A Convenient Synthesis of D-Psicofuranosyl Nucleosides1

Abstract

As part of our studies on the synthesis of conformationally restricted nucleosides of types 1 and 2, where X = CH₂, O or S, we required access to differentially substituted D-psicofuranosyl nucleosides such as 3. As shown in the table, we have developed a convenient approach to such compounds that depends on the direct condensation of the 1,2:3,4-di-O-isopropylidene-β-D-psicofuranose derivative 4 with an appropriate silylated purine or pyrimidine base.² Although the α and β anomers of 3 are formed in a 1:1 ratio, the yields of the β anomers are generally comparable with earlier condensation methods that use psicofuranosyl- halide², 2-benzoates⁴ or 2-nitro derivative⁵. However, the present method has the advantage that the starting sugar 4 is more readily accessible. The precursor 6′-alcohol can be prepared in very large amounts from D-fructose using the method of Prisbe et al.⁴     

STEREOSELECTIVE SYNTHESIS OF NOVEL THIOISO DIDEOXY NUCLEOSIDES WITH EXOCYCLIC METHYLENE AS POTENTIAL ANTIVIRAL AGENTS

Novel thioiso pyrimidine and purine nucleosides substituted with exocyclic methylene have been synthesized, starting from D-xylose. Cyclization of the dimesylate to the 4-thiosugar 6a proceeded in pure S_N2 reaction in the presence of allylic functional group.     

Nucleosides,XLIV1 Synthesis,Properties and Biological Activity of Indazole Nucleosides

Abstract

Various new haloindazole-1-β-D-ribofuranosides (10-17,20,21) and a 2-β-D-ribofuranoside (18) have been synthesized by the fusion method and by direct halogenations, respectively. The new nucleosides have been characterized by UV and ¹H NMR spectra as well as pK_a determinations. Indazole ribofuranosides behave in aqueous acid like purine and benzimidazole nucleosides showing the same mechanism of cleavage of the glycosidic bonds. Toxicity studies against various cell populations indicate only little biological activities.     

FUNCTIONALIZATION OF PYRIMIDINE AND PURINE NUCLEOSIDES AT C4 AND C6: C-NUCLEOPHILIC SUBSTITUTION OF THEIR C4- AND C6-(1,2,4-TRIAZOL-1-YL) DERIVATIVES

A study of C-nucleophilic substitution at the C4-position on pyrimidine and C6-position on 2′-deoxyguanosine to produce novel nucleosides is presented with the spectroscopic properties of their respective substitution products. C4-(1,2,4-triazol-1-yl) pyrimidine nucleosides 1 were treated with nitroalkanes, malononitrile, acetylacetone, ethyl nitroacetate, acetoacetate and cyanoacetate at 100°C in dioxane in the presence of DBU resulting in the production of novel nucleosides 2–11. To explore the application of this methodology to purine chemistry, this approach was used to produce novel analogs from 2′-deoxyguanosine. We found that the triazolo derivative 12 undergoes C-nucleophilic substitution with nitromethane, malononitrile, acetylacetone, ethyl nitroacetate and cyanoacetate in the presence of potassium carbonate (K₂CO₃) in DMF at 100°C to give novel nucleosides 13–7.     

An Assessment of Electronic Properties of Pyrimidine and Purine Nucleosides by 15N-NMR Spectroscopy

Abstract

An ¹⁵N-NMR study at natural abundance of 0⁴/N³-substituted pyrimidine and C⁶-substituted purine ribonucleosides has shown that the exact location of the protecting group (substituent) on either 0⁴ or N³ in pyrimidines has a strong influence on the electronic properties of the resultant pyrimidine system, mainly because of the change of state of hybridization of the N³-nitrogen. The basicity of N³ in some C⁴-substituted pyrimidines has been studied by following the ¹⁵N chemical shifts of protonated species in the presence of CF₃COOH both in DMSO and in CH₂Cl₂ solution. A comparison of the basic character of N³ in C⁴-substituted pyrimidine and of N¹ in C⁶-substituted purine nucleosides has shown that the magnitude of the ¹⁵N shift of N³ (or N¹) upon protonation is governed mainly by the electronic properties of the heteroatom linked to C⁴ (or C⁶). It also clearly emerged in this study that there is very litle difference in basicities of N³ of pyrimidine and N¹ of purine nucleosides despite the presence of the fused imidazole moiety in the latter.     

