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Ribavirin and its analogues exhibit an in vitro antiproliferative effect in cancer cells. In this work, we studied the biological activities of a number of alkyl/aryloxymethyl derivatives of ribavirin's aglycon-1,2,4-triazole-3-carboxamide. Alkyl/arylxymethyl derivatives of 1,2,4-triazole-3-carboxamide with substitutions at the fifth or first position of the triazole ring, were synthesized and their antiproliferative and antimicrobial effects were assessed. For both series, the presence of an antiproliferative effect was investigated, and 1-alkyl/aryloxymethyl derivatives were shown an antimicrobial potential against a Gram-positive bacteria Micrococcus luteus and Gram-negative bacterium Pseudomonas aeruginosa . The obtained results showed that the n-decyloxymethyl derivatives induced leukemia cell death at low micromolar concentrations. We confirmed that n-decyloxymethyl derivatives of ribavirin inhibited the cell cycle progression and induced an accumulation of leukemia cells in the subG1-phase. The molecular docking results suggest that alkyl/aryloxymethyl derivatives may act by inhibiting translation initiation, due to interference with eIF4E assembly. The outcome results revealed that active derivatives (1- or 5-n-decyloxymethyl-1,2,4-triazole-3-carboxamides) can be considered as a lead compound for anticancer treatments.

Three novel tiazofurin analogues having d-arabino stereochemistry and nitrogen functionalities at the C-2' position (5-7) have been designed and synthesized in multistep sequences, starting from d-glucose. The known d-xylo stereoisomer of 1 (compound 2) along with two new analogues bearing nitrogen functions at the C-3' (3 and 4) has also been synthesized from the same sugar precursor. The synthetic sequence consisted of the following three stages: (i) the multistep synthesis of suitably protected pentofuranosyl cyanides, (ii) the construction of ethyl thiazole-4-carboxylate part by cyclocondensation of thus obtained glycofuranosyl cyanides with l-cysteine ethyl ester followed by dehydrogenation, and (iii) the final transformation of the ethyl thiazole-4-carboxylates into the target tiazofurin analogues using the esters ammonolysis. The tiazofurin analogues were evaluated for their antitumour activities in cell-culture-based assays. Compounds 3, 4 (d-xylo) and 7 (d-arabino), showed remarkable antitumour activities, with IC 50 values in the range of 4-7 nM. Preliminary structure-activity relationship allowed identification of two analogues with antiproliferative activities exceeding that of the parent compound 1 for several orders of magnitude (e.g. 4: 1354-fold against Raji, 7: 309-fold against K562). Flow cytometry data and Western blot analysis suggested that cytotoxic effects of d-xylo stereoisomers in the culture of K562 cells caused changes in the cell cycle distribution, as well as the induction of apoptosis in caspase-dependent way. The increase of apoptotic cells percentage in treated samples is also confirmed with fluorescent double-staining method. Genotoxicity testing showed that the analogues with the xylo-configuration (2-4) are far less genotoxic than tiazofurin., (Copyright © 2019 Elsevier Masson SAS. All rights reserved.)

The chemical ribosylation pathways of 5-substituted-1,2,4-triazole-3-carboxylates are discussed. For the products of the chemical synthesis of the 3(5)-alkyl- or 3(5)-aryl-substituted ribavirin analogues the anomer configuration and isomer composition were determined.

The novel isosteric ribavirin analogues were synthesized by two different ways. Some of them showed significant antiviral action against hepatitis C virus (HCV), herpes simplex (HCV-1) and influenza A virus comparable to that of ribavirin itself. The data obtained confirm the proposed theory of the ribavirin possible antiviral activity mechanism related with bioisosterism., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Synthesis of three tiazofurin (1) isosteres with nitrogen functionalities at the C-2' position (N3, NH2 and NH3(+)Cl(-)) has been achieved, in multistep sequences, starting from monoacetone d-glucose. A number of potential bioisosteres of 1 bearing acylamido functions at the C-2' position have also been synthesized from the same sugar precursor. In vitro cytotoxicities of target molecules against a number of human tumour cell lines were recorded and compared with those observed for lead molecule 1. Some of the synthesized compounds showed potent in vitro antitumour activity, such as 2'-azido derivative 2, which is the most potent of all molecules under evaluation (IC50 0.004 μM against MCF-7 cells). Flow cytometry data suggest that cytotoxic effects of these compounds in the culture of K562 cells might be mediated by apoptosis, additionally revealing that these molecules induced changes in cell cycle distribution of these cells. Results of Western blot analysis indicate that the synthesized tiazofurin analogues induce apoptosis in a caspase-dependent way., (Copyright © 2016 Elsevier Masson SAS. All rights reserved.)

