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The article discusses the threats faced by coral reefs due to climate change, including bleaching and aggressive algal blooms. Scientists are working on ways to track and analyze reef health, as well as constructing artificial reefs to protect these ecosystems. Additionally, research shows that playing healthy reef sounds can encourage coral larvae to recolonize damaged reefs, offering hope for reef restoration efforts. French researchers have developed a non-invasive device to analyze dissolved compounds in seawater, providing insights into ecosystem health. [Extracted from the article]

The mechanisms of action of pyrimidine nucleoside derivatives on model lipid membranes of various compositions were studied. A systematic analysis of the tested agents' effects on the membrane physicochemical properties was performed. Differential scanning microcalorimetry data indicated that the ability of nucleoside derivatives to disorder membrane lipids depended on the types of nucleoside bases and membrane-forming lipids. The 5′-norcarbocyclic uracil derivatives were found to be ineffective, while N4-alkylcytidines demonstrated the most pronounced effects, significantly decreasing the dipalmitoylphosphocholine melting temperature and cooperativity of phase transition. The elongation of hydrophobic acyl radicals potentiated the disordering action of N4-alkylcytidines, while an increase in hydrophilicity due to replacing deoxyribose with ribose inhibited this effect. The ability of compounds to form transmembrane pores was also tested. It was found that 5-alkyluridines produced single, ion-permeable pores in phosphatidylglycerol membranes, and that methoxy-mycolic acid and trehalose monooleate potentiated the pore-forming activity of alkyloxymethyldeoxyuridines. The results obtained open up perspectives for the development of innovative highly selective anti-tuberculosis agents, which may be characterized by a low risk of developing drug resistance due to the direct action on the membranes of the pathogen. [ABSTRACT FROM AUTHOR]

Nucleoside phosphorylases (NPs) are pivotal enzymes in the salvage pathway, catalyzing the reversible phosphorolysis of nucleosides to produce nucleobases and α-D-ribose 1-phosphate. Due to their efficiency in catalyzing nucleoside synthesis from purine or pyrimidine bases, these enzymes hold significant industrial importance in the production of nucleoside-based drugs. Given that the thermodynamic equilibrium for purine NPs (PNPs) is favorable for nucleoside synthesis—unlike pyrimidine NPs (PyNPs, UP, and TP)—multi-enzymatic systems combining PNPs with PyNPs, UPs, or TPs are commonly employed in the synthesis of nucleoside analogs. In this study, we report the first development of two engineered bifunctional fusion enzymes, created through the genetic fusion of purine nucleoside phosphorylase I (PNP I) and thymidine phosphorylase (TP) from Thermus thermophilus. These fusion constructs, PNP I/TP-His and TP/PNP I-His, provide an innovative one-pot, single-step alternative to traditional multi-enzymatic synthesis approaches. Interestingly, both fusion enzymes retain phosphorolytic activity for both purine and pyrimidine nucleosides, demonstrating significant activity at elevated temperatures (60–90 °C) and within a pH range of 6–8. Additionally, both enzymes exhibit high thermal stability, maintaining approximately 80–100% of their activity when incubated at 60–80 °C over extended periods. Furthermore, the transglycosylation capabilities of the fusion enzymes were explored, demonstrating successful catalysis between purine (2′-deoxy)ribonucleosides and pyrimidine bases, and vice versa. To optimize reaction conditions, the effects of pH and temperature on transglycosylation activity were systematically examined. Finally, as a proof of concept, these fusion enzymes were successfully employed in the synthesis of various purine and pyrimidine ribonucleoside and 2′-deoxyribonucleoside analogs, underscoring their potential as versatile biocatalysts in nucleoside-based drug synthesis. [ABSTRACT FROM AUTHOR]

Hymedesmiidae is one of the largest families of marine sponges and stands out as an exceptional source of variable metabolites with diverse biological activities. In this study, the ethyl acetate fraction (HE) of a Hymedesmia sp. marine sponge from the Red Sea, Egypt, was analyzed for the first time using Ultra-performance liquid chromatography electrospray ionization tandem mass spectrometry (UPLC-ESI-MS/MS) analysis. The analysis tentatively identified 29 compounds in this fraction, including the isolation and identification of six compounds (two pyrimidine nucleosides, one purine, and two pyrimidine bases in addition to one cerebroside) for the first time. The structures of the isolated compounds were established by 1D and 2D NMR (nuclear magnetic resonance), MS (mass spectrometry), and IR (infrared) spectroscopy. Furthermore, the cytotoxic, antioxidant, and antimicrobial activities of the ethyl acetate fraction were evaluated in vitro. The fraction exhibited strong DPPH scavenging activity with an IC50 of 78.7 µg/mL, compared to ascorbic acid as a positive control with an IC50 of 10.6 µg/mL. It also demonstrated significant cytotoxic activity with IC50 values of 13.5 µg/mL and 25.3 µg/mL against HCT-116 and HEP-2 cell lines, respectively, compared to vinblastine as a positive control with IC50 values of 2.34 µg/mL and 6.61 µg/mL against HCT-116 and HEP-2, respectively. Additionally, the ethyl acetate fraction displayed promising antibacterial activity against S. aureus with a MIC value of 62.5 µg/mL, compared to ciprofloxacin as a positive control with MIC values of 1.56 µg/mL for Gram-positive bacteria and 3.125 µg/mL for Gram-negative bacteria. It also exhibited activity against E. coli and P. aeruginosa with MIC values of 250 µg/mL and 500 µg/mL, respectively. Briefly, this is the first report on the biological activities and secondary metabolite content of the ethyl acetate fraction of Hymedesmia sp. marine sponge, emphasizing the potential for further research against resistant bacterial and fungal strains, as well as different cancer cell lines. The ethyl acetate fraction of Hymedesmia sp. is a promising source of safe and unique natural drugs with potential therapeutic and pharmaceutical benefits. [ABSTRACT FROM AUTHOR]

