Preparation and biological evaluation of 1′-cyano-2′-C-methyl pyrimidine nucleosides as HCV NS5B polymerase inhibitors

Multistep Synthesis of Analogues of Remdesivir: Incorporating Heterocycles at the C-1' Position

Studies suggest that the 1'β-CN moiety in remdesivir sterically clashes with the Ser861 residue of the RNA-dependent-RNA polymerase (RdRp), causing a delayed chain termination in the RNA replication process. Replacing C1'β-CN with 5-membered heterocycles such as tetrazoles, oxadiazoles, and triazoles can augment the inhibitory activity and pharmacokinetic profile of C-nucleotides. Synthesis of tetrazole-, triazole-, and oxadiazole-integrated C1' analogues of remdesivir was attempted using general synthetic routes. The final compounds 26, 28, and 29 did not inhibit viral replication; however, the synthetic intermediates, i.e., 27 and 50, exhibited an IC90 = 14.1 μM each. The trifluoromethyl-substituted 1,2,4-oxadiazole 59 showed an IC90 of 33.5 μM. This work adds to the growing evidence of the beneficial medicinal impact of C1,1'-disubstituted C-nucleotides.

Novel dodecyl-containing azido and glucuronamide-based nucleosides exhibiting anticancer potential

The synthesis and anticancer evaluation of new series of nucleosides constructed on 5/6-azidoglycosyl or glucuronamide moieties and containing an O- or an N-dodecyl chain, respectively, are disclosed. Based on our previous results, their structures were planned to preclude them to act via a similar metabolic pathway than that of clinically used nucleoside antimetabolites, against which cancer cells frequently acquire resistance. Xylo and gluco-configured 5/6-azido-1,2-di-O-acetyl furanosyl and pyranosyl donors containing a 3-O-dodecyl group were synthesized from diacetone-d-glucose and were subsequently coupled with silylated uracil or 2-acetamido-6-chloropurine. N-Dodecyl glucuronamide-based nucleosides were accessed from acetonide-protected glucofuranurono-6,3-lactone, which was converted in few steps into O-benzylated 1,2-di-O-acetyl furanuronamide or pyranuronamide derivatives to undergo further N-glycosylation. Both types of nucleosides demonstrated notorious antiproliferative effects in chronic myeloid leukemia (K562) and in breast cancer (MCF-7) cells. The most potent molecules were a 6ʹ-azidoglucopyranosyl N7-linked purine nucleoside and glucofuranuronamide derivatives comprising N1-linked uracil and N7-linked purine units with activities in the single-digit micromolar order of concentration against both cell lines. Their GI50 values in MCF-7 cells were similar or ca. 3-fold lower than that of the standard drug 5-fluorouracil. Cell cycle studies and immunoblotting analysis of apoptosis-associated proteins in treated K562 cells indicated that the antiproliferative effect of the most effective nucleosides is based on apoptosis induction.

Exploitation of new structurally diverse d-glucuronamide-containing N-glycosyl compounds: synthesis and anticancer potential

The synthesis and anticancer evaluation of novel N-glycosyl derivatives containing N-substituted glucuronamide moieties, as nucleoside analogs or as prospective mimetics of glycosyl phosphates or of nucleotides, is reported. These compounds comprise N-anomerically-linked nucleobases or motifs that are surrogates of a phosphate group, such as sulfonamide or phosphoramidate moieties. 1-Sulfonamido glucuronamides containing N-benzyl, N-propargyl or N-dodecyl carboxamide units were synthesized through glycosylation of methanesulfonamide with tetra-O-acetyl glucuronamides. 1-Azido glucuronamides were accessed by microwave-assisted reactions of tetra-O-acetyl glucuronamides with TMSN₃ and were further converted into N-glycosylphosphoramidates by treatment with trimethyl phosphite. Potential glucuronamide-based nucleotide mimetics comprising both an anomeric sulfonamide/phosphoramidate group and a benzyltriazolylmethyl amide system at C-5, as nucleobase mimetics, were synthesized via 'click' cycloaddition of N-propargyl glucuronamide derivatives with benzyl azide. N-Dodecyl tetra-O-acetyl glucuronamides were converted into uracil and purine nucleosides via N-glycosylation of the corresponding silylated nucleobases. Biological screening revealed significant antiproliferative activities of the N-dodecyl glucuronamide-containing sulfonamide, phosphoramidate and nucleosides in K562 and MCF-7 cells. The highest effect was exhibited by the N⁹-linked purine nucleoside in the breast cancer cell MCF-7 with a GI₅₀ value similar to that of clinically used 5-fluorouracil. Immunoblotting and cell cycle analysis of K562 cells treated with the most active compound as well as evaluation of the effect of this nucleoside on the activities of caspases 3 and 7 showed induction of apoptosis as the mechanism of cell death.

