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Emerging and re-emerging viruses periodically cause outbreaks and epidemics around the world, which ultimately lead to global events such as the COVID-19 pandemic. Thus, the urgent need for new antiviral drugs is obvious. Over more than a century of antiviral development, nucleoside analogs have proven to be promising agents against diversified DNA and RNA viruses. Here, we present the synthesis and evaluation of the antiviral activity of nucleoside analogs and their deglycosylated derivatives based on a hydroxybenzo[4,5]imidazo[1,2-c]pyrimidin-1(2H)-one scaffold. The antiviral activity was evaluated against a panel of structurally and phylogenetically diverse RNA and DNA viruses. The leader compound showed micromolar activity against representatives of the family Coronaviridae , including SARS-CoV-2, as well as against respiratory syncytial virus in a submicromolar range without noticeable toxicity for the host cells. Surprisingly, methylation of the aromatic hydroxyl group of the leader compound resulted in micromolar activity against the varicella-zoster virus without any significant impact on cell viability. The leader compound was shown to be a weak inhibitor of the SARS-CoV-2 RNA-dependent RNA polymerase. It also inhibited biocondensate formation important for SARS-CoV-2 replication. The active compounds may be considered as a good starting point for further structure optimization and mechanistic and preclinical studies.

Herein we report the synthesis, conformational analysis and the evaluation of the antiviral activity of six-membered nucleoside analogues having a piperidine ring as the preorganized (deoxy)ribose bioisostere. Mutagenic nucleobase-containing nucleosides 1 and 2 were obtained by appropriate manipulation of the well-known glycomimetic agent deoxynojirimycin as easily accessible starting material. In vitro assays revealed activity of 5-iododeoxyuridine analogue 1 against all DNA viruses tested. As suggested by DFT analysis and pH-dependent NMR experiments, antiviral activity was correlated to the biomimetic character of the piperidine ring, as it is able to resemble the deoxyribose conformations adopted by natural nucleosides when interacting with viral enzymes., (Copyright © 2022 Elsevier Masson SAS. All rights reserved.)

Emerging and re-emerging viruses periodically cause outbreaks and epidemics all over the world, eventually leading to global events such as the current pandemic of the novel SARS-CoV-2 coronavirus infection COVID-19. Therefore, an urgent need for novel antivirals is crystal clear. Here we present the synthesis and evaluation of an antiviral activity of phenoxazine-based nucleoside analogs divided into three groups: (1) 8-alkoxy-substituted, (2) acyclic, and (3) carbocyclic. The antiviral activity was assessed against a structurally and phylogenetically diverse panel of RNA and DNA viruses from 25 species. Four compounds (11a-c, 12c) inhibited 4 DNA/RNA viruses with EC 50  ≤ 20 μM. Toxicity of the compounds for the cell lines used for virus cultivation was negligible in most cases. In addition, previously reported and newly synthesized phenoxazine derivatives were evaluated against SARS-CoV-2, and some of them showed promising inhibition of reproduction with EC 50 values in low micromolar range, although accompanied by commensurate cytotoxicity., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier Masson SAS. All rights reserved.)

The strong inhibition of Human Cytomegalovirus (HCMV) replication by benzimidazole nucleosides, like Triciribine and Maribavir, has prompted us to expand the structure-activity relationships of the benzimidazole series, using as a central core the imidazo[4,5-b]pyridine scaffold. We have thus synthesized a number of novel amino substituted imidazopyridine nucleoside derivatives, which can be considered as 4-(or 7)-aza-d-isosters of Maribavir and have evaluated their potential antiviral activity. The target compounds were synthesized upon glycosylation of suitably substituted 2-aminoimidazopyridines, which were prepared in six steps starting from 2-amino-6-chloropyridine. Even if the new compounds possessed only a slight structural modification when compared to the original drug, they were not endowed with interesting antiviral activity. Even so, three derivatives showed promising cytotoxic potential.

Herein, we report the synthetic strategies and characterization of some novel 1,3,4-oxadiazole homonucleoside analogs that are relevant to potential antitumor and cytotoxic activities. The structure of all compounds is confirmed using various spectroscopic methods such as 1 H-NMR, 13 C-NMR, HRMS, and FTIR. These compounds were evaluated against three human cancer cell lines (MCF-7, SKBR3, and HL60 Cell Line). Preliminary investigations showed that the cytotoxic activity was markedly dependent on the nucleobase. Introduction of 5-Iodouracil 4g and theobromine 6b proved to be extremely beneficial even they were more potent than the reference drug (DOX). Also, the synthesized compounds were tested for their antiviral activities against the human varicella-zoster virus (VZV). The product 4h was (6-azauracil derivative) more potent to the reference (acyclovir) against the deficient TK - VZV strain by about 2-fold. Finally, molecular docking suggested that the anticancer activities of compounds 6b and 4g mediated by inhibiting dual proteins EGFR/HER2 with low micromolar inhibition constant Ki range. The 1,3,4-oxadiazole homonucleosides showed a strong affinity to binding sites of target proteins by forming H-bond, carbon-hydrogen bond, Pi-anion, Pi-sulfur, Pi-sigma, alkyl, and Pi-alkyl interactions.

Homonucleoside analogues cis - 16 and trans - 17 having a (5-methoxycarbonyl)isoxazolidine framework were synthesized via the 1,3-dipolar cycloaddition of nucleobase-derived nitrones with methyl acrylate. Hydrogenolysis of the isoxazolidines containing thymine, dihydrouracil, theophylline and adenine moieties efficiently led to the formation of the respective γ-lactam analogues. γ-Lactam analogues having 5-bromouracil and 5-chlorouracil fragments were synthesized by treatment of uracil-containing γ-lactams with NBS and NCS. Isoxazolidine and γ-lactam analogues of homonucleosides obtained herein were evaluated for activity against a broad range of DNA and RNA viruses. None of the compounds that were tested exhibited antiviral or cytotoxic activity at concentrations up to 100 µM. The cytostatic activities of all compounds toward nine cancerous cell lines was tested. γ-Lactams trans - 15e (Cl-Ura) and cis - 15h (Theo) appeared the most active toward pancreatic adenocarcinoma cells (Capan-1), showing IC 50 values 21.5 and 18.2 µM, respectively. Isoxazolidine cis - 15e (Cl-Ura) inhibited the proliferation of colorectal carcinoma (HCT-116).