Clickable nucleosides, most often 5-ethynyl-2′-deoxyuridine (EtU), are widely used in studies of DNA replication in living cells and in DNA functionalization for bionanotechology applications. Although clickable dNTPs are easily incorporated by DNA polymerases into the growing chain, afterwards they might become targets for DNA repair systems or interfere with faithful nucleotide insertion. Little is known about the possibility and mechanisms of these post-synthetic events. Here, we investigated the repair and (mis)coding properties of EtU and two bulkier clickable pyrimidine nucleosides, 5-(octa-1,7-diyn-1-yl)-U (C8-AlkU) and 5-(octa-1,7-diyn-1-yl)-C (C8-AlkC). In vitro, EtU and C8-AlkU, but not C8-AlkC, were excised by SMUG1 and MBD4, two DNA glycosylases from the base excision repair pathway. However, when placed into a plasmid encoding a fluorescent reporter inactivated by repair in human cells, EtU and C8-AlkU persisted for much longer than uracil or its poorly repairable phosphorothioate-flanked derivative. DNA polymerases from four different structural families preferentially bypassed EtU, C8-AlkU and C8-AlkC in an error-free manner, but a certain degree of misincorporation was also observed, especially evident for DNA polymerase β. Overall, clickable pyrimidine nucleotides could undergo repair and be a source of mutations, but the frequency of such events in the cell is unlikely to be considerable. [ABSTRACT FROM AUTHOR]

This article provides an overview of the current strategies for the enantioselective synthesis of modified nucleosides, which have been used in the treatment of various diseases, including viruses. The focus is on the modifications that can be made to different parts of the nucleoside structure to create therapeutically useful compounds. The article discusses the latest developments in the synthesis of cyclic and acyclic nucleosides, highlighting various methods and reactions that can be used to achieve high yields and enantioselectivities. The authors also acknowledge the institutions that supported their research. [Extracted from the article]

This article discusses the synthesis of 5-Hydroxyuridine (5-OHU) and its formation in bacterial tRNA. The authors explore the reaction mechanism and the impact of different parameters on the yield of the desired compounds. They also discuss the conformation of nucleosides, specifically focusing on the sugar geometry and its influence on the overall structure. The study utilizes various techniques to analyze the sugar conformation and its impact on the nucleoside structure. Overall, this research provides insights into the synthesis and properties of 5-hydroxuridine, an important RNA lesion. [Extracted from the article]

This article explores the development of new nucleoside analogues for treating viral infections and cancer. Specifically, it focuses on fluorinated carbocyclic systems, which have shown promise in medicinal and biological chemistry. The authors discuss the synthesis of various analogues with unsaturation and stereoinversion, as well as different reaction methods. The article also highlights the relevance of nucleoside analogues in the context of the COVID-19 pandemic and the development of mRNA vaccines and antiviral medications. The researchers successfully synthesized a small library of fluorinated carbocyclic nucleoside analogues, achieving C2'-C3' unsaturation using Corey-Winter or Eastwood olefination. They also discovered an unusual C1'-C2' alkene scaffold as a side-product, enabling the synthesis of a 1',2'-didehydro 6'-fluorinated carbauridine and carbacytidine. NMR data was used to investigate the conformations of the analogues in solution, revealing that C2'-C3' unsaturation favored a 6'-endo envelope conformation. Biological evaluation of these nucleoside motifs is currently ongoing. [Extracted from the article]

A series of new dimers of pyrimidine nucleoside analogues have been synthesized. The dimers are composed of two uracil or thymine fragments linked at N3 through a polymethylene bridge and bearing a β-D-ribofuranose residue linked to N1 of the nucleobase through a 1,2,3-triazolylalkyl spacer. Biological screening revealed that some of the synthesized dimers are active against influenza A (H1N1) virus and coxsackievirus B3 with IC50 values of 13 and 4.5 μM, respectively. [ABSTRACT FROM AUTHOR]

This document provides a comprehensive overview of the chemoenzymatic synthesis of arabino-configured bicyclic nucleosides. The authors describe the synthesis process using enzymatic acetylation reactions and other chemical reactions, as well as the use of different enzymes and solvents. The structures of the synthesized compounds were confirmed through spectral data analysis. The document also includes detailed information on the synthesis and characterization of various nucleosides, including data such as melting points, yields, and spectroscopic data. Overall, this study presents an efficient and environmentally friendly method for synthesizing arabino-configured bicyclic nucleosides. [Extracted from the article]

Replication of the mitochondrial genome and expression of the genes it encodes both depend on a sufficient supply of nucleotides to mitochondria. Accordingly, dysregulated nucleotide metabolism not only destabilises the mitochondrial genome, but also affects its transcription. Here, we report that a mitochondrial nucleoside diphosphate kinase, NME6, supplies mitochondria with pyrimidine ribonucleotides that are necessary for the transcription of mitochondrial genes. Loss of NME6 function leads to the depletion of mitochondrial transcripts, as well as destabilisation of the electron transport chain and impaired oxidative phosphorylation. These deficiencies are rescued by an exogenous supply of pyrimidine ribonucleosides. Moreover, NME6 is required for the maintenance of mitochondrial DNA when the access to cytosolic pyrimidine deoxyribonucleotides is limited. Our results therefore reveal an important role for ribonucleotide salvage in mitochondrial gene expression. Synopsis: The source of rNTPs used in mitochondrial transcription, which supports many key processes, is not well understood. This study shows that they are supplied through the phosphorylation of pyrimidine nucleosides via mitochondrial nucleoside diphosphate kinase NME6. NME6 sustains mitochondrial supply of pyrimidine nucleotides.NME6 ensures accumulation of mitochondrial transcripts and respiratory complexes.Pyrimidine nucleoside supplementation restores levels of mitochondrial transcripts and respiratory complexes in cells lacking NME6.NME6‐dependent nucleotide salvage maintains mtDNA when the cytosolic supply of pyrimidine deoxyribonucleotides is limited. [ABSTRACT FROM AUTHOR]

Pathogenic parasites of the Trichomonas genus are causative agents of sexually transmitted diseases affecting millions of individuals worldwide and whose outcome may include stillbirths and enhanced cancer risks and susceptibility to HIV infection. Trichomonas vaginalis relies on imported purine and pyrimidine nucleosides and nucleobases for survival, since it lacks the enzymatic activities necessary for de novo biosynthesis. Here we show that T. vaginalis additionally lacks homologues of the bacterial or mammalian enzymes required for the synthesis of the nicotinamide ring, a crucial component in the redox cofactors NAD+ and NADP. Moreover, we show that a yet fully uncharacterized T. vaginalis protein homologous to bacterial and protozoan nucleoside hydrolases is active as a pyrimidine nucleosidase but shows the highest specificity toward the NAD+ metabolite nicotinamide riboside. Crystal structures of the trichomonal riboside hydrolase in different states reveals novel intermediates along the nucleoside hydrolase–catalyzed hydrolytic reaction, including an unexpected asymmetry in the homotetrameric assembly. The active site structure explains the broad specificity toward different ribosides and offers precise insights for the engineering of specific inhibitors that may simultaneously target different essential pathways in the parasite. [ABSTRACT FROM AUTHOR]

