Synthesis and anti-HIV properties of novel 6-phenylselenenyl-5-propyluracils.

Novel 6-phenylselenenyl-5-propyluracils were synthesized from 5-propyluracil with the use of regioselective synthesis to give 1-[(2-hydroxyethoxy)-methyl]-6-phenylselenenyl-5-propyluracil (6), 1-ethoxymethyl-6-phenylselenenyl-5-propyluracil (9) and 1-benzyloxymethyl-6-phenylselenenyl-5-propyluracil (10). Interaction of these compounds with recombinant HIV-1 reverse transcriptase (RT) was evaluated using a non-isotopic colorimetric method. Compounds 9 and 10 exerted potent HIV RT inhibition (IC(50) 0.06 and 0.05 microM respectively) while compound 6 showed moderate inhibition (IC(50) = 3.5 microM). Potent anti-HIV-1 activity in MT-2 cells inoculated by a syncythia-inducing HIV-1 (cat #3 strain) laboratory isolate was exerted by compounds 9 and 10 (EC(50) 0.62 microM and 0.025 microM, respectively), while compound 6 showed only moderate activity (IC(50) = 4.1 microM). In addition, compound 10 showed very good in vitro therapeutic index (TI > 2046), indicating that it is a potential anti-HIV/AIDS drug.

Synthesis and biological activity of 1H-benzotriazole and 1H-benzimidazole analogues--inhibitors of the NTpase/helicase of HCV and of some related Flaviviridae.

To improve anti-helical activity of analogues of 1H-benzotriazole and 1H-benzimidazole their N-alkyl derivatives were synthesized and tested for antihelicase activity against enzymes of selected Flaviviridae including hepatitis C virus (HCV), West Nile virus (WNV), Dengue virus (DENV) and Japanese encephalitis virus (JEV). 1- and 2-alkyl derivatives of 4,5,6,7-tetrabromo-1H-benzotriazole were obtained by direct alkylation of 4,5,6,7-tetrabromo-1H-benzotriazole with the use of respective alkyl halides in the presence of KOH in methanol, to give a mixture of 1- and 2- isomers, which was separated by flash column chromatography in good yield. The proportion of isomers strongly depended on the reaction time and temperature. 1- and 2-hydroxyethyl and 1- and 2-chloroethyl derivatives of the tetrabromobenzo-triazole were synthesized with the use of 2-bromoethanol and 1-bromo-2-chloroethane respectively as alkylating agents. N-alkylation of this benzotriazole compound enhanced inhibitory activity and selectivity towards the helicase activity of HCV NTPase/helicase. The most active were the 2-methyl, 2-ethyl and 2-propyl derivatives (IC50 approximately 6.5 microM in the presence of DNA as a substrate). Derivatives of the benzotriazole in which hydroxyethyl or chloroethyl replaced the alkyl substituents lost their inhibitory activity. Brominated or methylated benzotriazole N(1) ribosides also did not exert helicase inhibitory activity. Although a number of N(1) and N(2) alkyl derivatives exerted good HCV and WNV helicase inhibitory activity when DNA was used as substrate, the activity was strongly decreased or even disappeared when RNA was used as substrate. The cytotoxicity tests in Vero and HeLa Tat cells showed a substantial decrease of cytotoxicity of N-alkyl derivatives as compared to the parent benzotriazole.

Synthesis, solution conformation and anti-HIV activity of novel 3'-substituted-2',3'-dideoxy-5-hydroxymethyluridines and their 4,5-substituted analogues.