The phenoxazine scaffold is widely used to stabilize nucleic acid duplexes, as a part of fluorescent probes for the study of nucleic acid structure, recognition, and metabolism, etc. Here we present the synthesis of phenoxazine-based nucleoside derivatives and their antiviral activity against a panel of structurally diverse viruses: enveloped DNA herpesviruses varicella zoster virus (VZV) and human cytomegalovirus, enveloped RNA tick-borne encephalitis virus (TBEV), and non-enveloped RNA enteroviruses. Studied compounds were effective against DNA and RNA viruses reproduction in cell culture. 3-(2'-Deoxy-β-D-ribofuranosyl)-1,3-diaza-2-oxophenoxazine proved to be a potent inhibitor of VZV replication with superior activity against wild type than thymidine kinase deficient strains (EC 50 0.06 and 10 μM, respectively). This compound did not show cytotoxicity on all the studied cell lines. Several compounds showed promising activity against TBEV (EC 50 0.35-0.91 μM), but the activity was accompanied by pronounced cytotoxicity. These compounds may be considered as a good starting point for further structure optimization as antiherpesviral or antiflaviviral compounds., (Copyright © 2019 Elsevier B.V. All rights reserved.)

A focused nucleoside library was constructed around a 3'-C-ethynyl-d-ribofuranose sugar scaffold, which was coupled to variously modified purine nucleobases. The resulting nucleosides were probed for their ability to inhibit tumor cell proliferation, as well as for their activity against a panel of relevant human viruses. While C6-aryl substituted purine nucleosides were found to be weakly active, several C7-substituted 7-deazapurine nucleosides elicited potent antiproliferative activity. Their activity spectrum was evaluated in the NCI-60 tumor cell line panel indicating activity against several solid tumor derived cell lines. Analog 32, equipped with a 7-deaza 7-chloro-6-amino-purin-9-yl base was evaluated in a metastatic breast tumor (MDA-MB-231-LM2) xenograft model. It inhibited both tumor growth and reduced the formation of lung metastases as revealed by BLI analysis. The dideazanucleoside analog 66 showed interesting activity against hCMV. These results highlight the potential advantages of recombining known sugar and nucleobase motifs as a library design strategy to discover novel antiviral or antitumor agents., (Copyright © 2018 Elsevier Masson SAS. All rights reserved.)

The synthesis of both 2'-hydroxy-3'-deoxy and 2'-deoxy-3'-hydroxy cyclopentyl nucleoside phosphonates with the natural nucleobases adenine, thymine, cytosine and guanine from a single precursor has been performed. The guanine containing analogues showed antiviral activity. Especially the 3'-deoxy congener 23 was active, displaying an EC 50 of 5.35 μM against TK + VZV strain and an EC 50 of 8.83 μM against TK - VZV strain, besides lacking cytotoxicity. However, the application of phosphonodiamidate prodrug strategy did not lead to a boost in antiviral activity., (Copyright © 2018 Elsevier Masson SAS. All rights reserved.)

Several hitherto unknown (E)-but-2-enyl nucleoside phosphonoamidate analogs (ANPs) were prepared directed with nitrogen reagents by cross-metathesis in water-under ultrasound irradiation. Two diastereoisomers were formally identified by X-ray diffraction. These compounds were evaluated against a large spectrum of DNA and RNA viruses. Among them, the phosphonoamidate thymine analogue 19 emerged as the best prodrug against varicella-zoster virus (VZV) with EC 50 values of 0.33 and 0.39 μM for wild-type and thymidine kinase deficient strains, respectively, and a selectivity index ≥200 μM. This breakthrough approach paves the way for new purine and pyrimidine (E)-but-2-enyl phosphonoamidate analogs., (Copyright © 2018 Elsevier Masson SAS. All rights reserved.)

The synthesis of emimycin, 5-substituted emimycin analogues and the corresponding ribo- and 2'-deoxyribonucleoside derivatives is described. Emimycin, its 5-substituted congeners and the ribonucleoside derivatives are completely devoid of antiviral activity against RNA viruses. In contrast, some of the 2'-deoxyribosyl emimycin derivatives are potent inhibitors of the replication of herpes simplex virus-1 and varicella-zoster virus, lacking cytotoxicity., (Copyright © 2017 Elsevier Masson SAS. All rights reserved.)

While noncanonic xanthine nucleotides XMP/dXMP play an important role in balancing and maintaining intracellular purine nucleotide pool as well as in potential mutagenesis, surprisingly, acyclic nucleoside phosphonates bearing a xanthine nucleobase have not been studied so far for their antiviral properties. Herein, we report the synthesis of a series of xanthine-based acyclic nucleoside phosphonates and evaluation of their activity against a wide range of DNA and RNA viruses. Two acyclic nucleoside phosphonates within the series, namely 9-[2-(phosphonomethoxy)ethyl]xanthine (PMEX) and 9-[3-hydroxy-2-(phosphonomethoxy)propyl]xanthine (HPMPX), were shown to possess activity against several human herpesviruses. The most potent compound was PMEX, a xanthine analogue of adefovir (PMEA). PMEX exhibited a single digit µM activity against VZV (EC 50  = 2.6 µM, TK + Oka strain) and HCMV (EC 50  = 8.5 µM, Davis strain), while its hexadecyloxypropyl monoester derivative was active against HSV-1 and HSV-2 (EC 50 values between 1.8 and 4.0 µM). In contrast to acyclovir, PMEX remained active against the TK - VZV 07-1 strain with EC 50  = 4.58 µM. PMEX was suggested to act as an inhibitor of viral DNA polymerase and represents the first reported xanthine-based acyclic nucleoside phosphonate with potent antiviral properties.

