Synthesis and anticancer and antiviral activities of various 2'- and 3'-methylidene-substituted nucleoside analogues and crystal structure of 2'-deoxy-2'-methylidenecytidine hydrochloride

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. Herein, new nucleoside analogues including morpholino-nucleoside hybrids and thio-substituted nucleoside derivatives were prepared and evaluated for in vitro and in vivo antiparasitic activity that led a few hits especially nucleoside-thiopyranoside conjugates, which are highly effective against Pf3D7 and PfRKL-9 strains in submicromolar concentration. One adenosine derivative and four pyrimidine nucleoside analogues significantly reduced the parasite burden in mouse models infected with Plasmodium berghei ANKA. Importantly, no significant hemolysis and cytotoxicity towards human cell line (RAW) was observed for the hits, suggesting their safety profile. Preliminary research suggested that these thiosugar-nucleoside conjugates could be used to accelerate the antimalarial drug development pipeline and thus deserve further investigation.

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’-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.

In vitro Anti-Herpesvirus Activities of 5-Substituted 2′-Deoxy-2′-Methylidene Pyrimidine Nucleosides

New pyrimidine deoxyribonucleoside analogues, 2′-deoxy-2′-methylideneuridine (DMDU), 2′-deoxy-2′-methylidenecytidine (DMDC), and their 5-substituted derivatives were tested for the anti-herpesvirus activities and anti-proliferative activity. E-5-(2-Bromovinyl)uracil derivative (BV-DMDU) and its cytosine congener were synthesized from 1-β-D-arabinofuranosyl- E-5-(2-bromovinyl)uracil (BV-araU). 5-Bromo, 5-iodo, 5-methyl, and 5-ethyl derivatives of DMDU and BV-DMDU showed activities against herpes simplex virus type 1 (HSV-1) and varicella-zoster virus (VZV). The corresponding DMDC derivatives had no or only weak antiviral activity. Among the 2′-deoxy-2′-methylidene pyrimidine nucleosides, BV-DMDU showed the most potent and selective anti-VZV activity. BV-DMDU was more potent than acyclovir, but less active than BV-araU. BV-DMDU was inactive against human diploid and tumour cells. DMDC and F-DMDC (5-fluoro derivative) were potent inhibitors of HSV-1, herpes simplex virus type 2, VZV, and human cytomegalovirus (HCMV) and also had significant anti-proliferative activity. Their potency against HCMV was better than that of ganciclovir and araC. Some DMDU derivatives also showed anti-HCMV activity, but they had anti-proliferative activity. The anti-HCMV activity of these DMDC and DMDU compounds was generally more potent than those against HSV-1 and VZV thereof, suggesting the participation of cellular kinase in their antiviral action.

Synthesis and biological evaluation of novel C6-cyclo secondary amine substituted purine steroid-nucleosides analogues

Novel C6-cyclo secondary amine substituted purine steroid-nucleoside analogues (2-9) were efficiently synthesized through displacement of the C6 chloro on the purine ring of series 1 with versatile cyclic secondary amines, including pyrrolidines, piperidine, morpholine, and piperazines. All the newly-synthesized compounds were evaluated for their anticancer activity in vitro against Hela, PC-3 and MCF-7 cell lines. Among them, compounds 5c and 6b exhibited significant cytotoxicity on PC-3 cell lines.

Synthesis and anticancer activity of novel C6-piperazine substituted purine steroid-nucleosides analogues

Novel C6-piperazine substituted purine nucleoside analogues (2-9) bearing a modified pyranose-like D ring of the 4-azasteroid moiety were efficiently synthesized through nucleophilic substitution at C6 position of the steroid-nucleoside precursors (1) with versatile piperazines. All newly-synthesized compounds were evaluated for their anticancer activity in vitro against Hela, PC-3 and MCF-7 cell lines. Among them, compounds 8b and 9b exhibited significant cytotoxicity on PC-3 cell lines.

