Multicomponent Reaction of Aldehydes, Amines and Oxalacetate Analogues Leading to Biologically Attractive Pyrrole Derivatives.

Pyrrole is a very important pharmacophoric moiety. It has been widely incorporated into the skeleton of antitumor, anti-inflammatory, antibacterial, antioxidant and antifungal active substances. Access to this key heterocycle by diverse routes is particularly attractive in terms of chemistry, and also from the environmental point of view. The present minireview summarizes the reported methods for the preparation of highly substituted pyrrole derivatives based on the one-pot multicomponent reaction of aldehydes, primary amines, and oxalacetate analogues as well as their biology.

Design, Synthesis, and Biological Evaluation of Novel C5-Modified Pyrimidine Ribofuranonucleosides as Potential Antitumor or/and Antiviral Agents.

BACKGROUND: Nucleoside analogues are well-known antitumor, antiviral, and chemotherapeutic agents. Alterations on both their sugar and the heterocyclic parts may lead to significant changes in the spectrum of their biological activity and the degree of selective toxicity, as well as in their physicochemical properties. METHODS: C5-arylalkynyl-ß-D-ribofuranonucleosides 3-6, 3΄-deoxy 12-15, 3΄-deoxy-3΄-C-methyl- ß-D-ribofurananucleosides 18-21 and 2΄-deoxy-ß-D-ribofuranonucleosides 23-26 of uracil, were synthesized using a one-step Sonogashira reaction under microwave irradiation and subsequent deprotection. RESULTS: All newly synthesized nucleosides were tested for their antitumor or antiviral activity. Moderate cytostatic activity against cervix carcinoma (HeLa), murine leukemia (L1210) and human lymphocyte (CEM) tumor cell lines was displayed by the protected 3΄-deoxy derivatives 12b,12c,12d, and the 3΄-deoxy-3΄-methyl 18a,18b,18c. The antiviral evaluation revealed appreciable activity against Coxsackie virus B4, Respiratory syncytial virus, Yellow Fever Virus and Human Coronavirus (229E) for the 3΄-deoxy compounds 12b,14, and the 3΄-deoxy-3΄-methyl 18a,18c,18d, accompanied by low cytotoxicity. CONCLUSION: This report describes the total and facile synthesis of modified furanononucleosides of uracil, with alterations on both the sugar and the heterocyclic portions. Compounds 12b,14 and 18a,c,d showed noticeable antiviral activity against a series of RNA viruses and merit further biological and structural optimization investigations.

Synthesis of novel N-acyl-ß-d-glucopyranosylamines and ureas as potential lead cytostatic agents.

Novel classes of acetylated and fully deprotected N-acyl-ß-d-glucopyranosylamines and ureas have been synthesized and biologically evaluated. Acylation of the per-O-acetylated ß-d-glucopyranosylurea (5), easily prepared via its corresponding phosphinimine derivative, by zinc chloride catalyzed reaction of the corresponding acyl chlorides RCOCl (a-f) gave the protected N-acyl-ß-d-glucopyranosylureas (6a-f), in acceptable-to-moderate yields. Subsequent deacetylation of analogues 6a-f under Zemplén conditions afforded the fully deprotected derivatives 7a,b,d,e,f, while the desired urea 7c was formed after treatment of 6c with dibutyltin oxide. All protected and unprotected compounds were examined for their cytotoxic activity in different L1210, CEM and HeLa tumor cell lines and were also evaluated against a broad panel of DΝΑ and RNA viruses. Derivative 7c exhibited cytostatic activity against the three evaluated tumor cell lines (IC50 9-24 µΜ) and might be the basis for the synthesis of structure-related derivatives with improved cytostatic potential. Only analogue 6f weakly but significantly inhibited the replication of parainfluenza-3 virus, Sindbis virus and Coxsackie virus B4 in cell cultures at concentrations of 45-58 µM.

Dissipation, metabolism and sorption of pesticides used in fruit-packaging plants: Towards an optimized depuration of their pesticide-contaminated agro-industrial effluents.

