluoro-2',3'-dideoxyadenosine and 2'-fluoro-2',3'-dideoxyinosine, anti-HIV agents, in rats.

A single and multiple dose pharmacokinetic (PK) study was conducted in rats following oral administration of 2'-fluoro-2',3'-dideoxyadenosine (FddA) and 2'-fluoro-2',3'-dideoxyinosine (FddI) at three dose levels. Six rats/gender were assigned to one of the three FddA or FddI dose levels: 40, 250, and 1000 mg/kg/day. Three rats/gender were assigned to the PK study on day 1, while the remaining 3 rats/gender were assigned to the PK study on day 14. The rats received the appropriate doses of either FddA or FddI orally by gavage once a day for 14 days. Serial blood samples up to 24 h and cumulative urine samples (0-24 h) were collected on both days 1 and 14. Plasma and urine samples were analyzed for the concentrations of intact FddA and/or FddI using a validated assay. The data were subjected to non-compartmental PK analyses. Over the dose range of 40-1000 mg/kg. both FddA and FddI exhibited dose dependent pharmacokinetics in rats. Following FddA administration, there was a rapid and extensive in vivo conversion of FddA to FddI; FddI was the major circulating moiety as reflected by Cmax and AUC values (generally 2-3-fold greater than those of FddA at each dose level) as well as the amount excreted (%UR) in the urine. In contrast, following FddI administration, Cmax, AUC, and %UR values were 2-5-fold lower as compared to the FddI generated from FddA administration at each dose level, which also suggested that FddI was not absorbed as extensively as FddA. Based on the findings of this study, FddA is an excellent prodrug of FddI.     

5-Halogeno-3'-fluoro-2',3'-dideoxyuridines as inhibitors of human immunodeficiency virus (HIV): potent and selective anti-HIV activity of 3'-fluoro-2',3'-dideoxy-5-chlorouridine

The novel 5-chloro-, 5-bromo-, and 5-iodo-derivatives of 3'-fluoro-2',3'-dideoxyuridine (FddUrd), designated FddCIUrd, FddBrUrd, and FddIUrd, respectively, have been synthesized and evaluated for their antiretrovirus activity against human immunodeficiency virus (HIV) and murine Moloney sarcoma virus. All three 5-halogeno-FddUrd analogues inhibited HIV-1 replication in MT4 cells with an effective dose (ED50) of about 0.2-0.4 microM. However, FddCIUrd was markedly more selective in its anti-HIV-1 activity than FddBrUrd or FddIUrd. The selectivity index of FddCIUrd was similar to that of 3'-azido-2',3'-dideoxythymidine (AZT) when evaluated in parallel (1408 and 1603, respectively). The FddUrd derivatives also had a marked inhibitory effect on HIV-2 replication in MT4 cells and HIV-1 induced antigen expression in HUT-78 cells. However, neither FddUrd nor its 5-halogeno derivatives were inhibitory to Moloney sarcoma virus-induced transformation of murine C3H cells. The anti-HIV-1 activity of FddUrd, FddCIUrd, FddBrUrd, and FddIUrd was reversed by the addition of thymidine and 2'-deoxycytidine. The 5-halogeno-FddUrd analogues had a markedly higher affinity for MT4 thymidine kinase than FddUrd (Ki/Km, 4.0-4.7, as compared with 302 for FddUrd).     

Chemistry and anti-HIV properties of 2'-fluoro-2',3'-dideoxyarabinofuranosylpyrimidines.

The synthesis, chemistry, biochemistry, and anti-HIV activity of a series of 1-(2,3-dideoxy-2-fluoro-beta-D-threopentofuranosyl)pyrimidines have been studied in an attempt to find useful anti-AIDS drugs. Synthesis is carried out via a 2,3-dideoxyribose intermediate which facilitates the preparation of analogues by removing the sugar 3'-hydroxyl group prior to, rather than after, condensation with a uracil or cytosine aglycon. The 2'-F-dd-uridine analogues 7a-d (with H, F, Cl, and CH3 substitution in the 5-position) as well as the 4-deoxy compound (12b) are nonprotective to ATH8 or CEM cells infected with HIV-1. In the corresponding cytidine series, the 5-chloro analogue (11) is inactive. However, 2'-fluoro-2',3'-dideoxyarabinosylcytosine, 10a, and its 5-fluoro analogue, 10b, are both active. While neither compounds is a potent as ddC or 5-F-ddC (2b), 10b gives complete protection against the cytopathic effects of HIV in both host cell lines. 2'-Fluoro substitution confers increased chemical and enzymatic stability on dideoxynucleosides. Even though dideoxy pyrimidine nucleosides are inherently more stable than the corresponding purine analogues toward acid-catalyzed cleavage of the glycosidic bond, 2'-fluoro substitution (10a) still increases stabilization relative to ddC (2b). No detectable deamination by partially purified cytidine deaminase is observed with the 2'-fluoro compounds 10a, 10b, or 11 under conditions which rapidly deaminate cytidine. A small amount of 2'-F-dd-ara-U (7a) is formed from 10a in monkey plasma after greater than 24 h of exposure. The octanol-water partition coefficients for the dideoxynucleosides in this study indicate their hydrophilic character, with log P values varying from -0.28 to -1.18.     

