Phosphoralaninate pronucleotides of pyrimidine methylenecyclopropane analogues of nucleosides: synthesis and antiviral activity

The Z- and E-thymine and cytosine pronucleotides 3d, 4d, 3e, and 4e of methylenecyclopropane nucleosides analogues were synthesized, evaluated for their antiviral activity against human cytomegalovirus (HCMV), herpes simplex virus 1 and 2 (HSV-1 and HSV-2), varicella zoster virus (VZV), Epstein-Barr virus (EBV), human immunodeficiency virus type 1 (HSV-1), and hepatitis B virus (HBV) and their potency was compared with the parent compounds 1d, 2d, 1e, and 2e. Prodrugs 3d and 4d were obtained by phosphorylation of parent analogues 1d or 2d with reagent 8. A similar phosphorylation of N4-benzoylcytosine methylenecyclopropanes 9a and 9b gave intermediates 11a and 11b. Deprotection with hydrazine in pyridine-acetic acid gave pronucleotides 3e and 4e. The Z-cytosine analogue 3e was active against HCMV and EBV The cytosine E-isomer 4e was moderately effective against EBV.     

Phosphoralaninate Pronucleotides of Pyrimidine Methylenecyclopropane Analogues of Nucleosides: Synthesis and Antiviral Activity

The Z- and E-thymine and cytosine pronucleotides 3d, 4d, 3e, and 4e of methylenecyclopropane nucleosides analogues were synthesized, evaluated for their antiviral activity against human cytomegalovirus (HCMV), herpes simplex virus 1 and 2 (HSV-1 and HSV-2), varicella zoster virus (VZV), Epstein-Barr virus (EBV), human immunodeficiency virus type 1 (HSV-1), and hepatitis B virus (HBV) and their potency was compared with the parent compounds 1d, 2d, 1e, and 2e. Prodrugs 3d and 4d were obtained by phosphorylation of parent analogues 1d or 2d with reagent 8. A similar phosphorylation of N⁴-benzoylcytosine methylenecyclopropanes 9a and 9b gave intermediates 11a and 11b. Deprotection with hydrazine in pyridine–acetic acid gave pronucleotides 3e and 4e. The Z-cytosine analogue 3e was active against HCMV and EBV. The cytosine E-isomer 4e was moderately effective against EBV.     

Synthesis, antiviral, and antitumor activity of 2-substituted purine methylenecyclopropane analogues of nucleosides

The Z- and E-2-fluoro- and 2-chloropurine methylenecyclopropanes 9a,b and 10a,b as well as enantiomeric Z-isoguanine methylenecyclopropanes 11a,b and their phenyl phosphoralaninate pronucleotides 11c,d were synthesized and their antiviral activity against several viruses was evaluated. Fluoro analogues 9a and 10a were active against human cytomegalovirus but they were cytotoxic at approximately the same concentrations. Chloro derivatives 9b and 10b were non-cytotoxic and effective against Epstein-Barr virus in Daudi cells. Isoguanine analogues 11a-d lacked antiviral activity but pronucleotides 11c,d were substrates for porcine liver esterase. From the group of 9a,b and 10a,b, the fluoro analogues 9a and 10a exhibited antitumor activity but only the Z-isomer 9a had a selective effect.     

Increase of the anti-HIV activity of D4T in human T-cell culture by the use of the sate pronucleotide approach

The bis(S-acetyl-2-thioethyl) phosphotriester derivative of 2′,3′-didehydro-2′,3′-dideoxythymidine has been synthesized and evaluated for its inhibitory effects on the replication of HIV-1 in several cell culture systems. This pronucleotide showed potent anti-HIV activity and proved to be significantly superior to the parent nucleoside with regard to the antiviral efficiency.     

Special feature of mixed phosphotriester derivatives of cytarabine

Despite the unquestionable therapeutic interest of bis(SATE) pronucleotides, a presystemic metabolism preventing the delivery of the prodrugs in target cancer cells or tumours may constitute a limitation to the in vivo development of such derivatives. In order to overcome these drawbacks several strategies have been envisaged and we report herein the application of the S-acyl-2-thioethyl (SATE) phenyl pronucleotide approach to the well-known cytotoxic nucleoside cytosine-1-β-d-arabinofuranoside (cytarabine, araC). We describe modifications of the SATE moieties with the introduction of polar groups on the acyl residue, in order to study how these changes affect antitumoral activity and metabolic stability. Two different synthetic pathways were explored and lead to obtain the corresponding mixed derivatives in satisfactory yields. Cytotoxicity was studied in murine leukaemia cells L1210 as well as in cells derived from solid human tumours (Messa and MCF7). Biological evaluation of these compounds in cell culture experiments with nucleoside analogue-sensitive and resistant cell lines showed that the modified compounds were active at higher concentrations than unmodified cytarabine, yet were much able to partially reverse resistance due to deficient nucleoside transport or activation. These results can be correlated with an incomplete decomposition mechanism into the corresponding 5′-mononucleotide.     

