Synthesis and antiviral evaluation of unnatural beta-L-enantiomers of 3'-fluoro- and 3'-azido-2',3'-dideoxyguanosine derivatives

3'-fluoro-2',3'-dideoxy- (3) and 3'-azido-2',3'-dideoxy- (4) beta-L-ribofuranonucleoside derivatives of guanine have been synthesized and their antiviral properties examined. All these derivatives were regioselectively and stereospecifically prepared by glycosylation of 2-N-acetyl-6-O-(diphenylcarbamoyl)guanine 5 with a suitable peracylated L-xylo-furanose sugar 6, followed by appropriate chemical modifications. The prepared compounds were tested for their activity against HIV and HBV viruses, but they did not show significant activity.

Synthesis and in vitro anti-HIV activity in human monocyte-derived macrophages of 2-oxothiazolidine-4(R)-carboxylic acid derivatives

Oxidative stress and glutathione (GSH) deficit may play an important role in HIV infection pathogenesis, and oral administration of GSH-replenishing drugs such as N-acetylcysteine (NAC) and 2-oxothiazolidine-4(R)-carboxylic acid (OTC) may be associated with an increased survival rate of HIV-infected patients. Nevertheless, beneficial effects of these molecules are restricted in vivo by the high concentrations that are necessary to obtain biological effects, rapid extracellular metabolization, and low availability and plasma concentrations. We synthesized OTC derivatives that are more lipophilic than OTC and theoretically able to overcome these limitations and to generate, in addition to cysteine, other substrates of the gamma-glutamyl cycle. Their antiviral effects were investigated in human HIV-1/Ba-L-infected monocyte-derived macrophages. In our experimental conditions, OTC exhibited anti-HIV-1 effects and little cytotoxicity at high doses. None of the nine tested derivatives showed higher cytotoxicity than OTC, nor anti-HIV-1/Ba-L activity.

Synthesis and biological evaluation of 9-(beta-L-arabinofuranosyl)adenine

For the first time, the stereospecific synthesis of 9-(beta-L-arabinofuranosyl) adenine was carried out. Unfortunately, and unlike its "natural" D-counterpart Vidarabine, this L-enantiomer did not show significant activity when evaluated against a broad range of viruses.

Low enantioselectivities of human deoxycytidine kinase and human deoxyguanosine kinase with respect to 2'-deoxyadenosine, 2'-deoxyguanosine and their analogs

The antiviral activity of L-nucleoside analogs depends in part on the enantioselectivity of nucleoside kinases which catalyse their monophosphorylation. The substrate properties of human recombinant deoxycytidine kinase (dCK) and human recombinant deoxyguanosine kinase (dGK) with respect to L-adenosine and L-guanosine analogs, in the presence of saturating amounts of ATP and relatively high concentrations of substrates, demonstrated a marked lack of enantioselectivity of both these enzymes. Human dCK catalysed the phosphorylation of D- and L-enantiomers of beta-dA, beta-araA, and beta-dG with enantioselectivities favoring the unnatural enantiomer for the adenosine derivatives and the natural enantiomer for 2'-deoxyguanosine. No other tested L-adenosine or L-guanosine analog was a substrate of dCK. Similarly, D- and L-enantiomers of beta-dA, beta-araA, and beta-dG were substrates of human dGK but with different enantioselectivities compared to dCK, especially concerning beta-dA. The present results indicate that human dCK and dGK have similar properties including substrate properties, relaxed enantioselectivities, and possibly catalytic cycles.

Lipophilic pro-oligonucleotides are rapidly and efficiently internalized in HeLa cells

Model t-Bu-SATE pro-dodecathymidines labeled with fluorescein and exhibiting various lipophilicities were evaluated for their uptake by cells in culture. Pro-oligonucleotides with appropriate lipophilicity were found to permeate across the HeLa cell membrane much more extensively than the control phosphorothioate oligo or than the hydrophilic pro-oligos. Fluorescence patterns of internalization were consistent with a diffusion mechanism resulting in the appearance of a uniform cytoplasmic distribution and nuclear accumulation, as confirmed by confocal microscopy.

Synthesis and anti-retroviral activity of O,O'-bis(3'-azido-2',3'-dideoxythymidin-5'-yl) phosphoramidate derivatives

A simple and efficient protocol for the preparation of various symmetrical dinucleoside phosphoramidates derived from AZT, is presented. It consists of the phosphonylation of AZT with phosphonic acid in the presence of DCC to produce the symmetrical H-phosphonate diester, followed by its oxidative conversion to various phosphoramidate analogues. The synthesized compounds were evaluated for their anti-HIV activity in different cell cultures.

Synthesis of the tBuSATE pronucleotide of AZT by two different synthetic approaches

A large scale synthesis of the tBuSATE pronucleotide of AZT was required for in vivo studies. A comparative synthesis of this derivative by phosphoramidite and monophosphate approaches is reported.