To decrease the toxicity of potent anti-HIV nucleosides 3'-azido-2',3'-dideoxythymidine (AZT) and 2',3'-dideoxy-3'-fluorothymidine (3'-FddThd, FLT), their new analogues, 3'-azido-2',3'-dideoxy-5-hydroxymethyluridine (3'-Az5HmddUrd) and 2',3'-dideoxy-3'-fluoro-5-hydroxymethyluridine (3'-F5HmddUrd), were synthesized. The reaction of 3'-azido-2',3'-dideoxyuridine (3'-AzddUrd) and 2',3'-dideoxy-3'-fluorouridine (3'-FddUrd) with formaldehyde, under strongly alkaline conditions and at elevated temperature, proceeded after 4 days to completion to afford the corresponding 5-hydroxymethyl derivatives 3'-Az5HmddUrd and 3'-F5HmddUrd in good yield. These compounds were also prepared by oxidation of AZT and FLT with the use of K2S2O8. 1H NMR analyses were subjected to the series of 3', 4 and 5-substituted pyrimidine 2'-deoxy- and 2',3'-dideoxynucleosides involving 3'-Az5HmddUrd and 3'-F5HmddUrd. Analysis of the sugar furanose ring puckering demonstrated that all 3'-fluorine derivatives exhibited strong domination of the S conformation (approximately 100%) while 3'-substitution by electron-donating groups, such as NH2, increased population of the N conformation. Experimentally observed substituent effect on the furanose ring puckering equilibrium was reconstructed in the 100 ps molecular dynamic trajectories obtained for AZT, FLT, dThd, 2',3'-ddThd and 3'-amino-2',3'-ddThd. It may be concluded that anti-HIV activity is linked to a direct interaction of the 3'-substituent with reverse transcriptase (RT) binding site. Anti-HIV activities of 3'-Az5HmddUrd and 3'-F5HmddUrd are lower than activity of AZT and FLT; however, 3'-Az5HmddUrd and 3'-F5HmddUrd are less toxic than AZT and FLT.

Synthesis and evaluation of ATP-binding site directed potential inhibitors of nucleoside triphosphatases/helicases and polymerases of hepatitis C and other selected Flaviviridae viruses.

5'-O-(4-fluorosulphonylbenzoyl)-esters of ribavirin (FSBR), adenosine (FSBA), guanosine (FSBG) and inosine (FSBI) were obtained by acylation of the 5'-OH of adenosine, guanosine, inosine, and ribavirin with 4-fluorosulphonylbenzoyl chloride (FSBCI) in HMPA. The above derivatives were tested as inhibitors of nucleoside triphosphatase (NTPase)/helicase activities of Flaviviridae: hepatitis C virus (HCV), West Nile virus (WNV), Japanese encephalitis virus (JEV) and dengue virus (DENV) and polymerase activity of HCV and WNV. When the unwinding activity of viral NTPase/helicases was tested under standard conditions, only weak inhibition was obtained with FSBI (IC50 > or = 120 microM) and in the case of FSBG even an activation was seen. The preincubation of the NTPase/helicases with the 5'-O-FSB derivatives increased the inhibitory effect. Screening of the 5'-O-FSB derivatives on inhibition of the WNV and HCV RNA polymerases employing GTP or UTP substrates revealed rather modest inhibitory effect. FSBI exhibited the highest inhibitory activity against WNV (IC50 = 70 microM with UTP substrate) and HCV polymerase (IC50 = 80 microM with GTP substrate). Other 5'-O-FSB derivatives were very weak inhibitors or completely failed to show any activity against HCV and WNV enzymes. In contrast to the NTPase/helicases the preincubation of the polymerases did not influence the inhibition.

NTPase/helicase of Flaviviridae: inhibitors and inhibition of the enzyme.

RNA nucleoside triphosphatases (NTPase)/helicases represent a large family of proteins that are ubiquitously distributed over a wide range of organisms. The enzymes play essential role in cell development and differentiation, and some of them are involved in transcription and replication of viral single-stranded RNA genomes. The enzymatic activities of a NTPase/helicase were also detected in the carboxyl-terminal non-structural protein 3 (NS3) of members of the Flaviviridae family. The crucial role of the enzyme for the virus life cycle was demonstrated in knock out experiments and by using NTPase/helicase specific inhibitors. This makes the enzyme an attractive target for development of Flaviviridae-specific antiviral therapies. This review will summarize our knowledge about the function and structure of the enzyme, update the spectrum of inhibitors of the enzymatic activities of the NTPase/helicase and describe the different mechanisms by which the compounds act. Some of the compounds reviewed herein could show potential utility as antiviral agents against Flaviviridae viruses.