Reactive 5'-substituted 2',5'-dideoxyuridine derivatives as potential inhibitors of nucleotide biosynthesis

5'-(Bromoacetamido)-2',5'-dideoxyuridine (3) and derivatives (8, 10, 12, and 14) substituted at the 5-position with bromo, iodo, fluoro, and ethyl groups have been synthesized as potential inhibitors of enzymes that metabolize pyrimidine nucleosides. Also prepared were 2',5'-dideoxyuridine derivatives (4-6) substituted at the 5'-position with 2-bromopropionamido, iodoacetamido, and 4-(fluorosulfonyl)benzamido groups. Compounds 3, 5, 8, 12, and 14 were examined for effect on macromolecular synthesis in L1210 leukemia cells in culture and compared with 5'-(bromoacetamido)-5'-deoxythymidine (1, BAT), a compound with demonstrated cytotoxicity and activity in vivo against P388 murine leukemia. Compounds 3, 8, 12, and 14 inhibited DNA synthesis without significant inhibition of RNA synthesis, and protein synthesis was affected less than DNA synthesis. Compounds 3, 5, 6, 8, 10, 12, and 14 were cytotoxic to H.Ep.-2 and L1210 cells in culture, and 3, 5, 8, and 12 showed activity in the P388 mouse leukemia screen.     

Stereoselective synthesis and antiviral activity of D-2',3'-didehydro-2',3'-dideoxy-2'-fluoro-4'-thionucleosides

As 2',3'-didehydro-2',3'-dideoxy-2'-fluoronucleosides have exhibited interesting antiviral effects against HIV-1 as well as HBV, it is of interest to synthesize the isosterically substituted 4'-thionucleosides in which 4'-oxygen is replaced by a sulfur atom. To study structure-activity relationships, various pyrimidine and purine nucleosides were synthesized from the key intermediate (2R,4S)-1-O-acetyl-5-O-(tert-butyldiphenylsilyl)-2,3-dideoxy-2-fluoro-2-phenylselenyl-4-thio-beta-D-ribofuranoside 8, which was prepared from the 2,3-O-isopropylidene-D-glyceraldehyde 1 in 13 steps. The antiviral activity of the synthesized compounds were evaluated against HIV-1 in human peripheral blood mononuclear (PBM) cells, among which cytidine 17, 5-fluorocytidine 18, adenosine 24, and 2-fluoroadenosine 32 showed moderate to potent anti-HIV activities (EC(50) 1.3, 11.6, 8.1, and 1.2 microM, respectively). It is noteworthy that 2-fluoroadenosine analogue 32 showed antiviral potency as well as high cytotoxicity (IC(50) 1.5, 1.1, and 7.6 microM for PBM, CEM, and Vero, respectively) whereas no other compound showed cytotoxicity up to 100 microM. The cytidine 17 and 5-fluorocytidine 18 analogues showed significantly decreased antiviral activity against the clinically important lamivudine-resistant variants (HIV-1(M184V)), whereas the corresponding D-2'-Fd4 nucleosides showed limited cross-resistance. Molecular modeling studies demonstrated that the larger van der Waals radius as well as the close proximity to Met184 of the 4'-sulfur atom of D-2'-F-4'-Sd4C (17) may be the reasons for the decreased antiviral potency of synthesized 4'-thio nucleosides against the lamivudine-resistant variants (HIV-1(M184V)).     