Background: The phenanthroindolizidine alkaloid antofine and its analogues have excellent antiviral activity against tobacco mosaic virus (TMV). To simplify the structure and the synthesis of the phenanthroindolizidine alkaloid, a series of phenanthrene-containing N-heterocyclic compounds (compounds 1 to 33) were designed and synthesised, based on the intermolecular interaction of antofine and TMV RNA, and systematically evaluated for their anti-TMV activity., Result: Most of these compounds exhibited good to reasonable anti-TMV activity. The optimum compounds 5, 12 and 21 displayed higher activity than the lead compound antofine and commercial ribavirin. Compound 12 was chosen for field trials of antiviral efficacy against TMV, and was found to exhibit better activity than control plant virus inhibitors. Compounds 5 and 12 were chosen for mode of action studies. The changes in fluorescence intensity of compounds 5 and 12 on separated TMV RNA showed that these small molecules can also bind to TMV RNA, but the mode is very different from that of antofine., Conclusion: The compounds combining phenanthrene and an N-heterocyclic ring could maintain the anti-TMV activity of phenanthroindolizidines, but their modes of action are different from that of antofine. The present study lays a good foundation for us to find more efficient anti-plant virus reagents., (© 2015 Society of Chemical Industry.)

Ribavirin is used to treat hepatitis C but causes serious hemolytic anemia. The objective of the study was to develop a ribavirin prodrug to achieve liver-specific drug delivery and to reduce its off-target effect in red blood cells (RBCs). The approach aimed to target the human sodium taurocholate cotransporting polypeptide (NTCP), which is a bile acid transporter predominately expressed in the liver. Six prodrugs with ribavirin conjugation at C-3 or C-24 of the bile acids were synthesized. In vitro uptake studies indicated that all six prodrugs were NTCP substrates. Metabolic studies in vitro indicated that ribavirin-l-Val-glycochenodeoxycholic acid (GCDCA) was able to release ribavirin in the mouse liver S9 fraction. Additionally, in vitro studies showed that ribavirin in RBC was reduced by 16.7-fold from prodrug compared with parent drug incubation. Moreover, almost no prodrug was present in RBC. In vivo study in mice also showed that ribavirin-l-Val-GCDCA could provide almost the same ribavirin exposure in the liver as ribavirin administration, but with about 1.8-fold less exposure of ribavirin in RBC, plasma, and kidney. Overall, the study suggested that ribavirin-l-Val-GCDCA has the potential to achieve ribavirin-specific liver delivery., (© 2015 Wiley Periodicals, Inc. and the American Pharmacists Association.)

Efficacious, potent, and at the same time nontoxic macromolecular prodrugs of ribavirin are designed taking advantage over prodrug activation by the intracellular milieu. Activity of these prodrugs is illustrated in the cells hosting hepatitis C virus replication and also in the cells implicated in the inflammatory response to the viral infection., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

N-(2-hydroxyl) propyl-3-trimethyl ammonium chitosan chloride (HTCC) is hydro-soluble chitosan (CS) derivative, which can be obtained by the reaction between epoxypropyl trimethyl ammonium chloride (ETA) and CS. The preparation parameters for the synthesis of HTCC were optimized by orthogonal experimental design. ETA was successfully grafted into the free amino group of CS. Grafting of ETA with CS had great effect on the crystal structure of HTCC, which was confirmed by the XRD results. HTCC displayed higher capability to form nanoparticles by crosslinking with negatively charged sodium tripolyphosphate (TPP). Ribavrin- (RIV-) loaded HTCC nanoparticles were positively charged and were spherical in shape with average particle size of 200 nm. More efficient drug encapsulation efficiency and loading capacity were obtained for HTCC in comparison with CS, however, HTCC nanoparticles displayed faster release rate due to its hydro-soluble properties. The results suggest that HTCC is a promising CS derivative for the encapsulation of hydrophilic drugs in obtaining sustained release of drugs.

Herein we report the site-selective silylation of the ribonucelosides. The method enables a simple and efficient procedure for accessing suitably protected monomers for automated RNA synthesis. Switching to the opposite enantiomer of the catalyst allows for the selective silylation of the 3'-hydroxyl, which could be used in the synthesis of unnatural RNA or for the analoging of ribonucelosides. Lastly, the procedure was extended to ribavirin a potent antiviral therapeutic.

Improved biotechnological method of receiving the antiviral drug ribavirin by the reaction of transglycosilation by addition of catalytic amounts of sodium arsenate in the reaction mixture. Such approach allows to hydrolyze the amount of the excess natural nucleoside donor--ribose and, as a consequence, to simplify the composition of the reaction mixture and the process of separation of ribavirin. The effect of ribavirin and ozeltamivir carboxylate and their combination on the reproduction of the virus of the influenza A in cell culture and in experiments on laboratory animals (mouse Balb/C). The greatest anti-influenza effect is observed when using a combination of drugs, as compared to each of them taken separately.

