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PubMed1993

Structure-activity relationships of beta-D-(2S,5R)- and alpha-D-(2S,5S)-1,3-oxathiolanyl nucleosides as potential anti-HIV agents.

The beta-D-(2S,5R)- and alpha-D-(2S,5S)-1,3-oxathiolanylpyrimidine and -purine nucleosides with natural nucleoside configuration were synthesized and evaluated against HIV-1 in human peripheral blood mononuclear (PBM) cells. The key intermediate 14, which was utilized for the synthesis of various nucleosides, was synthesized from D-mannose or D-galactose. Condensation of the acetate 14 with thymine, uracil, cytosine, and 5-substituted uracils and cytosines gave various pyrimidine nucleosides. The acetate 14 was also condensed with 6-chloropurine and 6-chloro-2-fluoropurine which were converted to various purine nucleosides. In the case of thymine, uracil, and 5-substituted uracil derivatives, most of the compounds did not exhibit any significant anti-HIV activity except 5-fluorouracil (alpha-isomer) derivative 55. Among 5-substituted cytosine analogues, 5-bromocytosine derivative (beta-isomer) 68 was found to be the most potent anti-HIV agent. In the case of purine derivatives, inosine analogue (beta-isomer) 78 was found to be the most potent anti-HIV agent in the 6-substituted purines and 2-amino-6-chloropurine derivative (beta-isomer) 90 showed the most potent activity in the 2,6-disubstituted purine series. The beta-isomers of 6-chloropurine (74), adenine (76), and N6-methyladenine (77) derivatives showed similar potencies against HIV-1, and the corresponding alpha-isomers also exhibited significant anti-HIV activity, although they were generally less potent than the beta-isomers.

Antiviral Agents↗

PubMed1986

Carbocyclic analogues of 5-halocytosine nucleosides.

Carbocyclic analogues of 5-halocytosine nucleosides were prepared by direct halogenation of the carbocyclic analogues of cytidine, 2'-deoxycytidine, 3'-deoxycytidine, or ara-C. The 5-chloro and 5-bromo derivatives of the cytidine (carbodine) and of the 2'-deoxycytidine analogues and the 5-iodo derivatives of all four of the cytosine nucleoside analogues were prepared. All of the C-5-halocytosine nucleosides, as well as the parent C-cytosine nucleosides, were tested against a strain of herpes simplex virus type 1 (HSV-1) that induces thymidine kinase in host cells. Carbodine, 5-bromocarbodine, C-2'-deoxycytidine, C-5-bromo-2'-deoxycytidine, the four C-5-iodocytosine nucleosides, and C-ara-C inhibited replication of this strain of HSV-1 in cultured cells. Most of these compounds were tested also against the type 2 virus (HSV-2) in vitro and were active. The greatest activity observed was exerted by C-5-iodo-2'-deoxycytidine in inhibiting replication of HSV-1 in L929 cells. In tests against these DNA viruses, carbodine, a ribofuranoside analogue that had been shown previously to be highly active against human influenza A virus in vitro, was the most active compound against HSV-2 and one of the most active compounds against HSV-1 in Vero cells. 5-Bromocarbodine was active against influenza virus, but it was less active than carbodine.

Bromodeoxycytidine↗

PubMed1987

Synthesis and antitumor activity of fluorine-substituted 4-amino-2(1H)-pyridinones and their nucleosides. 3-Deazacytosines.