Cellular metabolism of 3'-azido-2',3'-dideoxyuridine with formation of 5'-O-diphosphohexose derivatives by previously unrecognized metabolic pathways for 2'-deoxyuridine analogs

3'-Azido-2',3'-dideoxyuridine (AzdU, CS-87) is a potent inhibitor of human immunodeficiency virus replication in human peripheral blood mononuclear cells (PBMC) with limited toxicity for human bone marrow cells (BMC). In the present study, metabolism of AzdU was investigated in human PBMC and BMC after exposure of cells to 2 or 10 microM [3H]AzdU. 3'-Azido-2',3'-dideoxyuridine-5'-monophosphate (AzdU-MP) was the predominant metabolite, representing approximately 55 to 65% of intracellular radioactivity in both PBMC and BMC at all times. The AzdU-5'-diphosphate and -5'-triphosphate intracellular levels were 10- to 100-fold lower than the AzdU-MP levels and, of note, AzdU-5'-triphosphate was not detected in human BMC. Using anion exchange chromatography, a new peak of radioactivity, distinct from any known anabolites, was detected. This chromatographic peak was found to be resistant to alkaline phosphatase but was hydrolyzed by 5'-phosphodiesterase, yielding AzdU-MP. Incubation of [3H]AzdU and D-[1-14C]glucose in PBMC and BMC produced a double-labeled peak with the same retention time as the anabolite, suggesting formation of a hexose derivative of AzdU. A novel high performance liquid chromatography method was developed that allowed for the separation of nucleosides, nucleotides, and carbohydrate derivatives thereof. Using this highly specific method, the putative AzdU-hexose actually was separated into two chromatographic peaks. These novel metabolites were identified as 3'-azido-2',3'-dideoxyuridine-5'-O-diphosphoglucose and 3'-azido-2',3'-dideoxyuridine-5'-O-diphospho-N-acetylglucosamine. Following 48 hr of incubation with [3H] AzdU, as much as 20 and 30% of these AzdU metabolites accumulated in PBMC and BMC, respectively. When AzdU was removed from the cell cultures, intracellular AzdU diphosphohexose concentrations decayed in a monophasic manner, with an elimination half-life of 14.3 hr. By 48 hr, levels of 0.3 pmol/10(6) cells were still detected, reflecting a gradual anabolism of these metabolites. Elimination of AzdU-MP and AzdU-5'-diphosphate was characterized by a two-phase process, with a short initial half-life of 0.83 and 0.24 hr and a long terminal half-life of 14.10 and 8.24 hr, respectively. Similar diphosphohexoses of deoxyuridine (dUrd) were also detected in human PBMC and BMC after exposure to [3H]dUrd, suggesting that dUrd derivatives are metabolized in a similar manner. In summary, the discovery of novel metabolic pathways for dUrd analogs demonstrates that AzdU has unique metabolic features that may contribute to the low toxicity of this anti-HIV agent in human BMC and also affect its mechanism of action.(ABSTRACT TRUNCATED AT 400 WORDS)     

5'-phosphonate derivatives of 2',3'-dideoxy-3'-thiacytidine as new anti-HIV prodrugs

Two new phosphonate 3TC prodrugs were synthesized and studied in MT-4 cells as inhibitors of HIV replication. Their pharmacokinetic parameters were evaluated following intragastric administration in rabbits and oral administration in dogs. Both compounds were much less toxic than parent 3TC in cell cultures and could generate the active nucleoside in laboratory animals.     

Synthesis and antiviral activity of several 2,5'-anhydro analogues of 3'-azido-3'-deoxythymidine, 3'-azido-2',3'-dideoxyuridine, 3'-azido-2',3'-dideoxy-5-halouridines, and 3'-deoxythymidine against human immunodeficiency virus and Rauscher-murine leukemia virus

Several 2,5'-anhydro analogues of 3'-azido-3'-deoxythymidine (AZT), 3'-azido-2'3'-dideoxyuridine (AZU), 3'-azido-2'3'-dideoxy-5-bromouridine, 3'-azido-2',3'-dideoxy-5-iodouridine, and 3'-deoxythymidine and the 3'-azido derivative of 5-methyl-2'-deoxyisocytidine have been synthesized for evaluation as potential anti-HIV (human immunodeficiency virus) agents. These 2,5'-anhydro derivatives, compounds 13-17, demonstrated significant anti-HIV-1 activity with IC50 values of 0.56, 4.95, 26.5, 27.1, and 48 microM, respectively. Compared to that of the parent compounds AZT and AZU, the respective 2,5'-anhydro analogues, compounds 13 and 14, were somewhat less active. Whereas AZT was cytotoxic with a TCID50 of 29 microM, the toxicity of the 2,5'-anhydro derivative of AZT, compound 13, was reduced considerably to a TCID50 value of greater than 100 microM. The 2,5'-anhydro analogue of 5-methyl-2'-deoxyisocytidine also demonstrated anti-HIV-1 activity with an IC50 value of 12 microM. These compounds were also evaluated against Rauscher-Murine leukemia virus (R-MuLV) in cell culture. Among them, AZT, 3'-azido-2',3'-dideoxy-5-iodouridine, 3'-azido-2',3'-dideoxy-5-bromouridine, and 2,5'-anhydro-3'-azido-3'-deoxythymidine (13) were found to be most active, with IC50 values of 0.023, 0.21, 0.23, and 0.27 microM, respectively.     