Separation of nucleoside phosphoramidate diastereoisomers by high performance liquid chromatography and capillary electrophoresis

Separations of five diastereoisomers of nucleoside phosphoramidate derivatives (pronucleotides) were performed by both HPLC method using derivatized cellulose and amylose chiral stationary phases and CE method using anionic cyclodextrins added in the background electrolyte (BGE). An optimal baseline separation (Rs > 1.5) was readily obtained with all silica-based celluloses and amyloses using in a normal-phase methodology. Capillary electrophoresis was used as an alternative technique to HPLC for the separation of pronucleotides. The diastereoisomers were fully resolved with sulfated cyclodextrins at both BGE pH (2.5 and 6.2). Limits of detection and limits of quantification, calculated for both methods, are up to 200 times higher in CE separations than in HPLC separations. The analytical HPLC method was then applied in a preliminary study for the pronucleotide 1 quantification in cellular extract.     

抗病毒核苷酸类似物磷酸化修饰研究进展

核苷(酸)类似物是一类抗病毒前药,其进入人体细胞后经过逐步磷酸化生成核苷三磷酸类似物发挥抗代谢药作用,主要通过抑制病毒复制和促进侵染细胞凋亡,达到疾病治疗效果.其中,核苷类似物在细胞内经激酶活化的代谢转化过程通常是不充分的,导致最后生成的核苷三磷酸类似物浓度较低,降低了作用效果.因此,通过直接制备核苷酸类似物作为抗病毒...     

Bicyclic anti-VZV nucleosides: thieno analogues bearing an alkylphenyl side chain have reduced antiviral activity

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.     

Exploring tryptamine conjugates as pronucleotides of phosphate-modified 7-methylguanine nucleotides targeting cap-dependent translation

Eukaryotic translation initiation factor 4E (eIF4E) is overexpressed in many cancers deregulating translational control of the cell cycle. mRNA 5′ cap analogs targeting eIF4E are small molecules with the potential to counteract elevated levels of eIF4E in cancer cells. However, the practical utility of typical cap analogs is limited because of their reduced cell membrane permeability. Transforming the active analogs into their pronucleotide derivatives is a promising approach to overcome this obstacle. 7-Benzylguanosine monophosphate (bn⁷GMP) is a cap analog that has been successfully transformed into a cell-penetrating pronucleotide by conjugation of the phosphate moiety with tryptamine. In this work, we explored whether a similar strategy is applicable to other cap analogs, particularly phosphate-modified 7-methylguanine nucleotides. We report the synthesis of six new tryptamine conjugates containing N⁷-methylguanosine mono- and diphosphate and their analogs modified with thiophosphate moiety. These new potential pronucleotides and the expected products of their activation were characterized by biophysical and biochemical methods to determine their affinity towards eIF4E, their ability to inhibit translation in vitro, their susceptibility to enzymatic degradation and their turnover in cell extract. The results suggest that compounds containing the thiophosphate moiety may act as pronucleotides that release low but sustainable concentrations of 7-methylguanosine 5′-phosphorothioate (m⁷GMPS), which is a translation inhibitor with in vitro potency higher than bn⁷GMP.     

Inactivity of the bicyclic pyrimidine nucleoside analogues against simian varicella virus (SVV) does not correlate with their substrate activity for SVV-encoded thymidine kinase

Simian varicella virus (SVV) and human varicella-zoster virus (VZV) are closely related viruses that share many structural and functional properties. 5-Substituted 2'-deoxyuridine derivatives (e.g., BVDU, BVaraU) and acyclic guanine nucleoside derivatives (i.e., ACV and GCV) show comparable antiviral efficacy against VZV and SVV in cell culture. In contrast, the novel bicyclic nucleoside analogues (BCNAs) are exquisitely inhibitory to VZV (EC50 in the lower nanomolar range) but completely inactive against SVV. The VZV-encoded thymidine kinase (TK) appeared to be essential for BCNA activation (phosphorylation) and anti-VZV activity. Also SVV TK is able to recognize the BCNAs as substrate, although with a different structure-affinity relationship. Thus, viral TK-catalyzed phosphorylation is necessary but not sufficient for the BCNAs to display antiviral activity. Our data suggest that the eventual target of the BCNAs against VZV is either absent in SVV or, alternatively, is insensitive for the (phosphorylated) BCNAs.     