Wastewaters from the fruit-packaging industry constitute a serious point source contamination with pesticides. In the absence of effective depuration methods, they are discharged in municipal wastewater treatment plants or spread to land. Modified biobeds could be an applicable solution for their treatment. We studied the dissipation of thiabendazole (TBZ), imazalil (IMZ), ortho-phenylphenol (OPP), diphenylamine (DPA) and ethoxyquin (EQ), used by the fruit-packaging industry, in anaerobically digested sewage sludge, liquid aerobic sewage sludge and in various organic substrates (biobeds packing materials) composed of soil, straw and spend mushroom substrate (SMS) in various volumetric ratios. Pesticide sorption was also determined. TBZ and IMZ showed higher persistence especially in the anaerobically digested sewage sludge (DT50=32.3-257.6d), in contrast to OPP and DPA which were rapidly dissipated especially in liquid aerobic sewage sludge (DT50=1.3-9.3d). EQ was rapidly oxidized mainly to quinone imine (QI) which did not persist and dimethyl ethoxyquinoline (EQNL, minor metabolite) which persisted for longer. Sterilization of liquid aerobic sewage sludge inhibited pesticide decay verifying the microbial nature of pesticide dissipation. Organic substrates rich in SMS showed the highest dissipation capacity with TBZ and IMZ DT50s of ca. 28 d compared to DT50s of >50 d in the other substrates. TBZ and IMZ showed the highest sorption affinity, whereas OPP and DPA were weakly sorbed. Our findings suggest that current disposal practices could not guarantee an efficient depuration of effluents from the fruit-packaging industry, whereas SMS-rich biobed organic substrates show efficient depuration of effluents from the fruit-packaging industry via accelerated dissipation even of recalcitrant fungicides.

An easy microwave-assisted synthesis of C8-alkynyl adenine pyranonucleosides as novel cytotoxic antitumor agents.

We describe the synthesis of C8-alkynyl adenine pyranonucleosides 4, 5, and 8-phenylethynyl-adenine (II), via Sonogashira cross-coupling reaction under microwave irradiation. Compounds 4e and II were less cytostatic than 5-fluorouracil (almost an order of magnitude) against murine leukemia (L1210) and human cervix carcinoma (HeLa) cells, while the same compounds proved to be more active than 5-fluorouracil against human lymphocyte (CEM) cells.

Branched-chain sugar nucleosides: stereocontrolled synthesis and bioevaluation of novel 3'-C-trifluoromethyl and 3'-C-methyl pyranonucleosides.

A new series of 3'-C-trifluoromethyl- and 3'-C-methyl-ß-d-allopyranonucleosides of 5-fluorouracil and their deoxy derivatives has been designed and synthesized. Treatment of ketosugar 1 with trifluoromethyltrimethylsilane under catalytic fluoride activation and methyl magnesium bromide, gave 1,2:5,6-di-O-isopropylidene-3-C-trifluoromethyl (2a) and 3-C-methyl (2b)-α-D-allofuranose, respectively, in a virtually quantitative yield and with complete stereoselectivity. Hydrolysis followed by acetylation led to the 1,2,4,6-tetra-O-acetyl-3-C-trifluoromethyl (3a) and 3-C-methyl (3b)-ß-D-allopyranose. Compounds 3a,b were then condensed with silylated 5-fluorouracil and deacetylated to afford the target nucleosides 5a,b. Deoxygenation of the peracylated allopyranoses 3a,b followed by condensation with silylated 5-fluorouracil and subsequent deacetylation yielded the target 3'-deoxy-3'-C-trifluoromethyl and 3'-deoxy-3'-C-methyl-ß-d-glucopyranonucleosides 14a,b. The newly synthesized compounds were evaluated for their potential antiviral and cytostatic activities. The 3'-deoxy-3'-C-methyl- ribonucleoside 11b showed significant cytotoxic activity (∼7 µM) almost equally active against a variety of tumor cell lines.

Synthesis of novel thiopurine pyranonucleosides: evaluation of their bioactivity.