Hydroxylamine (NH2OH) is a key precursor of both the formation of amino acids and the concurrent synthesis of pyrimidine and purine nucleosides. Recently, NH2OH was detected towards the quiescent molecular cloud G+0.693-0.027, which is located in the Galactic Centre. In this study, we construct the chemical network for NH2OH and its related species via quantum chemical calculations, and simulate their chemistry using the astrochemical code Nautilus in isothermal models and shock models. According to the disagreement distance formula and molecular abundance ratios, we acquire the best-fitting isothermal model T18 and the best-fitting C-shock model S2, respectively. Of these two models, S2 is more suitable for G+0.693-0.027 due to its reproduction of abundances of all considered molecules. From the model, we found that NH2OH and CH3NH2 are mainly formed on grain surfaces, while HNCN and CH2NH, which are the post-shock tracers, are produced by both gas-phase and grain-surface reactions. Our chemical modelling also agrees with the observed abundances or upper limits of NH2OH and its related species towards IRAS 16293-2422 B and Sgr B2(N). Moreover, we predict that NH2OH and the undiscovered species H2NO and HNOH are of high abundance, thus are detectable in cold clouds and pre-stellar cores, and in G+0.693-0.027, respectively. [ABSTRACT FROM AUTHOR]

Accessing homogenous glycoconjugates is of significance for assessing their biophysical activities and sometimes as vaccine candidate. Synthesis of glycoconjugates involves two species of which, glycosyl donor plays pivotal role in controlling the outcome of the glycosylation. Recently discovered alkynyl glycosyl carbonate donors possess self‐stability, high reactivity, and fast reaction time (15–30 min) when activated with [Au]/[Ag]‐catalysts. Herein, we report metal free conditions for the activation of the same alkynyl glycosyl carbonate donors using I2/TMSOTf in stoichiometric quantities. Extrusion product was characterized to be the vinylidene iodide by single crystal X‐ray analysis. The reaction conditions were illustrated to be suitable for synthesis of various glycosides, purine/pyrimidine nucleosides and a pentasaccharide repeating unit of Klebsiella pneumoniae (O‐3‐antigen). [ABSTRACT FROM AUTHOR]

The complexation reactions of phosphocholine and pyrimidine nucleosides as well as nucleotides with copper(II) ions were studied in the water system. Using potentiometric methods and computer calculations, the stability constants of the species were determined. Using spectroscopic methods such as UV-vis, EPR, 13C NMR, 31P NMR, FT–IR and CD, the coordination mode was established for complexes created in pH range 2.5–11.0. These studies will lead to a better understanding the role of copper(II) ions in living organisms and explain the interactions between them and the studied bioligands. The differences and similarities between nucleosides and nucleotides in the studied systems were also described, which testify to the significant influence of phosphate groups on the processes of metal ion complexation and interactions between ligands. [ABSTRACT FROM AUTHOR]

Biosynthesis of the pyrimidine nucleotide uridine monophosphate (UMP) is essential for cell proliferation and is achieved by the activity of convergent de novo and salvage metabolic pathways. Here we report the development and application of a cell-based metabolic modifier screening platform that leverages the redundancy in pyrimidine metabolism for the discovery of selective UMP biosynthesis modulators. In evaluating a library of protein kinase inhibitors, we identified multiple compounds that possess nucleotide metabolism modifying activity. The JNK inhibitor JNK-IN-8 was found to potently inhibit nucleoside transport and engage ENT1. The PDK1 inhibitor OSU-03012 (also known as AR-12) and the RAF inhibitor TAK-632 were shown to inhibit the therapeutically relevant de novo pathway enzyme DHODH and their affinities were unambiguously confirmed through in vitro assays and co-crystallization with human DHODH.

Colorectal cancer (CRC) represents a major public health problem as the second leading cause of cancer-related mortality in the United States. Of an estimated 140,000 newly diagnosed CRC cases in 2018, roughly one-third of these patients will have a primary tumor located in the distal large bowel or rectum. The current standard-of-care approach includes curative-intent surgery, often after preoperative (neoadjuvant) radiotherapy (RT), to increase rates of tumor down-staging, clinical and pathologic response, as well as improving surgical resection quality. However, despite advancements in surgical techniques, as well as sharpened precision of dosimetry offered by contemporary RT delivery platforms, the oncology community continues to face challenges related to disease relapse. Ongoing investigations are aimed at testing novel radiosensitizing agents and treatments that might exploit the systemic antitumor effects of RT using immunotherapies. If successful, these treatments may usher in a new curative paradigm for rectal cancers, such that surgical interventions may be avoided. Importantly, this disease offers an opportunity to correlate matched paired biopsies, radiographic response, and molecular mechanisms of treatment sensitivity and resistance with clinical outcomes. Herein, the authors highlight the available evidence from preclinical models and early-phase studies, with an emphasis on promising developmental therapeutics undergoing prospective validation in larger scale clinical trials. This review by the National Cancer Institute's Radiation Research Program Colorectal Cancer Working Group provides an updated, comprehensive examination of the continuously evolving state of the science regarding radiosensitizer drug development in the curative treatment of CRC.

Abstract The question of how nucleosides might have formed as essential precursor molecules on the early Earth is one of the many challenges associated with the origin of life. In this context, the prebiotic synthesis of pyrimidine nucleosides is controversially discussed. For the pyrimidines, two at first glance contradictory prebiotically plausible reaction pathways have been proposed, based on either oxazole or isoxazole chemistry. This study shows that these two reaction sequences can be merged under prebiotically reasonable conditions, suggesting that both pathways could have co‐existed and possibly interacted. The key precursor 3‐aminoisoxazole was found to react with the key intermediate of the oxazole route (ribo‐2‐(methylthio)oxazoline), to form a ribo‐isoxazole‐oxazoline hybrid structure, which collapses upon reductive N−O bond cleavage to give the nucleoside cytidine. The data suggest that different, interacting prebiotically plausible chemical pathways may have created the key molecules of life on the early Earth.

