Shaping the future of antiviral Treatment: Spotlight on Nucleobase-Containing drugs and their revolutionary impact

Nucleobases serve as essential molecular frameworks present in both natural and synthetic compounds that exhibit notable antiviral activity. Through molecular modifications, novel nucleobase-containing drugs (NCDs) have been developed, exhibiting enhanced antiviral activity against a wide range of viruses, including the recently emerged SARS‑CoV‑2. This article provides a detailed examination of the significant advancements in NCDs from 2015 till current, encompassing various aspects concerning their mechanisms of action, pharmacology and antiviral properties. Additionally, the article discusses antiviral prodrugs relevant to the scope of this review. It fills in the knowledge gap by examining the structure-activity relationship and trend of NCDs as therapeutics against a diverse range of viral diseases, either as approved drugs, clinical candidates or as early-stage development prospects. Moreover, the article highlights on the status of this field of study and addresses the prevailing limitations encountered.

BODIPY-fused uracil: synthesis, photophysical properties, and applications

Fluorescent nucleobase and nucleic acid analogs are important tools in chemical and molecular biology as fluorescent labelling of nucleobases has applications in cellular imaging and anti-tumor activity. Boron-dipyrromethene (BODIPY) dyes exhibiting high brightness and good photostability are extensively used as fluorescent labelling agents and as type II photosensitizers for photodynamic therapy. Thus, the combination of nucleobases and BODIPY to obtain new compounds with both anti-tumor activity and fluorescent imaging functions is the focus of our research. We synthesized two new nucleobase analogs 1 and 2 by fusing the BODIPY core directly with uracil which resulted in favorable photophysical properties and high emission quantum efficiencies particularly in organic solvents. Further, we explored the newly synthesized derivatives, which possessed good singlet oxygen generation efficiencies and bio-compatibility, as potential PDT agents and our results show that they exhibit in vitro anti-tumor activities.

Selective recovery of Re(VII) by nucleobases functionalized cellulose microspheres from the simulated uranium ore leaching solution

From a practical standpoint, it is still challenging to develop adsorbents with high adsorption capacity and outstanding selectivity for rhenium in uranium ore leaching solution. In this study, in order to explore the structure-property relationship, four nucleobases (Adenine, Guanine, Hypoxanthine and Xanthine) were used as functionalization reagents to modify cellulose (MCC-g-GMA-A, MCC-g-GMA-G, MCC-g-GMA-H and MCC-g-GMA-X) via radiation method. The effect of the type of nucleobases on the adsorption performance was evaluated by batch and dynamic experiments. The order of maximum adsorption capacity was MCC-g-GMA-A (194.0 mg g-1) > MCC-g-GMA-G (123.4 mg g-1) > MCC-g-GMA-H (45.59 mg g-1) > MCC-g-GMA-X (23.43 mg g-1), which was associated with the category of nitrogen-functional groups. Different nitrogen-containing functional groups have different degrees of protonation, which leads to differences in the interaction of the adsorbent with Re(VII). Notably, the adsorbents were able to selectively capture trace Re(VII) from the simulated uranium ore leaching solution. The FT-IR, XPS analyses, DFT theoretical calculations exhibited that the adsorption mechanism of nucleobases functionalized cellulose microspheres and Re(VII) was electrostatic interaction. MCC-g-GMA-A and MCC-g-GMA-G exhibited excellent selectivity towards Re(VII), which are potential adsorbents for Re(VII) recovery in uranium ore leaching solutions.