Ribavirin is an important broad-spectrum antiviral drug. However, its utilization can be limited by its potential to cause hemolytic anemia as well as its variability in dosing levels and efficacy outcomes. To overcome these issues, we report on a new alkoxyalkylphosphodiester prodrug of ribavirin (2) that is designed to release the active ribavirin-monophosphate species selectively in nucleated cells while limiting its exposure in anucleated red blood cells (RBCs). Prodrug 2 displays improved in vitro antiviral activity against the hepatitis C virus replicon and influenza virus. Unlike ribavirin, prodrug 2 does not significantly decrease ATP levels in RBCs. Prodrug 2 demonstrates decreased uptake in RBCs but increased uptake in HepG2 hepatocytes when compared to ribavirin. In vivo, prodrug 2 is orally bioavailable and well-tolerated in rats in which it is processed to ribavirin and accumulates in the liver. These results indicate that prodrug 2 has the potential for safer, lower, less frequent, and less variable administration than ribavirin., (Copyright © 2013 Elsevier B.V. All rights reserved.)

Chemi-enzymatic synthesis of ribavirin acrylate and subsequent RAFT co-polymerization with acrylic acid afforded a formulation of a broad spectrum antiviral drug which avoids accumulation in erythrocytes, the origin of the main side effect of ribavirin. In cultured macrophages the macromolecular prodrugs exhibited decreased toxicity while maintaining the anti-inflammatory action of ribavirin.

The potentialities and restrictions of chemoenzymatic approach to the synthesis of new structural analogues of antiviral drug Ribavirin (1-beta-D-ribofuranosyl-1,2,4-triazole-3-carboxamide) have been determined. Syntheses of various amides of 1H-1,2,4-triazole-3-carboxylic acid and its 5-substituted analogues, prospective substrates of purine nucleoside phosphorylase (PNP), have been reported. The comparative effectiveness of the methods for obtaining amides aforementioned and also the methods for introducing functional groups to the C5 position of the heterocyclic system has been studied. New Ribavirin analogues bearing various substituents in the carboxamide group have been synthesized. The biotechnological method for the preparation of 1-beta-D-ribofuranosyl- 1,2,4-triazole-3-carbonitrile used as the intermediate in the synthesis of Viramidine, a contemporary Ribavirin analogue, has been developed.

2-(β-D-xylofuranosyl)thiazole-4-carboxamide (2) and two new tiazofurin analogues with 5-hydroxymethyl-2-methyl-tetrahydro-furo[2,3-d][1,3]dioxol-6-ol moiety as a sugar mimic (27 and 28) have been synthesized and evaluated for their in vitro antitumour activity against a panel of human tumour cell lines (K562, HL 60, Jurkat, Raji and HeLa). In contrast to previous literature reports, a metabolic MTT assay revealed remarkable cytotoxicity of 2 against K562 (IC(50)=0.15 μM) and HL-60 (IC(50)=0.13 μM) cells. Flow cytometry data suggest that cytotoxic effects of analogue 2 in the culture of K562 cells might be mediated by apoptosis, in opposite to tiazofurin, which did not induce apoptosis of K562 cells after 24h, thus suggesting a different mechanism of action. All three analogues 2, 27 and 28 were also active against Jurkat, Raji and HeLa cells, with IC(50) values in the range from 0.06 to 5.61 μM, but were completely inactive against the normal foetal lung fibroblasts (MRC-5)., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

The novel aza-analogues of tiazofurin (TZF) with 2-[5,5-bis(hydroxymethyl)pyrrolidin-2-yl] moiety, as sugar mimic, were synthesized from O,O-cyclohexylidene derivative of 4,4-bis(hydroxymethyl)-4-nitrobutanal in multi-gram scale. The synthetic route consisted of three stages: (i) the synthesis of corresponding derivative of 5,5-bis(hydroxymethyl)pyrrolidine-2-carbonitrile, (ii) the construction of ethyl thiazole-2-carboxylate part by the conversion of the pyrrolidine-2-carbonitrile into the N-trifluoroacetyl derivative followed by cyclocondensation with L-cysteine ethyl ester and then by dehydrogenation, and (iii) the final transformation of the ethyl thiazole-4-carboxylate into the aza-analogues of TZF. The TZF aza-analogues were evaluated for their antiviral activities in cell-culture-based assays.