Enzymes from thermophilic organisms are interesting biocatalysts for a wide variety of applications in organic synthesis, biotechnology, and molecular biology. Next to an increased stability at elevated temperatures, they were described to show a wider substrate spectrum than their mesophilic counterparts. To identify thermostable biocatalysts for the synthesis of nucleotide analogs, we performed a database search on the carbohydrate and nucleotide metabolism of Thermotoga maritima. After expression and purification of 13 enzyme candidates involved in nucleotide synthesis, these enzymes were screened for their substrate scope. We found that the synthesis of 20-deoxynucleoside 50-monophosphates (dNMPs) and uridine 50-monophosphate from nucleosides was catalyzed by the already known wide-spectrum thymidine kinase and the ribokinase. In contrast, no NMP-forming activity was detected for adenosine-specific kinase, uridine kinase, or nucleotidase. The NMP kinases (NMPKs) and the pyruvate-phosphate-dikinase of T. maritima exhibited a rather specific substrate spectrum for the phosphorylation of NMPs, while pyruvate kinase, acetate kinase, and three of the NMPKs showed a broad substrate scope with (20-deoxy)nucleoside 50-diphosphates as substrates. Based on these promising results, TmNMPKs were applied in enzymatic cascade reactions for nucleoside 50-triphosphate synthesis using four modified pyrimidine nucleosides and four purine NMPs as substrates, and we determined that base- and sugar-modified substrates were accepted. In summary, besides the already reported TmTK, NMPKs of T. maritima were identified to be interesting enzyme candidates for the enzymatic production of modified nucleotides. [ABSTRACT FROM AUTHOR]

Concentrative nucleoside transporters (CNTs) are active nucleoside influx systems, but their in vivo roles are poorly defined. By generating CNT1 knockout (KO) mice, here we identify a role of CNT1 in the renal reabsorption of nucleosides. Deletion of CNT1 in mice increases the urinary excretion of endogenous pyrimidine nucleosides with compensatory alterations in purine nucleoside metabolism. In addition, CNT1 KO mice exhibits high urinary excretion of the nucleoside analog gemcitabine (dFdC), which results in poor tumor growth control in CNT1 KO mice harboring syngeneic pancreatic tumors. Interestingly, increasing the dFdC dose to attain an area under the concentration-time curve level equivalent to that achieved by wild-type (WT) mice rescues antitumor efficacy. The findings provide new insights into how CNT1 regulates reabsorption of endogenous and synthetic nucleosides in murine kidneys and suggest that the functional status of CNTs may account for the optimal action of pyrimidine nucleoside analog therapeutics in humans. Concentrative nucleoside transporters (CNTs) are cellular nucleoside influx systems, but their in vivo roles are poorly defined. By generating CNT1 knockout (KO) mice, here the authors show a role of CNT1 in the renal reabsorption of endogenous and synthetic nucleosides. [ABSTRACT FROM AUTHOR]

Developing efficient and comprehensive analysis methods for metabolomics and lipidomics in the biological tissues and body fluids is essential for understanding the disease mechanisms. Although various two-dimensional liquid chromatography-mass spectrometry (2D-LC-MS) methods have been proposed to expand metabolite coverage, achieving higher efficiency in integrated metabolomics and lipidomics studies remains a technical challenge. In this work, a novel 4in1 online analysis system with excellent reproducibility and mass accuracy was constructed for metabolomics and lipidomics study in various biological samples from atherosclerotic mice. This system enabled the simultaneous detection in both positive and negative ion modes with extensive polarity separation in a single analytical run. Using the 4in1 online analysis system, we identified distinct but complementary metabolic signatures associated with atherosclerosis in different biological samples. Specifically, a total of 230 and 170 differential metabolites or lipids were detected in mice plasma samples and aortic tissue samples, respectively, including glycerophospholipids, sphingolipids, fatty acyls, glycerolipids, carboxylic acids, and pyrimidine nucleosides. Additionally, atherosclerosis-related metabolic pathways involved in biosynthesis of unsaturated fatty acids, sphingolipid metabolism, cholesterol metabolism, glycerophospholipid metabolism, and choline metabolism further revealed. These findings demonstrate that the novel 4in1 online analysis system is a faithful, stable and powerful tool for comprehensive metabolomics and lipidomics studies in complex biological matrices. [Display omitted] • A 4in1 online analysis system with polarity partition 2D-LC and LCMS-9050 was developed. • Ultra-stable rapid polarity switching technology improved metabolomics analysis efficiency. • Comprehensive information on metabolome and lipidome was covered within a single injection. • The method successfully revealed metabolic signatures in atherosclerotic mice. [ABSTRACT FROM AUTHOR]

A series of novel 1,2,3‐triazole‐linked hexopyranosyl mono/double‐headed pyrimidine nucleosides from D‐glucose was synthesized by Cu(I)‐mediated [3+2] cycloaddition reactions (CuAAC) of mono/diazido 2,6‐anhydro‐glucoheptitol and propynylated pyrimidines in good yields. It was observed that all the four synthesized pyrimidine nucleosides were found to be non‐cytotoxic upto 500 μM concentration. The 1,2,3‐triazole‐linked hexopyranosyl mono/double‐headed pyrimidine nucleosides have shown significant suppression of Hepatitis B surface antigen (HBsAg) and Hepatitis B e‐antigen (HBeAg). Amongst all the synthesized compounds, nucleoside dimer 1‐[1‐(6′‐deoxy‐6′‐(4‐(1‐methyluracil)‐1,2,3‐triazol‐1‐yl)‐β‐D‐glucopyranosyl methyl)‐1,2,3‐triazol‐4‐yl]methyl‐uracil was found to be more effective against HBeAg. In the suppression of viral DNA level, all the four synthesized nucleoside analogues were comparable to known drug Entecavir (ETV) with IC50 value in the range of 8.39 μM–18.58 μM and are two folds significant as compared to control. [ABSTRACT FROM AUTHOR]

The synthesis of N‐glycosides from stable glycosyl donors in a catalytic fashion is still challenging, though they exist ubiquitously in DNA, RNA, glycoproteins, and other biological molecules. Herein, silver‐assisted gold‐catalyzed activation of alkynyl glycosyl carbonate donors is shown to be a versatile approach for the synthesis of purine and pyrimidine nucleosides, asparagine glycosides and quinolin‐2‐one N‐glycosides. Thus synthesized nucleosides were subjected to the oxidation–reduction sequence for the conversion of Ribf‐ into Araf‐ nucleosides, giving access to nucleosides that are otherwise difficult to synthesize. Furthermore, the protocol is demonstrated to be suitable for the synthesis of 2'‐modified nucleosides in a facile manner. Direct attachment of an asparagine‐containing dipeptide to the glucopyranose and subsequent extrapolation to afford the dipeptide disaccharide unit of chloroviruses is yet another facet of this endeavor. [ABSTRACT FROM AUTHOR]