Reactive oxygen species-responsive thymine-conjugated chitosan: Synthesis and evaluation as cryogel

Chitosan (CS) is a biodegradable, biocompatible cationic polysaccharide based natural polymer with antibacterial and anti-inflammatory properties. Hydrogels made from CS have been found their applications in wound healing, tissue regeneration and drug delivery. Although, mucoadhesive properties resulted from the polycationic nature of CS, in hydrogel form amines are engaged in interactions with water leading to decrease in mucoadhesive properties. In case of injury, presence of elevated level of reactive oxygen species (ROS) has inspired many drug delivery platform to conjugate ROS responsive linkers for on demand drug delivery. In this report we have conjugated a reactive oxygen species (ROS) responsive thioketal (TK) linker and nucleobase thymine (Thy) with CS. Cryogel from this doubly functionalized polymer CS-Thy-TK was prepared through crosslinking with sodium alginate. Inosine was loaded on the scaffold and studied for its release under oxidative condition. We anticipated that the presence of thymine shall retain the mucoadhesive nature of the CS-Thy-TK polymer in hydrogel form and when placed at the site of injury, due to the presence of excessive ROS at inflammatory condition, loaded drug shall release due to degradation of the linker. Porous cryogel scaffold was prepared via chemical crosslinking of amine functional group of chitosan with carboxylic acid containing polysaccharide sodium alginate. The cryogel was evaluated for porosity (FE-SEM), rheology, swelling, degradation, mucoadhesive properties and biocompatibility. Resulted scaffold was found to be porous with average pore size of 107 ± 23 μm, biocompatible, hemocompatible and possesses improved mucoadhesive property (mucin binding efficiency of 19.54 %) which was found to be 4 times better as compared to chitosan (4.53 %). The cumulative drug release found to be better in the presence of H₂O₂ (~90 %) when compared to that of PBS alone (~60-70 %)_. Therefore, the modified CS-Thy-TK polymer may hold potential as interesting scaffold in case of conditions associated with elevated ROS level such as injury and tumor.

Application of thymine-based nucleobase-modified acrylamide as a functional co-monomer in electropolymerised thin-film molecularly imprinted polymer (MIP) for selective protein (haemoglobin) binding

Molecularly imprinted polymers (MIPs) are fast becoming alternatives to biological recognition materials, offering robustness and the ability to work in extreme environments. Here, a modified thymine-based nucleobase, with acrylamide at the 5-postion (AA-dT) was used as a co-monomer in the synthesis of a thin-film electropolymerised MIP system for the molecular recognition of the protein haemoglobin. The AA-dT co-monomer incorporated into a N-hydroxymethylacrylamide (NHMAm) MIP offered a two-fold superior binding affinity of the NHMAm only MIP, with K_D values of 0.72 μM and 1.67 μM, respectively. A unique AA-dT:NHMAm MIP bilayer was created in an attempt to increase the amount AA-dT incorporated into the film, and this obtained a respectable K_D value of 7.03 μM. All MIPs produced excellent selectivity for the target protein and when applied to a sensor platform (Surface Plasma Resonance), the limit of detection for the MIPs is in the nM range (3.87, 3.47, and 3.87 nM, for the NHMAm MIP, AA-dT:NHMAm MIP, and AA-dT:NHMAm MIP bilayer, respectively). The introduction of the modified thymine-based nucleobase offers a promising strategy for improving the properties of a MIP, allowing these MIPs to potentially be a highly robust and selective material for molecular recognition.

On the origin of the genetic code: a 27-codon hypothetical precursor of an intricate 64-codon intermediate shaped the modern code