Bicyclic anti-VZV nucleosides: Thieno analogues retain full antiviral activity.

Thieno analogues of the potent and selective furo-pyrimidine anti-VZV nucleoside family are herein reported. The compounds retain full antiviral potency in comparison to the furo parent.     

Synthesis of novel 4'-cyclopropyl-5'-norcarbocyclic adenosine phosphonic acid analogues

Novel 4'-cyclopropyl-5'-norcarbocyclic adenosine phosphonic acid analogues were designed and racemically synthesized from propionaldehyde 5 through a de novo acyclic stereoselective route using triple Grignard addition and ring-closing metathesis (RCM) as key reactions. To improve cellular permeability and enhance the anti-HIV activity of this phosphonic acid, SATE phosphonodiester nucleoside prodrug 23 was prepared. The synthesized adenosine phosphonic acids analogues 17, 18, 19, 21, and 23 were subjected to antiviral screening against HIV-1. Compound 23 exhibits enhanced anti-HIV activity than its parent nucleoside phosphonic acid 18.     

Aryl nucleoside H-phosphonates. Part 16: Synthesis and anti-HIV-1 activity of di-aryl nucleoside phosphotriesters

Di-aryl nucleoside phosphotriesters have been explored as a new type of pronucleotides for the purpose of anti-HIV-1 therapy and efficient synthetic protocols, based on H-phosphonate chemistry, have been developed for the preparation of this class of compounds. It was found that anti-HIV-1 activity of the phosphotriesters bearing an antiviral nucleoside moiety (AZT, ddA) and also ddU was due, at least partially, to intracellular conversion into the corresponding nucleoside 5′-monophosphates, and their efficiency correlated well with the pK_a values of the aryloxy groups present.     

Fluoroanalogues of anti-cytomegalovirus agent cyclopropavir: synthesis and antiviral activity of (E)- and (Z)-9-{[2,2-bis(hydroxymethyl)-3-fluorocyclopropylidene]methyl}-adenines and guanines

Synthesis of fluorinated cyclopropavir analogues 13a, 13b, 14a, and 14b is described starting from alkene 15. Addition of carbene derived from dibromofluoromethane gave bromofluoro cyclopropane 16. Reduction (compound 17) followed by desilylation gave intermediate 18, which was transformed to 2-nitrophenylselenenyl derivative 19. Oxidation to selenoxide 20 was followed by beta-elimination to afford methylenecyclopropane 21. Addition of bromine provided compound 22 for alkylation-elimination of adenine and 2-amino-6-chloropurine. The resultant E,Z isomeric mixtures of methylenecyclopropanes 23a + 24a and 23c + 24c were resolved and the individual isomers were deprotected to give adenine analogues 13a and 14a as well as compounds 13c and 14c. Hydrolytic dechlorination of 13c and 14c furnished guanine analogues 13b and 14b. The only significant antiviral effects were observed with analogue 13a against HCMV and 14a against VZV in cytopathic inhibition assays.     

Synthesis and cytotoxicity of 4'-C- and 5'-C-substituted toyocamycins

Toyocamycin and some analogues have shown potent antitumor activities; however, none of them could be used clinically primarily owing to their cytotoxicity to normal human cells. In order to overcome the weakness of these nucleoside analogues, substitution of a variety of modified sugars for the ribofuranose was explored in our laboratories with expectation that certain sugar-modified toyocamycin analogues may be selectively cytotoxic to cancer cells. In this article, we report synthesis and cytotoxicity of 4'-C- and 5'-C-substituted toyocamycins, which were prepared via the condensations of 4-C- and 5-C-substituted ribofuranose derivatives 11, 12, 13, 20, 21, and 26 with the silylated form of 4-amino-6-bromo-5-cyanopyrrolo[2,3-]pyrimidine (27) and subsequent debromination and debenzoylation. When compared to the parent toyocamycin, all these analogues showed much lower cytotoxicity to human prostate cancer cells (HTB-81), mouse melanoma cancer cells (B16) as well as normal human fibroblasts. Compound 1e showed a significant cytotoxicity to the prostate cancer cells and a moderate selectivity. The results suggested that sugar modifications, especially those that may affect phosphorylation of nucleosides, could alter cytotoxicity profile significantly.     