We report the synthesis of novel thiopurine pyranonucleosides. Direct coupling of silylated 6-mercaptopurine and 6-thioguanine with the appropriate pyranoses 1a-e via Vorbrüggen nucleosidation, gave the N-9 linked mercaptopurine 2a-e and thioguanine 4a-e nucleosides, while their N-7 substituted congeners 10a-e and 7a-e, were obtained through condensation of the same acetates with 6-chloro and 2-amino-6-chloropurines, followed by subsequent thionation. Nucleosides 3a-e, 5a-e, 8a-e, and 11a-e were evaluated for their cytostatic activity in three different tumor cell proliferative assays.

Rapid microwave-enhanced synthesis of C5-alkynyl pyranonucleosides as novel cytotoxic antitumor agents.

A microwave-assisted, one-pot, coupling reaction for the synthesis of C5-alkynyl-uracil and cytosine glucopyranonucleosides has been developed. The reaction is carried out under standard Sonogashira coupling conditions from glucopyranonucleosides of 5-iodouracil or 5-iodocytosine and various terminal alkynes. All compounds were evaluated for their cytostatic and antiviral activity. The 5-phenylethynyluracil pyranonucleoside derivative 6a showed the most promising cytostatic activity (50% inhibitory concentration in the lower micromolar range). No meaningful antiviral activity was recorded.

An integrated in silico approach to design specific inhibitors targeting human poly(a)-specific ribonuclease.

Poly(A)-specific ribonuclease (PARN) is an exoribonuclease/deadenylase that degrades 3'-end poly(A) tails in almost all eukaryotic organisms. Much of the biochemical and structural information on PARN comes from the human enzyme. However, the existence of PARN all along the eukaryotic evolutionary ladder requires further and thorough investigation. Although the complete structure of the full-length human PARN, as well as several aspects of the catalytic mechanism still remain elusive, many previous studies indicate that PARN can be used as potent and promising anti-cancer target. In the present study, we attempt to complement the existing structural information on PARN with in-depth bioinformatics analyses, in order to get a hologram of the molecular evolution of PARNs active site. In an effort to draw an outline, which allows specific drug design targeting PARN, an unequivocally specific platform was designed for the development of selective modulators focusing on the unique structural and catalytic features of the enzyme. Extensive phylogenetic analysis based on all the publicly available genomes indicated a broad distribution for PARN across eukaryotic species and revealed structurally important amino acids which could be assigned as potentially strong contributors to the regulation of the catalytic mechanism of PARN. Based on the above, we propose a comprehensive in silico model for the PARN's catalytic mechanism and moreover, we developed a 3D pharmacophore model, which was subsequently used for the introduction of DNP-poly(A) amphipathic substrate analog as a potential inhibitor of PARN. Indeed, biochemical analysis revealed that DNP-poly(A) inhibits PARN competitively. Our approach provides an efficient integrated platform for the rational design of pharmacophore models as well as novel modulators of PARN with therapeutic potential.

Stereocontrolled synthesis of 4'-C-cyano and 4'-C-cyano-4'-deoxy pyrimidine pyranonucleosides as potential chemotherapeutic agents.

A new series of 4'-C-cyano and 4'-C-cyano-4'-deoxy pyrimidine pyranonucleosides has been designed and synthesized. Commercially available 1,2,3,4,6-penta-O-acetyl-D-mannopyranose (1) was condensed with silylated 5-fluorouracil, uracil, and thymine, respectively to afford after deacetylation 1-(α-D-mannopyranosyl)nucleosides (2a-c). Subjecting 2a-c to the sequence of specific acetalation, selective protection of the primary hydroxyl group and oxidation, the 4'-ketonucleosides 6a-c and 7c were obtained. Reaction of compounds 6a,b, and 7c with sodium cyanide and subsequent deprotection gave the target 1-(4'-C-cyano-α-D-mannopyranosyl)nucleosides 12a-c. Deoxygenation at the 4'-position of cyanohydrins 8a,b, and 11c followed by deprotection led to the desired 1-(4'-C-cyano-4'-deoxy-α-D-talopyranosyl)nucleosides (15a-c). The newly synthesized compounds were evaluated for their potential antiviral and cytostatic activities in cell culture.

