Formation of l-Butyl-5-hydroxy-methylpyrrole-2-carboxaldehyde in the Maillard Reaction between Lactose and n-Butylamine

A new mutant Shm^r-001-1 has been isolated by treating showdomycin-resistant mutant Shm^r-001 cells with N-methyl-N′-nitro-N-nitrosoguanidine. This mutant was resistant to high level of showdomycin, and took up practically no showdomycin and little pyrimidine nucleosides, and it showed different ability to take up purine nucleosides. Strains Shm^r-001–1, Shm^r-001, and K–12 (wild type) were compared: in susceptibility to showdomycin, in ability to take up the antibiotic and various nucleosides, on effects of other nucleosides on entry of particular nucleosides, and on kinetics of the entry of nucleosides and showdomycin. From these experiments, at least three different nucleoside transport systems were observed in Escherichia coli K–12 cells: the first system was common to adenine nucleosides, pyrimidine nucleosides, and showdomycin; the second system was common to adenine nucleosides, guanine nucleosides, inosine, pyrimidine nucleosides, and showdomycin; and the third system was common to adenine nucleosides, guanine nucleosides, and inosine. The first system was not observable in Shm^r-001 cells. In Shm^r-001–1 cells both the first and the second systems were no longer detectable but the third system was found to be active.     

Deoxynucleoside composition of DNAs and modified nucleoside composition of tRNAs determined at nanomole sensitivity by reversed-phase liquid chromatography

Selected purified tRNA and DNA samples were digested by standard enzymatic methods, and the nucleosides were separated by high-pressure liquid chromatography on reversedphase columns. Nanomole sensitivity was obtained by use of an integrator. The nucleosides were detected at wavelengths near their uv-absorption maxima, including 220 nm for dihydrouridine, and 330 nm for 4-thiouridine. Recovery values for the individual nucleosides were in the range of 94–100%. The nucleoside composition of the DNA and tRNA digests were in accurate and precise agreement with published values.     

Labeling of nucleosides with fluorescamine and detection by spectrofluorometer for End Stage Renal Disease

Nucleosides are characterized as biomarkers in AIDS, Alzheimer, tumor, breast cancer and various malignant diseases. In the present work a direct method for the detection of nucleosides (adenosine, cytidine, uridine and guanosine) from urine samples has been developed. Nucleosides represent the extent of damage in genetic material, analysis of nucleosides by ultrasonic assisted microextraction effectively eliminates the interfering constituent of urine. This has made it a highly selective and sensitive method to analyze the nucleosides with a lower limit of detection 0.220 μmol/L and Limit of quantitation 0.660 μmol/L. The method has been validated with good linearity and correlation of coefficients of the calibration curves was higher than 0.997. The coefficients were in the range of 0.11–16.92% (inter-day) and 0.38–16.43% (intra-day), respectively.     

Utilization Of Tetrabutylammonium Triphenyldifluorosilicate (TBAT) In The Synthesis of 6-Fluoropurine Nucleosides

Abstract

Tetrabutylammonium triphenydifluorosilicate (TBAT) has been found to be a useful reagent for the conversion of 6-chloropurine nucleosides to 6-fluoropurine derivatives. The 6-chloropurine nucleosides were reacted with trimethylamine to form quaternary trimethylammonium salts which were treated in situ with TBAT in DMF to effect conversion to the 6-fluoro derivatives in yields of 59–72%.     

Synthesis and Biological Evaluation of 3-Chloro-4-(D-Ribofuranosyl)-Pyridine and 3-(D-Ribofuranosyl)-2- Pyridone

Abstract

Condensation of 2-fluoro-3-lithio pyridine and 3-chloro-4-lithio pyridine with 2,4:3,5-di-O-benzylidene-alde-hydo-D-ribose gives the corresponding D-allo- and D-altro-addition products. These were converted into the corresponding mesylates and cyclized to the ribofuranosyl nucleosides with an overall yield of 60–70 %. Both nucleosides did not show any inhibitory effect on L-₁₂₁₀-cells.     

