Synthesis and Biological Properties of the Four Optical Isomers of 5-o-Carboranyl-2′,3′-didehydro-2′,3′-dideoxyuridine

Abstract

The four isomers of the 5-o-carboranyl-2′,3′-didehydro-2′,3′-dideoxyuridine (d4CU) were synthesized and their antiviral activity and cytotoxicity in normal and cancer human cells determined. Coupling of silylated 5-o-carboranyluracil with the protected D/L 2,3-dideoxy-2-phenylselenenylribosylacetates provided after oxidative elimination and deprotection, the desired compounds. The presence of the electron deficient 5-o-carboranyl moiety on uracil influenced the yield of the various isomers. In general, the compounds demonstrated weak anti-human immunodeficiency virus activity in primary human lymphocytes. No marked difference in the biological profile was noted for the various optical isomers, suggesting that the high lipophilicity of these nucleosides imparted by the carboranyl moiety overrides stereochemical considerations in the 2′,3′-didehydro-2′,3′-dideoxy-aglycon moiety.     

Cellular Pharmacology of the D- and L-Enantiomers of β-5-o-Carboranyl-2′-deoxyuridine

Abstract

The cellular pharmacology of the D- and L-enantiomers of β-5-o-carboranyl-2′-deoxyuridine (CDU), compounds designed for boron neutron capture therapy (BNCT), were studied using human CEM lymphoblast and U-251 glioblastoma cells, at a physiologically achievable concentration (1 μM). Accumulation of the enantiomers was rapid and indistinguishable, reaching cellular concentrations > 40-fold higher than extracellular levels, with ～5% persisting in cells after incubation in fresh medium for more than 2 hr. Uptake was not affected by nucleoside uptake inhibitors, but was inhibited by the purine base uptake inhibitor papaverine.     

Synthesis and Anti-HIV Activity of β-D-3′-Azido-2′,3′-unsaturated Nucleosides and β-D-3′-Azido-3′-deoxyribofuranosylnucleosides

Since the discovery of 3′-azido-3′-deoxythymidine (AZT) and 2′,3′-didehydro-2′,3′-dideoxythymidine (d4T) as potent and selective inhibitors of the replication of human immunodeficiency virus (HIV), there has been a growing interest for the synthesis of 2′,3′-didehydro-2′,3′-dideoxynucleosides with electron withdrawing groups on the sugar moiety. Here we described an efficient method for the synthesis of such nucleoside analogs bearing structural features of both AZT and d4T. The key intermediate, 3-azido-1,2-bis-O-acetyl-5-O-benzoyl-3-deoxy-D-ribofuranose, 5 was synthesized from commercially available D-xylose in five steps, from which a series of pyrimidine and purine nucleosides were synthesized in high yields. The resultant protected nucleosides were converted to target nucleosides using appropriate chemical modifications. The final nucleosides were evaluated as potential anti-HIV agents.     

Derivatives of 1-(2-Deoxy-2-fluoro-β-D-arabinofuranosyl)-5-phenyluracil and 5-Benzyluracil. Synthesis and Biological Properties

Abstract

A number of 1-(2-deoxy-2-fluoro-β-D-arabinofuranosyl)uracil and -cytosine nucleosides substituted at the 5 position with a nitrophenyl or nitrobenzyl group were synthesized from 5-phenyl- and 5-benzyluracil via condensation of the fluorinated sugar, followed by nitration. The corresponding amino analogues were also prepared by reduction of the nitro nucleosides. The uracil nucleosides were converted into the corresponding cytosine nucleosides by way of the triazole intermediates. None of these nucleosides exhibited significant activity against herpes simplex virus type 1 in Vero cells. However, cytosine nucleosides containing the o-nitrophenyl, p-nitrophenyl, p-nitrobenzyl or p-aminobenzyl substituent were found to be toxic (even at 1 μM) to uninfected Vero cells, although they were essentially nontoxic in HL-60 cells. The 5′-monophosphates of the uracil nucleosides were inhibitors of the reaction catalyzed by purified Ehrlich ascites carcinoma thymidylate synthase, the 5-phenyluracil nucleotides causing a strong inhibition, competitive vs dUMP, described by the K_i value of 0.01 μM.     

The 1,1-Dianisyl-2,2,2-trichloroethyl Moiety as a New Protective Group for the Synthesis of Dinucleostde Trifluoromethylphosphonates

Abstract

The new 1,1-Dianisyl-2,2,2-trichloroethyl moiety (DATE) is used as an acid and base stable protective group for nucleosides. 5′-O-DATE-thymidine and 3′-O-acetyl-thymidine are phosphorylated with CF₃P(NR₂)₂ to the corresponding thymidine trifluoromethylphosphonous amidites. These building blocks are coupled with appropriate protected thymidines to a dinucleotide trifluoromethylphosphonate.

     

Oligonucleotides Containing Disaccharide Nucleosides: Synthesis,Physicochemical, and Substrate Properties

Abstract

The efficient synthesis of oligonucleotides containing 2′-O-β-D-ribofuranosyl (and β-D-ribopyranosyl)nucleosides, 2′-O-α-D-arabinofuranosyl (and α-L-arabinofuranosyl)nucleosides, 2′-O-β-D-erythrofuranosylnucleosides, and 2′-O-(5′-amino-5-deoxy-β-D-ribofuranosyl)nucleosides have been developed.     