Following our findings on the anti-human immunodeficiency virus (HIV) activity of acyclovir (ACV) phosphate prodrugs, we herein report the ProTide approach applied to a series of acyclic nucleosides aimed at the identification of novel and selective antiviral, in particular anti-HIV agents. Acyclic nucleoside analogues used in this study were identified through a virtual screening using HIV-reverse transcriptase (RT), adenylate/guanylate kinase, and human DNA polymerase γ. A total of 39 new phosphate prodrugs were synthesized and evaluated against HIV-1 (in vitro and ex vivo human tonsillar tissue system) and human herpes viruses. Several ProTide compounds showed substantial potency against HIV-1 at low micromolar range while the parent nucleosides were not effective. Also, pronounced inhibition of herpesvirus replication was observed. A carboxypeptidase-mediated hydrolysis study was performed for a selection of compounds to assess the formation of putative metabolites and support the biological activity observed.

A new strategy for the synthesis of N 3 -benzoylated- and N 3 -benzylated N 1 -propargylquinazoline-2,4-diones 30a-d and 31a-d from isatoic anhydride 41 is reported. The alkynes 30a-d and 31a-d were applied in the 1,3-dipolar cycloadditions with azides 27 and 28 to synthesize acyclic 1,2,3-triazole nucleosides. The obtained alkynes and 1,2,3-triazole were evaluated for antiviral activity against a broad range of DNA and RNA viruses. The alkyne 30d showed activity against adenovirus-2 (EC 50  = 8.3 μM), while compounds 37a and 37d were also active toward herpes simplex virus-1 wild-type and thymidine kinase deficient (HSV-1 TK - ) strains (EC 50 values in the range of 4.6-13.8 μM). In addition, compounds 30a, 30b, 37b, and 37c exhibited activity toward varicella-zoster virus (VZV) TK + and TK - strains (EC 50  = 2.1-9.5 μM). The compound 30b proved to be the most selective against VZV and displayed marginal activity against human cytomegalovirus (HCMV). Although the compound 30a had improved anti-HCMV activity, the increase in anti-HCMV activity was accompanied by significant toxicity. Compounds 37a and 37d showed inhibitory effects toward the human T lymphocyte (CEM) cell line (IC 50  = 21 ± 7 and 22 ± 1 μM, respectively), while compound 35 exhibited cytostatic activity toward HMEC-1 cells (IC 50  = 28 ± 2 μM)., (© 2017 Deutsche Pharmazeutische Gesellschaft.)

Acyclic nucleosides containing a 3-fluoro-2-(phosphonomethoxy)propyl (FPMP) side chain are known to be moderately potent antihuman immunodeficiency virus (HIV) agents, while being completely devoid of antiviral activity against a wide range of DNA viruses. The derivatization of the phosphonic acid functionality of FPMPs with a diamyl aspartate phenoxyamidate group led to a novel generation of compounds that not only demonstrate drastically improved antiretroviral potency but also are characterized by an expanded spectrum of activity that also covers hepatitis B and herpes viruses. The best compound, the (S)-FPMPA amidate prodrug, exerts anti-HIV-1 activity in TZM-bl and peripheral blood mononuclear cells at low nanomolar concentrations and displays excellent potency against hepatitis B virus (HBV) and varicella-zoster virus (VZV). This prodrug is stable in acid and human plasma media, but it is efficiently processed in human liver microsomes with a half-life of 2 min. The (R) isomeric guanine derivative emerged as a selectively active anti-HIV and anti-HBV inhibitor, while being nontoxic to human hepatoblastoma cells. Notably, the pyrimidine containing prodrug (S)-Asp-FPMPC is the only congener within this series to demonstrate micromolar antihuman cytomegalovirus (HCMV) potency.

Transition metal-catalyzed halosulfonylation of 5-ethynyl uracil nucleosides provided (E)-5-(1-chloro-2-tosylvinyl)uridines. Tetrabutylammonium fluoride-mediated direct CH arylation of 5-iodouracil nucleosides with furan or 2-heptylfuran gave 5-furyl-substituted nucleosides without the necessity of using the organometallic substrates. These two classes of 5-substituted uracil nucleosides as well their corresponding ester derivatives were tested against a broad range of DNA and RNA viruses and the human immunodeficiency virus (HIV). The 3',5'-di-O-acetyl-5-(E)-(1-chloro-2-tosylvinyl)-2'-deoxyuridine (24) inhibited the growth of L1210, CEM and HeLa cancer cells in the lower micromolar range. The (β-chloro)vinyl sulfone 24 and 5-(5-heptylfur-2-yl)-2'-deoxyuridine (10) displayed micromolar activity against varicella zoster virus (VZV). The 5-(5-heptylfur-2-yl) analog 10 and its 3',5'-di-O-acetyl-protected derivative showed similar activity against the cytomegalovirus (CMV). The 5-(fur-2-yl) derivatives of 2'-deoxyuridine and arabino-uridine inhibited the replication of herpes simplex virus (HSV) TK + strains while the 5-(5-heptylfur-2-yl) derivative 10 displayed antiviral activity against the parainfluenza virus., (© 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The efficient synthesis of a new series of polyhydroxylated dibenzyl ω-(1H-1,2,3-triazol-1-yl)alkylphosphonates as acyclic nucleotide analogues is described starting from dibenzyl ω-azido(polyhydroxy)alkylphosphonates and selected alkynes under microwave irradiation. Selected O,O-dibenzylphosphonate acyclonucleotides were transformed into the respective phosphonic acids. All compounds were evaluated in vitro for activity against a broad variety of DNA and RNA viruses and for cytostatic activity against murine leukemia L1210, human T-lymphocyte CEM and human cervix carcinoma HeLa cells. Compound (1S,2S)-16b exhibited antiviral activity against Influenza A H3N2 subtype (EC50=20μM-visual CPE score; EC50=18μM-MTS method; MCC >100μM, CC50 >100μM) in Madin Darby canine kidney cell cultures (MDCK), and (1S,2S)-16k was active against vesicular stomatitis virus and respiratory syncytial virus in HeLa cells (EC50=9 and 12μM, respectively). Moreover, compound (1R,2S)-16l showed activity against both herpes simplex viruses (HSV-1, HSV-2) in HEL cell cultures (EC50=2.9 and 4μM, respectively) and feline herpes virus in CRFK cells (EC50=4μM) but at the same time it exhibited cytotoxicity toward uninfected cell (MCC⩾4μM). Several other compounds have been found to inhibit proliferation of L1210, CEM as well as HeLa cells with IC50 in the 4-50μM range. Among them compounds (1S,2S)- and (1R,2S)-16l were the most active (IC50 in the 4-7μM range)., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