Stereocontrolled facile synthesis and biological evaluation of (3'S) and (3'R)-3'-amino (and Azido)-3'-deoxy pyranonucleosides.

This article describes the synthesis of (3 'S) and (3 'R)-3 '-amino-3 '-deoxy pyranonucleosides and their precursors (3 'S) and (3 'R)-3 '-azido-3 '-deoxy pyranonucleosides. Azidation of 1,2:5,6-di-O-isopropylidene-3-O-toluenesulfonyl-α-D-allofuranose followed by hydrolysis and subsequent acetylation afforded 3-azido-3-deoxy-1,2,4,6-tetra-O-acetyl-D-glucopyranose, which upon coupling with the proper silylated bases, deacetylation, and catalytic hydrogenation, obtained the target 3 '-amino-3 '-deoxy-ß-D-glucopyranonucleosides. The desired 1-(3 '-amino-3 '-deoxy-ß-D-allopyranosyl)5-fluorouracil was readily prepared from the suitable imidazylate sugar after azidation followed by a protection/deprotection sequence and reduction of the unprotected azido precursor. No antiviral activity was observed for the novel nucleosides. Moderate cytostatic activity was recorded for the 5-fluorouracil derivatives.

Synthesis and biological evaluation of 3'-C-ethynyl and 3'-C-(1,4-disubstituted-1,2,3-triazolo) double-headed pyranonucleosides.

A novel series of 3'-C-ethynyl and 3'-C-(1,4-disubstituted-1,2,3-triazolo) double-headed pyranonucleosides has been designed and synthesized. Reaction of 3-keto glucoside 1 with ethynyl magnesium bromide gave the desired precursor 3-C-ethynyl-1,2:5,6-di-O-isopropylidene-α-D-allofuranose (2). Hydrolysis followed by acetylation led to the 1,2,4,6-tetra-O-acetyl-3-C-ethynyl-ß-D-allopyranose (3). Compound 3 was condensed with silylated 5-fluorouracil, uracil, thymine, N4-benzoylcytosine and N6-benzoyladenine, respectively and deacetylated to afford the target 1-(3'-C-ethynyl-ß-D-allopyranosyl)nucleosides 5a-c,f,g. Copper-Catalyzed Azide-Alkyne Cycloaddition (CuAAC) reaction was utilized to couple the 3'-C-ethynyl pyranonucleoside derivatives with azidoethyl adenine, 5-fluorouracil and thymine, respectively to afford novel triazole double-headed nucleoside analogs 8a-h. 3'-C-Ethynyl pyranonucleosides and the new double-headed analogues were evaluated for their antiviral and cytostatic activities. Although none of the compounds showed pronounced cytostatic activity and were devoid of a significant antiviral potential, the double-headed nucleoside derivatives 8a, 8c and 8e showed a moderate cytostatic activity against human cervix carcinoma HeLa cells which may be the basis for the synthesis of analogous derivatives with improved cytostatic potential.

Kinetic and in silico analysis of the slow-binding inhibition of human poly(A)-specific ribonuclease (PARN) by novel nucleoside analogues.