Comparative pharmacokinetics of 3'-azido-3'-deoxythymidine (AZT) and 3'-azido-2',3'-dideoxyuridine (AZddU) in mice

The pharmacokinetics of 3'-azido-3'-deoxythymidine (AZT) and 3'-azido-2',3'-dideoxyuridine (AZddU, CS-87), active anti-HIV compounds, were characterized in uninfected mice. Sensitive and specific HPLC techniques were used to quantitate AZT and AZddU concentrations in serum and brain homogenates following iv doses of 50 mg/kg and 250 mg/kg. The pharmacokinetic parameters of t1/2, CIt, and Vss were similar for both compounds at each dose; however, CIt and Vss decreased at the higher dose, indicating a dose dependency. At the 50 mg/kg doses, the CIt of AZddU and AZT was 1.27 liters/hr/kg and 1.38 liters/hr/kg, respectively, which is analogous to the clearance value of AZT observed in humans. Brain/serum concentration ratios for AZddU tended to be greater than those obtained for AZT and were significantly different at the 50 mg/kg dose, being 0.234 +/- 0.282 for AZddU and 0.064 +/- 0.025 for AZT.     

Synthesis and anti-HIV activity of carbocyclic 2',3'-didehydro-2',3'-dideoxy 2,6-disubstituted purine nucleosides

(+-)-cis-[4-[(2,5-Diamino-6-chloropyrimidinyl)amino]-2- cyclopentenyl]carbinol (5a) was synthesized from 2-amino-4,6-dichloropyrimidine and cis-4-(hydroxymethyl)cyclopentenylamine (2a) by subsequent preparation of the 5-[(4-chlorophenyl)azo] derivative of the resulting pyrimidine (3a) and reduction of the azo moiety with zinc and acetic acid. The carbocyclic analogue of 2',3'-didehydro-2',3'-dideoxy 2-amino-6-chloropurine (6a) and the corresponding 8-azapurine (9a) were prepared from 5a. The carbocyclic 2',3'-didehydro-2',3'-dideoxy analogues of guanine (7a) and 2,6-diaminopurine (8a), and 8-azaguanine (10a) and 8-aza-2,6-diaminopurine (11a) were prepared from 6a and 9a, respectively. The corresponding 2',3'-saturated series of 2-amino-6-substituted-purine carbocyclic nucleosides was prepared following the same scheme starting with cis-4-(hydroxymethyl)cyclopentylamine (2b). Carbocyclic 2',3'-didehydro-2',3'-dideoxyguanosine (carbovir, 7a) emerged as a potent and selective anti-HIV agent. Its hydrolytic stability and its ability to inhibit the infectivity and replication of HIV in T-cells at concentrations of approximately 200-400-fold below toxic concentrations make carbovir an excellent candidate for development as a potential antiretroviral agent.     

Potent and selective activity of 3'-azido-2,6-diaminopurine-2',3'-dideoxyriboside, 3'-fluoro-2,6-diaminopurine-2',3'-dideoxyriboside, and 3'-fluoro-2',3'-dideoxyguanosine against human immunodeficiency virus

Several sugar-modified 2,6-diaminopurine and guanine 2',3'-dideoxyribosides were synthesized and evaluated in vitro for their ability to inhibit the cytopathic effect and replication of human immunodeficiency virus (HIV), the causative agent of acquired immunodeficiency syndrome (AIDS). 3'-Azido-2,6-diaminopurine-2',3'-dideoxyriboside (AzddDAPR), 3'-fluoro-2,6-diaminopurine-2',3'-dideoxyriboside (FddDAPR), and 3'-fluoro-2',3'-dideoxyguanosine emerged as potent and selective anti-HIV agents in MT4 cells (50% effective antiviral dose: 0.3-4.5 microM). Their selectivity indexes, based on the ratio of the 50% cytotoxic dose to the 50% antiviral effective dose, were 157, 80, and 96, respectively, as compared to 106 for 2,6-diaminopurine-2',3'-dideoxyriboside (ddDAPR) and 132 for 2',3'-dideoxyadenosine (ddAdo), two other potent anti-HIV agents. The 9-beta-D-arabinoside and 9-beta-D-2'-deoxyxyloside derivatives of 2,6-diaminopurine were devoid of any antiretrovirus activity. Both AzddDAPR and FddDAPR, like the parent compounds ddDAPR and ddAdo, proved susceptible to deamination by beef intestine adenosine deaminase (Km, 11, 148, 29, and 73 microM, respectively). 2'-Deoxycoformycin, a potent inhibitor of adenosine deaminase, decreased the antiretrovirus and cytostatic activity of ddDAPR and FddDAPR to a greater extent than that of AzddDAPR. This suggests that ddDAPR and FddDAPR are primarily active as their guanine analogues, whereas AzddDAPR may be potentially active as a 2,6-diaminopurine derivative as well.     