Ribavirin and its 553 analogues have been docked with NS5-methyltransferase of Dengue viruses using Glide-HTVS and Glide-XP computational tools and the compounds have been screened based on their Glide-Gscores to identify lead ribavirin analogues that may act as inhibitors to the enzyme. Upon studying the interactions of ribavirin triphosphate (RTP) and triphosphate of lead ribavirin analogues with NS5-methyltransferase and Janus tyrosine Kinase-2 (JAK2) enzymes using molecular docking and dynamic methods, the possible mechanism by which the ribavirin causes haemolytic anaemia has been proposed. De novo RTP-analogues showing stronger affinities with NS5-methyltransferase and weaker affinities with JAK2 have been designed. The essential structural features of the de novo RTP-analogues for developing them as specific antiviral drugs against the infections due to dengue viruses have been discussed in detail.

Members of the GATA family of transcription factors are zinc finger proteins that were shown to play evolutionary conserved roles in cell differentiation and proliferation in different organisms. We hypothesized that by finding new molecules that inhibit their function to be crucial in future therapeutical interventions for various diseases. By virtual high throughput screening using a version of glide (Schrodinger®) program with both crystal and NMR structure of GATA C-terminal zinc finger, we identified new small molecular weight chemicals with lead-like properties. We used in vitro cell-based assays to show that these molecules selectively and efficiently inhibit GATA4 activity by inhibiting its interaction with the DNA. In addition we showed that these molecules can block the activation of downstream target genes by GATA4. Moreover these compounds can moderately enhanced a mouse model of myoblast differentiation into myotubes. This might be partially due to decreased GATA4/DNA interaction as shown by gel retardation assays. Further investigation is needed to reach selectivity and efficacy. Our study however do show that in silico screening combined with in vitro studies are efficient tools to unravel new molecules that interact with zinc finger proteins such as GATA4., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

Ribavirin is a nucleoside analogue with broad antiviral activity. Here we report the synthesis and biological evaluation of novel ribavirin ProTides designed to deliver the bioactive ribavirin monophosphate into cells. Some of the compounds display activity similar to the parent nucleoside against a range of viruses. Enzymatic, cell lysate and preliminary modeling studies have been performed to investigate the lack of enhancement of potency by the ProTides, and these indicate a failure at the final, amino acid cleavage step in the ProTide activation process, leading to inefficient release of the nucleoside monophosphate., (Copyright 2010 Elsevier Ltd. All rights reserved.)

Diadenosine disulfide (5) was reported to inhibit NAD kinase from Listeria monocytogenes and the crystal structure of the enzyme-inhibitor complex has been solved. We have synthesized tiazofurin adenosine disulfide (4) and the disulfide 5, and found that these compounds were moderate inhibitors of human NAD kinase (IC(50)=110 microM and IC(50)=87 microM, respectively) and Mycobacterium tuberculosis NAD kinase (IC(50)=80 microM and IC(50)=45 microM, respectively). We also found that NAD mimics with a short disulfide (-S-S-) moiety were able to bind in the folded (compact) conformation but not in the common extended conformation, which requires the presence of a longer pyrophosphate (-O-P-O-P-O-) linkage. Since majority of NAD-dependent enzymes bind NAD in the extended conformation, selective inhibition of NAD kinases by disulfide analogues has been observed. Introduction of bromine at the C8 of the adenine ring restricted the adenosine moiety of diadenosine disulfides to the syn conformation making it even more compact. The 8-bromoadenosine adenosine disulfide (14) and its di(8-bromoadenosine) analogue (15) were found to be the most potent inhibitors of human (IC(50)=6 microM) and mycobacterium NAD kinase (IC(50)=14-19 microM reported so far. None of the disulfide analogues showed inhibition of lactate-, and inosine monophosphate-dehydrogenase (IMPDH), enzymes that bind NAD in the extended conformation.

Carbonated analogues of ribavirin were synthesized from ethyl C-ribosylpropiolate obtained by an alkynylation reaction mediated by indium(0). The C-ribosides were then engaged in a Huisgen 1,3-dipolar cycloaddition reaction under a micellar catalysis. In these conditions, formation of 1,2,3-triazoles with control of the regioselectivity was observed. The regiochemistry of the adducts was determined by HMBC 2D-NMR analysis.