The modern genetic code reveals numerous traces of specific relationships between the early codons which, together with its internal asymmetries, suggest a sequential appearance of the nucleobases in primitive RNA molecules. Keeping the hypothesis of triplet pairings between primitive RNA molecules at the origin of the code, this work systematically examines complete codon-anticodon interaction matrices assuming distinct pairing options at each position of the triplet duplexes. Application of these principles suggests that a 27-codon precursor having a reasonable coding capacity for short peptide synthesis could have started with primitive RNA molecules able to form two distinct pairs with different free energies between a single purine and two pyrimidines (such as G with C and U). Conservation of the same pairing options at positions 1 and 2 of codons at the arrival of a second purine with distinct pairing preferences (such as A) generated a 64-codon intermediate code made of interrelated pairs or groups of codons (designated here as intricacy). The numerous traces of this hypothetical scheme that are visible in the standard and variant forms of the modern code demonstrate without ambiguity that the ancestral codon-anticodon duplexes required high energetic pairings at their central position (Watson-Crick) but tolerated less energetic pairings at the first codon position (G • U type). Combined with the sequential appearance of the nucleobases, the predicted codon intricacy allows a stepwise reconstruction of the evolution of the coding repertoire, by simple a posteriori comparison to the modern code. This reconstruction reveals a remarkable internal coherence in terms of amino acids and tRNA synthetases recruitment. The code started with a group of amino acids (Ala, Gly, Pro, Ser and Thr) that are now all activated by class II tRNA synthetases before reaching an intermediate period during which up to 14 distinct amino acids could be encoded by a full set of intricated codons. The perfect coincidence between the last 6 amino acids predicted in this reconstruction and the speculated action of the arrival of free atmospheric oxygen on proteins is spectacular, and suggests that the code has only reached its present form after the great oxidation event.

From Nucleic Acids to Drug Discovery: Nucleobases as Emerging Templates for Drug Candidates

Nucleobases represent key structural motif in biologically active molecules including synthetic and natural products. Molecular modifications made on nucleobases or their isolation from natural sources are being widely investigated for the development of drugs with improved potency for the treatment of different diseases, such as cancer, as well as viral and bacterial infections. This review article focuses on the nucleobase analogue drug developments of the past 20 years (2000-2020). Various pharmacological and medicinal aspects of nucleobases and their analogues are discussed. The current state and limitations are also highlighted.

Context-dependent Cryptic Roles of Specific Residues in Substrate Selectivity of the UapA Purine Transporter

Members of the ubiquitous Nucleobase Ascorbate Transporter (NAT) family are H⁺ or Na⁺ symporters specific for the cellular uptake of either purines and pyrimidines or L-ascorbic acid. Despite the fact that several bacterial and fungal members have been extensively characterised at a genetic, biochemical or cellular level, and crystal structures of NAT members from Escherichia coli and Aspergillus nidulans have been determined pointing to a mechanism of transport, we have little insight on how substrate selectivity is determined. Here, we present systematic mutational analyses, rational combination of mutations, and novel genetic screens that reveal cryptic context-dependent roles of partially conserved residues in the so-called NAT signature motif in determining the specificity of the UapA transporter of A. nidulans. We show that specific NAT signature motif substitutions, alone and in combinations with each other or with distant mutations in residues known to affect substrate selectivity, lead to novel UapA versions possessing variable transport capacities and specificities for nucleobases. In particular, we show that a UapA version including the quadruple mutation T405S/F406Y/A407S/Q408E in the NAT signature motif (UapA-SYSE) becomes incapable of purine transport, but gains a novel pyrimidine-related profile, which can be further altered to a more promiscuous purine/pyrimidine profile when combined with replacements at distantly located residues, especially at F528. Our results reveal that UapA specificity is genetically highly modifiable and allow us to speculate on how the elevator-type mechanism of transport might account for this flexibility.

A DFT study on the adsorption of nucleobases with Au20

The interactions of nucleobase with Au₂₀ cluster were studied utilizing density functional theory (DFT). We find that the nucleobases were attached with Au₂₀ through Au-N or Au-O bonds. The orders of calculated adsorption energy are cytosine > adenine > guanine > thymine. The maximum adsorption energy is - 0.787 eV which belongs to the adsorption of cytosine on Au₂₀ cluster. Our calculations show that the HOMO-LUMO gaps of Au₂₀ are significantly decreased by the nucleobase adsorption, suggesting the potential detection for nucleobases. The interactions between Au₂₀ and nucleobases are revealed through the QTAIM analysis. The NBO analysis was investigated for the electron transfer of donor-acceptor of all types of complexes. The IR and UV-vis spectra were simulated for the further identification in the experiment.