Synthesis and antiproliferative evaluation of novel azido nucleosides and their phosphoramidate derivatives

New xylofuranosyl and glucopyranosyl nucleoside phosphoramidates were synthesized as potential mimetics of nucleoside 5′-monophosphates. Their access involved N-glycosylation of uracil and 2-acetamido-6-chloropurine with 5′/6′-azido-1,2-di-O-acetyl glycosyl donors and subsequent Staudinger-phosphite reaction of the resulting azido nucleosides. The coupling of the purine derivative with the pyranosyl donor furnished N9- and N7-linked nucleosides in 1:1 ratio, whereas with the furanosyl donor, the N9-nucleoside was the major regioisomer formed. When using uracil, only 5′/6′-azido N1-linked nucleosides were obtained. The purine 5′/6′-azido nucleosides were converted into corresponding phosphoramidates in good yields. The antiproliferative effects of the nucleoside phosphoramidates and those of the azido counterparts on cancer cells were evaluated. While the nucleoside phosphoramidates did not show significant activities, the purine 5′/6′-azido nucleosides displayed potent effects against K562, MCF-7 and BT474 cell lines. The 5′-azidofuranosyl N9 and N7-linked purine nucleosides exhibited highest activity towards the chronic myeloid leukemia cell line (K562) with GI50 values of 13.6 and 9.7 μM, respectively. Among pyranosyl nucleosides, the N7-linked nucleoside was the most active compound with efficacy towards all cell lines assayed and a highest effect on K562 cells (GI50=6.8 μM). Cell cycle analysis of K562 and MCF-7 cells showed that the most active compounds cause G2/M arrest.

Ultrasonic-assisted synthesis of 1,4-disubstituted 1,2,3-triazoles via various terminal acetylenes and azide and their quorum sensing inhibition

An efficient synthesis of 1,4-disubstituted 1,2,3-triazole derivatives was studied. 1,4-Disubstituted 1,2,3-triazoles containing isoxazole and thymidine structures were synthesized in 84-96% yields starting from various terminal isoxazole ether alkynes and β-thymidine azide derivatives via a 1,3-dispolar cycloaddition using copper acetate, sodium ascorbate as the catalyst under ultrasonic assisted condition. All the target compounds were characterized by HRMS, FT-IR, ¹H NMR and ¹³C NMR spectroscopy. Furthermore, the quorum sensing inhibitory activities of synthesized compounds were evaluated with Chromobacterium violaceum (C. Violaceum CV026) based on their inhibition of violacein production, with compound C₁₀-HSL as a positive control. The compounds 8a, 8c and 8f exhibited considerable levels of inhibitory activity against violacein production, and IC₅₀ values were 217±19, 223±20 and 42.8±4.5μM, respectively, which highlighted the potential of these compounds as lead structures for further research towards the development of novel QS inhibitors.

C-Nucleosides To Be Revisited

Two new C-nucleoside analogues, BCX4430, an imino-C-nucleoside, and GS-6620, a phosphoramidate derivative of 1'-cyano-2'-C-methyl-4-aza-7,9-dideazaadenosine C-nucleoside, have been recently described as effective against filovirus infections (Marburg) and hepatitis C virus (HCV), respectively. The first C-nucleoside analogues were described about half a century ago. The C-nucleoside pseudouridine is a natural component of RNA, and various other C-nucleoside analogues have been reported previously for their antiviral and/or anticancer potential, the most prominent being pyrazofurin, tiazofurin, and selenazofurin. In the meantime, showdomycin, formycin, and various triazole, pyrazine, pyridine, dihydroxyphenyl, thienopyrimidine, pyrazolotriazine, and porphyrin C-nucleoside analogues have been described. It would be worth revisiting these C-nucleosides and derivatives thereof, including their phosphoramidates, for their therapeutic potential in the treatment of virus infections and, where appropriate, cancer as well.

Synthesis of 1'-C-cyano pyrimidine nucleosides and characterization as HCV polymerase inhibitors

Ribose modified 1'-C-cyano pyrimidine nucleosides were synthesized. A silver triflate mediated Vorbrüggen reaction was used to generate the nucleoside scaffold and follow-up chemistry provided specific ribose modified analogs. Nucleosides and phosphoramidate prodrugs were tested for their anti-HCV activity.

Recent advances on the synthesis of hepatitis C virus NS5B RNA-dependent RNA-polymerase inhibitors

Hepatitis C is a viral liver infection considered as the major cause of cirrhosis and hepatocellular carcinoma (HCC). The HCV NS5B polymerase, an RNA-dependent RNA polymerase, is essential for HCV replication, which is able to catalyze the synthesis of positive (genomic) and negative (template) strand HCV RNA, but has no functional equivalent in mammalian cells. Therefore, the NS5B polymerase has emerged as an attractive target for the development of specifically targeted antiviral therapy for HCV (DAA, for direct-acting antivirals). Recently, a growing number of compounds have been reported as the NS5B polymerase inhibitors, some of which especially have been licensed in clinical trials. This review describes recent advances on the synthesis of the NS5B polymerase inhibitors, focusing on the merits and demerits of their synthetic methods. In particular, inspiration from the synthesis and the future direction of the NS5B polymerase inhibitors are highlighted.

Synthesis and characterization of 1'-C-cyano-2'-fluoro-2'-C-methyl pyrimidine nucleosides as HCV polymerase inhibitors

The first synthesis of 1'-C-CN, 2'-F, 2'-C-Me pyrimidines is described. Anti-HCV activity was assessed and compared to the 1'-C-CN, 2'-C-Me as well as the 2'-F, 2'-C-Me pyrimidines. A phosphoramidate prodrug of the cytidine derivative showed activity in the low micromolar range against HCV replicons.