Synthesis, anti-HIV activity and stability studies of 3'-azido-2',3'-dideoxythymidine 5'-fluorophosphate

The synthesis, in vitro anti-HIV activity, and stability studies of AZT 5'-fluorophosphate (F-AZTMP) are reported. The present results demonstrate that such compound is a bioprecursor of its parent 5'-mononucleotide (AZTMP) but its biotransformation does not allow its selective intracellular delivery. Moreover, several attempts were carried out in order to improve the biological activity of this compound by the use of a SATE prodrug strategy.

Comparison of anti-HBV activity of beta-D- and beta-L-DDA-5'monophosphate prodrugs and effectiveness in combination with lamivudine

We have investigated the effects of several beta-D-ddA 5'-monophospate (beta-D-ddAMP), and their corresponding beta-L-enantiomers prodrugs against HBV replication. All ddAMP prodrugs inhibited HBV replication in a dose-dependent manner.

3'-(N-hydroxyimino)-2',3-dideoxynucleosides and their derivatives: synthesis, broad spectrum antiviral properties and synthetical application for the preparation of other nucleoside analogues

A series of 3'-(N-hydroxyimino)-2',3'-dideoxynucleosides bearing different nucleic bases has been prepared. In vitro antiviral activity studies showed that among these compounds the thymine derivative possesses significant activity against HIV, HSV, EBV and HBV. Conveniently 5'-protected 3'-(N-hydroxyimino)-2',3'-dideoxythymidine was further used as a synthon for the preparation of other nucleoside analogues.

Synthesis and anti-HIV activity of some S-acyl-2-thioethyl (SATE) phosphoramidate derivatives of 3'-azido-2',3'-dideoxythymidine

The synthesis and in vitro anti-HIV activity of tBuSATE phosphoramidate derivatives of AZT incorporating several methyl-esterified alpha-amino acids are reported. The biological evaluation strongly supports the hypothesis that such compounds exert their anti-HIV effects via intracellular delivery of the corresponding 5'-mononucleotide.

Synthesis and in vitro antiviral activity of some symmetrical phosphoramidate dimers of AZT

The synthesis of some symmetrical phosphoramidate dimers of AZT is presented. The synthetic scheme includes the formation of the symmetrical H-phosphonate diester of AZT, followed by its conversion to several dinucleoside phosphoramidate analogues. The compounds were evaluated for their anti-retroviral activity.

Anti-HIV pronucleotides: SATE versus phenyl as a protecting group of AZT phosphoramidate derivatives

We comparatively studied the decomposition pathways in CEM cell extract of several PHENYL phosphoramidate diesters of AZT. A correlation between anti-HIV activities in TK- cell lines and pharmacokinetic data has been observed. This study would help to design corresponding SATE phosphoramidate diesters which revealed potent anti-HIV properties.

Stereospecific synthesis and antiviral activities of beta-L-2',3'-dideoxy-5-chloropyrimidine nucleoside derivatives

Several 5-chlorouracil and 5-chlorocytosine beta-L-dideoxynucleosides were stereospecifically synthesized and their activities against human immunodeficiency virus (HIV) and hepatitis B virus (HBV) were examined in cell culture.

Structural determinants of HIV-1 reverse transcriptase stereoselectivity towards (beta)-L-deoxy- and dideoxy-pyrimidine nucleoside triphosphates: molecular basis for the combination of L-dideoxynucleoside analogs with non-nucleoside inhibitors in anti HIV chemotherapy

We have compared the HIV-1 RT mutants containing the single substitutions L100I, K103N, V106A, V179D, Y181I and Y188L, known to confer NNI-resistance in treated patients, to HIV-1 RT wt for their sensitivity towards inhibition by D- and L-deoxy- and dideoxy-nucleoside tiphosphates. The results showed a differential effect of the substitutions on the affinity for both D- and L-enantiomers of deoxy- and dideoxy-nucleoside triphosphates and provide a rationale for the utilization of L-dideoxynucleoside analogs with NNI in combination chemotherapy.

Interaction of beta-L-adenosine-5'-triphosphate (L-ATP) with human deoxycytidine kinase, human DNA primase and T4 DNA ligase: does the chance direct enzymatic enantioselectivity?

We demonstrate that L-ATP: 1) as well as its natural D-enantiomer, acts as a phosphate donor in the reaction catalysed by human deoxycytidine kinase; 2) inhibits human DNA-primase and the ATP-dependent T4 DNA ligase. Thus, the lack of enantioselectivity of the enzymes is more frequent than it was believed a few years ago and we suggest that it would depend on chance more than on an evolutionary strategy.

Prodrugs of Ara-CMP and Ara-AMP with a S-acyl-2-thioethyl (SATE) biolabile phosphate protecting group: synthesis and biological evaluation

The bis(S-pivaloyl-2-thioethyl) phosphotriesters of Ara-C and Ara-A were synthesized as potential bioreversible mononucleotide prodrugs. Some N- and O-acylated derivatives were also prepared with the aim to modify the lipophilicity of the title pronucleotides. Compounds were tested for their antitumor/antiviral activity against a variety of tumor cells and viruses.