Poly(A)-specific ribonuclease (PARN) is a 3'-exoribonuclease that efficiently degrades poly(A) tails and regulates, in part, mRNA turnover rates. We have previously reported that adenosine- and cytosine-based glucopyranosyl nucleoside analogues with adequate tumour-inhibitory effect could effectively inhibit PARN. In the present study we dissect the mechanism of a more drastic inhibition of PARN by novel glucopyranosyl analogues bearing uracil, 5-fluorouracil or thymine as the base moiety. Kinetic analysis showed that three of the compounds are competitive inhibitors of PARN with K(i) values in the low µM concentration and significantly lower (11- to 33-fold) compared to our previous studies. Detailed kinetic analysis of the most effective inhibitor, the uracil-based nucleoside analogue (named U1), revealed slow-binding behaviour. Subsequent molecular docking experiments showed that all the compounds which inhibited PARN can efficiently bind into the active site of the enzyme through specific interactions. The present study dissects the inhibitory mechanism of this novel uracil-based compound, which prolongs its inhibitory effect through a slow-binding and slow-release mode at the active site of PARN, thus contributing to a more efficient inhibition. Such analogues could be used as leading compounds for further rationale design and synthesis of efficient and specific therapeutic agents. Moreover, our data reinforce the notion that human PARN can be established as a novel molecular target of potential anti-cancer agents through lowering mRNA turnover rates.

Branched-chain C-cyano pyranonucleosides: synthesis of 3'-C-cyano & 3'-C-cyano-3'-deoxy pyrimidine pyranonucleosides as novel cytotoxic agents.

This report describes the total and facile synthesis of 3'-C-cyano & 3'-C-cyano-3'-deoxy pyrimidine pyranonucleosides. Reaction of 3-keto glucoside 1 with sodium cyanide gave the desired precursor 3-C-cyano-1,2:5,6-di-O-isopropylidene-α-D-glucofuranose (2). Hydrolysis followed by acetylation led to the 1,2,3,4,6-penta-O-acetyl-3-C-cyano-D-glucopyranose (4). Compound 4 was condensed with silylated 5-fluorouracil, uracil, thymine and N(4)-benzoylcytosine, respectively and deacetylated to afford the target 1-(3'-C-cyano-ß-D-glucopyranosyl)nucleosides 6a-d. Routine deoxygenation at position 3' of cyanohydrin 2, followed by hydrolysis and acetylation led to the 3-C-cyano-3-deoxy-1,2,4,6-tetra-O-acetyl-D-allopyranose (10). Coupling of sugar 10 with silylated pyrimidines and subsequent deacetylation yielded the target 1-(3'-C-cyano-3'-deoxy-ß-D-allopyranosyl)nucleosides 12a-d. The new analogues were evaluated for their antiviral and cytostatic activities. It was found that 6a was endowed with a pronounced anti-proliferative activity that was only 2- to 8-fold less potent than that shown for the parental base 5-fluorouracil. None of the compounds showed activity against a broad panel of DNA and RNA viruses.

Synthesis and biological evaluation of unsaturated keto and exomethylene D-arabinopyranonucleoside analogs: novel 5-fluorouracil analogs that target thymidylate synthase.

The synthesis of pyrimidine unsaturated keto and exomethylene arabinopyranonucleoside analogs as potential antitumor and antiviral agents is described. Commercially available 1,2,3,4-tetra-O-acetyl-D-arabinopyranose (1) was condensed with silylated thymine, uracil, 5-fluorouracil, N(4)-benzoyl cytosine and 5-(trifluoromethyl)uracil, respectively, deacetylated and acetylated to afford 1-(3,4-O-isopropylidene-α-D-arabinopyranosyl)pyrimidine analogs 4. Two different synthetic routes were investigated for the conversion of compounds 4 into the new 1-(2,3,4-trideoxy-2-methylene-α-pent-3-enopyranosyl)nucleoside derivatives of thymine (10a), uracil (10b), 5-fluorouracil (10c) and N(4)-benzoyl cytosine (10d). Only the first approach could afford derivative 10d. Debenzoylation of 10d afforded 1-(2,3,4-trideoxy-2-methylene-α-pent-3-enopyranosyl)cytosine (10f). The first approach resulted also to the 2-keto-3,4-unsaturated analogs 9. The new analogs did not show inhibition of DNA and RNA virus replication in cell culture. The 2'-ketonucleoside derivatives 9 were found to be more cytostatic than the corresponding 2'-exomethylene nucleosides 10. The 5-fluorouracil unsaturated keto derivative 9c and the exomethylene derivatives 10c and 13c showed antiproliferative activity in the lower micromolar range. Experimental evidence revealed that 9c, 10c and 13c may act as novel types of 5-fluorouracil releasing prodrugs, and points to thymidylate synthase as target for their cytostatic action.