Novel fluorine-substituted deaza analogues of 5-azacytidine (AZC) and 5-aza-2'-deoxycytidine (dAZC) (3-deazacytosines) have been synthesized and tested for antitumor activity. Thus, 4-amino-3,5-difluoro-1-beta-D-ribofuranosyl-2(1H)-pyridinone (16), 4-amino-3-fluoro-1-beta-D-ribofuranosyl-2(1H)-pyridinone (17), 4-amino-5-fluoro-1-beta-D-ribofuranosyl-2(1H)-pyridinone (18), 4-amino-1-(2-deoxy-beta-D-erythro-pentofuranosyl)-3,5-difluoro-2 (1H)-pyridinone (25), 4-amino-1-(2-deoxy-beta-D-erythro-pentofuranosyl)-3-fluoro-2(1H)-pyridin one (26) 4-amino-1-(2-deoxy-alpha-D-erythro-pentofuranosyl)-3,5-difluoro-2(1H)-++ +pyridinon e (27), and 4-amino-1-(2-deoxy-alpha-D-erythro-pentofuranosyl)-3-fluoro-2 (1H)-pyridinone (28) were prepared by standard glycosylation procedures. Requisite heterocycle 4-amino-3,5-difluoro-2(1H)-pyridinone (6) was prepared in five steps from pentafluoropyridine (1). Other requisite fluoro heterocycles, 4-amino-3-fluoro-2(1H)-pyridinone (7) and 4-amino-5-fluoro-2(1H)-pyridinone (8), were obtained from a bis-defluorination of 4-amino-3,5,6-trifluoro-2(1H)-pyridinone (3) with hydrazine. Acetylation of 17 provided 4-amino-3-fluoro-1-(2,3,5-tri-O-acetyl-beta-D-ribofuranosyl)-2(1H)-pyrid inone (29). Structure proof of target nucleosides and heterocyclic compounds was provided by X-ray diffraction, 19F and 1H NMR, and UV. The ID50 values of fluorine-substituted 3-deazacytosines and 3-deazacytidines were greater than 1 X 10(-5) M in L1210 lymphoid leukemia cells in culture. Nucleoside 17 and its tri- and tetraacetates were the most active compounds with ID50 values of 1.07 X 10(-5), 1.23 X 10(-5), and 1.25 X 10(-5) M, respectively. The target nucleosides and intermediate heterocycles were inactive against P388 and L1210 lymphocytic leukemia in mice, except nucleoside 17 (NSC-378066) and its triacetate 29 (NSC-382021). Nucleoside 17 exhibited confirmed DN2 activity (% T/C 169-230) at five dose levels (25-300 mg/kg). Prodrug 29 exhibited similarly confirmed L1210 in vivo activity.

Animals↗

PubMed1988

Ara-tiazofurin: conservation of structural features in an unusual thiazole nucleoside.

Tiazofurin (2-beta-D-ribofuranosylthiazole-4-carboxamide, NSC 286193) is a C-glycosyl thiazole nucleoside with antitumor activity. Crystal structures of tiazofurin and its alpha,2'-deoxy and xylo analogues all show close contacts between the thiazole sulfur (S) and the furanose ring oxygen (O1'). These contacts have been interpreted in terms of an attractive intramolecular S-O interaction in the thiazole nucleosides. Ara-tiazofurin (2-beta-D-arabinofuranosylthiazole-4-carboxamide, ara-T) is the inactive arabinose analogue of tiazofurin. The crystal structure of ara-T is reported. This structure provides evidence for an attractive S-O interaction not seen in the other thiazole nucleosides. The conformation about the C-glycosyl bond in ara-T is such that close contacts are formed between the thiazole sulfur and both O1' and the 2'-hydroxyl oxygen O2'. This conformation is interpreted in terms of an additional attractive interaction between S and O2'. This interpretation is supported by comparison of the conformation of ara-T with those of other ara-nucleosides. These findings provide further evidence for an attractive S-O interaction in the thiazole nucleosides. Ara-T also demonstrates a second conformational feature found in these compounds: the carboxamide nitrogen remains cis to the thiazole nitrogen. Implications of these potentially constrained conformational features are discussed in terms of the mechanism of activity of tiazofurin.

Chemical Phenomena↗

PubMed2002

Enhancement of nucleoside cytotoxicity through nucleotide prodrugs.

A common reason for the lack of cytotoxicity of certain nucleosides is thought to be their inability to be initially activated to the monophosphate level by a nucleoside kinase or other activating enzyme. In a search for other nucleosides that might be worthwhile anticancer agents, we have begun to examine the utilization of monophosphate prodrugs in order to explore whether any enhanced cytotoxicity might be found for the prodrugs of candidate nucleosides that have little or no cytotoxicity. To that end, 5'-bis(pivaloyloxymethyl) phosphate prodrugs of two weakly cytotoxic compounds, 8-aza-2'-deoxyadenosine (5) and 8-bromo-2'-deoxyadenosine (9), have been prepared. These prodrugs (8 and 12) were examined for their cytotoxicity in CEM cells and were found to possess significantly enhanced cytotoxicity when compared with the corresponding parent nucleosides. Further cell culture experiments were conducted to gain insight into the mechanisms of cytotoxicity of these two prodrugs, and those data are reported.