Inhibitors of the NTPase/helicases of hepatitis C and related Flaviviridae viruses.

Abstract: In the search for inhibitors of the non-structural protein 3 (NS3)-associated NTPase/helicase activities of the hepatitis C virus (HCV), and of the related West Nile Virus (WNV), and Japanese Encephalitis Virus (JEV), random screening of a broad range of unrelated low-molecular weight compounds revealed that 4,5,6,7-tetrabromo-1H-benzotriazole (TBBT) is a good inhibitor of the helicase activity of HCV and WNV NTPase/helicases (IC50 >> 20 mM and 1.7 mM with a DNA substrate), but a very weak inhibitor of the JEV enzyme (IC50 >> 200 mM). The synthesis of new TBBT derivatives was undertaken and their inhibitory activities against HCV, WNV, and JEV NTPase/helicases and cytotoxicities were examined. The N-alkyl derivatives showed good activity and lower cytotoxicity than TBBT.

Myristoylated derivatives of 2',3'-didehydro-2',3'-dideoxythymidine (stavudine) bi-functional prodrugs with potent anti-HIV-1 activity and low cytotoxicity.

BACKGROUND: To improve in vitro antiviral activity and selectivity of stavudine (d4T), a range of its bi-functional prodrugs, 5'-O-myristoylated derivatives, have been synthesized. METHODS: Stavudine 5'-O-myristoylated esters were synthesized using modified Parang's procedure. The cytotoxicity and anti-HIV activity was evaluated in the established MT-4 cell line. The level of p24 protein in culture medium was assayed, and EC50 and EC90 values were determined. RESULTS: Excellent anti-HIV activity was obtained for stavudine derivatives 2',3'-didehydro-2',3'-dideoxy-5'-O-(11-thioethylundecanoyl) thymidine, 2',3'-didehydro-2',3'-dideoxy-5'-O-(12-thioethyldodecanoyl) thymidine and 5'-O-(12-azidododecanoyl)-2',3'-didehydro-2',3'-dideoxythymidine with C10 and C11 alkyl chains bearing thioethyl- and azido- substituents. These prodrugs were more potent than the parent stavudine, as is clear from their EC50 values: 2',3'-didehydro-2',3'-dideoxy-5'-O-(11-thioethylundecanoyl) thymidine (R=CO(CH2)10SC2H5, EC50 0.06 µM), 2',3'-didehydro-2',3'-dideoxy-5'-O-(12-thioethyldodecanoyl) thymidine (R=CO(CH2)11SC2H5, EC50 0.09 µM) and 5'-O-(12-azidododecanoyl)-2',3'-didehydro-2',3'-dideoxythymidine (R=CO(CH2)11N3, EC50 0.06 µM), while 50% cytotoxic concentration was >16.65 µM, >7.5 µM and >18.53 µM, respectively. CONCLUSIONS: Overall data demonstrate that compounds 2',3'-didehydro-2',3'-dideoxy-5'-O-(11-thioethylundecanoyl) thymidine, 2',3'-didehydro-2',3'-dideoxy-5'-O-(12-thioethyldodecanoyl) thymidine and 5'-O-(12-azidododecanoyl)-2',3'-didehydro-2',3'-dideoxythymidine are very potent and selective anti-HIV agents and could be useful in treatment of HIV infections of the central nervous system.

Thiated derivatives of 2',3'-dideoxy-3'-fluorothymidine: synthesis, in vitro anti-HIV-1 activity and interaction with recombinant drug resistant HIV-1 reverse transcriptase forms.

