The ex vivo effects of hypoxanthine-tricyclano, a synthetic adenosine analogue, on rat left and right atria.

Hypoxanthine-tricyclano is a synthetic adenosine analogue, in which adenine and ribose have been replaced by hypoxanthine and a morpholino-derived tricyclic moiety, respectively. We investigated whether hypoxanthine-tricyclano could influence atrial inotropy and/or chronotropy, two important functions regulated by the A1 receptor, the main adenosine receptor type of the supraventricular myocardium. Paced left atria and spontaneously beating right atria, isolated from male, 30-35 weeks old, Wistar rats, were used.

The Design, Synthesis and Mechanism of Action of Paxlovid, a Protease Inhibitor Drug Combination for the Treatment of COVID-19.

The COVID-19 pandemic, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has presented an enormous challenge to health care systems and medicine. As a result of global research efforts aimed at preventing and effectively treating SARS-CoV-2 infection, vaccines with fundamentally new mechanisms of action and some small-molecule antiviral drugs targeting key proteins in the viral cycle have been developed. The most effective small-molecule drug approved to date for the treatment of COVID-19 is Paxlovid, which is a combination of two protease inhibitors, nirmatrelvir and ritonavir.

In vitro and in vivo antiplasmodial evaluation of sugar-modified nucleoside analogues.

Drug-resistant Plasmodium falciparum (Pf) infections are a major burden on the population and the healthcare system. The establishment of Pf resistance to most existing antimalarial therapies has complicated the problem, and the emergence of resistance to artemisinin derivatives is even more concerning. It is increasingly difficult to cure malaria patients due to the limited availability of effective antimalarial drugs, resulting in an urgent need for more efficacious and affordable treatments to eradicate this disease.

Allosteric regulation and crystallographic fragment screening of SARS-CoV-2 NSP15 endoribonuclease.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the causative agent of coronavirus disease 2019 (COVID-19). The NSP15 endoribonuclease enzyme, known as NendoU, is highly conserved and plays a critical role in the ability of the virus to evade the immune system. NendoU is a promising target for the development of new antiviral drugs.

Triaza-tricyclanos - synthesis of a new class of tricyclic nucleoside analogues by stereoselective cascade cyclocondensation.

Herein, we report a stereoselective synthesis of a novel type of conformationally constrained nucleoside analogue in which the sugar part is replaced by a new symmetrical tricycle consisting of a morpholine ring condensed with two imidazolidines. 1,5-Dialdehydes obtained from trityl- and dimethoxytrityl-protected uridine, ribothymidine, inosine, cytidine, adenosine and guanosine by metaperiodate oxidation were reacted with ,-dibenzyl-1,2,3-triaminopropane; the latter reactant was produced using a new method that avoids explosive intermediates. Reactions of dialdehydes with propane-triamine cascade tricyclization resulted in the corresponding triaza-tricyclic derivatives bearing three new stereogenic centers in high yields.

N-Fluoroalkylated Morpholinos - a New Class of Nucleoside Analogues.

The first concise and efficient synthesis of some fluorine-containing morpholino nucleosides has been developed. One synthetic strategy was based on the oxidative ring cleavage of the vicinal diol unit of uridine, cytidine adenosine and guanosine derivatives, followed by cyclisation of the dialdehyde intermediates by double reductive amination with fluorinated primary amines to obtain various N-fluoroalkylated morpholinos. Another approach involved cyclisation of the diformyl intermediates with ammonia source, followed by dithiocarbamate formation and desulfurization-fluorination with diethylaminosulfur trifluoride yielding the corresponding morpholine-based nucleoside analogues with a N-CF element in their structure.

Synthesis and Anticancer and Antiviral Activities of C-2'-Branched Arabinonucleosides.

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'--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.

The Medicinal Chemistry of Artificial Nucleic Acids and Therapeutic Oligonucleotides.

Nucleic acids play a central role in human biology, making them suitable and attractive tools for therapeutic applications. While conventional drugs generally target proteins and induce transient therapeutic effects, nucleic acid medicines can achieve long-lasting or curative effects by targeting the genetic bases of diseases. However, native oligonucleotides are characterized by low in vivo stability due to nuclease sensitivity and unfavourable physicochemical properties due to their polyanionic nature, which are obstacles to their therapeutic use.

The Very First Modification of Pleuromutilin and Lefamulin by Photoinitiated Radical Addition Reactions-Synthesis and Antibacterial Studies.

