Synthesis and Reactions of Some Glycosylamine Derivatives of 6-Azauracil Nucleosides

Abstract

Reaction of the silylated 6-azauracil (2) with 2-acetamido-1,3,4,6-tetra-O-acetyl-2-deoxy-D-glucose (3) gave 1-(2-acetamido-3,4,6-tri-O-acetyl-2-deoxy-ß-D-glucopyranosyl)-6-azauracil (4), which gave the free nucleoside 5 on deblocking. Acetalation of 5 gave the monoacetal 6 which was oxidized into the ketone 7. Reduction of 7 gave the allo-nucleoside 9 which on hydrolysis afforded the free nucleoside 10. Alternatively, compound 10 was obtained from mesylation of 6 to give 8 followed by subsequent acetolysis and hydrolysis.     

POTENT IN VITRO ANTICANCER ACTIVITIES OF RING-EXPANDED (“FAT”) NUCLEOSIDES CONTAINING THE IMIDAZO[4,5-E][1,3]DIAZEPINE RING SYSTEM

The ring-expanded (“fat”) nucleoside, 4,8-diamino-6-imino-6H-1-β-D-ribo- furanosylimidazo[4,5-e][1,3]diazepine (1) and its 2′,3′,5′-tri-O-benzoyl derivative (2) exhibited potent broad spectrum anticancer activities in vitro against a wide variety of human tumor cell lines. The tribenzoyl derivative 2 was found to be considerably more active than the parent nucleoside 1. Further studies using human prostate cancer cells PC-3 and DU-145 suggest that the treatment of exponentially growing culture cells with 1 and 2 leads to marked loss of cell viability in a dose-dependent manner.     

Synthesis and Structural Analysis of Oxadiazole Carboxamide Deoxyribonucleoside Analogs

Two novel C-linked oxadiazole carboxamide nucleosides 5-(2′-deoxy-3′,5′-β-D-erythro-pentofuranosyl)-1,2,4-oxadiazole-5-carboxamide (1) and 5-(2′-deoxy-3′,5′-β-D-erythro-pentofuranosyl)-1,2,4-oxadiazole-3-carboxamide (2) were successfully synthesized and characterized by X-ray crystallography. The crystallographic analysis shows that both unnatural nucleoside analogs 1 and 2 adapt the C2′-endo (“south”) conformation. The orientation of the oxadiazole carboxamide nucleobase moiety was determined as anti (conformer A) and high anti (conformer B) in the case of the nucleoside analog 1 whereas the syn conformation is adapted by the unnatural nucleoside 2. Furthermore, nucleoside analogs 1 and 2 were converted with high efficiency to corresponding nucleoside triphosphates through the combination chemo-enzymatic approach. Oxadiazole carboxamide deoxyribonucleoside analogs represent valuable tools to study DNA polymerase recognition, fidelity of nucleotide incorporation, and extension.

     

1,5-Translocation Strategy for Nucleoside Anomeric Radicals

Abstract

A new method for generating nucleoside anomeric radicals utilizing radical 1,5-translocation was developed. Two kinds of β-halogenovinyl groups at the C6-position of uracil nucleosides were found to be a good radical source, which subsequently forms a nucleoside anomeric radical. The following 5-endo-trig cyclization gave anomeric spiro nucleosides as products.     

Enzymatic Synthesis of 2′,5′-Dideoxv Purine Nucleosides and Related Compounds

Abstract

A wide range of 2′,5′-dideoxy-nucleosides, including 6- substituted purine, pyrazolo[3,4-d]pyrimidine and 1-deazapurine derivatives, has been enzymatically prepared using purine nucleoside phosphorylase. Specificity towards cleavage by bacterial versus mammalian purine nucleoside phosphorylase was evaluated.     

An Efficient Method for the Synthesis of β-d-Ribonucleosides Catalyzed by Metal Iodides

Abstract

Several β-d-ribonucleosides were synthesized in high yields under mild conditions by N-glycosylations of methyl 2,3,5-tri-O-benzoyl-β-d-ribofuranosyl carbonate (1) with trimethylsilylated nucleoside bases in acetonitrile using a catalytic amount of metal iodide such as SnI₂, SbI₃ or TeI₄. A deprotection of N⁶ -benzoyl group of coupling product took place to a considerable extent when N⁶ -benzoyl-N⁶ , N⁹ -bis(trimethylsilyl)adenine was employed as a nucleoside base using SnI₂ or SnCI₂ as a catalyst while it was minimized when SbI₃ or TeI₄ was used. Further, the N-glycosylation of 1 with 7-trimethylsilyltheophylline in the presence of a catalytic amount of metal iodide was more effectively achieved in nitrile solvents other than acetonitrile.