There are no FDA approved drugs for the treatment of hemorrhagic fever with renal syndrome (HFRS), a serious human illnesses caused by hantaviruses. Clinical studies using ribavirin (RBV) to treat HFRS patients suggest that it provides an improved prognosis when given early in the course of disease. Given the unique antiviral activity of RBV and the lack of other lead scaffolds, we prepared a diverse series of 3-substituted 1,2,4-triazole-beta-ribosides and identified one with antiviral activity, 1-beta-d-ribofuranosyl-3-ethynyl-[1,2,4]triazole (ETAR). ETAR showed an EC(50) value of 10 and 4.4 microM for Hantaan virus (HTNV) and Andes virus, respectively. ETAR had weak activity against Crimean Congo hemorrhagic fever virus, but had no activity against Rift Valley fever virus. Intraperitoneally delivered ETAR offered protection to suckling mice challenged with HTNV with a approximately 25% survival at 12.5 and 25mg/kg ETAR, and a MTD of 17.1+/-0.7 days. ETAR was phosphorylated in Vero E6 cells to its 5'-triphosphate and reduced cellular GTP levels. In contrast to RBV, ETAR did not increase mutation frequency of the HTNV genome, which suggests it has a different mechanism of action than RBV. ETAR is an exciting and promising lead compound that will be elaborated in further synthetic investigations as a framework for the rational design of new antivirals for treatment of HFRS.

We established a facile regioselectively chemo-enzymatic synthesis procedure for the preparation of mutual derivatives of nucleosides and pyrimidines by sequential Markovnikov addition and acylation. Firstly, pyrimidine derivatives containing vinyl ester group were synthesized from pyrimidines and divinyl esters through Markovnikov addition catalyzed by K(2)CO(3) in DMSO at 80 degrees C, and the yields were ranged from 50% to 87%. Then regioselective acylation of ribavirin and cytarabine with pyrimidine vinyl ester was catalyzed by CAL-B (immobilized lipase from Candida antarctica) in anhydrous acetone. Reaction conditions of enzymatic acylation including enzyme resource and solvents were optimized. A series of mutual derivatives of nucleosides and pyrimidines were synthesized successfully and characterized with NMR, IR, and HRMS. This chemo-enzymatic protocol involving sequential Markovnikov addition and acylation provided a novel way of synthesizing complicated functional compounds regioselectively which was hard to be achieved either by chemical or by enzymatic methods.

One of the possible mechanisms of antiviral action of ribavirin (1-beta- d-ribofuranosyl-1,2,4-triazole-3-carboxamide, 1) is the accumulation of mutations in viral genomic RNA. The ambiguous incorporation of 5'-triphosphate of ribavirin (RTP, 8) by a viral RNA-dependent RNA polymerase (RdRp) is a key step of the mutation induction. We synthesized three ribavirin analogues that possess hydrophobic groups, 4-iodo-1-beta- d-ribofuranosylpyrazole-3-carboxamide ( 7a), 4-propynyl-1-beta- d-ribofuranosylpyrazole-3-carboxamide ( 7b), and 4-phenylethynyl-1-beta-D-ribofuranosylpyrazole-3-carboxamide ( 7c), and the corresponding triphosphates ( 9a, 9b, and 9c, respectively). Steady-state kinetics analysis of the incorporation of these triphosphate analogues by a poliovirus RdRp, 3D (pol), revealed that while the incorporation efficiency of 9a was comparable to RTP, 9b and 9c showed lower efficiency than RTP. Antipolioviral activity of 7a and 7b was much more moderate than ribavirin, and 7c showed no antipolioviral activity. Effects of substituting groups on the incorporation efficiency by 3D (pol) and a strategy for a rational design of more active ribavirin analogues are discussed.

Ribavirin (1,2,4-triazole-3-carboxamide riboside) is a well-known antiviral drug. Ribavirin has also been reported to inhibit human S-adenosyl-L-homocysteine hydrolase (Hs-SAHH), which catalyzes the conversion of S-adenosyl-L-homocysteine to adenosine and homocysteine. We now report that ribavirin, which is structurally similar to adenosine, produces time-dependent inactivation of Hs-SAHH and Trypanosoma cruzi SAHH (Tc-SAHH). Ribavirin binds to the adenosine-binding site of the two SAHHs and reduces the NAD(+) cofactor to NADH. The reversible binding step of ribavirin to Hs-SAHH and Tc-SAHH has similar K(I) values (266 and 194 microM), but the slow inactivation step is 5-fold faster with Tc-SAHH. Ribavirin may provide a structural lead for design of more selective inhibitors of Tc-SAHH as potential anti-parasitic drugs.

Novel tiazofurin adenine dinucleotide (TAD) analogues 25-33 containing a substituent at C2 of the adenine ring have been synthesized as inhibitors of the two isoforms of human IMP-dehydrogenase. The 2-ethyl TAD analogue 33 [Ki = 1 nM (type I), Ki = 14 nM (type II)] was found to be the most potent. It did not inhibit three other cellular dehydrogenases up to 50 microM. Mycophenolic adenine bis(phosphonate)s containing a 2-phenyl (37) or 2-ethyl group (38), were prepared as metabolically stable compounds, both nanomolar inhibitors. Compound 38 [Ki = 16 nM (type I), Ki = 38 nM (type II)] inhibited proliferation of leukemic K562 cells (IC50 = 1.1 microM) more potently than tiazofurin (IC50 = 12.4 microM) or mycophenolic acid (IC50 = 7.7 microM).