A series of seventeen hitherto unknown ANP analogs bearing the (E)-but-2-enyl aliphatic side chain and modified heterocyclic base such as cytosine and 5-fluorocytosine, 2-pyrazinecarboxamide, 1,2,4-triazole-3-carboxamide or 4-substituted-1,2,3-triazoles were prepared in a straight approach through an olefin acyclic cross metathesis as key synthetic step. All novel compounds were evaluated for their antiviral activities against a large number of DNA and RNA viruses including herpes simplex virus type 1 and 2, varicella zoster virus, feline herpes virus, human cytomegalovirus, hepatitis C virus (HCV), HIV-1 and HIV-2. Among these molecules, only compound 31 showed activity against human cytomegalovirus in HEL cell cultures with at EC50 of ∼10 μM. Compounds 8a, 13, 14, and 24 demonstrated pronounced anti-HCV activity without significant cytotoxicity at 100 μM., (Copyright © 2013 Elsevier Masson SAS. All rights reserved.)

Hexadecyloxypropyl esters of acyclic nucleoside phosphonates containing guanine (G) or hypoxanthine (Hx) and a (S)-[3-hydroxy-2-(phosphonomethoxy)propyl] [(S)-HPMP] or 2-(2-phosphonoethoxy)ethyl (PEE) acyclic moiety have been prepared. The activity of the prodrugs was evaluated in vitro against different virus families. Whereas ester derivatives of PEEHx and (S)-HPMPHx were antivirally inactive, monoesters of PEEG, and mono- and diesters of (S)-HPMPG showed pronounced antiviral activity against vaccinia virus and/or herpesviruses. Monoesters of (S)-HPMPG emerged as the most potent and selective derivatives against these DNA viruses. None of the compounds were inhibitory against RNA viruses and retroviruses., (Crown Copyright © 2012. Published by Elsevier Masson SAS. All rights reserved.)

Series of novel acyclic nucleoside phosphonates (ANPs) with various nucleobases and 2-(2-phosphonoethoxy)ethyl (PEE) chain bearing various substituents in β-position to the phosphonate moiety were prepared. The influence of structural alternations on antiviral activity was studied. Several derivatives exhibit antiviral activity against HIV and vaccinia virus (middle micromolar range), HSV-1 and HSV-2 (lower micromolar range) and VZV and CMV (nanomolar range), although the parent unbranched PEE-ANPs are inactive. Adenine as a nucleobase and the methyl group attached to the PEE chain proved to be a prerequisite to afford pronounced antiviral activity., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

We present the first report of the application of the dipeptidyl peptidase IV (DPPIV/CD26) based prodrug approach to hydroxy-containing drug derivatives. In particular, we applied this strategy to the highly lipophilic antiviral drug family of bicyclic furanopyrimidine nucleoside analogues (BCNA) in order to improve their physicochemical and pharmacokinetic properties. Our stability data demonstrated that the prodrugs efficiently release the parent BCNA drug upon selective conversion by purified DPPIV/CD26 and by soluble DPPIV/CD26 present in bovine, murine, and human serum. Vildagliptin, a specific inhibitor of DPPIV/CD26, was able to completely block the hydrolysis of the prodrugs in the presence of purified DPPIV/CD26 human, murine, and bovine serum. Several novel prodrugs showed remarkable increases in water solubility (up to more than 3 orders of magnitude) compared to the poorly soluble parent drug. We also demonstrated a markedly enhanced oral bioavailability of the prodrugs versus the parent drug in mice.

We report the preparation of 2'-alpha-F, 2'-beta-F and 2',2'-difluoro analogues of the leading anti-varicella zoster virus (VZV) pentylphenyl BCNA Cf 1743. VZV thymidine kinase showed the highest phosphorylating capacity for the beta-fluoro derivative, that retained equal antiviral potency as the parent compound. In contrast, the alpha-fluoro- and 2',2'-difluoro BCNA derivatives were markedly less (approximately 100-fold) antivirally active.

Novel alkenyl substituted aryl bicyclic furano pyrimidines have been prepared and evaluated in vitro against Varicella Zoster Virus (VZV). The para-substituted analogues retain the nanomolar potency we have reported for p-alkyl analogues, while the ortho- and meta-alkenyl systems lose 3-4 orders of potency.