Adsorption studies of nucleobases on ε-arsenene nanosheet based on first-principles research

The electronic attributes and energetics of ε-arsenene nanosheet (ε-As) are explored with regard to the density functional theory basis. Initially, based on formation energy (-3.715 eV/atom), we ensured the structural firmness of ε-As. The ε-As is used as a base substrate to adsorb nucleobases viz., adenine (A), guanine (G), thymine (T), cytosine (C) & uracil (U). The surface adsorption of nucleobases on ε-As is analysed based on band structure, the density of states, adsorption energy, energy gap variation & charge transfer. Besides, we observed the exothermic nature of binding energy (ranging from -0.453 eV to -0.819 eV) upon nucleobase adsorption on ε-As. Also, the energy gap variation & charge transfer takes place owing to adsorption of nucleobases on the ε-As sheet. The present report reveals the adsorption of nucleobases on ε-arsenene nanosheet.

Mechanical characterization of bio composite films as a novel drug carrier platform for sustained release of 5-fluorouracil for colon cancer: Methodological investigation

In this study, we employed Pectin (PC) as a matrix that is hybridized with three different nucleobase (NB) units (cytosine, thymine, uracil) to generate pectin-nucleobase(PC-NB) biocomposite films stabilized through bio-multiple hydrogen bonds (BMHBs) as drug carrier for anticancer 5-Fluorouracil (5-FU). Prepared biocomposite films were characterized by Fourier Transform Infra-red Spectroscopy (FTIR), X-ray Diffraction (XRD), Thermogravimmetry Analysis (TGA) and Scanning Electron Microscope (SEM). Mechanical and sorption properties were also evaluated. In vitro drug release performed in both acidic pH 1.2 (stomach pH) and alkaline pH 7.4 (intestinal pH) showed that incorporation of nucleobases into pectin significantly restricted release rate of 5-FU particularly under acidic condition (pH 1.2). Hemolysis assays demonstrated that PC-NB-5-FU biocomposite film drug carriers were hemocompatible. Confocal microscope analysis indicates facilitated cellular uptake of PC-NB-5-FU film in HT-29 colon cancer cell line, which in turn result in a higher potential of apoptosis. Confocal imaging of fluorescent live/dead cell indicators and MTT assay outcomes, both demonstrated significant decreases in cellular viability of PC-NB-5-FU biocomposite films. Collectively, our findings indicate that this PC-NB-5-FU biocomposite films can be conferred as a proficient formulation for targeted delivery of colon cancer drugs.

New metal-free route towards imidazole substituted uridine

Nucleosides with a bi(hetero)aryl nucleobase have unique potential applications as antiviral drugs and molecular probes. The need for transition metal catalysis to synthetize these nucleosides from pre-functionalized building blocks and the use of nucleobase protection groups results in expensive and tedious syntheses. Herein we report that 5-imidazolyl-uracil can be obtained by scalable Van Leusen imidazole synthesis and regioselectively introduced on ribose to obtain the desired nucleoside in a 5 step synthesis (total yield 55%). The 5-imidazolyl moiety leads to improved fluorescence properties. The only side-product formed was characterized by 2D-NMR and X-ray crystallography and could be suppressed during synthesis in favor of the desired product.

Structural and Energetic Effects of O2'-Ribose Methylation of Protonated Pyrimidine Nucleosides

The 2'-substituents distinguish DNA from RNA nucleosides. 2'-O-methylation occurs naturally in RNA and plays important roles in biological processes. Such 2'-modifications may alter the hydrogen-bonding interactions of the nucleoside and thus may affect the conformations of the nucleoside in an RNA chain. Structures of the protonated 2'-O-methylated pyrimidine nucleosides were examined by infrared multiple photon dissociation (IRMPD) action spectroscopy, assisted by electronic structure calculations. The glycosidic bond stabilities of the protonated 2'-O-methylated pyrimidine nucleosides, [Nuom+H]⁺, were also examined and compared to their DNA and RNA nucleoside analogues via energy-resolved collision-induced dissociation (ER-CID). The preferred sites of protonation of the 2'-O-methylated pyrimidine nucleosides parallel their canonical DNA and RNA nucleoside analogues, [dNuo+H]⁺ and [Nuo+H]⁺, yet their nucleobase orientation and sugar puckering differ. The glycosidic bond stabilities of the protonated pyrimidine nucleosides follow the order: [dNuo+H]⁺ < [Nuo+H]⁺ < [Nuom+H]⁺. The slightly altered structures help explain the stabilization induced by 2'-O-methylation of the pyrimidine nucleosides.