Pleuromutilin is a fungal diterpene natural product with antimicrobial properties, semisynthetic derivatives of which are used in veterinary and human medicine. The development of bacterial resistance to pleuromutilins is known to be very slow, which makes the tricyclic diterpene skeleton of pleuromutilin a very attractive starting structure for the development of new antibiotic derivatives that are unlikely to induce resistance. Here, we report the very first synthetic modifications of pleuromutilin and lefamulin at alkene position C19-C20, by two different photoinduced addition reactions, the radical thiol-ene coupling reaction, and the atom transfer radical additions (ATRAs) of perfluoroalkyl iodides.

MTT Test and Time-lapse Microscopy to Evaluate the Antitumor Potential of Nucleoside Analogues.

Background/aim: Conventional viability tests, help to screen the cellular effects of candidate molecules, but the endpoint of these measurements lacks sufficient information regarding the molecular aspects. A non-invasive, easy-to-setup live-cell microscopic method served to in-depth analysis of mechanisms of potential anticancer drugs.

Materials And Methods: The proposed method combining the MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) test with time-lapse scanning microscopy (TLS), provided additional data related to the cell-cycle and the dynamic properties of cell morphology.

Synthesis and oligomerization of cysteinyl nucleosides.

Nucleoside and nucleic acid analogues are known to possess a considerable therapeutic potential. In this work, by coupling cysteine to nucleosides, we successfully synthesized compounds that may not only have interesting biological properties in their monomeric form, but can be used beyond that, for oligomerization, in order to produce new types of synthetic nucleic acids. We elaborated different strategies for the synthesis of cysteinyl nucleosides as monomers of cysteinyl nucleic acids using nucleophilic substitution or thiol-ene coupling as a synthetic tool, and utilised on two complementary nucleosides, uridine and adenosine.

Stereoselective Thioconjugation by Photoinduced Thiol-ene Coupling Reactions of Hexo- and Pentopyranosyl d- and l-Glycals at Low-Temperature-Reactivity and Stereoselectivity Study.

A comprehensive optimization and mechanistic study on the photoinduced hydrothiolation of different d- and l- hexo- and pentoglycals with various thiols was performed, at the temperature range of RT to -120 °C. Addition of thiols onto 2-substituted hexoglycals proceeded with complete 1,2-cis-α-stereoselectivity in all cases. Hydrothiolation of 2-substituted pentoglycals resulted in mixtures of 1,2-cis-α- and -β-thioglycosides of varying ratio depending on the configuration of the reactants.

Synthesis and Cytostatic Effect of 3'-deoxy-3'--Sulfanylmethyl Nucleoside Derivatives with d- Configuration.

A small library of 3'-deoxy-C3'-substituted xylofuranosyl-pyrimidine nucleoside analogues were prepared by photoinduced thiol-ene addition of various thiols, including normal and branched alkyl-, 2-hydroxyethyl, benzyl-, and sugar thiols, to 3'-exomethylene derivatives of 2',5'-di---butyldimethylsilyl-protected ribothymidine and uridine. The bioactivity of these derivatives was studied on tumorous SCC (mouse squamous carcinoma cell) and immortalized control HaCaT (human keratinocyte) cell lines. Several alkyl-substituted analogues elicited promising cytostatic activity in low micromolar concentrations with a slight selectivity toward tumor cells.

Promotion of a Reaction by Cooling: Stereoselective 1,2-cis-α-Thioglycoconjugation by Thiol-Ene Coupling at -80 °C.

The photoinitiated thiol-ene coupling reactions of 2-substituted glycals were studied as a generally applicable strategy for stereoselective 1,2-cis-α-thioconjugation. Although all glycals reacted with full α-selectivity, the efficacy of the reactions varied in a broad range depending on their configuration and glycals bearing axial acetoxy substituents reacted with very low efficacy at room temperature. The study revealed that the reaction progress could be promoted by cooling and inhibited by heating.

A low-temperature, photoinduced thiol-ene click reaction: a mild and efficient method for the synthesis of sugar-modified nucleosides.

Sugar-modified nucleosides are prime synthetic targets in anticancer and antiviral drug development. Radical mediated thiol-ene coupling was applied for the first time on nucleoside enofuranoside derivatives to produce a broad range of thio-substituted d-ribo, -arabino, -xylo and l-lyxo configured pyrimidine nucleosides. In contrast to the analogous reactions of simple sugar exomethylenes, surprisingly, hydrothiolation of nucleoside alkenes under the standard conditions of various initiation methods showed low to moderate yields and very low stereoselectivity.

A three-component reagent system for rapid and mild removal of O-, N- and S-trityl protecting groups.

A new reagent system consisting of a Lewis acid such as BF3·Et2O or Cu(OTf)2, the mild protic acid hexafluoroisopropanol and the reducing quenching agent triethylsilane was elaborated for O-, N- and S-detritylation of nucleoside, carbohydrate and amino acid derivatives. The method is compatible with acetyl, silyl, acetal and Fmoc groups.