Camelpox virus (CMLV) is the closest known virus to variola virus. Here we report on the anti-CMLV activities of several acyclic nucleoside phosphonates (ANPs) related to cidofovir [(S)-1-(3-hydroxy-2-phosphonomethoxypropyl)cytosine (HPMPC; Vistide)] against two CMLV strains, CML1 and CML14. Cytopathic effect (CPE) reduction assays performed with human embryonic lung fibroblast monolayers revealed the selectivities of the first two classes of ANPs (cHPMPA, HPMPDAP, and HPMPO-DAPy) and of the hexadecyloxyethyl ester of 1-{[(5S)-2-hydroxy-2-oxido-1,4,2-dioxaphosphinan-5-yl]methyl}-5-azacytosine (HDE-cHPMP-5-azaC), belonging to the newly synthesized ANPs, which are HPMP derivatives containing a 5-azacytosine moiety. The inhibitory activities of ANPs against both strains were also confirmed with primary human keratinocyte (PHK) monolayers, despite the higher toxicity of those molecules on growing PHKs. Virus yield assays confirmed the anti-CML1 and anti-CML14 efficacies of the compounds selected for the highest potencies in CPE reduction experiments. Ex vivo studies were performed with a 3-dimensional model of human skin, i.e., organotypic epithelial raft cultures of PHKs. It was ascertained by histological evaluation, as well as by virus yield assays, that CMLV replicated in the human skin equivalent. HPMPC and the newly synthesized ANPs proved to be effective at protecting the epithelial cells against CMLV-induced CPE. Moreover, in contrast to the toxicity on PHK monolayers, signs of toxicity in the differentiated epithelium were seen only at high ANP concentrations. Our results demonstrate that compounds belonging to the newly synthesized ANPs, in addition to cidofovir, represent promising candidates for the treatment of poxvirus infections.

Murine polyomavirus and simian virus 40 were used to evaluate the potencies of the compounds of three classes of acyclic nucleoside phosphonates: (i) the original HPMP (3-hydroxy-2-phosphonomethoxypropyl) and PME (2-phosphonomethoxyethyl) derivatives, (ii) the 6-[2-(phosphonomethoxy)alkoxy]-2,4-diaminopyrimidine (DAPy) derivatives, and (iii) a new class of HPMP derivatives containing a 5-azacytosine moiety. The last class showed the highest activities and selectivities against both polyomaviruses.

Hitherto unknown 1,4-disubstituted-[1,2,3]-triazolo-4',4'-dihydroxymethyl-3'-deoxy carbanucleosides were synthesized based on a "click approach." Various alkynes were introduced on a key azido intermediate by the "click" 1,3-dipolar Huisgen cycloaddition. Their antiviral activities and cellular toxicities were evaluated on vaccinia virus. None of the synthesized compounds exhibited a significant antiviral activity.

With the commercial availability of well-defined ruthenium metathesis catalysts which combine high stability and broad functional group compatibility, olefin metathesis is now routinely integrated in various syntheses. We will report here the overwhelming power and scope of cross-metathesis in the area of new acyclic nucleoside phosphonates. Scope and limitations of this approach, and especially the E/Z stereocontrol, are discussed on selected examples from our drug discovery group.

TSAO derivatives are a unique group of potent and highly specific inhibitors of HIV-1 replication. We have recently reported 4''-ureido TSAO derivatives that are devoid of anti-HIV-1 activity, but inhibit human cytomegalovirus with an activity comparable to that of Ganciclovir. We herein report the synthesis and biological evaluation of novel 4''-ureido TSAO derivatives in order to evaluate the structural features required for anti-HCMV activity. Interestingly, these studies revealed that the compounds may inhibit HCMV at the DNA polymerase step via a non-nucleoside mechanism.

Further to the discovery of bicyclic furanopyrimidine nucleoside analogues (BCNAs) as potent anti-VZV agents, a branched series of this family of compounds was synthesised. The aim was to study the impact of the geometry and steric hindrance in the side chain as well as lipophilic role of this moiety on biological activity. The results showed a detrimental effect of branching on antiviral activity, with a different magnitude depending on the position of branching in the side chain. This study again showed the importance of this moiety for biological activity, as well as the limited efficacy of the ClogP value as a tool for predicting the potency of BCNAs, while suggesting an alternative rationale behind the design of future series.

Varicella-zoster virus (VZV) is responsible for primary infections as well as reactivations after latency in the dorsal root ganglia. The treatment of such infections is mandatory for immunocompromised patients and highly recommended for elderly patients with herpes zoster infections (also called zona or shingles). The treatment of choice is presently based on four molecules, acyclovir (ACV), valaciclovir, famciclovir, and (in Europe) brivudine (BVDU). We present here our data on the antiviral activity of a new class of potent and selective anti-VZV compounds, bicylic pyrimidine nucleoside analogues (BCNAs), against a broad variety of clinical isolates and different drug-resistant virus strains. The results show that the BCNAs are far more potent inhibitors than ACV and BVDU against clinical VZV isolates as well as the VZV reference strains Oka and YS. The BCNAs were not active against ACV- and BVDU-resistant VZV strains bearing mutations in the viral thymidine kinase gene but kept their inhibitory potential against virus strains with mutations in the VZV DNA polymerase gene. Mutant virus strains selected in the presence of the BCNAs were solely cross-resistant to drugs, such as ACV and BVDU, that depend for their antiviral action on metabolic activation by the viral thymidine kinase.