     

Human herpesvirus 6A U27 plays an essential role for the virus propagation

Human herpesvirus 6A (HHV-6A) is a member of the genus Roseolovirus and the subfamily Betaherpesvirinae. It is similar to and human cytomegalovirus (HCMV). HHV-6A encodes a 41 kDa nuclear phosphoprotein, U27, which acts as a processivity factor in the replication of the viral DNA. HHV-6A U27 has 43% amino acid sequence homology with HCMV UL44, which is important for DNA replication. A previous study on HHV-6A U27 revealed that it greatly increases the in vitro DNA synthesis activity of HHV-6A DNA polymerase. However, the role of U27 during the HHV-6A virus replication process remains unclear. In this study, we constructed a U27-deficient HHV-6A mutant (HHV-6ABACU27mut) with a frameshift insertion at the U27 gene using an HHV-6A bacterial artificial chromosome (BAC) system. Viral reconstitution from the mutant BAC DNA was not detected, in contrast to the wild type and the revertant from the U27 mutant. This suggests that U27 plays a critical role in the life cycle of HHV-6A.     

Design and Synthesis of Novel Carbocyclic Versions of 2′-spirocyclopropyl Ribonucleosides as Potent Anti-HCV Agents

The discovery of 2′-spirocyclopropyl-ribocytidine as a potent inhibitor of RNA synthesis by NS5B (IC₅₀ = 7.3 μM), the RNA polymerase encoded by hepatitis C virus (HCV), has led to the synthesis and biological evaluation of carbocyclic versions of 2′-spiropropyl-nucleosides from cyclopentenol 6. Spirocyclopropylation of enone 7 was completed by using (2-chloroethyl)-dimethylsulfonium iodide and potassium t-butoxide to form the desired intermediate 9a. The synthesized nucleoside analogues, 18, 19, 26, and 27, were assayed for their ability to inhibit HCV RNA replication in a subgenomic replicon Huh7 cell line. The synthesized cytosine nucleoside 19 showed moderate anti-HCV activity (IC₅₀ = 14.4 μM).     

Synthesis of Some Hydroxamic Acids Related to Uridine: Potential Inhibitors of Ribonucleoside Diphosphate Reductase

Abstract

5-(N-Hydroxy) carboxamidouridine (5) and 5-(N-hydroxy) carboxamido-methyluridine (6) have been synthesized; these hydroxamic acids incorporate a radical trap into a nucleoside structure, and are designed as potential inhibitors of ribonucleotide diphosphate reductase.     

Nucleosides Having Quinolone Derivatives as Nitrogenated Base: Regiospecific and Stereospecific Ribosylation of 3-Carbethoxy-1,4-dihydro-4-oxoquinolines

Abstract

Ribosylation reactions of previously silylated 3-carbethoxy-8-methyl-1,4-dihydro-4-oxoquinoline (6a) and 3-carbethoxy-6-methyl-1,4-dihydro-4-oxoquinoline (6b) with 1-O-acetyl-2,3,5-tri-O-benzoyl-β-D-ribofuranose (7), under Lewis acid catalysis, were studied. The method using hexamethyldisilazane (HMDS)/trimethylchlorosilane (TMCS) mixture for silylation and anhydrous stannic chloride as catalyst for ribosylation failed to give any nucleoside product. On the other hand, the protected nucleoside 3-carbethoxy-6-methyl-1-(2,3,5-tri-O-benzoyl-β-D-ribofuranosyl)-1,4-dihydro-4-oxoquinoline (8b) was obtained in good yields using bis(trimethylsilyl)trifluoroacetamide (BSTFA) containing 1% of TMCS and the same catalyst. Compound 8b was more easily isolated in higher yields with an improvement of the later method by replacing stannic chloride with trimethylsilyl trifluoromethanesulfonate (TMSOTf).

De-O-benzoylation of 8b with methanolic sodium hydroxide solution afforded the free riboside 3-carbomethoxy-6-methyl-1-β-D-ribofuranosyl-1,4-dihydro-4-oxoquinoline (9b). The structures of the obtained products were confirmed by their LTV, MS, IR, ¹H and ¹³C-NMR data.     

Diastereocontrolled Synthesis of Phosphorothioate DNA via an Oxazaphospholidine Approach Using a Novel Class of Activators,Dialkyl(cyanomethyl)ammonium Salts

Abstract

Dialkyl(cyanomethyl)ammonium salts 1 were synthesized and used as a novel class of activators for the stereospecific condensations of diastereopure nucleoside 3′-O-oxazaphospholidines with a nucleoside. This new oxazaphospholidine method could efficiently produce both (Rp)- and (Sp)-dinucleoside phosphorothioates.     