This paper describes a divergent de novo synthesis of 2-(2,3-anhydro-beta-dribofuranosyl)thiazole-4-carboxamide (2',3'-anhydro-tiazofurin) and the corresponding alpha- and beta-homo-C-nucleosides, as well as evaluation of their antitumour activities in vitro.

A new tiazofurin analogue, 2-(3-amino-3-deoxy-beta-d-xylofuranosyl)thiazole-4-carboxamide (3), was synthesized starting from d-glucose and evaluated for its in vitro antiproliferative activity against a panel of human tumour cell lines. Compound 3 exhibited the most powerful cytotoxicity against K562 cells, being approximately 100-fold more potent than tiazofurin. This analogue was also active against Jurkat, HT-29 and HeLa malignant cells, with respective IC(50) values being ca. 2-, 27- and 17-fold lower than those observed for tiazofurin. Remarkably, compound 3 did not exhibit any significant cytotoxicity towards normal foetal lung MRC-5 cell line.

Eightfold higher yields and three times faster reaction rates were achieved by means of using a mixture solvent system composed of 90% acetone and 10% [BMIM]BF4 in the lipase-catalyzed regioselective synthesis of polymerizable ester of nucleoside drugs.

Two novel tiazofurin analogues 2 and 3 were synthesized starting from d-glucose. The key step of the synthesis was the efficient one-step hydrogen sulfide-mediated conversion of 2-azido-3-O-acyl-ribofuranosyl cyanides to the corresponding 2-amido thiocarboxamides. Compounds 2 and 3 were evaluated for their in vitro antiproliferative activity against certain human tumour cell lines. Remarkably, compound 2 was found to be 570-fold more potent than tiazofurin against MCF-7 cells, while compound 3 showed the most powerful cytotoxicity against HT-29 cancer cells, being almost 100-fold more active than tiazofurin.

Three new 5'-O-acyl tiazofurin derivatives 2-4 were synthesized and evaluated for their antiproliferative activity against different tumour cell lines as well as for their ability to induce apoptosis in C6 cells in vitro. Apart of the antitumour assays, the cell membrane permeation of 2-4 and their intracellular metabolism in C6 cells in vitro was also studied in order to evaluate their potential as possible tiazofurin bioisosteres or prodrugs.

[reaction: see text] The cycloaddition reaction between C-(2-thiazolyl) nitrones and allylic alcohol takes place with complete exo selectivity when the reactions are carried out in the presence of 1 equiv of zinc triflate. The rate of the reaction is increased enormously under microwave irradiation. The use of a chiral dipolarophile allowed application of the methodology to the synthesis of a hitherto unknown enantiomerically pure isoxazolidinyl analogue of the C-nucleoside tiazofurin.

The eukaryotic initiation factor eIF4E binds the mRNA 5' cap structure and has a central role during translational initiation. eIF4E and the mechanisms to control its activity have oncogenic properties and thus have become targets for anticancer drug development. A recent study (Kentsis et al. 2004) presented evidence that the antiviral nucleoside ribavirin and its phosphorylated derivatives were structural mimics of the mRNA cap, high-affinity ligands for eIF4E, and potent repressors of eIF4E-mediated cell transformation and tumor growth. Based on these findings, we tested ribavirin, ribavirin triphosphate (RTP), and the dinucleotide RpppG for their ability to inhibit translation in vitro. Surprisingly, the ribavirin-based compounds did not affect translation at concentrations where canonical cap analogs efficiently block cap-dependent translation. Using a set of reporter mRNAs that are translated via either cap-dependent or viral internal ribosome entry sites (IRES)-dependent initiation, we found that these ribavirin-containing compounds did inhibit translation at high (millimolar) concentrations, but there was no correlation of this inhibition with an eIF4E requirement for translation. The addition of a ribavirin-containing cap to mRNA did not stimulate translation. Fluorescence titration experiments with eIF4E and the nuclear cap-binding complex CBC indicated affinities for RTP and RpppG that were two to four orders of magnitude lower than those of m(7)GTP and m(7)GpppG. We conclude that, at least with respect to translation, ribavirin does not act in vitro as a functional mimic of the mRNA cap.

On the basis of potent biological activity of 3'-branched-3'-deoxynucleoside analogues, novel ribavirin and tiazofurin derivatives with 3'-C-hydroxymethyl substituent were synthesized, starting from D-xylose.