SYNTHESIS AND ANTIVIRAL ACTIVITY OF NOVEL EXOMETHYLENE CYCLOPROPYL NUCLEOSIDES

Novel cyclopropyl nucleosides were synthesized as potential antiviral agents. The key intermediate 5, prepared from Feist's acid 1 was condensed with purine derivatives by the S_N2 type reaction. All the synthesized compounds were evaluated for antiviral activity.     

Purification, Characterization, and Gene Cloning of Purine Nucleosidase from Ochrobactrum anthropi

A bacterium, Ochrobactrum anthropi, produced a large amount of a nucleosidase when cultivated with purine nucleosides. The nucleosidase was purified to homogeneity. The enzyme has a molecular weight of about 170,000 and consists of four identical subunits. It specifically catalyzes the irreversible N-riboside hydrolysis of purine nucleosides, the K_m values being 11.8 to 56.3 μM. The optimal activity temperature and pH were 50°C and pH 4.5 to 6.5, respectively. Pyrimidine nucleosides, purine and pyrimidine nucleotides, NAD, NADP, and nicotinamide mononucleotide are not hydrolyzed by the enzyme. The purine nucleoside hydrolyzing activity of the enzyme was inhibited (mixed inhibition) by pyrimidine nucleosides, with K_i and K_i′ values of 0.455 to 11.2 μM. Metal ion chelators inhibited activity, and the addition of Zn²⁺ or Co²⁺ restored activity. A 1.5-kb DNA fragment, which contains the open reading frame encoding the nucleosidase, was cloned, sequenced, and expressed in Escherichia coli. The deduced 363-amino-acid sequence including a 22-residue leader peptide is in agreement with the enzyme molecular mass and the amino acid sequences of NH₂-terminal and internal peptides, and the enzyme is homologous to known nucleosidases from protozoan parasites. The amino acid residues forming the catalytic site and involved in binding with metal ions are well conserved in these nucleosidases.     

A specific effect of copper on methylene blue sensitized photodegradation of nucleic acid derivatives

Among several metal ions tested, Cu²⁺ was unique in slowing down methylene blue sensitized photodynamic breakdown of some nucleic acid bases and nucleosides. The t_1/2 values were increased in the case of xanthine and uric acid by Cu²⁺, but without any alteration in the nature or amounts of photoproducts formed. Xanthine was degraded quantitatively to allantoin and urea. The breakdown of the sugar moiety of nucleosides was more drastically retarded than that of the purine ring. The decomposition rate and its magnitude was dependent on the concentration of Cu²⁺ as well as the nucleoside. The most profound increase in t_1/2 values was found with xanthosine—7 min for the purine ring and 65 min for the ribose moiety, at 0.6 mM Cu²⁺ Hg²⁺ in the case of xanthine, and some paramagnetic metal ions in the case of the nucleosides, slowed down the photobreakdown to a small extent; however, differential effects were not observed unlike with Cu²⁺. None of the other metal ions tested significantly influenced the process.     

Some Examples of the Use of Trifluoromethane Sulfonic Anhydride in Nucleic Acid Chemistry

Abstract

Trifluoromethane sulfonic anhydride has been used for the inversion of configuration at the 3′-position of 2′-deoxypurine nucleosides, for the modification of the base moiety of purine and pyrimidine nucleosides, for nucleophilic substitution in the sugar moiety, for the synthesis of O²,3′-cyclothymidine and for sugar-base condensation reactions. Reaction can be carried out under very mild conditions. The conditions for these reactions are quite different so that a good selectivity can be obtained when different reactive groups are present.     

Oligonucleotides Incorporating N7-(2′-Deoxy-β-d-erythro-pentofuranosyl)isoguanine

Abstract

The H-phosphonate and the phosphoramidite of N⁷-2′-deoxyisoguanosine (2) were prepared and incorporated into oligonucleotide duplexes. Their base pairing properties were investigated and compared with those of the parent purine nucleosides.     