Bicyclic furanopyrimidine nucleoside analogues (BCNAs) have been previously reported as potent and selective anti-varicella-zoster virus (VZV) agents. Few modifications on the sugar moiety have been considered so far but some of them have shown interesting activity against human cytomegalovirus (HCMV) while losing activity against VZV. In addition, recent work has led to an entirely new series of anti-HCMV bicyclic furopyrimidine agents, acting through a non-nucleoside mechanism. In order to further investigate structure-activity relationship studies on the sugar moiety, some 3'- and 5'-chloro derivatives and 5'-deoxygenated derivatives have been synthesized. The lack of anti-VZV activity of the 5'-modified derivatives is further proof of a mechanism of action involving VZV thymidine kinase (TK)-mediated phosphorylation. Similarly, the replacement of the 3'-OH with chlorine showed a decrease of antiviral activity, which can be correlated to the lack of interaction with VZV TK as demonstrated by enzyme assays. These results confirm free 5'-OH and 3'-OH as necessary requirements for efficient recognition by VZV TK and for potent anti-VZV activity in cell culture.

Thieno analogues of the potent and selective furo-pyrimidine anti-VZV nucleoside family bearing a p-alkylphenyl side chain have been synthesised and tested for their antiviral activity against Varicella-Zoster virus (VZV). While the alkyl chain analogues were shown to retain full antiviral activity against VZV, these new analogues did not when compared to their furo parent nucleosides.

2,4-Diamino-6-hydroxypyrimidines substituted in position 5 by an allyl, benzyl, cyanomethyl, ethoxycarbonylmethyl, phenyl, cyclopropyl, or methyl group were prepared either by C5-alkylation or by formation of the pyrimidine ring by cyclization. Their alkylation with 2-[(diisopropoxyphosphoryl)methoxy]ethyl tosylate afforded N1- and O6-regioisomers that were separated and converted to the free phosphonic acids by treatment with bromotrimethylsilane followed by hydrolysis. Reaction of 2,4-diamino-6-[[(diisopropoxyphosphoryl)methoxy]ethoxy]pyrimidine with elemental bromine, N-chloro-, or N-iodosuccinimide gave the corresponding phosphorus-protected 5-bromo-, 5-chloro-, and 5-iodo derivatives, respectively. Their deprotection afforded 2,4-diamino-5-bromo- and -5-chloro-6-[2-(phosphonomethoxy)ethoxy]pyrimidines. 2,4-Diamino-5-methyl-6-[2-(phosphonomethoxy)ethoxy]pyrimidine was synthesized also by cross-coupling of the 5-bromo compound with AlMe(3), followed by deprotection. The compounds showed poor, if any, inhibitory activity against DNA viruses such as herpes simplex virus type 1 and type 2, cytomegalovirus, varicella-zoster virus, and vaccinia virus. In contrast, several 5-substituted 2,4-diaminopyrimidine derivatives markedly inhibited retrovirus replication in cell culture. The 5-methyl derivative was exquisitely inhibitory to human immunodeficiency virus and Moloney murine sarcoma virus-induced cytopathicity in cell culture (EC(50) approximately 0.00018 mumol/mL) but also cytostatic to CEM cell cultures. In contrast, the 5-halogen-substituted derivatives showed pronounced antiretroviral activity (EC(50) = 0.0023-0.0110 mumol/mL), comparable to that of the reference drugs adefovir and tenofovir, but were devoid of measurable toxicity at 0.3 mumol/mL.

Synthesis of 5‐alkynyl furopyrimidine nucleoside analogs, with free‐ribose groups, was carried out, and their biological activity was evaluated. The substituents introduced at the C‐5 included propargyl and homopropargyl alcohols, 4‐methylphenyl (p‐tolyl), and 4‐pentylphenyl substituted alkynyl groups (56%–88%). Subsequently, alkyne function was coordinated to dicobalt hexacarbonyl unit, yielding the corresponding dicobalt hexacarbonyl 5‐alkynyl furopyrimidine nucleosides (51%–75%). All compounds contained 4‐pentylphenyl group attached at the C‐6 position of the bicyclic base, in line with most active antiviral structures. The antiproliferative effect of these modified nucleosides on cancer cells of different phenotypes was determined using in vitro studies. The tested compounds show antiproliferative effects with median inhibitory concentration (IC50) values of 16–23 and 9–15 μM for HeLa and K562 cells, respectively. The determination of reactive oxygen species (ROS) formation in K562 cells in the presence of modified nucleosides may suggest that the mode of action of the examined compounds may be attributed to the induction of oxidative stress. [ABSTRACT FROM AUTHOR]

Strongly pairing ethynylpyridone C‐nucleosides are attractive surrogates for thymidine in oligonucleotides. Exploratory work on the antiviral activity of 3′‐azidothymidine (AZT) derivatives with ethynylpyridone as base had identified strong lipophilicity as a limiting factor. Two strategies are being pursued to overcome this issue. In order to make the base more polar, the ethynyl group has been replaced with a cyano group, leading to a cyanopyridone C‐nucleoside, whose eleven‐step synthesis is reported here, together with the synthesis of a 3′‐azido‐2′,3′‐dideoxynucleoside derivative. The base pairing with adenine in a DNA duplex was studied by UV melting analysis of a self‐complementary hexamer containing the 6‐cyano‐2′‐deoxynucleoside instead of thymidine. A melting point increase of 2 °C compared to the unmodified control was found. The other strategy employs a phosphoramidate prodrug design with less lipophilic amino acid esters. Here, anti‐HIV test of the alaninyl and prolinyl methyl esters of AZT gave promising results in cell culture experiments, increasing the selectivity index up to 5.8‐fold for the IIIB strain and up to 5‐fold for the ROD strain of the virus, as compared to the parent nucleoside. These findings help to design the next generation of pyridone C‐nucleosides with potential applications as antivirals. [ABSTRACT FROM AUTHOR]