2′-Modified Guanosine Analogs for the Treatment of HCV

Novel 2′-modified guanosine nucleosides were synthesized from inexpensive starting materials in 7–10 steps via hydroazidation or hydrocyanation reactions of the corresponding 2′-olefin. The antiviral effectiveness of the guanosine nucleosides was evaluated by converting them to the corresponding 5′-O-triphosphates (compounds 38–44) and testing their biochemical inhibitory activity against the wild-type NS5B polymerase.     

Simultaneous Determination of Purine and Pyrimidine Metabolites in Hprt-Deficient Cell Lines

Genetic mutations in the purine salvage enzyme, hypoxanthine-guanine phosphoribosyltransferase (HPRT), are known to cause Lesch–Nyhan syndrome and Kelley–Seegmiller syndrome. In patients, purine metabolism is different from that of normal persons. We have previously developed a method for simultaneously determining the concentration of purine and pyrimidine nucleosides and nucleotides. This system was applied to determine the concentrations of nucleosides and nucleotides in HPRT-deficient cell lines. The amount of inosine 5′-monophosphate (IMP) was different in Lesch–Nyhan syndrome, Kelley–Seegmiller syndrome, and control cell lines. The difference in the amount of IMP confirmed the mutation of the enzyme.     

Enzymatic acylation of nucleosides—Novel route to nucleopeptides

An efficient and straightforward proteolytic enzyme-catalyzed approach towards the regioselective synthesis of nucleopeptides was developed. Appropriate reaction conditions were investigated and certain peptide-modified nucleosides were obtained with 70–90% yields. The obtained compounds could be efficiently used for medicinal diagnostic kits and therapeutic treatment.     

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.     

Urinary Nucleosides as Biomarkers of Breast,Colon, Lung,and Gastric Cancer in Taiwanese

Urinary nucleosides are associated with many types of cancer. In this study, six targeted urinary nucleosides, namely adenosine, cytidine, 3-methylcytidine, 1-methyladenosine, inosine, and 2-deoxyguanosine, were chosen to evaluate their role as biomarkers of four different types of cancer: lung cancer, gastric cancer, colon cancer, and breast cancer. Urine samples were purified using solid-phase extraction (SPE) and then analyzed using high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). The Mann-Whitney U test and Principal Component Analysis (PCA) were used to compare differences in urinary nucleosides between patients with one of four types of cancer and healthy controls. The diagnostic sensitivity of single nucleosides for different types of cancer ranged from 14% to 69%. In contrast, the diagnostic sensitivity of a set of six nucleosides ranged from 37% to 69%. The false-positive identification rate associated with the set of six nucleosides in urine was less than 2% compared with that of less than 5% for a single nucleoside. Furthermore, combining the set of six urinary nucleosides with carcinoembryonic antigen improved the diagnostic sensitivity for colon cancer. In summary, the study show that a set of six targeted nucleosides is a good diagnostic marker for breast and colon cancers but not for lung and gastric cancers.     

Design and Synthesis of 2′-Deoxy-2′-[(1,2,3)Triazol-1-Yl]Uridines Using Click Chemistry Approach

A series of novel nucleosides bearing a 1,2,3-triazole moiety at the 2′-position of the sugar moiety has been synthesized starting from 2′-azidouridine and using the copper (I)-catalyzed Huisgen–Sharpless–Meldal 1,3-dipolar cycloaddition reaction. The reactions proceeded in overall yield of 52–82% and gave almost exclusively the 1,4-disubstituted 1,2,3-triazoles. The 2′-azidouridine was synthesized from uridine in two steps, and reacted with a variety of differently substituted alkynes to give the desired 2′-triazole-substituted uridine derivatives.     