Adenosine Monophosphate↗

PubMed2005

Synthesis and evaluation of S-acyl-2-thioethyl esters of modified nucleoside 5'-monophosphates as inhibitors of hepatitis C virus RNA replication.

Several triphosphates of modified nucleosides (1-6) were identified as inhibitors (IC(50) = 0.08-3.8 microM) of hepatitis C virus RNA-dependent RNA polymerase (RdRp). Although the initial SAR developed by determining the ability of the triphosphates to inhibit the in vitro activity of the HCV RdRp identified several potent inhibitors, none of the corresponding nucleosides exhibited significant inhibitory potency in a cell-based replicon assay. To improve upon the activity, bis(tBu-S-acyl-2-thioethyl) nucleoside 5'-monophosphate esters (7-12) were synthesized, and these derivatives exhibited improved potency compared to the corresponding nucleosides in the cell-based assay. Analysis of the intracellular metabolism demonstrated that the S-acyl-2-thioethyl (SATE) prodrug is metabolized to the 5'-triphosphate 40- to 155-fold more efficiently compared to the corresponding nucleoside. The prodrug approach involving bis(tBuSATE)cytidine 5'-monophosphate ester significantly reduced the deamination of cytidine derivatives by cellular deaminases. Additionally, chromosomal aberration studies with the SATE prodrug in cells showed no statistically relevant increase in aberrations compared to the concurrent controls.

Animals↗

PubMed2005

Synthesis, antiviral activity, and mechanism of drug resistance of D- and L-2',3'-didehydro-2',3'-dideoxy-2'-fluorocarbocyclic nucleosides.

Carbocyclic nucleosides have received much attention due to their interesting biological activity and metabolic stability. Among nucleoside analogues, a fluorine substitution on the carbohydrate moiety or introduction of a 2',3'-unsaturated structure motif has been proven to be successful in producing effective antiviral agents. By combining these structural features, both D- and L-2',3'-dideoxy-2',3'-didehydro-2'-fluoro-carbocyclic nucleosides (D- and L-2'F-C-d4Ns) were synthesized as potential anti-HIV agents. The target D- and L-carbocyclic nucleosides were both stereospecifically synthesized from D-ribose. The structure-activity relationships of synthesized compounds against HIV-1 in activated human peripheral blood mononuclear (PBM) cells were studied, from which we found that the L-2',3'-dideoxy-2'3'-didehydro-2'-fluoroadenosine analogue (L-2'F-C-d4A) 46 showed potent anti-HIV activity (EC50 = 0.77 microM), although it is cross-resistant to the lamivudine-resistant variant (HIV-1M184V). Modeling studies demonstrated a good correlation between calculated relative binding energies and activity/resistance data. The modeling study also indicated that an additional hydrogen bond and a favorable van der Waals interaction contribute to the higher antiviral activity of L-2'F-C-d4A in comparison to its D-counterpart. Also, like other L-nucleosides, the unfavorable steric hindrance of the sugar moiety of L-2'F-C-d4A and the side chain of Val184 could explain the cross-resistance of L-2'F-C-d4A with the M184V mutant. The significant difference of antiviral activity between carbovir and its analogue L-2'F-C-d4G 25 may be due to distortion of the phenyl ring of Tyr115 in the L-2'F-C-d4G-TP/HIV-RT complex, which resulted in a poor pi-pi interaction.

Adenine↗

PubMed2005

Synthesis of novel apio carbocyclic nucleoside analogues as selective a(3) adenosine receptor agonists.

On the basis of the biological activity of neplanocin A and apio-dideoxyadenosine (apio-ddA), novel apio-neplanocin A analogues 5a-d, combining the properties of two nucleosides, were stereoselectively synthesized. The apio moiety of the target nucleosides 5a-d was stereoselectively introduced by treating lactol 10 with 37% formaldehyde in the presence of potassium carbonate. The carbasugar moiety of neplanocin A was successively built by exposing diene 12 on a Grubbs catalyst in methylene chloride. The final nucleosides 5a-d were synthesized from the condensation of the glycosyl donor 14 with nucleic bases under the standard Mitsunobu conditions. Similarly, apio-aristeromycin 6 and (N)-apio-methanocarbaadenosine 7 were derived from the common intermediate 13 using catalytic hydrogenation and Simmons-Smith cyclopropanation as key steps. All of the final nucleosides 5a-d, 6, and 7 did not show significant inhibitory activity against S-adenosylhomocysteine hydrolase (SAH) up to 100 muM, maybe due to the absence of the secondary hydroxyl group at the C3'-position, which should be oxidized by cofactor-bound NAD(+). However, apio-neplanocin A (5a) showed potent and highly selective binding affinity (K(i) = 628 +/- 69 nM) at the A(3) adenosine receptor without any binding affinity at the A(1) and A(2A) adenosine receptors. In conclusion, we have first developed novel carbocyclic nucleosides with unnatural apio-carbasugars using stereoselective hydroxymethylation and RCM reaction and also discovered a new template of human A(3) adenosine receptor agonist, which play a great role in developing new A(3) adenosine receptor agonist as well as in identifying the binding site of the receptor.