5-Hydroxymethyl derivatives of pyrimidine nucleosides are an important class of biologically relevant compounds. In addition, such derivatives and related compounds can be functionalized for various applications. To enable fast, economical, and efficient access to 5-hydroxymethylated derivatives of 2′-deoxyuridine, we report a method for the O-5 chemoselective transformation of unprotected 5-(hydroxymethyl)-2′-deoxyuridine through selective etherification in the presence of an alcohol promoted by acidic Amberlyst 15 resin at room temperature. These mild conditions constitute a significant improvement compared with the harsh conditions previously described. Applied to various primary or secondary alcohols, the reaction showed a broad substrate scope, and 24 C(5)-modified derivatives of 5hmdU were synthesized with good isolated yields. Notably, this efficient procedure represents a straightforward method for preparing (i) several useful building blocks for subsequent chemical ligation by using CuAAC reactions; (ii) natural hypermodified thymidines and analogues, including glycosylated derivatives; and (iii) cyanoethyl-protected 5hmdU, useful for solid-phase oligonucleotide syntheses. [ABSTRACT FROM AUTHOR]

Glycosylation of 2-oxo(sulfanylidene)-3-phenyl-6-[4-(propan-2-yl)phenyl]pyrimidine-5-carbo-nitritles with glucosyl and galactosyl bromides in the presence of potassium hydroxide afforded mixtures of N- and O- or N- and S-glycosides which were deacetylated with triethylamine to give the corresponding free nucleosides. Alkylation of the same pyrimidinecarbonitriles with 3-chloropropan-1-ol and epichlorohydrin yielded N- and S-derivatives. The structure of the new compounds was established using spectral data. Some of the synthesized compounds showed moderate activity against gram-positive and gram-negative bacteria and fungi. [ABSTRACT FROM AUTHOR]

Several naturally occurring purine and pyrimidine nucleosides contain an amide linkage as part of the heterocyclic aglycone. Enolization of the amide and conversion to leaving groups at the amide carbon atom permits base modification by addition‐elimination types of processes. Although a number of methods have been developed over the years for accomplishing such conversions, the present Personal Account describes efforts from the Lakshman laboratories. Facile activation of the amido groups in nucleobases can be achieved with peptide‐coupling agents. Subsequent reaction with nucleophiles then accomplishes the base modifications. In many cases, the activation and displacement steps can be done as two‐step, one‐pot processes, whereas in other cases, discrete storable activated nucleosides can be isolated for subsequent displacement reactions. Using such an approach a wide range of nucleoside base modifications is readily achievable. In many instances, mechanistic investigations have been conducted so as to understand the activation process. [ABSTRACT FROM AUTHOR]

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE; OMIM 603041) is a rare inherited metabolic disorder mostly caused by mutations in TYMP gene encoding thymidine phosphorylase (TP) protein that affects the mitochondrial nucleotide metabolism. TP, functionally active as a homodimer, is involved in the salvage pathway of pyrimidine nucleosides. MNGIE-like syndrome having an overlapping phenotype of MNGIE was also described and has been associated with mutations in POLG and RRM2B genes. In the present study, we report the molecular investigation of a consanguineous family including two patients with clinical features suggestive of MNGIE syndrome. Bioinformatics analyses were carried out in addition to mtDNA deletion screening and copy number quantification in the blood of the two patients. Whole exome sequencing and Sanger sequencing analyses revealed the segregation in the affected family a novel mutation c.1205T>A (p.L402Q) within the exon 9 of the TYMP gene. In addition, mtDNA analysis revealed the absence of mtDNA deletions and a decrease of the copy number in the blood of the two patients of the studied family. The p.Leu402Gln mutation was located in a conserved amino acid within the α/β domain of the TP protein and several software supported its pathogenicity. In addition, and based on docking and molecular dynamic simulation analyses, results revealed that L402Q caused a conformational change in TP mutated structure and could therefore alter its flexibility and stability. These changes prevent also the formation of stable homodimer leading to non-functional protein with partial or complete loss of its catalytic activity. [ABSTRACT FROM AUTHOR]

d-Arabinofuranosyl-pyrimidine and -purine nucleoside analogues containing alkylthio-, acetylthio- or 1-thiosugar substituents at the C2' position were prepared from the corresponding 3',5'-O-silylene acetal-protected nucleoside 2'-exomethylenes by photoinitiated, radical-mediated hydrothiolation reactions. Although the stereochemical outcome of the hydrothiolation depended on the structure of both the thiol and the furanoside aglycone, in general, high d-arabino selectivity was obtained. The cytotoxic effect of the arabinonucleosides was studied on tumorous SCC (mouse squamous cell) and immortalized control HaCaT (human keratinocyte) cell lines by MTT assay. Three pyrimidine nucleosides containing C2'-butylsulfanylmethyl or -acetylthiomethyl groups showed promising cytotoxicity at low micromolar concentrations with good selectivity towards tumor cells. SAR analysis using a methyl β-d-arabinofuranoside reference compound showed that the silyl-protecting group, the nucleobase and the corresponding C2' substituent are crucial for the cell growth inhibitory activity. The effects of the three most active nucleoside analogues on parameters indicative of cytotoxicity, such as cell size, division time and cell generation time, were investigated by near-infrared live cell imaging, which showed that the 2'-acetylthiomethyluridine derivative induced the most significant functional and morphological changes. Some nucleoside analogues also exerted anti-SARS-CoV-2 and/or anti-HCoV-229E activity with low micromolar EC50 values; however, the antiviral activity was always accompanied by significant cytotoxicity. [ABSTRACT FROM AUTHOR]

Using advanced genetic engineering methodology, a series of silent mutations was originally introduced into initial fragment of gene cloned in E. coli and coding for pyrimidine nucleoside phosphorylase of T. thermophilus. As a result, 70% rise in the synthesis level of studied thermostable enzyme was achieved. We were able to establish that pyrimidine fluoro-deoxy nucleosides may serve as substrates of phosphorolysis reaction catalyzed by thermostable pyrimidine nucleoside phosphorylase of T. thermophilus. Moreover, recombinant nucleoside phosphorylases were never before involved in enzymatic synthesis of biologically significant purine 3'-fluoronucleosides [ABSTRACT FROM AUTHOR]

A set of unique nucleoside analogs, containing 'spirocyclic orthoester-type' scaffolds, were synthesized from a common isothiazolo[4,3-d]pyrimidine-riboside precursor. The key reaction, using 1,2-di-heteroatomic nucleophiles (e.g., 1,2-ethandithiol) and BF3•OEt2, converts an exocyclic imine into the spirocyclic analogs. The novel structural scaffold is confirmed through the use of one- and two-dimensional 1H and 13C NMR experiments.