Asymmetric Synthesis of Cyclopropyl Carbocyclic Nucleosides

Abstract

A number of nucleosides have been synthesized as potential antiviral and antitumor agents.¹ More recently, various dideoxynucleosides have been synthesized and found to be potent anti-HIV agents.² As a part of our drug discovery program for the treatment of HIV and HBV, we have initiated to synthesize cyclopropyl carbocyclic nucleosides as potential antiviral agents. Several papers regarding the synthesis of cyclopropyl carbocyclic nucleosides have appeared in the literature.^3–5 However, they are all reported as racemic mixtures. In this abstract, we wish to report the asymmetric synthesis of cylopropyl carbocyclic nucleosides from optically active common intermediates, 6 and 11.     

Preparation of Nucleoside H-Phosphonoselenoate Monoesters Via the Phosphinate Approach

An efficient entry to nucleoside 3′-H-phosphonoselenoate monoesters via phosphinate intermediates was developed. It involves a reaction of suitably protected nucleosides with triethylammonium phosphinate in the presence of pivaloyl chloride, followed by selenization of the intermediate nucleoside phosphinates with triphenylphosphine selenide, to produce the corresponding nucleoside H-phosphonoselenoates in 86–92% yields.     

Induction of phosphoribomutase in Bacillus cereus growing on nucleosides

In this paper we show that phosphoribomutase is induced in Bacillus cereus by the same metabolizable purine and pyrimidine ribonucleosides previously shown to induce the purine nucleoside phosphorylase (Tozzi, M.G., Sgarrella, F. and Ipata, P.L. (1981) Biochim. Biophys. Acta 678, 460–466). The mutase allows ribose 1-phosphate formed from nucleosides to be utilized by the cell through the pentose cycle, upon transformation to ribose 5-phosphate. The equilibrium constant of the mutase reaction is towards ribose-5-phosphate formation. The coordinate induction of the two enzymes completes the picture of the molecular events leading to the utilization of the sugar moiety of purine nucleosides and nucleosides as an energy source (Mura, U., Sgarrella, F. and Ipata, P.L. (1978) J. Biol. Chem. 253, 7905–7909).     

A 31P NMR Study of the Reaction of Adenosine 3′ 5′-Cyclic Monophosphate with 2, 4, 6-Triisopropylbenzenesulfonyl Chloride

Abstract

Detection limits for the minor component in binary mixtures of Ado/AraA, Ado/XyloA, and Urd/dUrd depend strongly on the combined concentration of analytes. Limiting concentrations (in which ≤1% of the minor component was detected) were about two orders of magnitude lower with HPLC (UV detection) than with ¹H NMR and TLC (UV detection) with these nucleosides (ε_max 10 000–15 000). Minimum molar percentages of minor components detected in the 0.1–10 mM range were 0.25–1% with HPLC (UV), 1–2% with ¹H NMR, and ～2% with TLC (UV).     

Nucleosides,XLVIII. Syntheses and Properties of Quinazoline N-1-Ribofuranosides

Abstract

Several 6- and 7-substituted quinazoline-2, 4-(1H, 3H)-diones (1–7) have been ribosylated with 1-0-acetyl-–2, 3, 5-tri-0-benzoyl-β-D-ribofuranose (8)via the “silyl”-method and Lewis acid catalysis in a highly regioselective manner to give the corresponding protected N-1 ribosides 9–15. Debenzoylation to the free nucleosides 16–22 was achieved by sodium methoxide. Thiation of 9–15 by Lawesson's reagent effected the conversion of the 4-oxo into the 4-thioxo function (23–29). Removal of the sugar protecting groups in these derivatives worked best with potassium carbonate in anhydrous MeOH to form in high yields 30–35. Treatment of the peracylated 4-thioxo quinazoline nucleosides with methanolic ammonia resulted in deacylation of the sugar moiety and in displacement of the sulfur function to give the corresponding 4-amino-1-β-D-ribofuranosylquinazolin-2(1H)-ones 36–41. The newly synthesized, nucleosides have been characterized by elemental analysis, UV- and ¹H-NMR-spectra.     