Adenosine↗

PubMed1998

5'-Amino acid esters of antiviral nucleosides, acyclovir, and AZT are absorbed by the intestinal PEPT1 peptide transporter.

PURPOSE: General use of nucleoside analogues in the treatment of viral infections and cancer is often limited by poor oral absorption. Valacyclovir, a water soluble amino acid ester prodrug of acyclovir has been reported to increase the oral bioavailability of acyclovir but its absorption mechanism is unknown. This study characterized the intestinal absorption mechanism of 5' -amino acid ester prodrugs of the antiviral drugs and examined the potential of amino acid esters as an effective strategy for improving oral drug absorption. METHODS: Acyclovir (ACV) and Zidovudine (AZT) were selected as the different sugar-modified nucleoside antiviral agents and synthesized to L-valyl esters of ACV and AZT (L-Val-ACV and L-Val-AZT), D-valyl ester of ACV (D-Val-ACV) and glycly ester of ACV (Gly-ACV). The intestinal absorption mechanism of these 5' -amino acid ester prodrugs was characterized in three different experimental systems; in situ rat perfusion model, CHO/hPEPT1 cells and Caco-2 cells. RESULTS: Testing 5' -amino acid ester prodrugs of acyclovir and AZT, we found that the prodrugs increased the intestinal permeability of the parent nucleoside analogue 3- to 10-fold. The dose- dependent permeation enhancement was selective for L-amino acid esters. Competitive inhibition studies in rats and in CHO cells transfected with the human peptide transporter, hPEPT1, demonstrated that membrane transport of the prodrugs was mediated predominantly by the PEPT1 H+/dipeptide cotransporter even though these prodrugs did not possess a peptide bond. Finally, transport studies in Caco-2 cells confirmed that the 5' - amino acid ester prodrugs enhanced the transcellular transport of the parent drug. CONCLUSIONS: This study demonstrates that L-amino acid-nucleoside chimeras can serve as prodrugs to enhance intestinal absorption via the PEPT1 transporter, providing a novel strategy for improving oral therapy of nucleoside drugs.

Acyclovir↗

PubMed2005

Functional analysis of genetic variants in the human concentrative nucleoside transporter 3 (CNT3; SLC28A3).

The human concentrative nucleoside transporter, CNT3 (SLC28A3), plays an important role in mediating the cellular entry of a broad array of physiological nucleosides and synthetic anticancer nucleoside analog drugs. As a first step toward understanding the genetic basis for interindividual differences in the disposition and response to antileukemic nucleoside analogs, we examined the genetic and functional diversity of CNT3. In all, 56 variable sites in the exons and flanking intronic region of SLC28A3 were identified in a collection of 270 DNA samples from US populations (80 African-Americans, 80 European-Americans, 60 Asian-Americans, and 50 Mexican-Americans). Of the 16 coding region variants, 12 had not been previously reported. Also, 10 resulted in amino-acid changes and three of these had total allele frequencies of >/=1%. Nucleotide diversity (pi) at nonsynonymous and synonymous sites was estimated to be 1.81 x 10(4) and 18.13 x 10(4), respectively, suggesting that SLC28A3 is under negative selection. All nonsynonymous variants, constructed by site-directed mutagenesis and expressed in Xenopus laevis oocytes, transported purine and pyrimidine model substrates, except for c. 1099G>A (p. Gly367Arg). This rare variant alters an evolutionarily conserved site in the putative substrate recognition domain of CNT3. The presence of three additional evolutionarily conserved glycine residues in the vicinity of p. Gly367Arg that are also conserved in human paralogs suggest that these glycine residues are critical in the function of the concentrative nucleoside transporter family. The genetic analysis and functional characterization of CNT3 variants suggest that this transporter does not tolerate nonsynonymous changes and is important for human fitness.