Objectives: To investigate the efficacy of cidofovir to block gammaherpesvirus replication in the context of sexual transmission.Methods: A luciferase-expressing strain of murid herpesvirus 4 (MuHV-4) was used to monitor genital virus excretion from infected female BALB/c mice and sexual transmission to naive males. The efficiency of cidofovir to block genital excretion from infected females or replication and host colonization of naive males after sexual contact was tested by treating infected females (either once daily or at a single timepoint), naive males before exposure (either once daily or at a single timepoint) or males 24 h post-exposure.Results: We showed that daily treatment of infected females can reduce MuHV-4 genital shedding by 75%. Similarly, daily preventive treatment of naive males was sufficient to block viral replication and latency establishment in males. In contrast, a single administration of cidofovir to infected females at day 14 post-infection or to naive males 2 to 6 days before contact with MuHV-4-excreting females was not sufficient to significantly reduce viral shedding from females or infection of males, respectively. Interestingly, a single administration of cidofovir to males 24 h after contact with MuHV-4-infected females excreting the virus in the genital tract significantly reduced virus replication in males and seroconversion.Conclusions: Altogether, our results show that cidofovir can significantly reduce gammaherpesvirus replication, excretion and colonization of the naive partner in the context of sexual transmission. Such treatments could therefore be recommended in some specific conditions where gammaherpesvirus infections could be deleterious. [ABSTRACT FROM AUTHOR]

A series of novel trisubstituted 1,2,3-triazole purine nucleosides were efficiently synthesized via Huisgen 1,3-dipolar cycloaddition in good yields. Bioactivity against cytomegalovirus (CMV) and varicella-zoster virus (VZV) in human embryonic lung cell cultures was evaluated and all compounds show low antiviral activity. [ABSTRACT FROM AUTHOR]

Cidofovir [(S)-1-(3-hydroxy-2-phosphonylmethoxypropyl)cytosine, HPMPC] is an acyclic nucleoside analog approved since 1996 for clinical use in the treatment of cytomegalovirus (CMV) retinitis in AIDS patients. Cidofovir (CDV) has broad-spectrum activity against DNA viruses, including herpes-, adeno-, polyoma-, papilloma- and poxviruses. Among poxviruses, cidofovir has shown in vitro activity against orthopox [vaccinia, variola (smallpox), cowpox, monkeypox, camelpox, ectromelia], molluscipox [molluscum contagiosum] and parapox [orf] viruses. The anti-poxvirus activity of cidofovir in vivo has been shown in different models of infection when the compound was administered either intraperitoneal, intranasal (aerosolized) or topically. In humans, cidofovir has been successfully used for the treatment of recalcitrant molluscum contagiosum virus and orf virus in immunocompromised patients. CDV remains a reference compound against poxviruses and holds potential for the therapy and short-term prophylaxis of not only orthopox- but also parapox- and molluscipoxvirus infections. [ABSTRACT FROM AUTHOR]

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The synthesis of 3'-fluoro analogues of recently discovered highly potent anti-VZV furanopyrimidine deoxynucleosides (BCNAs) is herein reported, for both the alkyl and alkylphenyl series. The compounds are tested against a range of herpes viruses and display poor activity, strongly supporting the notion of the importance of the presence of a 3'-OH for antiviral activity. [ABSTRACT FROM AUTHOR]

Reports on the discovery that a synthetic by-product in the preparation of the parent 5-alkynyl nucleosides displayed prominent potency and exclusive selectivity for Varicella-Zoster Virus (VZV). Possible development of topical applications; Details of experiments; Conclusion that the p-alkylaryl series of furo pyrimidine nucleosides could be a potential treatment for herpes zoster.

As part of an ongoing research program, we have prepared novel bicyclic nucleoside inhibitors bearing long alkyl side-chains for evaluation against VZV. In particular, we report the synthesis of analogues with terminal unsaturation in the side-chain. Terminal alkenyl derivatives were found to be potent antivirals whereas the terminal alkynyls displayed poor activity. [ABSTRACT FROM AUTHOR]

The importance of phosphonoamidate prodrugs (ProTides) of acyclic nucleoside phosphonate (ANPs) is highlighted by the approval of Tenofovir Alafenamide Fumarate for the treatment of HIV and HBV infections. In the present paper we are reporting an expedient, one-pot, two-steps synthesis of allyl phosphonoamidates and diamidates that offers a time saving strategy when compared to literature methods. The use of these substrates in the cross metathesis reactions with alkenyl functionalised thymine and uracil nucleobases is reported. ANPs prodrugs synthesized via this methodology were evaluated for their antiviral activities against DNA and RNA viruses. It is anticipated that the use of 5,6,7,8-tetrahydro-1-napthyl as aryloxy moiety is capable to confer antiviral activity among a series of otherwise inactive uracil ProTides. [ABSTRACT FROM AUTHOR]

Acyclic nucleosides containing a 3-fluoro-2-(phosphonomethoxy)propyl (FPMP) side chain are known to be moderately potent antihuman immunodeficiency virus (HIV) agents, while being completely devoid of antiviral activity against a wide range of DNA viruses. The derivatization of the phosphonic acid functionality of FPMPs with a diamyl aspartate phenoxyamidate group led to a novel generation of compounds that not only demonstrate drastically improved antiretroviral potency but also are characterized by an expanded spectrum of activity that also covers hepatitis B and herpes viruses. The best compound, the (S)-FPMPA amidate prodrug, exerts anti-HIV-1 activity in TZM-bl and peripheral blood mononuclear cells at low nanomolar concentrations and displays excellent potency against hepatitis B virus (HBV) and varicella-zoster virus (VZV). This prodrug is stable in acid and human plasma media, but it is efficiently processed in human liver microsomes with a half-life of 2 min. The (R) isomeric guanine derivative emerged as a selectively active anti-HIV and anti-HBV inhibitor, while being nontoxic to human hepatoblastoma cells. Notably, the pyrimidine containing prodrug (S)-Asp-FPMPC is the only congener within this series to demonstrate micromolar antihuman cytomegalovirus (HCMV) potency. [ABSTRACT FROM AUTHOR]