Synthesis and anti-HIV and anti-HBV activities of 2'-fluoro-2', 3'-unsaturated L-nucleosides

The synthesis of L-nucleoside analogues containing 2'-vinylic fluoride was accomplished by direct condensation method, and their anti-HIV and anti-HBV activities were evaluated in vitro. The key intermediate 8, the sugar moiety of our target compounds, was prepared from 1,2-O-isopropylidene-L-glyceraldehyde via (R)-2-fluorobutenolide intermediate 5 in five steps. Coupling of the acetate 8 with the appropriate heterocycles (silylated uracil, thymine, N4-benzoylcytosine, N4-benzoyl-5-fluorocytosine, 6-chloropurine, and 6-chloro-2-fluoropurine) in the presence of Lewis acid afforded a series of 2'-fluorinated L-nucleoside analogues (15-18, 23-26, 36-45). The newly synthesized compounds were evaluated for their antiviral activities against HIV-1 in human peripheral blood mononuclear (PBM) cells and HBV in 2.2.15 cells. Cytosine 23, 5-fluorocytosine 25, and adenine 36 derivatives exhibited moderate to potent anti-HIV (EC50 0.51, 0.17, and 1.5 microM, respectively) and anti-HBV (EC50 0.18, 0.225, and 1.7 microM, respectively) activities without significant cytotoxicity up to 100 microM in human PBM, Vero, CEM, and HepG2 cells.     

Synthesis and antiviral and cytostatic properties of 3'-deoxy-3'-fluoro- and 2'-azido-3'-fluoro-2',3'-dideoxy-D-ribofuranosides of natural heterocyclic bases

A series of 3'-deoxy-3'-fluoro- and 2'-azido-2',3'-dideoxy-3'-fluoro-D-ribofuranosides of natural heterocyclic bases have been synthesized with the use of universal carbohydrate precursors, viz., 1-O-acetyl-2,5-di-O-benzoyl-3-deoxy-3-fluoro-D-ribofuranose and methyl 2-azido-5-O-benzoyl-2,3-dideoxy-3-fluoro-beta-D-ribofuranoside, respectively. The cytostatic and antiviral activity of the compounds was evaluated against a variety of tumor cell lines and DNA/RNA viruses, respectively. As the most active compound, from both a cytostatic and antiviral activity viewpoint, emerged 3'-deoxy-3'-fluoroadenosine. It inhibited the proliferation of some tumor cell lines (i.e. murine leukemia L1210 and human T-lymphocyte MT-4) at a concentration of 0.2-2 micrograms/mL, and proved inhibitory to the replication of positive-stranded RNA viruses (i.e. polio, Coxsackie, Sindbis, Semliki forest), double-stranded RNA viruses (i.e. reo), and some DNA viruses (i.e. vaccinia) at a concentration of 1-4 micrograms/mL, which is well below the cytotoxicity threshold (40 micrograms/mL).     

Structure-activity relationships of 2'-fluoro-2',3'-unsaturated D-nucleosides as anti-HIV-1 agents

We studied the structure-activity relationships of a series of 2'-fluoro-2',3'-unsaturated D-nucleosides against HIV-1 in human peripheral blood mononuclear (PBM) cells. The target compounds 10-21 and 28-33 were prepared by N-glycosylation of the acetate 4, which was readily prepared from 2,3-O-isopropylidene-D-glyceraldehyde in five steps. Among the newly synthesized nucleosides, 2-amino-6-chloropurine (11), adenine (14), inosine (16), guanine (18), 2,6-diaminopurine (20), and 5-fluorocytosine (30) derivatives were found to exhibit interesting anti-HIV activities with EC(50) values of 4.3, 0.44, 1.0, 2.6, 3.0, and 0.82 microM, respectively. The implications for drug resistance of the titled nucleosides with respect to lamivudine-resistant variants (M184V) were also examined, and no significant cross-resistance with the variants was observed with the D-series.