Dideoxy fluoro-ketopyranosyl nucleosides as potent antiviral agents: synthesis and biological evaluation of 2,3- and 3,4-dideoxy-3-fluoro-4- and -2-keto-beta-d-glucopyranosyl derivatives of N(4)-benzoyl cytosine

The synthesis of the dideoxy fluoro ketopyranonucleoside analogues, 1-(2,3-dideoxy-3-fluoro-6-O-trityl-beta-d-glycero-hexopyranosyl-4-ulose)-N(4)-benzoyl cytosine (7a), 1-(3,4-dideoxy-3-fluoro-6-O-trityl-beta-d-glycero-hexopyranosyl-2-ulose)-N(4)-benzoyl cytosine (13a) and their detritylated analogues 8a and 14a, respectively, is described. Condensation of peracetylated 3-deoxy-3-fluoro-D-glucopyranose (1) with silylated N(4)-benzoyl cytosine, followed by selective deprotection and isopropylidenation afforded compound 2. Routine deoxygenation at position 2', followed by a deprotection-selective reprotection sequence afforded the partially tritylated dideoxy nucleoside of cytosine 6, which upon oxidation of the free hydroxyl group at the 4'-position, furnished the desired tritylated 2,3-dideoxy-3-fluoro ketonucleoside 7a in equilibrium with its hydrated form 7b. Compound 2 was the starting material for the synthesis of the dideoxy fluoro ketopyranonucleoside 13a. Similarly, several subsequent protection and deprotection steps as well as routine deoxygenation at position 4', followed by oxidation of the free hydroxyl group at the 2'-position of the partially tritylated dideoxy nucleoside 12, yielded the desired carbonyl compound 13a in equilibrium with its hydrated form 13b. Finally, trityl removal from 7a/b and 13a/b provided the unprotected 2,3-dideoxy-3-fluoro-4-keto and 3,4-dideoxy-3-fluoro-2-ketopyranonucleoside analogues 8a and 14a, in equilibrium with their gem-diol forms 8b and 14b. None of the compounds showed inhibitory activity against a wide variety of DNA and RNA viruses at subtoxic concentrations, except 7a/b that was highly efficient against rotavirus infection. Nucleoside 7a/b also exhibited cytostatic activity against cells of various cancers. BrdU-cell cycle analysis revealed that the mechanism of cytostatic activity may be related to a delay in G1/S phase and initiation of programmed cell death.

Unsaturated fluoro-ketopyranosyl nucleosides: Synthesis and biological evaluation of 3-fluoro-4-keto-β-d-glucopyranosyl derivatives of N4-benzoyl cytosine and N6-benzoyl adenine

The protected beta-nucleosides 1-(2,4,6-tri-O-acetyl-3-deoxy-3-fluoro-beta-d-glucopyranosyl)-N(4)-benzoyl cytosine (2a) and 9-(2,4,6-tri-O-acetyl-3-deoxy-3-fluoro-beta-d-glucopyranosyl)-N(6)-benzoyl adenine (2b), were synthesized by the coupling of peracetylated 3-deoxy-3-fluoro-d-glucopyranose (1) with silylated N(4)-benzoyl cytosine and N(6)-benzoyl adenine, respectively. The nucleosides were deacetylated and several subsequent protection and deprotection steps afforded the partially acetylated nucleosides of cytosine 7a and adenine 7b, respectively. Finally, direct oxidation of the free hydroxyl group at 4'-position of 7a and 7b, and simultaneous elimination reaction of the beta-acetoxyl group, afforded the desired unsaturated 3-fluoro-4-keto-beta-d-glucopyranosyl derivatives. These newly synthesized compounds were evaluated for their potential antitumor and antiviral activities. Compared to 5FU, the newly synthesized derivatives showed to be more efficient as antitumor growth inhibitors and they exhibited direct antiviral effect toward rotavirus.