Pyrimidine nucleosides, as intermediate materials of significant commercial value, find extensive applications in the pharmaceutical industry. However, the current production of pyrimidine nucleosides largely relies on chemical synthesis, creating environmental problems that do not align with sustainable development goals. Recent progress in systemic metabolic engineering and synthetic biology has enabled the synthesis of natural products like pyrimidine nucleosides through microbial fermentation, offering a more sustainable alternative. Nevertheless, the intricate and tightly regulated biosynthetic pathways involved in the microbial production of pyrimidine nucleosides pose a formidable challenge. This study focuses on metabolic engineering and synthetic biology strategies aimed at enhancing pyrimidine nucleoside production. These strategies include gene modification, transcriptional regulation, metabolic flux analysis, cofactor balance optimization, and transporter engineering. Finally, this research highlights the challenges involved in the further development of pyrimidine nucleoside-producing strains and offers potential solutions in order to provide theoretical guidance for future research endeavors in this field. [ABSTRACT FROM AUTHOR]

The prebiotic origins of biopolymers and metabolic co‐factors are key questions in Origins of Life studies. In a simple warm‐little‐pond model, using a drying phase to produce a urea‐enriched solution, we present a prebiotic synthetic path for the simultaneous formation of neopterins and tetrahydroneopterins, along with purine nucleosides. We show that, in the presence of ribose and in a formylating environment consisting of urea, ammonium formate, and water (UAFW), the formation of neopterins from pyrimidine precursors is robust, while the simultaneous formation of guanosine requires a significantly higher ribose concentration. Furthermore, these reactions provide a tetrahydropterin–pterin redox pair. This model suggests a prebiotic link in the origin of purine nucleosides and pterin cofactors that provides a possible deep prebiotic temporal connection for the emergence of nucleic acids and metabolic cofactors. [ABSTRACT FROM AUTHOR]

Tuberculosis (TB) is the oldest human infection disease. Mortality from TB significantly decreased in the 20th century, because of vaccination and the widespread use of antibiotics. However, about a third of the world's population is currently infected with Mycobacterium tuberculosis (Mtb) and the death rate from TB is about 1.4–2 million people per year. In the second half of the 20th century, new extensively multidrug-resistant strains of Mtb were identified, which are steadily increasing among TB patients. Therefore, there is an urgent need to develop new anti-TB drugs, which remains one of the priorities of pharmacology and medicinal chemistry. The antimycobacterial activity of nucleoside derivatives and analogues was revealed not so long ago, and a lot of studies on their antibacterial properties have been published. Despite the fact that there are no clinically used drugs based on nucleoside analogues, some progress has been made in this area. This review summarizes current research in the field of the design and study of inhibitors of mycobacteria, primarily Mtb. [ABSTRACT FROM AUTHOR]

Tuberculosis (TB) is the second leading infectious killer after COVID-19, causing 10 million new cases and claiming the lives of more than 1.5 million people every year [[1]]; furthermore, a growing number of multidrug-resistant TB strains constitute a major health threat. Several clinical trials tested antiparasitic drugs in TB patients and experienced difficulties with effective dose and toxicity, consistent with natural differences between TB and parasitic infections. The spectrum of drug resistance is represented by a diverse combination of anti-TB drugs, including second-line drugs, which significantly narrows the variety of effective treatment and increases the risk of adverse outcomes related to tuberculosis. [Extracted from the article]

The chemical functionalization at C‐5' position of nucleosides has been significantly less studied compared to the C‐1', C‐2' and C‐3' sugar positions in spite of its potential important role for biological activity. We describe here the synthesis of new carbothioate nucleosides which were then engaged in a Liebeskind‐Srogl reaction with various boronic acids for the preparation of diversely modified C‐5'‐acyl nucleosides. Applied to pyrimidine nucleosides in the DNA and RNA series, the reaction showed a broad substrate scope and more than 25 examples were synthesized in good‐to‐excellent isolated yields. This general and efficient Pd‐catalyzed and Cu(I)‐mediated cross‐coupling represents a convenient method to prepare a diverse set of 5'‐modified nucleosides and paves the way for further transformation into a variety of potentially bioactive compounds via the possible conversion of the C‐5'‐ketone. [ABSTRACT FROM AUTHOR]

Pyrimidine nucleoside analogues are widely used to treat infections caused by the human immunodeficiency virus (HIV) and DNA viruses from the herpes family. It has been shown that 5-substituted uracil derivatives can inhibit HIV-1, herpes family viruses, mycobacteria and other pathogens through various mechanisms. Among the 5-substituted pyrimidine nucleosides, there are not only the classical nucleoside inhibitors of the herpes family viruses, 2′-deoxy-5-iodocytidine and 5-bromovinyl-2′-deoxyuridine, but also derivatives of 1-(benzyl)-5-(phenylamino)uracil, which proved to be non-nucleoside inhibitors of HIV-1 and EBV. It made this modification of nucleoside analogues very promising in connection with the emergence of new viruses and the crisis of drug resistance when the task of creating effective antiviral agents of new types that act on other targets or exhibit activity by other mechanisms is very urgent. In this paper, we present the design, synthesis and primary screening of the biological activity of new nucleoside analogues, namely, 5′-norcarbocyclic derivatives of substituted 5-arylamino- and 5-aryloxyuracils, against RNA viruses. [ABSTRACT FROM AUTHOR]