Impact of Sodium Cationization on Gas-Phase Conformations of DNA and RNA Cytidine Mononucleotides

Gas-phase conformations of the sodium-cationized forms of the 2'-deoxycytidine and cytidine mononucleotides, [pdCyd+Na]⁺ and [pCyd+Na]⁺, are examined by infrared multiple photon dissociation action spectroscopy. Complimentary electronic structure calculations at the B3LYP/6-311+G(2d,2p)//B3LYP/6-311+G(d,p) level of theory provide candidate conformations and their respective predicted IR spectra for comparison across the IR fingerprint and hydrogen-stretching regions. Comparisons of the predicted IR spectra and the measured infrared multiple photon dissociation action spectra provide insight into the impact of sodium cationization on intrinsic mononucleotide structure. Further, comparison of present results with those reported for the sodium-cationized cytidine nucleoside analogues elucidates the impact of the phosphate moiety on gas-phase structure. Across the neutral, protonated, and sodium-cationized cytidine mononucleotides, a preference for stabilization of the phosphate moiety and nucleobase orientation is observed, although the details of this stabilization differ with the state of cationization. Several low-energy conformations of [pdCyd+Na]⁺ and [pCyd+Na]⁺ involving several different orientations of the phosphate moiety and sugar puckering modes are observed experimentally.

Prebiotic Chemistry of Pluto

We present the case for the presence of complex organic molecules, such as amino acids and nucleobases, formed by abiotic processes on the surface and in near-subsurface regions of Pluto. Pluto's surface is tinted with a range of non-ice substances with colors ranging from light yellow to red to dark brown; the colors match those of laboratory organic residues called tholins. Tholins are broadly characterized as complex, macromolecular organic solids consisting of a network of aromatic structures connected by aliphatic bridging units (e.g., Imanaka et al., 2004; Materese et al., 2014, 2015). The synthesis of tholins in planetary atmospheres and in surface ices has been explored in numerous laboratory experiments, and both gas- and solid-phase varieties are found on Pluto. A third variety of tholins, exposed at a site of tectonic surface fracturing called Virgil Fossae, appears to have come from a reservoir in the subsurface. Eruptions of tholin-laden liquid H₂O from a subsurface aqueous repository appear to have covered portions of Virgil Fossae and its surroundings with a uniquely colored deposit (D.P. Cruikshank, personal communication) that is geographically correlated with an exposure of H₂O ice that includes spectroscopically detected NH₃ (C.M. Dalle Ore, personal communication). The subsurface organic material could have been derived from presolar or solar nebula processes, or might have formed in situ. Photolysis and radiolysis of a mixture of ices relevant to Pluto's surface composition (N₂, CH₄, CO) have produced strongly colored, complex organics with a significant aromatic content having a high degree of nitrogen substitution similar to the aromatic heterocycles pyrimidine and purine (Materese et al., 2014, 2015; Cruikshank et al., 2016). Experiments with pyrimidines and purines frozen in H₂O-NH₃ ice resulted in the formation of numerous nucleobases, including the biologically relevant guanine, cytosine, adenine, uracil, and thymine (Materese et al., 2017). The red material associated with the H₂O ice may contain nucleobases resulting from energetic processing on Pluto's surface or in the interior. Some other Kuiper Belt objects also exhibit red colors similar to those found on Pluto and may therefore carry similar inventories of complex organic materials. The widespread and ubiquitous nature of similarly complex organic materials observed in a variety of astronomical settings drives the need for additional laboratory and modeling efforts to explain the origin and evolution of organic molecules. Pluto observations reveal complex organics on a small body that remains close to its place of origin in the outermost regions of the Solar System.