Fluoro-ketopyranosyl nucleosides: synthesis and biological evaluation of 3-fluoro-2-keto-beta-D-glucopyranosyl derivatives of N4-benzoyl cytosine

1,2:5,6-Di-O-isopropylidene-alpha-d-glucofuranose on mild oxidation, reduction, fluorination, and deisopropylidenation followed by acetylation gave peracetylated 3-deoxy-3-fluoro-d-glucopyranose. This was coupled with silylated N(4)-benzoyl cytosine. The nucleoside was deacetylated and after several subsequent protection and deprotection steps afforded the desired 3-fluoro-2-keto-beta-d-glucopyranosyl derivatives. These novel synthesized compounds were evaluated for antiviral and cytotoxic activities against rotavirus, vesicular stomatitis virus, and the human colon adenocarcinoma cell line Caco-2, and have a promising potential in combating the rotaviral infections and in the treatment of colon cancer. As compared to AZT, a nucleoside analogue of reverse transcriptase inhibitor, the novel synthesized 1-(3,4-dideoxy-3-fluoro-beta-d-glycero-hex-3-enopyranosyl-2-ulose)-N(4)-benzoyl cytosine showed to be more effective at lower concentrations in inhibition of rotavirus infection as well as in the same range of antitumor activity.

4′-α-C-Branched N,O-nucleosides: synthesis and biological properties

The synthesis of 4'-alpha-C-branched N,O-nucleosides has been described, based on the 1,3-dipolar cycloaddition of nitrones with vinyl acetate followed by coupling with silylated nucleobases, The obtained compounds have been evaluated for their activity against HSV-1, HSV-2, HTLV-1. Cytotoxicity and apoptotic activity have been also investigated: compound 10c shows moderate apoptotic activity in Molt-3 cells.

Synthesis of 2'-methylene-substituted 5-azapyrimidine, 6-azapyrimidine, and 3-deazaguanine nucleoside analogues as potential antitumor/antiviral agents

2'-Deoxy-2'-methylene-6-azauridine (5) and 2'-deoxy-2'-methylene-6-azacytidine (8) have been synthesized via a multi-step procedure from 6-azauridine. 2'-Deoxy-2'-methylene-5-azacytidine (14a) and 2'-deoxy-2'-methylene-3-deazaguanosine (19a) and their corresponding alpha-anomers (14b and 19b) have been synthesized by the transglycosylation of 3',5'-O-(1,1,3,3- tetraisopropyldisiloxane-1,3-diyl)-2'-deoxy-2'-methyleneu ridine (12) with silylated 5-azacytosine and silylated N2-palmitoyl-3-deazaguanine, respectively, in the presence of trimethylsilyl trifluoromethanesulfonate as the catalyst in anhydrous dichloroethane, followed by separation of the isomers and deprotection of the blocking groups. These compounds were tested for cytotoxicity against B16F10, L1210, and CCRF-CEM tumor cell lines and for antiviral activity against HIV-1, HSV-1, and HSV-2.

Nucleosides and nucleotides. 176. 2'-Deoxy-2'-hydroxylaminocytidine: a new antitumor nucleoside that inhibits DNA synthesis although it has a ribonucleoside structure

The design and synthesis of potential antitumor antimetabolites 2'-deoxy-2'-hydroxylaminouridine (2'-DHAU) and -cytidine (2'-DHAC) are described. We found that 2'-DHAC in neutral solution generated 2'-aminoxy radicals at room temperature. 2'-DHAC inhibited the growth of L1210 and KB cells, with IC50 values of 1.58 and 1.99 microM, respectively, more potently than 2'-DHAU, with IC50 values of 34.5 and 27.3 microM, respectively. 2'-DHAC was effective against 9 human cell lines, with IC50 values of in the micromolar range. The in vivo antitumor activity of 2'-DHAC was also examined using the mouse leukemia P388 model, which gave a T/C value 167%. Phosphorylation of 2'-DHAC by uridine/cytidine kinase was essential for its cytotoxicity, as suggested by a competition experiment using several common nucleosides. Inhibition of DNA synthesis was the predominant mechanism of action of 2'-DHAC, although it has a ribo-configuration.

Nucleosides and Nucleotides. 156. Chelation-Controlled and Nonchelation-Controlled Diastereofacial Selective Thiophenol Addition Reactions at the 2'-Position of 2'-[(Alkoxycarbonyl)methylene]-2'-deoxyuridines: Conversion of (Z)-2'-[(Alkoxycarbonyl)methylene]-2'-deoxyuridines into Their (E)-Isomers(1)