Adenosine↗

PubMed1996

Raman spectroscopic determination of thymidine nucleoside structures in nucleotides.

Several spectral differences in Raman spectra were observed for thymidine (TM), 3'-O-acetylthymidine (3'OATM), 3',5'-di-O-acetylthymidine (3'5'DOATM), thymidine 5'-monophosphoric acid (H2TMP) and its Ca2+, Sr2+ and Ba2+ salts owing to nucleoside conformational differences in the thymidine moiety. The spectroscopic characterization of the nucleoside structures was made on the basis of previous crystallographic works relative to TM, 3'OATM, 3'5'DOATM and Ba(TMP).6H2O. The crystal structures of the other compounds reported here are, as yet, unknown. However, their nucleoside structures were inferred from the position of the phosphoester stretching band. The results show that C(2')-endo-anti, C(3')-endo-anti and C(2')-endo/C(3')-exo-anti puckers generate marker bands useful to characterize and titrate these thymidine nucleoside conformations. The furanose sugar puckering of the C(2')-endo-anti geometry has been suggested to account for the enhanced activity of thymidine derivatives against human immunodeficiency virus-type 1. A Raman spectroscopic method is described for the determination of this structure in thymidine nucleosides and nucleotides.

Crystallization↗

PubMed2003

Oligonucleotides incorporating 8-aza-7-deazapurines: synthesis and base pairing of nucleosides with nitrogen-8 as a glycosylation position.

Oligonucleotides incorporating the unusually linked 8-aza-7-deazapurine N8-(2'-deoxyribonucleosides) 3a,b (purine and 6-amino-2-chloropurine analogues) were used as chemical probes to investigate the base pairing motifs of the universal nucleoside 8-aza-7-deazapurin-6-amine N8-(2'-deoxyribofuranoside) 2 (adenine analogue) and that of the 2,6-diamino compound 1. Owing to the absence of an amino group on the nucleoside 3a the low stability of oligonucleotide duplexes incorporating this compound opposite to the four canonical DNA-constituents indicate hydrogen bonding and base pairing for the universal nucleosides 1 and 2 which form much more stable duplexes. When the 6-amino-2-chloro-8-aza-7-deazapurine nucleoside 3b replaces 1 and is located at the same positions, two sets of duplexes are formed (i) high Tm duplexes with 3b located opposite to dA or dC and (ii) low Tm duplexes with 3b located opposite to dG or dT. These results are due to the steric clash of the 2-chloro substituent of 3b with the 2-oxo group of dT or the 6-oxo group of dG while the 2-halogeno substituents are well accommodated in the base pairs formed with dA or dC. For comparison duplexes incorporating the regularly linked nucleosides 4-6a,b containing the same nucleobases as those of 1-3a,b were studied.

Adenine↗

PubMed2004

Therapeutic drug monitoring of lopinavir/ritonavir given alone or with a non-nucleoside reverse transcriptase inhibitor.

AIMS: To evaluate the interindividual variability in the plasma concentrations of lopinavir in the context of routine monitoring with or without treatment with a non-nucleoside reverse transcriptase inhibitor and to assess the interaction between the coformulation of lopinavir/ritonavir and efavirenz or nevirapine. METHODS: Plasma trough and peak concentrations (C(trough), C(max)) of lopinavir from 182 HIV-1-infected patients were analysed by high-performace liquid chromatography. Three lopinavir/ritonavir regimens were assessed, namely (A) 400 mg lopinavir/100 mg ritonavir twice daily given alone (n = 125), (B) 400/100 mg twice daily together with a non-nucleoside reverse transcriptase inhibitor (n = 25), and (C) 533/133 mg twice daily together with a non-nucleoside reverse transcriptase inhibitor (n = 32). RESULTS: Median (ng ml(-1)) C(trough) and C(max) lopinavir (interquartile range, CV) were: (A) 4852 (3198-6891, 56%) and 8501 (6333-11 584, 41%), (B) 2979 (1704-5186, 74%) and 5612 (3362-11 704, 76%) and (C) 5082 (2696-7226, 74%) and 9757 (4883-12 963, 60%). Median C(trough) of lopinavir was lower in patients taking both efavirenz [P = 0.01, 95% confidence interval (CI) for difference between medians 343, 2713] and nevirapine (P = 0.019, 95% CI for difference between medians 354, 3681) compared with those taking lopinavir/ritonavir alone. A higher interindividual variability was observed when lopinavir/ritonavir was given with a non-nucleoside reverse transcriptase inhibitor. The risk of achieving a 'suboptimal'C(trough) of lopinavir (below a threshold of 3000 ng ml(-1)) was statistically higher in patients treated with a non-nucleoside reverse transcriptase inhibitor (P < 0.001, 95% CI for difference between percentages 8.8, 43.1%) compared with those receiving lopinavir/ritonavir alone. CONCLUSIONS: Our results confirmed the interaction between lopinavir and efavirenz, and also demonstrated a significant interaction between the former drug and nevirapine, resulting in lower C(trough) of lopinavir. The wide interpatient variability in this interaction suggests that therapeutic drug monitoring may be useful in optimizing the dose of lopinavir.