Potential bioisosteres of β-uracilalanines derived from 1H-1,2,3-triazole-C-carboxylic acids

The 1H-1,2,3-triazole-originated derivatives of willardiine were obtained by: (i) construction of the 1H-1,2,3-triazole ring in 1,3-dipolar cycloaddition of the uracil-derived azides and the carboxylate-bearing alkynes or α-acylphosphorus ylide, or (ii) N-alkylation of the uracil derivative with the 1H-1,2,3-triazole-4-carboxylate-derived mesylate. The latter method offered: (i) reproducible results, (ii) a significant reduction of amounts of auxiliary materials, (iii) reduction in wastes and (iv) reduction in a number of manual operations required for obtaining the reaction product. Compound 6a exhibited significant binding affinity to hHS1S2I ligand-binding domain of GluR2 receptor (EC₅₀ = 2.90 µM) and decreased viability of human astrocytoma MOG-G-CCM cells in higher extent than known AMPA antagonist GYKI 52466.

Immobilization of a phosphonium ionic liquid on a silica monolith for hydrophilic interaction chromatography

A methodology for preparing phosphonium-based ionic liquid modified silica-based monolithic capillary columns is presented. The silica monolithic columns with dimensions of 150 × 0.1 mm were modified by a phosphonium-based ionic liquid (trioctyl(3/4-vinylbenzyl)phosphonium chloride) via 3-(trimethoxysilyl)propyl methacrylate. The prepared columns were evaluated under hydrophilic interaction liquid chromatography separation conditions, employing a sample mixture containing purine and pyrimidine bases and nucleosides. Detection was made by UV. The high efficiency of the original silica monolith was preserved even after modification, and it reached values in the range of 98,000-174,000 theoretical plates/m. The effects of the concentration of acetonitrile in the mobile phase, the presence of additives in the mobile phase, such as, acetic acid or ammonium acetate, and the pH of the mobile phase on the separation of some selected analytes were investigated. The prepared columns showed different separation selectivity compared to silica, phenyl and sulfobetaine stationary phases.

First-principles study of interaction of serine with nucleobases of DNA and RNA

The nature of interaction between serine-a vital molecule for cancer cell proliferation and nucleic acid bases-adenine (A), guanine (G), cytosine (C), thymine (T), and uracil (U) is investigated within the framework of Møller-Plesset perturbation theory (MP2) and density functional theory (DFT). To quantify the interaction strength between serine and nucleobases, the corresponding binding energies were computed, showing energetic ordering such that G > C > T > A > U. This shows that the interaction energy of serine with guanine is the highest, while with uracil it is the lowest. The amount of charge transferred is the lowest in case of the serine-guanine complex and highest in case of the serine-uracil complex. The results show the serine-guanine complex to be more stable and to have a salt bridge structure involving the -COOH group. Theoretical analysis based on MP2 and DFT shows that the interaction between the serine and nucleobases is mainly determined by hydrogen bonding.

High yield expression and purification of equilibrative nucleoside transporter 7 (ENT7) from Arabidopsis thaliana

BACKGROUND

Equilibrative nucleoside transporters (ENTs) facilitate the import of nucleosides and their analogs into cells in a bidirectional, non-concentrative manner. However, in contrast to their name, most characterized plant ENTs act in a concentrative manner. A direct characterization of any ENT protein has been hindered due to difficulties in overexpression and obtaining pure recombinant protein.

METHODS

The equilibrative nucleoside transporter 7 from Arabidopsis thaliana (AtENT7) was expressed in Xenopus laevis oocytes to assess mechanism of substrate uptake. Recombinant protein fused to enhanced green fluorescent protein (eGFP) was expressed in Pichia pastoris to characterize its oligomeric state by gel filtration and substrate binding by microscale thermophoresis (MST).