As a result of the scale of the Covid 19 pandemic that launched from China in December 2019 and to limit its spread, several treatments were used to control this virus, including, hydroxychloroquine, favipiravir, lopinavir, remidesivir, tocilizumab, and anakinra. Favipiravir is an antiviral drug that works by inhibiting RNA-dependent RNA polymerase, favipiravir inhibited viral genome replication, which was most noticeable in the middle of the viral proliferation period. Favipiravir was found to have antiviral activity, Purine nucleosides or purine bases inhibit favipiravir, meaning that it competes with purine nucleosides rather than pyrimidine nucleosides, In a time-of-drugaddition test, to treat a variety of RNA viruses (influenza, West Nile, yellow fever, flaviviruses, arenaviruses, bunyaviruses and alphaviruses). Here, we show for the first time the histologycal effect of favipiravir on the liver and kidneys using albino rats, using light microscopy, where the optical microscopic revealed that normal doses in liver showed hepatic cords arranged, normal central vein and mild sinusoildal infiltration of mono nuclear leukocytes mainly lymphocytes, the hepatocytes showed mild granular cytoplasm while double doses showed little hemorrhagic foci and disarrangement of hepatic cords. The magnified sections revealed few of hepatocytes showed mild cloudy swelling associated with little figures of cellular necrosis. As for kidneys, the optical microscopic observations showed multiple foci of hemorrhage, the magnified section revealed congestion of glomerular capillary tuft and few of renal tubules showed mild granular or vacular degeneration. On the other hand, sections of renal medulla revealed normal appearance for normal doses while renal cortex and medulla were showed marked interstitial nephritis, which characterized by interstitial thickening due to infiltration of mono nuclear leukocytes and the renal tubules showed sever vacular degeneration and necrosis for double doses. These results can guide the safe use of favipiravir and reduce the risks to tissue the liver and kidney by using double doses. [ABSTRACT FROM AUTHOR]

A facile synthetic approach has been proposed for a new series of uracil acyclic nucleosides and their sulfanyl analogs via reaction of pyrimidine derivatives with a number of acyclic halides such as 4-bromobutyl acetate, 2-(bromomethoxy)ethyl acetate, 3-chloropropan-1-ol, epichlorohydrin, allyl bromide, and propargyl bromide). The desired products were obtained in good yields (68–90%) at room temperature in the presence of potassium carbonate. Some of the synthesized compounds showed significant antibacterial activity against Bacillus cereus, Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa (inhibition zone diameter 19–29 mm compared to 21–26 mm for Ampicillin taken as reference drug). [ABSTRACT FROM AUTHOR]

Augustine (AUG) is a blood group system comprising four antigens: AUG1, AUG2 (Ata), and AUG4 are of very high frequency; AUG3 is of very low frequency. These antigens are located on ENT1, an equilibrative nucleoside transporter encoded by SLC19A1. AUG antibodies are of clinical relevance in blood transfusion and pregnancy: anti-AUG2 have caused haemolytic transfusion reactions; the only anti-AUG3 was associated with severe haemolytic disease of the fetus and newborn. ENT1 is present in almost all human tissues. It facilitates the transfer of purine and pyrimidine nucleosides and is responsible for the majority of adenosine transport across plasma membranes. Adenosine transport appears to be an important factor in the regulation of bone metabolism. The AUGnull phenotype (AUG:–1,–2,–3,–4) has been found in three siblings, who are homozygous for an inactivating splice-site mutation in SLC29A1. Although ENT1 is very likely to be absent from all cells in these three individuals, they were apparently healthy with normal lifestyles. However, they suffered frequent attacks of pseudogout, a form of arthritis, in various joints with multiple calcifications around their hand joints. Ectopic calcification in the hips, pubic symphysis, and lumbar discs was present in the propositus. The three AUGnull individuals had misshapen red cells with deregulated protein phosphorylation, but no anaemia or shortening of red cell lifespan. Defective in vitro erythropoiesis in the absence of ENT1 was confirmed by shRNA-mediated knockdown of ENT1 during in vitro erythropoiesis of CD34+ progenitor cells from individuals with normal ENT1. Nucleoside transporters, such as ENT1, are vital in the uptake of synthetic nucleoside analogue drugs, used in cancer and viral chemotherapy. It is feasible that the efficacy of these drugs would be compromised in patients with the extremely rare AUGnull phenotype. [ABSTRACT FROM AUTHOR]

DNA owes its remarkable photostability to its building blocks—the nucleosides—that efficiently dissipate the energy acquired upon ultraviolet light absorption. The mechanism occurring on a sub-picosecond time scale has been a matter of intense debate. Here we combine sub-30-fs transient absorption spectroscopy experiments with broad spectral coverage and state-of-the-art mixed quantum-classical dynamics with spectral signal simulations to resolve the early steps of the deactivation mechanisms of uridine (Urd) and 5-methyluridine (5mUrd) in aqueous solution. We track the wave packet motion from the Franck-Condon region to the conical intersections (CIs) with the ground state and observe spectral signatures of excited-state vibrational modes. 5mUrd exhibits an order of magnitude longer lifetime with respect to Urd due to the solvent reorganization needed to facilitate bulky methyl group motions leading to the CI. This activates potentially lesion-inducing dynamics such as ring opening. Involvement of the 1nπ* state is found to be negligible. The photophysical mechanism by which nucleosides dissipate energy after UV light irradiation is still under debate. Here the authors, using ultrafast time resolved optical spectroscopies and quantum chemical computations, resolve the early steps of such mechanism in uridine and 5-methyluridine in aqueous solution. [ABSTRACT FROM AUTHOR]

The evolution of microorganisms often involves changes of unclear relevance, such as transient phenotypes and sequential development of multiple adaptive mutations in hotspot genes. Previously, we showed that ageing colonies of an E. coli mutant unable to produce cAMP when grown on maltose, accumulated mutations in the crp gene (encoding a global transcription factor) and in genes involved in pyrimidine metabolism such as cmk; combined mutations in both crp and cmk enabled fermentation of maltose (which usually requires cAMP-mediated Crp activation for catabolic pathway expression). Here, we study the sequential generation of hotspot mutations in those genes, and uncover a regulatory role of pyrimidine nucleosides in carbon catabolism. Cytidine binds to the cytidine regulator CytR, modifies the expression of sigma factor 32 (RpoH), and thereby impacts global gene expression. In addition, cytidine binds and activates a Crp mutant directly, thus modulating catabolic pathway expression, and could be the catabolite modulating factor whose existence was suggested by Jacques Monod and colleagues in 1976. Therefore, transcription factor Crp appears to work in concert with CytR and RpoH, serving a dual role in sensing both carbon availability and metabolic flux towards DNA and RNA. Our findings show how certain alterations in metabolite concentrations (associated with colony ageing and/or due to mutations in metabolic or regulatory genes) can drive the evolution in non-growing cells. Microbial evolution often involves transient phenotypes and sequential development of multiple mutations of unclear relevance. Here, the authors show that the evolution of non-growing E. coli cells can be driven by alterations in pyrimidine nucleoside levels associated with colony ageing and/or due to mutations in metabolic or regulatory genes. [ABSTRACT FROM AUTHOR]