Adolescent↗

PubMed1993

Human immunodeficiency virus type 1 (HIV-1) strains selected for resistance against the HIV-1-specific [2',5'-bis-O-(tert-butyldimethylsilyl)-3'-spiro- 5''-(4''-amino-1'',2''-oxathiole-2'',2''-dioxide)]-beta-D-pentofurano syl (TSAO) nucleoside analogues retain sensitivity to HIV-1-specific nonnucleoside inhibitors.

We recently reported that a newly discovered class of nucleoside analogues--[2',5'-bis-O-(tert-butyldimethylsilyl)- 3'-spiro-5''-(4''-amino-1'',2''-oxathiole-2'',2''-dioxide)]-beta-D - pentofuranosyl derivatives of pyrimidines and purines (designated TSAO)--are highly specific inhibitors of human immunodeficiency virus type 1 (HIV-1) and targeted at the nonsubstrate binding site of HIV-1 reverse transcriptase (RT). We now find that HIV-1 strains selected for resistance against three different TSAO nucleoside derivatives retain sensitivity to the other HIV-1-specific nonnucleoside derivatives (tetrahydroimidazo[4,5,1-jk][1,4]benzodiazepin-2(1H)-one and -thione (TIBO), 1-[(2-hydroxyethoxy)methyl]-6-phenylthiothymine, nevirapine, and pyridinone L697,661, as well as to the nucleoside analogues 3'-azido-3'-deoxythymidine, ddI, ddC, and 9-(2-phosphonylmethoxyethyl)adenine. Pol gene nucleotide sequence analysis of the TSAO-resistant and -sensitive HIV-1 strains revealed a single amino acid substitution at position 138 (Glu-->Lys) in the RT of all TSAO-resistant HIV-1 strains. HIV-1 RT in which the Glu-138-->Lys substitution was introduced by site-directed mutagenesis and expressed in Escherichia coli could not be purified because of rapid degradation. However, HIV-1 RT containing the Glu-138-->Arg substitution was stable. It lost its sensitivity to the TSAO nucleosides but not to the other HIV-1-specific RT inhibitors (i.e., TIBO and pyridinone). Our findings point to a specific interaction of the 4''-amino group on the 3'-spiro-substituted ribose moiety of the TSAO nucleosides with the carboxylic acid group of glutamic acid at position 138 of HIV-1 RT.

Antiviral Agents↗

PubMed2000

Expression and characterization of soluble and membrane-bound human nucleoside triphosphate diphosphohydrolase 6 (CD39L2).

Ecto-nucleoside-triphosphate diphosphohydrolase-6 (eNTPDase6(1), also known as CD39L2) cDNA was expressed in mammalian COS-1 cells and characterized using nucleotidase assays as well as size exclusion, anion exchange, and cation exchange chromatography. The deduced amino acid sequence of eNTPDase6 is more homologous with the soluble E-type ATPase, eNTPDase5, than other E-type ATPases, suggesting it may also be soluble. To test this possibility, both the cell membranes and the growth media from eNTPDase6-transfected COS-1 cells were assayed for nucleotidase activities. Activity was found in both the membranes and the media. Soluble eNTPDase6 preferentially exhibits nucleoside diphosphatase activity, which is dependent on the presence of divalent cations. Western blot analysis of eNTPDase6 treated with PNGase-F indicated both soluble and membrane-bound forms are glycosylated. However, unlike some membrane-bound ecto-nucleotidases, the eNTPDase6 activity was not specifically inhibited by deglycosylation with peptide N-glycosidase F. Soluble eNTPDase6 hydrolyzed nucleoside triphosphates poorly and nucleoside monophosphates not at all. Analysis of the relative rates of hydrolysis of nucleoside diphosphates (GDP = IDP > UDP > CDP >> ADP) suggests that soluble eNTPDase6 is a diphosphatase most likely not involved in regulation of ADP levels important for circulatory hemostasis.