Efficient synthesis of exomethylene- and keto-exomethylene-d-glucopyranosyl nucleoside analogs as potential cytotoxic agents.

A novel series of exomethylene- and keto-exomethylene-d-glucopyranonucleosides with thymine, uracil, and 5-fluorouracil as heterocyclic bases have been designed and synthesized. Wittig condensation of the 3-keto glucoside 1 gave the corresponding 1,2:5,6-di-O-isopropylidene-3-deoxy-3-methylene-d-glucofuranose (2), which after hydrolysis and acetylation led to the precursor 1,2,4,6-tetra-O-acetyl-3-deoxy-3-methylene-d-glucopyranose (4). Compound 4 was condensed with silylated thymine, uracil, and 5-fluorouracil, respectively, deacetylated and acetalated to afford 1-(3'-deoxy-4',6'-O-isopropylidene-3'-methylene-ß-d-glucopyranosyl)pyrimidines 7a-c. Oxidation of the free hydroxyl group in the 2'-position of the sugar moiety led to the formation of the labile 1-(3'-deoxy-4',6'-O-isopropylidene-3'-methylene-ß-d-glucopyranosyl-2'-ulose)pyrimidines 8a-c. Finally, deisopropylidenation of the resulted derivatives 8a-c afforded the diol nucleosides 9a-c. The target keto-exomethylene analogs 9a-c were more cytostatic against a variety of tumor cell lines than the corresponding saturated-hydroxy-exomethylene derivatives 6. In particular, the 5-fluorouracil derivative 9c was highly cytostatic at an IC(50) (50% inhibitory concentration) ranging between 0.56 and 9.4 microg/mL, which was comparable to the free parental 5-fluorouracil base.

Synthesis of 3-fluoro-6-S-(2-S-pyridyl) nucleosides as potential lead cytostatic agents.

The 3-deoxy-3-fluoro-6-S-(2-S-pyridyl)-6-thio-ß-D-glucopyranosyl nucleoside analogs 7 were prepared via two facile synthetic routes. Their precursors, 3-fluoro-6-thio-glucopyranosyl nucleosides 5a-e, were obtained by the sequence of deacetylation of 3-deoxy-3-fluoro-ß-D-glucopyranosyl nucleosides 2a-e, selective tosylation of the primary OH of 3 and finally treatment with potassium thioacetate. The desired thiolpyridine protected analogs 7a-c,f,g were obtained by the sequence of deacetylation of 5a-c followed by thiopyridinylation and/or condensation of the corresponding heterocyclic bases with the newly synthesized peracetylated 6-S-(2-S-pyridyl) sugar precursor 13, which was obtained via a novel synthetic route from glycosyl donor 12. None of the compounds 6 and 7 showed antiviral activity, but the 5-fluorouracil derivative 7c and particularly the uracil derivative 7b were endowed with an interesting and selective cytostatic action against a variety of murine and human tumor cell cultures.

Synthesis of 4,6-dideoxy-3-fluoro-2-keto-beta-D-glucopyranosyl analogues of 5-fluorouracil, N6-benzoyl adenine, uracil, thymine, N4-benzoyl cytosine and evaluation of their antitumor activities.