New series of mixed pronucleotides. Synthesis and anti-HIV activities of mononucleoside phenyl SATE phosphotriesters

The synthesis and anti-HIV activities of phenyl S-pivaloyl-2-thioethyl (tBuSATE) phosphotriesters of AZT and d4T are reported. These compounds show similar activity compared to bis(tBuSATE) phosphotriesters and appear to be able to deliver the corresponding 5'-mononucleotides inside the cells.

Synthesis of alkenyl acyclonucleosides derivatives of 5-halogenouracil as antiviral and antitumoral agents

Alkenyl acyclonucleosides derivatives of 5-halogenouracil have been synthesized via Michael addition reaction. These compounds were treated by allylbromide, propargylbromide or ethylbromoacetate to give the corresponding N-1,N-3-disubstituted 5-halogenouracil.

Synthesis of new fluorescent nucleoside analogues and application to the study of human deoxycytidine kinase

We have determined the affinity of human deoxycytidine kinase with respect to new fluorescent N-methylanthraniloyl cytidine derivatives or non fluorescent enantiomeric cytidine analogues. New results regarding the enantioselectivity and the mechanism of the enzyme are presented.

Derivatives of L-adenosine and L-guanosine as substrates for human deoxycytidine kinase

A series of analogues of L-adenosine and of L-guanosine, including beta-L-dA, beta-L-Ado, beta-L-araA, and beta-L-dG, have been shown to be substrates of human deoxycytidine kinase thus demonstrating the complete lack of enantioselectivity of this enzyme.

ddC- and 3TC-bis(SATE) monophosphate prodrugs overcome cellular resistance mechanisms to HIV-1 associated with cytidine kinase deficiency

A 2',3'-dideoxycytidine (ddC)-resistant T-lymphoid cell line (MOLT-4/8rddC250), in which deoxycytidine kinase (dCK) gene-expression was decreased when compared with parental cells, has been selected. Cytotoxic and antiretroviral activity of ddC and 3TC was significantly lower in MOLT-4/8rddC250-than in parental MOLT-4/8 cells. ddC- and 3TC-bis(SATE)phosphotriesters completely overcame cellular resistance mechanisms and showed comparable both cytotoxic and antiretroviral activity in parental and ddC-resistant cells.

Intracellular metabolism of beta-L-ddAMP-bis(tbutylSATE), a potent inhibitor of hepatitis B virus replication

beta-L-ddAMP-bis(tbutylSATE) is a potent inhibitor of HBV replication with an EC50 = 0.1 microM. Following a 0- to 72-hrs exposure of human hepatocytes to a 10 microM [2',3'-3H] beta-L-ddAMP-bis(tbutylSATE), the pharmacologically active beta-L-ddATP was the predominant metabolite attaining a concentration of 268.53 +/- 107.97 pmoles/10(6) cells at 2 hrs. In Hep-G2 cell, beta-L-ddATP accounted for 146.8 +/- 29.8 pmoles/10(6) cells at 2 hrs with an half life of approximately 5.4 hrs. This study reveals that extensive intracellular concentrations of beta-L-ddATP after incubation of cells to the parent drug is accounting for its potent antiviral activity.

Synthesis of new PMEA diphosphate mimics

We synthesized and characterized new diphosphate mimics of the acyclic nucleoside phosphonate PMEA [Adefovir, 9-(2-phosphonylmethoxyethyl)adenine].

Pharmacokinetics of beta-L-2',3'-dideoxy-5-fluorocytidine in rhesus monkeys

beta-L-2',3'-Dideoxy-5-fluorocytidine (beta-L-FddC), a novel cytidine analog with an unnatural beta-L sugar configuration, has been demonstrated by our group and others to exhibit highly selective in vitro activity against human immunodeficiency virus types 1 and 2 and hepatitis B virus. This encouraging in vitro antiviral activity prompted us to assess its pharmacokinetics in rhesus monkeys. Three monkeys were administered an intravenous dose of [3H] beta-L-FddC at 5 mg/kg of body weight. Following a 3-month washout period, an equivalent oral dose was administered. Plasma and urine samples were collected at various times for up to 24 h after dosing, and drug levels were quantitated by high-pressure liquid chromatography. Pharmacokinetic parameters were obtained on the basis of a two-compartment open model with a first-order elimination from the central compartment. After intravenous administration, the mean peak concentration in plasma (Cmax) was 29.8 +/- 10.5 microM. Total clearance, steady-state volume of distribution, terminal-phase plasma half-life (t1/2 beta), and mean residence time were 0.7 +/- 0.1 liters/h/kg, 1.3 +/- 0.1 liters/kg, 1.8 +/- 0.2 h, and 1.9 +/- 0.2 h, respectively. Approximately 47% +/- 16% of the intravenously administered radioactivity was recovered in the urine as the unchanged drug with no apparent metabolites. beta-L-FddC exhibited a Cmax of 3.2 microM after oral administration, with a time to peak drug concentration of approximately 1.5 h and a t1/2 of 2.2 h. One monkey in the oral administration arm of the study had a significant delay in the absorption of the aqueous administered dose. The absolute bioavailability of orally administered beta-L-FddC ranged from 56 to 66%.