RESULTS

AtENT7 expressed in X. laevis oocytes works as a classic equilibrative transporter. The expression of AtENT7-eGFP in the P. pastoris system yielded milligram amounts of pure protein that exists as stable homodimers. The concentration dependent binding of purine and pyrimidine nucleosides to the purified recombinant protein, assessed by MST, confirmed that AtENT7-eGFP is properly folded. For the first time the binding of nucleobases was observed for AtENT7.

SIGNIFICANCE

The availability of pure recombinant AtENT7 will permit detailed kinetic and structural studies of this unique member of the ENT family and, given the functional similarity to mammalian ENTs, will serve as a good model for understanding the structural basis of translocation mechanism for the family.

Hypoxanthine uptake by skeletal muscle microvascular endothelial cells from equilibrative nucleoside transporter 1 (ENT1)-null mice: effect of oxidative stress

Adenosine is an endogenous regulator of vascular tone. This activity of adenosine is terminated by its uptake and metabolism by microvascular endothelial cells (MVEC). The predominant transporter involved is ENT1 (equilibrative nucleoside transporter subtype 1). MVEC also express the nucleobase transporter (ENBT1) which is involved in the cellular flux of adenosine metabolites such as hypoxanthine. Changes in either of these transport systems would impact the bioactivity of adenosine and its metabolism, including the formation of oxygen free radicals. MVEC isolated from skeletal muscle of ENT1(+/+) and ENT1(-/-) mice were subjected to oxidative stress induced by simulated ischemia/reperfusion or menadione. The functional activities of ENT1 and ENBT1 were assessed based on zero-trans influx kinetics of radiolabeled substrates. There was a reduction in the rate of ENBT1-mediated hypoxanthine uptake by ENT1(+/+) MVEC treated with menadione or after exposure to conditions that simulate ischemia/reperfusion. In both cases, the superoxide dismutase mimetic MnTMPyP attenuated the loss of ENBT1 activity, implicating superoxide radicals in the response. In contrast, MVEC isolated from ENT1(-/-) mice showed no reduction in ENBT1 activity upon treatment with menadione or simulated ischemia/reperfusion, but they did have a significantly higher level of catalase activity relative to ENT1(+/+) MVEC. These data suggest that ENBT1 activity is decreased in MVEC in response to the increased superoxide radical that is associated with ischemia/reperfusion injury. MVEC isolated from ENT1(-/-) mice do not show this reduction in ENBT1, possibly due to increased catalase activity.

Separation of nucleobases, nucleosides, and nucleotides using two zwitterionic silica-based monolithic capillary columns coupled with tandem mass spectrometry

The capability of employing synthesized zwitterionic silica-based monolithic capillary columns (140 mm × 0.1mm) for separation of highly polar and hydrophilic nucleobases, nucleosides, and nucleotides in hydrophilic interaction chromatography is reported. The suitability of the columns for on-line conjunction with electrospray tandem mass spectrometry was explored. Our results show that the grafted layer of zwitterionic monomer ([2-(methacryloyloxy)ethyl]-dimethyl-(3-sulfopropyl)-ammonium hydroxide or 2-methacryloyloxyethyl phosphorylcholine) on the silica monolithic surface significantly improved the separation selectivity and reproducibility, as compared to the bare silica monolith. The stepwise elution from 90% to 70% of acetonitrile enabled separation of a complex sample mixture containing 21 compounds with a total analysis time less than 40 min.

Synthesis of N-methyl-d-ribopyranuronamide nucleosides

The synthesis of N-methyl-d-ribopyranuronamide nucleosides is described. The key route is the rearrangement of a 1,2-O-isopropylidene protected furanose sugar with a carboxamide function in the 4-position to a ribopyranuronamide ring. The Lewis acid catalyzed condensation of adenine and thymine nucleobases with the per-O-acetylated N-methyl-d-ribopyranuronamide sugar is used to give the target nucleosides as a mixture of the α and β anomers. The mixture was separated and the final compounds were obtained by deacetylation in basic conditions.