Main observation and conclusion: Amicetin and congeners constitute a small family of complex pyrimidine nucleosides, which exhibit strong antibiotic activities against Gram‐positive bacteria and notably against strains of Mycobacterium tuberculosis. Herein, we report chemical synthesis of a series of disaccharide congeners of the amicetin family, including amicetin, plicacetin, and cytosaminomycin A—D. It is the first time for successful synthesis of amicetin, the prototypical member, and cytosaminomycins. The synthetic approach employs glycosyl N‐phenyltrifluoroacetimidate and thioglycoside donors to construct the characteristic aminodeoxydisaccharides consisting of α‐(1→4)‐glycosidic linkage, uses gold(I)‐catalyzed N‐glycosylation to furnish 2‐deoxy‐β‐nucleosides, and finally exploits amidation and global deprotection to complete the syntheses. It is noteworthy that the 3‐O‐protecting group in the 2‐deoxydisaccharide donors is found to be crucial for a successful N‐glycosylation to assemble the cytosaminomycin disaccharide nucleosides. [ABSTRACT FROM AUTHOR]

The stereoselective synthesis of some 3'‐deoxy‐3'‐C‐methyl pyrimidine nucleosides is reported. The studied modifications concern the inversion of the configuration in 2'‐position as well as the introduction of fluoro and azido substituents. The corresponding arabinonucleoside and 2'‐substituted ribonucleoside analogs of uracil and cytosine have been obtained and fully characterized. Attempts to introduce fluoro and azido substituents with inversion at C‐2' are also presented. [ABSTRACT FROM AUTHOR]

Culturing of Mycoplasma hominis in the presence of arginine and thymidine and subsequent comparative proteomic analysis of cells showed that, in addition to the already known arginine dihydrolase pathway of energy metabolism, M. hominis can utilize deoxyribose phosphates formed as a result of catabolism of pyrimidine nucleosides. In this case, a sharp deceleration of cell growth was observed. This allows M. hominis to occupy new niches in the host organism and survive under competitive conditions when the main sources of energy are unavailable. [ABSTRACT FROM AUTHOR]

Malaria, initiated by apicomplexan parasite, is an old disease and continues to be a major public health threat in many countries. This article aims to present different aspects of malaria including causes, pathogenesis, prevention, and treatment in an articulate and comprehensive manner and it causes high levels of morbidity and mortality in human beings worldwide. The development of new molecular tools as well as the use of next-generation sequencing (NGS) technologies and novel bioinformatics approaches has improved our knowledge of malarial epidemiology, diagnosis, treatment, vaccine development, and surveillance strategies.The Plasmodium falciparum is the most dangerous species that can infect human. The enzyme hypoxanthine-guanine phosphorybosyltransferase (HGPRT) in the malarial parasite Plasmodium falciparum (Pf) is central to the salvage pathway for purine nucleotide biosynthesis and is a potential antimalarial chemotherapeutic target. As with all metabolic pathways, serious problems occur if steps in the pathway are blocked. Some people inherit a rare defective version of HGPRT, which leads to a serious illness termed Lesch-Nyhan syndrome. Vector and parasite drug resistance are two major challenges for malaria control that require special attention. Artemisinins are sesquiterpene lactones, and has been recently approved for the treatment of malaria due to its endoperoxidase properties. This approach also estimates the ligand-receptor binding free energy by evaluating critical phenomena involved in the intermolecular recognition process. Prodrugs of these compounds have IC50 values in the 4-6 mM range in antimalarial cellbased assays, making them attractive compounds for further development as antimalarial drug leads. The purpose of this review is to examine current molecular docking strategies used in drug discovery and medicinal chemistry, exploring the advances in the field and the role played by the integration of structure- and ligand-based methods. [ABSTRACT FROM AUTHOR]

Reaction of 6-amino-2-methylthio-3-methyluracil with ethyl ethoxymethyleneoxaloacetate or methyl(Z)-2-acetylamino-3-dimethylaminopropenoates afforded diethyl 2-(1,6-dihydro-1-methyl-2-(methylthio)-6-oxopyrimidin-4-yl-amino)methylene malonate or (2E)-methyl 3-(1,6-dihydro-1-methyl-2-(methylthio)-6-oxopyrimidin-4-yl-amino)-2-acetamidoacrylate, respectively. Cyclization of each of the latter products by sodium ethoxide afforded new pyrido [2,3-d]pyrimidines, which were ribosylated with 1-O-acetyl-2,3,5-O-benzoyl-β-D-ribofuranose by the silylation method yielded the protected nucleosides. The protected nucleosides were debenzoylated by sodium methoxide to afford novel pyrido[2,3-d]pyrimidine nucleosides. The structural assignmentsv for the new compounds were based on their elemental analysis and spectroscopic data. [ABSTRACT FROM AUTHOR]

The reaction of 1,5-bis[1-(prop-2-yn-1-yl)uracil-3-yl]pentane with 2',3',5'-tri-O-acetyl-β-d-ribofuranosylazide followed by removing of acetyl protective groups with a solution of sodium methylate in methanol afforded 1,5-bis{[1-methyl(β-d-ribofuranosyl)-1H-1,2,3-triazole-4-yl]uracil-3-yl}pentane which is the first analog of pyrimidine nucleosides with two nucleobases and two d-ribofuranose residues. [ABSTRACT FROM AUTHOR]

All four isomeric series of novel 4‐substituted pyrido‐fused 7‐deazapurine ribonucleosides possessing the pyridine nitrogen atom at different positions were designed and synthesized. The total synthesis of each isomeric fused heterocycle through multistep heterocyclization was followed by glycosylation and derivatization at position 4 by cross‐coupling reactions or nucleophilic substitutions. All compounds were tested for cytostatic and antiviral activity. The most active were pyrido[4′,3′:4,5]pyrimidine nucleosides bearing MeO, NH2, MeS, or CH3 groups at position 4, which showed submicromolar cytotoxic effects and good selectivity for cancer cells. The mechanism involved activation by phosphorylation and incorporation to DNA where the presence of the modified ribonucleosides causes double‐strand breaks and apoptosis. [ABSTRACT FROM AUTHOR]