Conjugates of Fluorescein and Saenta (5′-S-(2-Aminoethyl)-N 6-(4-nitrobenzyl)-5′-thioadenosine): Flow Cytometry Probes for the ES Nucleoside Transporter Elements of the Plasma Membrane

Abstract

SAENTA was linked to the C-5 or C-6 positions of fluorescein through several structures to form conjugates that were bound tightly to plasma membrane sites associated with es nucleoside transport activity. The conjugates imparted fluorescence to cells that expressed es nucleoside transport activity and served as es-selective plasma membrane stains suitable for flow cytometry. Prior treatment of es-expressing cells with nitrobenzylthioinosine prevented fluorescent staining with the conjugates. Seven SAENTA-fluorescein conjugates served as flow cytometric stains with high affinities for es sites, despite substantial differences in the SAENTA-fluorescein linkage structures.     

Synthesis and Evaluation of Novel Oligodeoxynucleotides Containing 3′-C-(3-Benzoyloxypropyl)thymidine and Bicyclo Nucleoside Derivatives

Abstract

The stereoselective synthesis of 3′-C-Allyluridine derivative 2 has been accomplished. This nucleoside was used as a key synthon for the synthesis of oligodeoxynucleotides containing 3′-C-(3-benzoyloxypropyl)thymidine (X) or bicyclo nucleoside (Y+Z) monomers. Preliminary thermal experiments are reported.     

Phosphoramidite Chemistry for the Synthesis of cycloSal-Pro-Nucleotides

Abstract

An alternative synthesis of 3-methyl-cycloSal-nucleotides 3–6 using phosphor-amidite chemistry is described. This protocol clearly shows advantages for the cycloSal-introduction into cytosine containing nucleoside analogues.     

Stereoselective Synthesis and X-Ray Structure of 1-(4-O-Benzyl-1,5-anhydro-2,3-dideoxy-D-arabino-hex-1-enitol-3-yl)-4-methoxy-1H-pyrimidin-2-one

Abstract

The intramolecular glycosylation of a 6-O-(4-methoxypyrimidin-2-yl) derivative of phenyl 2,3-didehydrohex-2-eno-1-thiopyranoside afforded 3-deoxy-3-(4-methoxypyrimidin-2-on-1-y1)glycal as the major product in a stereoselective manner. The isolated 3′-deoxyglycal nucleoside was characterized by X-ray and NMR spectral analyses.     

Synthesis of a New Analog of Thymidine for In Vivo Non-radioactive Labeling of DNA

Abstract

The introduction of 6-(p-bromobenzoylamino)caproyl radical in the methyl group of 2′-O-deoxythymidine is described. In vivo incorporation of this nucleoside to DNA was determined using a monoclonal antibody that recognized the radical.     

Thiosugars. X. Novel Nucleoside Analogues Derived from 4-Thio-L-lyxofuranose

Abstract

1-O-Acetyl-2,3,5-tri-O-benzyl-4-thio-L-lyxofuranose 1 was transformed into O-benzyl- and O-acetyl-protected 1-(4-thio-L-lyxofuranosyl) nucleoside derivatives by use of the TMSOTf method. Debenzylation with boron tribromide or deacetylation with sodium methoxide yielded the corresponding pyrimidine (7–11, 17, 18, 26 and 27) and purine (29 and 34) nucleoside analogues. The anomeric configurations were determined by NMR spectroscopy and, in the case of the 5-halo- (7–9) and nitrouridine derivative 11 and the 6-methylcytidine derivative 27, by X-ray structural analyses. – The unprotected nucleosides were not antivirically inhibitory at 250 µM.     

SYNTHESIS of 2′-DEOXY-2′-FLUOROGUANYL-(3′,5′)-GUANOSINE

ABSTRACT

The protected analogue of 2-amnio-6-chloropurine arabinoside (3b) was subjected to reaction with diethylaminosulfur trifluoride (DAST) and subsequently treated with NaOAc in Ac₂O/AcOH to give N ²,O ^3′,O ^5′-triacetyl-2′-deoxy-2′-fluoroguanosine (5a). After deacetylation of the sugar moiety and protection of 5′-OH by a 4,4′-dimethoxytrityl group, this nucleoside component was converted to 2′-deoxy-2′-fluoroguanyl-(3′,5′)-guanosine (6c, GfpG).     

2-Cyanoethyl H-Phosphonate. A Reagent for the Mild Preparation of Nucleoside H-Phosphonate Monoesters

Abstract

2-Cyanoethyl H-phosphonate was condensed with protected nucleoside derivatives and the cyanoethyl group subsequently removed by anhydrous base to give the corresponding nucleoside H-phosphonate in good yield.     

Studies on Reactions of Nucleoside H-Phosphonates with Bifunctional Reagents. Part VI. Reaction with Diols

Abstract

Reactions of nucleoside H-phosphonates with various diols using different types of condensing agents have been studied. Depending on the coupling procedure and the length of a polymethylene chain of the diol, acyclic H-phosphonate diesters or cyclic phosphite triesters were formed. The course of oxidation with iodine to produce cyclic nucleoside alkyl phosphotriesters or hydroxyalkyl nucleoside phosphodiesters can be controlled by the amount of water present in the reaction medium.