A Versatile Synthesis of Dihydropyrimidinone C‐Nucleosides

A versatile synthesis of N‐substituted dihydropyrimidinone C‐nucleosides (20–29) is described. Glycosyl amino esters (3–9), obtained by reductive alkylation of glycosyl amino esters 1 and 2, on condensation with different isocyanates afforded respective ureido derivatives (10–19) in good to quantitative yields. The latter on cyclative amidation with a combination of DBU/TBAB (tetrabutylammonium bromide)/4Å molecular sieve gave the corresponding nucleosides (20–29) in good yields.     

Enzymatic transglycosylation of natural and modified nucleosides by immobilized thermostable nucleoside phosphorylases from Geobacillus stearothermophilus

Natural and modified purine nucleosides have been synthesized using the recombinant thermostable enzymes purine nucleoside phosphorylase II (E. C. 2.4.2.1) and pyrimidine nucleoside phosphorylase (E. C. 2.4.2.2) from Geobacillus stearothermophilus B-2194. The enzymes were produced in recombinant E. coli strains and covalently immobilized on aminopropylsilochrom AP-CPG-170 after heating the cell lysates and the removal of coagulated thermolabile proteins. The resulting preparations of thermostable nucleoside phosphorylases retained a high activity after 20 reuses in nucleoside transglycosylation reactions at 70–75°C with a yield of the target products as high as 96%. Owing to the high catalytic activity, thermal stability, the ease of application, and the possibility of repeated use, the immobilized preparations of thermostable nucleoside phosphorylases are suitable for the production of pharmacologically important natural and modified nucleosides.     

SYNTHESIS OF SOME 2′-FLUORO-2′-DEOXY-3′-C-ETHYNYL AND 3′-C-VINYL-β-D-LYXOFURANOSYL NUCLEOSIDES

1-(2-Fluoro-2-deoxy-β-D-arabinofuranosyl)uracil (5) and 1-(2-fluoro-2-deoxy-β-D-arabinofuranosyl)cytosine (6) were synthesized as reported earlier. Both of these compounds were converted into 2′-fluoro-2′-deoxy-3′-C-ethynyl and 3′-C-vinyl-β-D-lyxofuranosyl nucleosides (16–19) by a multistep sequence. All these new nucleosides were evaluated against seven human tumor cell lines in vitro.     

Synthesis of novel purine nucleosides towards a selective inhibition of human butyrylcholinesterase

The search for new and potent cholinesterase inhibitors is an ongoing quest mobilizing many organic chemistry groups around the world as these molecules have been shown to treat the late symptoms of Alzheimer’s disease as well as to act as neuroprotecting agents. In this work, we disclose the synthesis of novel 2-acetamidopurine nucleosides and, for the first time, regioselective N⁷-glycosylation with 2-acetamido-6-chloropurine, promoted by trimethylsilyl triflate, was accomplished by tuning the reaction conditions (acetonitrile as solvent, 65 °C, 5 h) starting from 1-acetoxy bicyclic glycosyl donors, or by direct coupling of a methyl glucopyranoside with the nucleobase to obtain only N⁷ nucleosides in reasonable yield (55–60%). The nucleosides as well as their sugar precursors were screened for acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) inhibition. While none of the compounds tested inhibited AChE, remarkably, some of the N⁷ nucleosides and sugar bicyclic derivatives showed potent inhibition towards BChE. Nanomolar inhibition was obtained for one compound competing well with rivastigmine, a drug currently in use for the treatment of Alzheimer’s disease. Experimental results showed that the presence of benzyl groups on the carbohydrate scaffold and the N⁷-linked purine nucleobase were necessary for strong BChE inactivation. A preliminary evaluation of the acute cytotoxicity of the elongated bicyclic sugar precursors and nucleosides was performed indicating low values, in the same order of magnitude as those of rivastigmine.