Acyclic nucleoside phosphonates (ANPs), such as (S)-1-[(3-hydroxy-2-phosphonomethoxy)propyl)]cytosine (HPMPC), are an important group of broad-spectrum antiviral agents with activity against DNA viruses. In this report, we present the in vitro potencies of novel ANPs against gammaherpesviruses, including Kaposi's sarcoma-associated herpesvirus, Epstein- Barr virus (EBV), and three animal gammaherpesviruses. 1-(S)-[3-hydroxy-2-(phosphonomethoxy)propyl]-5-azacytosine (HPMP-5-azaC), (S)-9-[3-hydroxy-2-(phosphonomethoxy)propyl]-3-deazaadenine (3-deaza-HPMPA), and their cyclic derivatives have emerged as highly potent antigammaherpesvirus agents. Interestingly, cyclic prodrugs of ANPs exhibited reduced activities against EBV strain P3HR-1, but not against EBV strain Akata. Cell culture metabolism studies with HPMPC and cyclic HPMPC revealed that these differences were attributable to an altered drug metabolism in P3HR-1 cells after EBV reactivation and, more specifically, to a reduced hydrolysis of cyclic HPMPC by cyclic CMP phosphodiesterase. We did not correlate this effect with phosphodiesterase downregulation, or to functional mutations. Instead, altered cyclic AMP levels in P3HR-1 cells indicated a competitive inhibition of the phosphodiesterase by this cyclic nucleotide. Finally, both HPMPC and HPMP-5-azaC emerged as highly effective inhibitors in vivo through significant inhibition of murine gammaherpesvirus replication and dissemination. With the current need for potent antigammaherpesvirus agents, our findings underline the requirement of appropriate surrogate viruses for antiviral susceptibility testing and highlight HPMP-5-azaC as a promising compound for future clinical development. [ABSTRACT FROM AUTHOR]

O6-(Benzotriazol-1H-yl)guanosine and its 2'-deoxy analogue are readily converted to the O6-allyl derivatives that upon diazotization with t-BuONO and TMS-N3 yield the C-2 azido derivatives. We have previously analyzed the solvent-dependent azide⋅tetrazole equilibrium of C-6 azidopurine nucleosides, and in contrast to these, the O6-allyl C-2 azido nucleosides appear to exist predominantly in the azido form, relatively independent of solvent polarity. In the presently described cases, the tetrazole appears to be very minor. Consistent with the presence of the azido functionality, each neat C-2 azide displayed a prominent IR band at 2126-2130 cm-1. A screen of conditions for the ligation of the azido nucleosides with alkynes showed that CuCl in t-BuOH/H2O is optimal, yielding C-2 1,2,3-triazolyl nucleosides in 70-82% yields. Removal of the silyl groups with Et3N⋅3HF followed by deallylation with PhSO2Na/Pd(PPh3)4 gave the C-2 triazolylinosine nucleosides. In a continued demonstration of the versatility of O6-(benzotriazol-1H-yl)purine nucleosides, one C-2 triazolylinosine derivative was converted to two adenosine analogues via these intermediates, under mild conditions. Products were desilylated for biological assays. The two C-2 triazolyl adenosine analogues demonstrated pronounced antiproliferative activity in human ovarian and colorectal carcinoma cell cultures. When evaluated for antiviral activity against a broad spectrum of DNA and RNA viruses, some of the C-2 triazolylinosine derivatives showed modest inhibitory activity against cytomegalovirus. [ABSTRACT FROM AUTHOR]

Abstract: Introducing structural diversity into the nucleoside scaffold for use as potential chemotherapeutics has long been considered an important approach to drug design. In that regard, we have designed and synthesized a number of innovative 2′-deoxy expanded nucleosides where a heteroaromatic thiophene spacer ring has been inserted in between the imidazole and pyrimidine ring systems of the natural purine scaffold. The synthetic efforts towards realizing the expanded 2′-deoxy-guanosine and -adenosine tricyclic analogues as well as the preliminary biological results are presented herein. [Copyright &y& Elsevier]

Abstract: The synthesis and antiviral evaluation of a series of C5-(1,4- and 1,5-disubstituted-1,2,3-triazolo)-nucleoside derivatives is described. The key steps of this synthesis are regioselective Huisgen’s 1,3-dipolar cycloaddition, using either copper-catalyzed azide-alkyne cycloaddition (CuAAC) or ruthenium-catalyzed azide-alkyne cycloaddition (RuAAC) under microwave activation. Some compounds among the 5a–l series possess activity against herpes simplex viruses 1 and 2, varicella-zoster virus, human cytomegalovirus and vaccinia virus. Their cytostatic activities were determined against murine leukemia cells, human T-lymphocyte cells and cervix carcinoma cells. Compounds were also evaluated on a wide panel of RNA viruses, including Vesicular stomatitis virus, influenza viruses type A (H1N1 and H3N2) and B in MDCK cell cultures, parainfluenza-3 virus, reovirus-1, Sindbis virus and Punta Toro virus in Vero cell cultures and Vesicular stomatitis, Coxsackie B4 and respiratory syncytial virus, with no specific antiviral effect. [ABSTRACT FROM AUTHOR]

Abstract: A highly practical and efficient preparation of pyrano[3,2-c]pyridone and pyrano[4,3-b]pyran derivatives was developed via an ionic liquid mediated and promoted multi-component reaction of aldehyde (1), 4-hydroxy-pyridin-2(1H)-one or 4-hydroxy-2-pyranone (2), and malononitrile (3). As an application, a series of pyrimidine nucleoside-pyrano[3,2-c]pyridone or pyrano[4,3-b]pyran hybrids were efficiently obtained. These hybrid compounds were evaluated as potential antiviral and antileishmanial agents and showed encouraging biological activities. [Copyright &y& Elsevier]