Various thiated analogues of thymine 2',3'-dideoxy-3'-fluoronucleoside (FLT) and their 5'-monophosphates and 5'-triphosphates were prepared with the use of modified multistep procedures. The thiated analogues of FLT and FLTMP were evaluated against the wild type and drug- and multidrug-resistant strains of HIV-1, using the replicative phenotyping format of the deCIPhR assay, and showed potent inhibition of drug-resistant HIV-1 strains at low cytotoxicity. Additionally, inhibition of recombinant drug resistant forms of reverse transcriptase from single and multiple HIV-1 mutants by the synthesized 5'-triphosphates was investigated. The strongest inhibition was observed for K103N and Δ67 mutants and the most potent anti-HIV-1 activity against drug resistant strains and the lowest cytotoxicity was exerted by S4FLTMP and FLTMP which may be regarded as potential anti-HIV/AIDS agents.

Modified 5'-trityl nucleosides as inhibitors of Plasmodium falciparum dUTPase.

2'-Deoxyuridine triphosphate nucleotidohydrolase (dUTPase) is a potential drug target for the treatment of malaria. We previously reported the discovery of 5'-tritylated analogues of deoxyuridine as selective inhibitors of this Plasmodium falciparum enzyme. Herein we report further structure-activity studies; in particular, variations of the 5'-trityl group, the introduction of various substituents at the 3'-position of deoxyuridine, and modifications of the base. Compounds were tested against both the enzyme and the parasite. Variations of the 5'-trityl group and of the 3'-substituent were well tolerated and yielded active compounds. However, there is a clear requirement for the uracil base for activity, because modifications of the uracil ring result in loss of enzyme inhibition and significant decreases in antiplasmodial action.

Partial selective inhibition of HIV-1 reverse transcriptase and human DNA polymerases γ and ß by thiated 3'-fluorothymidine analogue 5'-triphosphates.

3'-Deoxy-3'-fluorothymidine (FLT, alovudine(®)) belongs to the most potent agents inhibiting HIV-1 replication. Its 5'-triphosphate (FLTTP) is a potent inhibitor of HIV-1 reverse transcriptase (HIV RT). Unfortunately, FLT exerts substantial hematologic toxicity both in vitro and in vivo. It was suggested that this toxicity may be related to inhibition of human DNA polymerases, especially mitochondrial DNA polymerase γ, by nucleoside analogue 5'-triphosphates leading to termination of DNA synthesis and mitochondrial dysfunction. To decrease the toxicity of FLT, its thiated analogues, 4-SFLT and 2-SFLT, were previously synthesized and shown to be potent inhibitors of HIV-1 with low in vitro cytotoxicity. To explain this phenomenon in the present study the synthesis of 5'-triphosphates of thiated FLT analogues was undertaken and their interaction with recombinant HIV-1 RT and human DNA polymerases γ (pol γ) and ß (pol ß) was investigated. It was shown that 3'-deoxy-3'-fluoro-4-thiothymidine 5'-triphosphate (4-SFLTTP) and 3'-deoxy-3'-fluoro-2-thiothymidine 5'-triphosphate (2-SFLTTP) were, similarly to FLTTP, potent competitive inhibitors of HIV-1 RT, with K(i)(app) values of 0.091 and 0.022 µM respectively. It is of interest that 2-SFLTTP, a compound in an unusual syn conformation around the glycosidic bond was an uncompetitive inhibitor of human mitochondrial DNA pol γ with K(i)(app) of 0.174 µM, while 4-SFLTTP in anti conformation inhibited this enzyme similarly to FLTTP, i.e., non-competitively, with K(i)(app) of 0.055 µM. Both 4-SFLTTP and 2-SFLTTP were competitive inhibitors of human DNA pol ß, with K(i)(app) values of 16.84 and 4.04 µM, respectively. The results point to partially selective inhibition of HIV RT by thiated 3'-fluorothymidine 5'-triphosphate analogues. Of special interest is that 2-SFLTTP, showing syn conformation, is a less potent inhibitor of human mitochondrial pol γ than 4-SFLTTP and FLTTP, both in the anti conformation, and has a higher inhibitory activity against HIV-1 RT than 4-SFLTTP. Moreover, the parent nucleoside 2-SFLT possessing the syn conformation shows a more potent anti-HIV-1 activity and a better selectivity index than its 4-thio isomer in the anti conformation (Matthes et al., 1989; Poopeiko et al., 1995), 2-SFLT is a potent and selective anti-HIV-1 agent with the selectivity index 4-fold higher than that of FLT. Findings regarding the mechanisms of antiviral and cytotoxic activities of FLT and its thioanalogues are discussed.