Adenosine Triphosphatases↗

PubMed2003

Inhibition of hepatitis C virus RNA replication by 2'-modified nucleoside analogs.

The RNA-dependent RNA polymerase (NS5B) of hepatitis C virus (HCV) is essential for the replication of viral RNA and thus constitutes a valid target for the chemotherapeutic intervention of HCV infection. In this report, we describe the identification of 2'-substituted nucleosides as inhibitors of HCV replication. The 5'-triphosphates of 2'-C-methyladenosine and 2'-O-methylcytidine are found to inhibit NS5B-catalyzed RNA synthesis in vitro, in a manner that is competitive with substrate nucleoside triphosphate. NS5B is able to incorporate either nucleotide analog into RNA as determined with gel-based incorporation assays but is impaired in its ability to extend the incorporated analog by addition of the next nucleotide. In a subgenomic replicon cell line, 2-C-methyladenosine and 2'-O-methylcytidine inhibit HCV RNA replication. The 5'-triphosphates of both nucleosides are detected intracellularly following addition of the nucleosides to the media. However, significantly higher concentrations of 2'-C-methyladenosine triphosphate than 2'-O-methylcytidine triphosphate are detected, consistent with the greater potency of 2'-C-methyladenosine in the replicon assay, despite similar inhibition of NS5B by the triphosphates in the in vitro enzyme assays. Thus, the 2'-modifications of natural substrate nucleosides transform these molecules into potent inhibitors of HCV replication.

Adenosine↗

PubMed1979

Dependence of the nucleoside effect on linear energy transfer.

L929 cells were irradiated by cyclotron-produced neutrons and by 14.8 MeV monoenergetic neutrons. For comparison cells were also irradiated by 60Co gamma rays. Following irradiation cells were treated by an equimolar solution of deoxyribonucleosides, and the effect on cell survival measured. Results show that nucleoside treatment was efficient after low-LET irradiation: gamma ray survival curves were altered by deoxyribonucleosides in terms of significantly increased extrapolation numbers only, but without Do change. Cells irradiated by neutrons from either of the two sources did not respond to nucleoside treatment, and consequently their survival curves remained unaltered. These results show that the nucleoside effect does occur after low-LET irradiation, but apparently not following high-LET irradiation. Since deoxyribonucleosides as well as other cell breakdown products are released in irradiated and necrotic tumours due to massive cell destruction, such a nucleoside effect could possibly enhance the cell survival and thus effect the result of radiotherapy. Absence of the nucleoside effect in case of high-LET irradiation may therefore be an additional potential gain from neutrons in radiotherapy.

Animals↗

PubMed2005

Synthesis and anti-HIV activity of beta-D-3'-azido-2',3'-unsaturated nucleosides and beta-D-3'-azido-3'-deoxyribofuranosylnucleosides.

Since the discovery of 3'-azido-3'-deoxythymidine (AZT) and 2',3'-didehydro-2',3'-dideoxythymidine (d4T) as potent and selective inhibitors of the replication of human immunodeficiency virus (HIV), there has been a growing interest for the synthesis of 2',3'-didehydro-2',3'dideoxynucleosides with electron withdrawing groups on the sugar moiety. Here we described an efficient method for the synthesis of such nucleoside analogs bearing structural features of both AZT and d4T The key intermediate, 3-azido-1,2-bis-O-acetyl-5-O-benzoyl-3-deoxy-D-ribofuranose, 5 was synthesized from commercially available D-xylose in five steps, from which a series of pyrimidine and purine nucleosides were synthesized in high yields. The resultant protected nucleosides were converted to target nucleosides using appropriate chemical modifications. The final nucleosides were evaluated as potential anti-HIV agents.

Anti-HIV Agents↗