Synthesis and Biological Evaluation of Pyrimidine and Purine α-L-2′,3′-Dideoxy Nucleosides

Abstract

A series of α-L-2′,3′-dideoxy nucleosides was prepared as potential antiviral agents. The pyrimidine nucleosides were prepared by standard Vorbrüggen coupling reactions. The purine analogues were prepared by enzymatic transfer of the dideoxy sugar from a pyrimidine to a purine base. These compounds were inactive against HIV-1, HBV, HSV-1 and -2, VZV, and HCMV.     

Synthesis and Biologic Evaluation of 8-Substituted Derivatives of Nebularine (9-β-D-Ribofuranosylpurine)

Abstract

A series of 8-substituted purine ribonucleosides were prepared from 2′, 3′, 5′-tri-O-acetyl-8-bromoadenosine and evaluated for cytotoxicity and antiviral activity. Four of these nucleosides (6b-9b) were significantly toxic to both HEp-2 and L1210 cells in culture but the most cytotoxic one (9b) was inactive against the P388 leukemia in mice. None of these nucleosides showed significant antiviral activity against Herpes Simplex 1 or 2, vaccinia, or influenza A.     

Synthesis of Novel 2′-Fluoro-3′-Hydroxymethyl-5′-Deoxythreosyl Phosphonic Acid Nucleoside Analogues As Antiviral Agents

A series of purine 5′-deoxyphosphonate analogues were designed and synthesized to mimic naturally occurring purine monophosphate from 1,3-dihydroxyacetone as starting material. The discovery of threosyl phosphonate nucleoside (PMDTA, EC₅₀ = 2.53 μM) as a potent anti-HIV agent has led to the synthesis and biological evaluation of 2′,3′-modified 5′-deoxyversions of the threosyl phosphonate nucleosides. The synthesized 2′-fluoro-3′-hydroxymethyl 5′-deoxythreosyl phosphonic acid nucleoside analogues 14, 18, 23, and 27 were tested for anti-HIV activity as well as cytotoxicity. The adenine analogue 18 exhibits weak in vitro anti-HIV-1 activity (EC₅₀ = 19.2 μM).     

Deaza- and Deoxyadenosine Derivatives: Synthesis and Inhibition of Animal Viruses as Human Infection Models

Abstract

N⁶-Cycloalkyl-2′,3′-dideoxyadenosine derivatives and (2-chloro)-N⁶-cycloheptyl-3-deazaadenosine have been synthesized and tested, along with other (deaza)purine (deoxy)nucleosides from our chemical library, as inhibitors of virus replication against Bovine Herpes Virus 1 (BHV-1) and sheep Maedi/Visna Virus (MVV). Most compounds demonstrated good antireplicative activity against MVV, showing also low cell toxicity.     

Cloning and pharmacological characterization of a novel gene encoding human nucleoside transporter 1 (hNT1) from a human breast cancer cDNA library

AimsWe isolated a novel gene encoding human nucleoside transporter 1 (hNT1), from a human breast cancer cDNA library.Main methodsA nondirectional cDNA library was screened by an EST clone (GenBank?/EMBL/DDBJ: BU944345). A Xenopus laevis oocyte expression system was used for functional characterization. Membrane localization in the human breast was determined by immunohistochemistry.Key findingsIsolated hNT1 cDNA consisted of 246 base pairs that encoded an 82-amino acid protein. By RT-PCR analysis, hNT1 mRNA was strongly detected in the breast cancer tissues. When expressed in X. oocytes, hNT1 mediated the high affinity transport of [³H]5-fluorouracil (5-FU) with a K_m value of 69.2 ± 24.5 nM in time- and pH-dependent, and Na⁺-independent manners. A cis-inhibition experiment revealed that hNT1 mediated transport of [³H]5-FU is strongly inhibited by various nucleosides such as pyrimidine, uracil, uridine, guanosine, inosine, thymidine, adenosine, cytidine and purine suggesting that hNT1 may be involved in the trans epithelial transport of these endogenous substrates. Immunohistochemical analysis revealed that the hNT1 protein is localized in the lactiferous duct epithelium.SignificanceOur present results indicate that a newly isolated cDNA clone, hNT1, is a key molecule for the breast handling of 5-FU in humans.     