The synthesis of the unsaturated 4,6-dideoxy-3-fluoro-2-keto-beta-d-glucopyranosyl nucleosides of 5-fluorouracil (6a), N(6)-benzoyl adenine (6b), uracil (6c), thymine (6d) and N(4)-benzoyl cytosine (6e), is described. Monoiodination of compounds 1a,b, followed by acetylation, catalytic hydrogenation and finally regioselective 2'-O-deacylation afforded the partially acetylated dideoxynucleoside analogues of 5-fluorouracil (5a) and N(6)-benzoyl adenine (5b), respectively. Direct oxidation of the free hydroxyl group at the 2'-position of 5a,b, with simultaneous elimination reaction of the beta-acetoxyl group, afforded the desired unsaturated 4,6-dideoxy-3-fluoro-2-keto-beta-D-glucopyranosyl derivatives 6a,b. Compounds 1c-e were used as starting materials for the synthesis of the dideoxy unsaturated carbonyl nucleosides of uracil (6c), thymine (6d) and N(4)-benzoyl cytosine (6e). Similarly a protection-selective deprotection sequence followed by oxidation of the free hydroxyl group at the 2'-position of the dideoxy benzoylated analogues 9c-e with simultaneous elimination reaction of the beta-benzoyl group, gave the desired nucleosides 6c-e. None of the compounds was inhibitory to a broad spectrum of DNA and RNA viruses at subtoxic concentrations. The 5-fluorouracil derivative 6a was more cytostatic (50% inhibitory concentration ranging between 0.2 and 12 microM) than the other compounds.

Unsaturated dideoxy fluoro-ketopyranosyl nucleosides as new cytostatic agents: a convenient synthesis of 2,6-dideoxy-3-fluoro-4-keto-beta-D-glucopyranosyl analogues of uracil, 5-fluorouracil, thymine, N4-benzoyl cytosine and N6-benzoyl adenine.

The beta-protected nucleosides of uracil (2a), 5-fluorouracil (2b), thymine (2c), N(4)-benzoyl cytosine (2d) and N(6)-benzoyl adenine (2e) were synthesized by condensation of the peracetylated 3-deoxy-3-fluoro-D-glucopyranose (1) with the corresponding silylated bases. The nucleosides were deacetylated and several subsequent protection and deprotection steps afforded the partially acetylated analogues 6a-e. Selective iodination followed by hydrogenation gave the acetylated dideoxy analogues of uracil (8a), 5-fluorouracil (8b), thymine (8c), N(4)-benzoyl cytosine (8d) and N(6)-benzoyl adenine (8e), respectively. Finally, direct oxidation of the free hydroxyl group at the 4'-position of 8a-e, and simultaneous elimination reaction of the beta-acetoxyl group, afforded the desired unsaturated 2,6-dideoxy-3-fluoro-4-keto-beta-D-glucopyranosyl derivatives 9a-e. The new analogues were evaluated for antiviral and cytostatic activity. Compounds 9a-e were not active against a broad panel of DNA and RNA viruses at subtoxic concentrations. However, they were markedly cytostatic against a variety of tumor cell lines. The compounds should be regarded as potential new lead compounds to be further investigated for anticancer therapy.

Competitive inhibition of human poly(A)-specific ribonuclease (PARN) by synthetic fluoro-pyranosyl nucleosides.

Poly(A)-specific ribonuclease (PARN) is a cap-interacting deadenylase that mediates, together with other exonucleases, the eukaryotic mRNA turnover and thus is actively involved in the regulation of gene expression. Aminoglycosides and natural nucleotides are the only reported modulators of human PARN activity, so far. In the present study, we show that synthetic nucleoside analogues bearing a fluoro-glucopyranosyl sugar moiety and benzoyl-modified cytosine or adenine as a base can effectively inhibit human PARN. Such nucleoside analogues exhibited substantial inhibitory effects, when tested against various cancer cell lines, as has been previously reported. Kinetic analysis showed that the inhibition of PARN is competitive and could not be released by altering Mg(II) concentration. Moreover, substitution of the 2', 4', or 6'-OH of the sugar moiety with acetyl and/or trityl groups was crucial for inhibitory efficacy. To understand how the nucleosides fit into the active site of PARN, we performed molecular docking experiments followed by molecular dynamics simulations. The in silico analysis showed that these compounds can efficiently dock into the active site of PARN. Our results support the idea that the sugar moiety mediates the stabilization of the nucleoside into the active site through interactions with catalytic amino acid residues. Taken together, our in vitro and in silico data suggest that human PARN is among the molecular targets of these compounds and could act therapeutically by lowering the mRNA turnover rate, thus explaining their known in vivo inhibitory effect at the molecular level.