Crystal structures of human and murine deoxyribonucleotidases: insights into recognition of substrates and nucleotide analogues

Cytosolic 5'(3')-deoxyribonucleotidase (cdN) and mitochondrial 5'(3')-deoxyribonucleotidase (mdN) catalyze the dephosphorylation of deoxyribonucleoside monophosphates and regulate dTTP formation in cytosol and mitochondria, protecting DNA replication from imbalanced precursor pools. They can also interfere with the phosphorylation-dependent activation of nucleoside analogues used in anticancer and antiviral treatment. To understand the relatively narrow substrate specificity of these two enzymes and their ability to use nucleotide analogues as substrates, we determined the crystal structures of human cdN in complex with deoxyuridine, murine cdN in complex with dUMP and dGMP, and human mdN in complex with the nucleotide analogues AZTMP and BVdUMP. Our results show that the active site residues Leu45 and Tyr65 in cdN form a more favorable binding surface for purine nucleotides than the corresponding Trp75 and Trp76 in mdN, explaining why cdN has higher activity for purine nucleotides than does mdN. The molecular interactions of mdN with AZTMP and BVdUMP indicate why these nucleotide analogues are poorer substrates as compared with the physiological substrate, and they provide a structural rationale for the design of drugs that are less prone to inactivation by the deoxyribonucleotidases. We suggest that introduction of substituents in the 3'-position may result in nucleoside analogues with increased resistance to dephosphorylation.     

5-alkylvinyl-1,2,4-triazole nucleosides: Synthesis and biological evaluation

Abstract

Some 5-substituted ribavirin analogues have a high antiviral and anticancer activity, but their mechanisms of action are obviously not the same as their parent compound. The SAR studies performed on 3 (5)-substituted 1,2,4-triazole nucleosides have shown a high dependency between the structure of the 3 (5)-substituent and the level of antiviral/anticancer activity. The most active substances of the row contain coplanar with the 1,2,4-triazole ring aromatic substituent which is connected by a rigid ethynyl bond. However, the compounds with the trans-vinyl linker also had antiviral activity. We decided to study the antitumor activity of ribavirin analogues with alkyl/aryl vinyl substituents in the 5th position of the 1,2,4-triazole ring. Protected nucleoside analogues with various 5-alkylvinyl substituents were obtained by Horner-Wadsworth-Emmons reaction from the common precursor and converted to the nucleosides. Arylvinyl nucleosides were synthesised according the reported procedures. All compounds did not show significant antiproliferative activity on several tumour cell lines. Coplanar aromatic motif in the 5-substituent for the anticancer activity manifestation was confirmed.     

Research on L-nucleosides. Synthesis and biological evaluation of a series of L- and D-2',3'-dideoxy-3'-[tris(methylthio)methyl]-beta-pentofuranosyl nucleosides

Novel nucleoside analogues of both D and L enantiomeric series were prepared by coupling reaction between a 2',3'-dideoxy-3'-modified furanose moiety and four different nucleobases. Though in all cases anomeric mixtures of nucleosides were obtained, the presence of the sterically bulky 3'-tris(methylthio)methyl group allowed a good stereoselectivity level. All the compounds of both enantiomeric series showed high IC(50) values as HSV-1 TK inhibitors and scarce ability to be phosphorylated by HSV-1 TK. In order to overcome possible problems related to the first phosphorylation step and to facilitate the penetration of the molecule through the cellular membrane, a monophosphate prodrug containing a long lipophilic chain was synthesized. No appreciable antiviral activity was exhibited by this molecule.     

Synthesis of novel bicyclic nucleosides with 3,6-anhydro sugar moiety

Based on the biological importance of conformationally restricted nucleoside analogues, we have efficiently synthesized 3,6-anhydro sugar moiety with 3-C-hydroxymethyl substituent from 1,2;5,6-di-O-isopropylidene-D-glucose and condensed 15 with silylated nucleobases to afford the bicyclic nucleoside with 3,6-anhydro skeleton as potential antiviral agent.     

Achievements and prospects of the directed search for antiviral agents in the nucleoside series and their derivatives]

Recent advances of antiviral drug design among nucleosides and their derivatives have been summarized. The first chapter deals with the history of nucleic acids components and further developments in this area. Next part discusses the mechanism of action of biologically active nucleosides: 2',3'-dideoxynucleosides, acyclic analogues, phosphonate derivatives and nucleoside antibiotics. The third chapter describes planning of complicated synthesis of nucleoside analogues from branched-chain sugars and stereo-specific formation of glycosidic bond upon synthesis of ribonucleoside and 2'-deoxyribonucleoside. The last part outlines further perspectives, i. e. preparation of antiviral compounds and use of nucleoside analogues in oligonucleotide synthesis.