Conformational Analysis of 3′-Deoxyribonucleosides using 1D-Noe Difference Spectroscopy

Abstract

The results of PMR studies on 3′Deoxyribo nucleosides (1a-d) reveals that the sugar puckering is predominantly in N state with g⁺ conformation of the 5′-CH₂OH group. Except in 1a, nucleobases in other nucleosides favour anti conformation.     

Stabilities and 1H NMR studies of (diethylenetriamine)Pd(II) and (1,1,4,7,7-pentamethyldien)Pd(II) with nucleosides and related ligands

Plots of stability constant logarithms versus pK_a for dienPd²⁺ binding to a variety of nitrogen heterocycles yield straight lines, all of 0.67 slope. Points for binding at pyridine like purine N1 and pyrimidine N3 nitrogens in nucleosides and 5′-mononucleotides fall on a single straight line. The base line for binding at imidazole like purine N7 nitrogens is 0.8 log units stronger than for N1 binding. N7 binding to purine bases with a 6-oxo group is enhanced by 1.6 log units above the N7 base line. The presence of a 5′-phosphate group enhances N7 binding (but not N1 binding) by 0.5–0.7 log units. Weaker binding occurs with pmdienPd²⁺ and the straight line slopes are 0.79. The N7 base line rises 1.2 log units above the N1 line. Presence of the 6-oxo group enhances pmdien binding by 2.3 units ruling out a significant coordinated dien hydrogen bond to the 6-oxo group. There is no enhancement of pmdienPd²⁺ binding to N7 due to the 5′-phosphate of nucleotides. This result suggests that the 0.5–0.7 log unit enhancement for dienPd²⁺ is due to a hydrogen bond from coordinated dien to the phosphate. Due to the terminal methyl groups, rotation of pyrimidines, benzimidazole, and purines is restricted in pmdienPd²⁺ complexes and two rotamers are evident in proton magnetic resonance spectra. With benzimidazole and purine nucleosides and 5′-nucleotides there is an approximately 2:1 mole ratio of the two rotamers. Nuclear Overhauser effect experiments and chemical shift analysis permit identification of all peaks for pmdien methyl groups and aromatic ring protons.     

Synthesis and Antiviral Activities of Enantiomeric 1-[2-(Hydroxymethyl) Cyclopropyl] Methyl Nucleosides

Abstract

Cyclopropyl carbocyclic nucleosides have been synthesized from the key intermediate 2 which was converted to the mesylated cyclopropyl methyl alcohol 3. Condensation of compound 3 with various purine and pyrimidine bases gave the desired nucleosides. All synthesized nucleosides were evaluated for antiviral activity and cellular toxicity. Among them adenine 22 and guanine 23 derivatives showed moderate antiviral activity against HIV-1 and HBV. None of the other compounds showed any significant antiviral activities against HIV-1, HBV, HSV-1 and HSV-2 in vitro up to 100μM.     

Synthesis and Biological Activity of Certain 4-Substituted Imidazo[4,5-d]Pyridazine Nucleosides

Abstract

Purine analogues and derivatives exhibit a broad range of pharmacological activities and are used in the chemotherapy of cancer, parasitic and viral infections, and for the suppression of immune responses. Undoubtedly, this wide range of biological activities reflect an equally wide number of biochemical sites of action, one of which is the purine de novo pathway. New agents which can either serve as inhibitors of enzymes involved in this pathway or as substrates are continually sought. The unique series of nucleosides described herein should meet these desired needs.

The synthesis of 1involved glycosylation of a suitably 4,5-disubstituted imidazole and subsequent cyclization of the imidazole nucleoside so formed to the imidazo[4,5-d]pyridazine nucleoside. Such methodology was successfully employed^1,2 in the preparation of certain 4,7-disubstituted imidazo[4,5-d]pyridazine nucleosides. Chlorination of 1furnished 4-chloro-1-(2,3,5-tri-O-acetyl-β-D-ribo-furanosyl)imidazo[4,5-dlpyridazine (2) in 80% yield. This versatile intermediate can now serve as a precursor to a variety of 4-substituted imidazo[4,5-d]pyridazine nucleosides.