The Wittig reaction of 1-[3,5-O-(1,1,3,3-tetraisopropyldisiloxane-1,3-diyl)-beta-D-erythro-pentofuranos-2-ulosyl]uracil (4) with Ph(3)P=CHCO(2)R (R = ethyl or tert-butyl) exclusively gave (Z)-2'-[(alkoxycarbonyl)methylene] derivatives 5 and 13, respectively, in high yields. An unusual beta-facial selectivity of thiophenol addition to the 2'-[(alkoxycarbonyl)methylene] moiety of 5 and 13 was observed, and this facial selectivity was found to be influenced by both the thiolate counter cation and the bulkiness of the alkoxy moiety. Treatment of 2'-[(ethoxycarbonyl)methylene] derivative 5with LiSPh (1.5 equiv) in the presence of PhSH in THF selectively gave 2'beta-(phenylthio) derivative 11 in high yield along with a trace of 2'alpha-(phenylthio) derivative 10. On the other hand, when 2'-[(tert-butoxycarbonyl)methylene] derivative13 was treated with KSPh in the presence of PhSH in dioxane/DMF, the facial selectivity was reversed to selectively give the 2'alpha-(phenylthio) adduct14 (alpha:beta, 77:23) in 90% yield. Oxidation of 14 with m-chloroperbenzoic acid in CH(2)Cl(2) and subsequent pyrolysis of the resulting sulfoxides exclusively gave the (Z)-isomer 13 in 92% yield. The oxidativesyn-elimination of the (2'R)-2'-[(tert-butoxycarbonyl)methyl]-2'-deoxy-2'-thiophenoxy-5'-O-(triisopropylsilyl)uridine (17), which was obtained from 14 in two steps, exclusively gave the desired (E)-[(tert-butoxycarbonyl)methylene] derivatives 18 in 90% yield. Deprotection of 18 gave the (E)-(carboxymethylene)-2'-deoxyuridine (3). The (Z)-(carboxymethylene)-2'-deoxyuridine (2) was synthesized from 13 in a similar manner.

Cell kill kinetics of an antineoplastic nucleoside, 1-(2-deoxy-2-methylene-beta-D-erythro-pentofuranosyl)cytosine

The cytotoxic properties of 1-(2-deoxy-2-methylene-beta-D-erythro-pentofuranosyl)cytosine (DMDC) were compared with those of 1-beta-D-arabinofuranosylcytosine (ara-C), using SK-MEL-28(P-36) human melanoma cells. DMDC and ara-C were most cytotoxic to cells in the S phase of the cell cycle. Cell cycle progression in S phase was blocked by both compounds. Treatment with DMDC (1 microgram/mL) or ara-C (1 and 30 micrograms/mL) did not increase cytotoxicity against asynchronous cells when the exposure time was prolonged from 1 to 6 hr, but did increase cytotoxicity thereafter. These findings suggest that cells in S phase are rapidly killed by the treatment but are temporarily prevented or delayed entry into the drug-sensitive S phase. On the other hand, DMDC treatment at a higher concentration (30 micrograms/mL) increased cytotoxicity in a time-dependent manner. Intracellular DMDC 5'-triphosphate (DMDCTP) increased in proportion to exogenous DMDC concentration, which was not saturated by treatment with a maximum concentration of the compound at 80 micrograms/mL. In contrast, intracellular ara-C 5'-triphosphate reached peak level when the cells were treated with ara-C at 8 micrograms/mL. The cytotoxicity of DMDC treatment for 4 hr increased relative to the intracellular DMDCTP accumulated during the period. These findings suggest that in cells treated with DMDC at a high concentration, an effective DMDCTP level is maintained for an extended period after washing out the compound from the medium. Consequently, the cells would be killed in the same way as in the case of extended exposures over 6 hr to DMDC at low concentration or to ara-C, in addition to acute S-phase-specific cytotoxicity.

8-Azidoadenosine and ribonucleotide reductase

Inhibitors of ribonucleotide reductase are potential antiproliferative agents, since they deplete cells from DNA precursors. Substrate nucleoside analogues, carrying azido groups at the base moiety, are shown to have strong cytostatic properties, as measured by the inhibition of the incorporation of thymidine into DNA. One compound, 8-azidoadenosine, inhibits CDP reduction in cytosolic extracts from cancer cells. The corresponding diphosphate behaves as a substrate for ribonucleotide reductase while the triphosphate is an allosteric effector.