The biotechnological method of synthesis of ribavirin, vidarabin, and 6-azauridine by the use of immobilized recombinant enzymatic preparations of nucleoside phosphorylase was improved. The effect of ribavirin and its combinations with the other synthesized nucleosides on the reproduction of Vaccinia virus was studied using cultures of Vero cells. The combination of ribavirin and vidarabin was shown to provide an antiviral effect at lesser concentrations than when these compounds were taken separately. The English version of the paper: Russian Journal of Bioorganic Chemistry, 2004, vol. 30, no. 6; see also http://www.maik.ru.

In view of biological activities of tiazofurin and azido or aminosugar nucleosides, novel azido- and amino-substituted tiazofurin derivatives (1 and 2) were efficiently synthesized starting from 1,2;5,6-di-O-isopropylidene-D-glucose.

An efficient synthesis of 5'-nor carbocyclic ribavirin (4) is described in 13 steps from conveniently available (+)-(IR,4S)-4-hydroxy-2-cyclopenten-1-yl acetate (6). Compound 4 was evaluated against the following viruses: herpes simplex type 1 and 2, vaccinia, cowpox, smallpox, Ebola, hepatitis B, hepatitis C, adenovirus type 1, influenza A (H1N1 and H3N2), influenza B, parainfluenza type 3, Pichinde, Punta Toro A, respiratory syncytial, rhinovirus type 2, Venezuelan equine encephalitis, yellow fever, and West Nile. No activity was found nor was there any cytotoxicity to the viral host cells.

A divergent synthesis of two novel tiazofurin analogues, 2-(3-deoxy-3-fluoro-beta-D-xylofuranosyl)thiazole-4-carboxamide (2) and 2-(3-acetamido-3-deoxy-beta-D-xylofuranosyl)thiazole-4-carboxamide (3), has been achieved starting from D-glucose. Both nucleoside analogues were evaluated for their in vitro cytotoxicity against several human leukaemia and solid tumour cell lines.

The synthesis of carbocyclic and phosphonocarbocyclic analogues of ribavirin, an anti-HCV inhibitor, are described. Those compounds were evaluated against HCV but also against other important viruses in order to determine their spectrum of antiviral activity. Compounds 6 and 13 displayed a moderate IC(50) against HIV-1 of 43.8 and 37 microM, respectively.

Several ribavirin congeners containing a hexitol moiety were prepared via ring opening of two different epoxides with the methylcarboxylate ester of triazole and further elaboration. Unfortunately, none of the newly synthesized compounds displayed appreciable antiviral activity.

Synthesis and biological activities of cyclosaligenyl-tiazofurin monophosphate (CycloSal-TRMP), a new tiazofurin pronucleotide, are reported. CycloSal-TRMP proved to be active in vitro against human myelogenous leukemia K562 cell line and as A1 adenosine receptor agonist.

Twenty-seven brassinosteroid derivatives were tested for antiviral activity against measles virus (MV) via a virus-yield reduction assay. Compounds 6b [(22S,235)-3beta-bromo-5alpha,22,23-trihydroxystigmastan-6-one], 1d [(22R,23R)-2alpha,3alpha,22,23-tetrahydroxy-beta-Homo-7-oxa-stigmastan-6-one], 8a [(22R,23R)-3beta-fluoro-22,23-dihydroxystigmastan-6-one], 9b [(22S,23S)-3beta-fluoro-5alpha,22,23-trihydroxystigmastan-6-one] and 10b [(22S,23S)-5alpha-fluor-3beta,22,23-trihydroxystigmastan-6-one], with selectivity indexes (SI) of 40, 57, 31, 37 and 53, are the derivatives with good antiviral activity against MV. These SI values are higher than those obtained with ribavirin (used as reference drug). A comparative analysis of 50% cytotoxic concentration (CC50) values, using confluent non-growing cells, gives and indication of structure-activity relationship. According to their degree of cytotoxicity the compounds were divided in three groups: low, intermediate and high cytotoxicity. By observing the chemical structures of compounds belonging to the first group we can see that less cytotoxic activities are related to the presence of a 3beta-hydroxy group on C-3 (ring A) and a double bond between C-22 and C-23 (side chain). The replacement of a 5alpha-hydroxy group by a 5alpha-fluoro group enhances cytotoxicity. Halogenated brassinosteroid derivatives in C-3 position are more cytotoxic than those with an acetoxy group in the same position. For compounds 1d, 6b, 10b and ribavirin, cytotoxicity measurements were also done with replicating cells; CC50 values were low, but they still competed favourably with ribavirin against MV.

A new synthesis of tiazofurin is described from 2,3-O-isopropylidene-5-O-benzoyl-beta-D-ribofuranosyl cyanide.

2-Beta-D-ribofuranosylimidazole-4-carboxamide, an imidazole analogue of the antitumor agent tiazofurin, was synthesized and evaluated for the growth inhibitory activity of human myelogenous leukemia K562 cells.