Interactions of 2'-fluoro-substituted dUMP analogues with thymidylate synthase.

A series of 2'-fluoro-substituted dUMP/FdUMP analogues were synthesized, their interaction with human recombinant thymidylate synthase investigated, and structural (1)H and (19)F NMR study of the corresponding nucleosides performed. While 2'-F-dUMP (fluorine in the "down" configuration), in striking contrast to 2'-F-ara-UMP (fluorine in the "up" configuration) and 2',2''-diF-dUMP, showed substrate activity, 2'-F-ara-UMP and 2',2''-diF-dUMP were classic inhibitors, and 2',5-diF-ara-UMP behaved as a strong slow-binding inhibitor, suggesting the 2'-F substituent in the "up" position to interfere with the active center cysteine thiol addition to the pyrimidine C(6) and the pyrimidine C(5)-F to prevent this interference. In support, the direct through space heteronuclear coupling J(HF) was observed for the fluorine "up" derivatives, 2'-F-ara-U and 2',5-diF-ara-U, causing the splitting of the H(6) resonance lines. The absence of such splitting in 2',2''-diF-dUrd, indicating an unusual orientation of the base in relation to the furanose, was associated with an exceptionally weak interaction with the enzyme.

Halogenated benzimidazoles and benzotriazoles as inhibitors of the NTPase/helicase activities of hepatitis C and related viruses.

A search has been initiated for lead inhibitors of the nonstructural protein 3 (NS3)-associated NTPase/helicase activities of hepatitis C virus, the related West Nile virus, Japanese encephalitis virus and the human mitochondrial Suv3 enzyme. Random screening of a broad range of unrelated low-molecular mass compounds, employing both RNA and DNA substrates, revealed that 4,5,6,7-tetrabromobenzotriazole (TBBT) hitherto known as a potent highly selective inhibitor of protein kinase 2, is a good inhibitor of the helicase, but not NTPase, activity of hepatitis C virus NTPase/helicase. The IC50 is approximately 20 micro m with a DNA substrate, but only 60 micro m with an RNA substrate. Several related analogues of TBBT were enzyme- and/or substrate-specific inhibitors. For example, 5,6-dichloro-1-(beta-d-ribofuranosyl)benzotriazole (DRBT) was a good, and selective, inhibitor of the West Nile virus enzyme with an RNA substrate (IC50 approximately 0.3 micro m), but much weaker with a DNA substrate (IC50 approximately 3 micro m). Preincubation of the enzymes, but not substrates, with DRBT enhanced inhibitory potency, e.g. the IC50 vs the hepatitis C virus helicase activity was reduced from 1.5 to 0.1 micro m. No effect of preincubation was noted with TBBT, suggesting a different mode of interaction with the enzyme. The tetrachloro congener of TBBT, 4,5,6,7,-tetrachlorobenzotriazole (TCBT; a much weaker inhibitor of casein kinase 2) is also a much weaker inhibitor than TBBT of all four helicases. Kinetic studies, supplemented by comparison of ATP-binding sites, indicated that, unlike the case with casein kinase 2, the mode of action of the inhibitors vs the helicases is not by interaction with the catalytic ATP-binding site, but rather by occupation of an allosteric nucleoside/nucleotide binding site. The halogeno benzimidazoles and benzotriazoles included in this study are excellent lead compounds for the development of more potent inhibitors of hepatitis C virus and other viral NTPase/helicases.