Tiazofurine is a nucleoside analog with oncolytic activity being developed by Ribapharm (formerly ICN Pharmaceuticals) as a potential treatment for leukemia. It is metabolized to TAD (thiazole-4-carboxamide adenine dinucleotide), an inhibitor of IMP dehydrogenase. This inhibition results in the reduction of guanylate levels and the halting of neoplastic proliferation. The compound is in phase II/III trials [215553]. It is expected that Ribapharm will file an orphan drug application for tiazofurine, as a treatment for myelogenous leukemia, following the drug's completion of phase III trials by the end of 2002. The company has reported that phase III trials will begin by the end of 2000. Preliminary studies involving 21 patients have been carried out and the results reported by the company. During these studies, seven patients with chronic myelogenous leukemia had a complete hematologic response and two patients had a partial response. Of the patients with a complete response, six had marrow and peripheral responses. Ribapharm, through a Russian subsidiary of ICN, is also planning to conduct phase II studies of tiazofurine involving patients suffering from advanced ovarian cancer or multiple myeloma which is resistant to conventional therapy. The company has reported that the multiple myeloma limited phase II study is still undergoing planning, with an intended start date in late 2000 [381453]. In March 2000, Chase Hambrecht & Quist predicted that first approval could be towards the end of 2001 [384894].

The syntheses of furanthiofurin [5beta-D-(4'-thioribofuranosyl)furan-3-carboxamide, 1] and thiophenthiofurin [5beta-D-(4'-thioribofuranosyl)thiophene-3-carboxamide, 2], two C-thioribonucleoside analogues of tiazofurin, are described. Direct trifluoroacetic acid-catalyzed C-glycosylation of ethyl furan-3-carboxylate with 1-O-acetyl-2,3,5-tri-O-benzyl-4-thio-D-ribofuranose gave 2- and 5-glycosylated regioisomers, as a mixture of alpha and beta anomers. Ethyl 5-(2,3,5-tri-O-benzyl)-beta-D-(4'-thioribofuranosyl)furan-3-carboxylate (6beta) was debenzylated and then converted into the corresponding amide (furanthiofurin) by reaction with ammonium hydroxide. A similar C-glycosylation of ethyl thiophene-3-carboxylate with 1,2,3,5-tetra-O-acetyl-4-thio-D-ribofuranose catalyzed by stannic chloride afforded an anomeric mixture of 2- and 5-glycosylated regioisomers. Deacetylation of ethyl 5-(2,3,5-tri-O-acetyl)-beta-D-(4'-thioribofuranosyl)thiophene-3-carboxylate (13beta) with methanolic ammonia and treatment of the ethyl ester with ammonium hydroxide gave thiophenthiofurin. The glycosylation site and anomeric configuration were established by (1)H NMR spectroscopy. Thiophenthiofurin was found to be cytotoxic in vitro toward human myelogenous leukemia K562, albeit 39-fold less than thiophenfurin, while furanthiofurin proved to be inactive. K562 cells incubated with thiophenthiofurin resulted in inhibition of inosine 5'-monophosphate dehydrogenase (IMPDH) and an increase in IMP pools with a concurrent decrease in GTP levels. From computational studies it was deduced that, among the C-nucleoside analogues of tiazofurin, activity requires an electrophilic sulfur adjacent to the C-glycosidic bond and an energetically favorable conformer around chi = 0 degrees. Among these, the more constrained (least flexible) compounds (tiazofurin and thiophenfurin) are more active than the less constrained thiophenthiofurin. Those compounds which contain a nucleophilic oxygen in place of the thiazole or thiophene (oxazofurin, furanfurin, and furanthiofurin) show the least activity.

A series of 1,2,4-triazole L-nucleosides were synthesized and evaluated for their ability to stimulate type 1 cytokine production by activated human T cells in direct comparison to the known active agent ribavirin. Among the compounds prepared, 1-beta-L-ribofuranosyl-1,2,4-triazole-3-carboxamide (5, ICN 17261) was found to be the most uniformly potent compound. Conversion of the 3-carboxamide group of 5 to a carboxamidine functionality resulted in 1-beta-L-ribofuranosyl-1,2,4-triazole-3-carboxamidine hydrochloride (10), which induced cytokine levels comparable to 5 for two of the three type 1 cytokines examined. Modification of the carbohydrate moiety of 5 provided compounds of reduced activity. Significantly, ICN 17261 offers interesting immunomodulatory potential for the treatment of diseases where type 1 cytokines play an important role.

A novel fluoropyrazole ribonucleoside has been shown to have significant anti-influenza activity in vitro. The compound is compared and contrasted with the structurally-related compound ribavirin in attempts to identify factors having significant bearing on the mode of action of both compounds.