Synthesis of Novel 3′-Hydroxymethyl 5′-Deoxythreosyl Phosphonic Acid Nucleoside Analogues as Potent Antiviral Agents

A very efficient synthetic route to novel 3′-hydroxymethyl 5′-deoxythreosyl phosphonic acid nucleosides was described. The discovery of threosyl phosphonate nucleoside (PMDTA, EC₅₀ = 2.53 μM) as a potent antihuman immunodeficiency virus (anti-HIV) agent has led to the synthesis and biological evaluation of 3′-modified 5′-deoxy versions of the threosyl phosphonate nucleosides. 3′-Hydroxymethyl 5 ′-deoxythreosyl phosphonic acid nucleoside analogues 15, 19, 24, and 28 were synthesized from 1,3-dihydroxyacetone and tested for anti-HIV activity as well as cytotoxicity. The adenine analogue 19 exhibits moderate in vitro anti-HIV-1 activity (EC₅₀ = 10.2 μM).     

Synthesis of a Novel Aldehyde: 4-O-Methyl-5-formylmethyl- 2′-deoxyuridine

Abstract

The synthesis of the blocked nucleoside 3′,5′-di-O-p-toluoyl-4-O-methyl-5-formylmethyl-2′-deoxyuridine (19) was accomplishied in eleven steps from gamma-butyrolactone. This aldehyde, which should facilitate the synthesis of nucleosides containing ¹⁸F, was converted to the corresponding blocked dithianyl nucleoside (21), and also to 5-(2,2-difluoroethyl)-substituted derivatives of 2′-deoxyuridine and 2′-deoxycytidine.     

Studies on Synthesis and Structure of O-β-D-Ribofuranosyl(1″→2′)-ribonucleosides and Oligonucleotides♣

Abstract

Minor nucleosides found in several eukaryotic initiator tRNAs_i ^Met, O-β-D-ribofuranosyl(1″→2′)adenosine and -guanosine (Ar and Gr), as well as their pyrimidine analogues, were obtained from N-protected 3′,5′-O-(1,1,3,3-tetraisopropyldisiloxane-1,3-diyl)ribonucleosides and 1-O-acetyl-2,3,5-tri-O-benzoyl-β-D-ribofuranose in the presence of tin tetrachloride in 1,2-dichloroethane. A crystal structure has been solved for 2′-O-ribosyluridine. The 3′-phosphoramidites of protected 2′-O-ribosylribonucleosides were prepared as the reagents for 2′-O-ribofuranosyloligonucleotides synthesis. O-β-D-Ribofuranosyl(1″→2′)adenylyl(3′→5′)guanosine (ArpG) was obtained and its structure was analysed by NMR spectroscopy.

     

Synthesis of Some 2′,3′-Dideoxy-3′-C-Fluoromethyl and 3′-C-Azidomethyl Nucleosides

Abstract

The synthesis of 3′-C-fluoromethyl and 3′-C-azidomethyl nucleosides is reported. The 3′-C-fluoromethyl furanoside 4 was synthesized via fluoride ion induced displacement of the corresponding trifluoromethanesulfonate. The 3′-C-hydroxymethyl furanoside 3 was converted to the corresponding 3′-C-azidomethyl furanoside 6 using triphenylphosphine-carbon tetrabromide-lithium azide. The 3′-C-fluoromethyl furanoside derivative 5 and the 3′-C-azidomethyl furanoside derivative 7 were subsequently condensed with silylated purine and pyrimidine bases. Deblocking and separation of the anomers by chromatography afforded the α- and β-nucleoside analogues. The nucleosides were tested for inhibition of HIV multiplication in vitro and were found to be inactive in the assay.     

SYNTHESIS AND BIOLOGICAL ACTIVITY OF 4′-C-HYDROXYMETHYL-2′-FLUORO- D-ARABINOFURANOSYLPURINE NUCLEOSIDES

A series of 4′-C-hydroxymethyl-2′-fluoro-D-arabinofuranosylpurine nucleosides was prepared and evaluated for cytotoxicity. The details of a convenient synthesis of the carbohydrate precursor 4-C-hydroxymethyl-3,5-di-O-benzoyl-2-fluoro-α-D-arabinofuranosyl bromide (13) are presented. Proof of the structure and configuration at all chiral centers of the sugars and the nucleosides were obtained by proton NMR. All five target nucleosides were evaluated for cytotoxicity in human tumor cell lines. The 4′-C-hydroxymethyl clofarabine analogue (16β) showed slight cytotoxicity in CCRF-CEM leukemia cells.     

The Synthesis of Some 5-Substituted-6-aza-2′-deoxyuridines

Abstract

5-(2-Thienyl)-1-(2-deoxy-3,5-di-O-p-toluoyl-β-D-erythro-pentofuranosyl)-6-azauracil [VIII] and 5-cyclopropyl-1-(2-deoxy-3,5-di-O-p-toluoyl-β-D-erythro-pentofuranosyl)-6-azauracil [X] were obtained in high yields (93.5% and 81.3% respectively) exclusively as β anomers, by condensation of the corresponding silylated triazine bases with 2-deoxyu-3,5-di-O-p-toluoyl-D-erythro-pentosyl chloride in chloroform. After deblocking both nucleosides with sodium methoxide in methanol, 5-(2-thienyl)-6-aza-2′-deoxyuridine [IX] and 5-cyclopropyl-6-aza-2′-deoxyuridine [XI] were obtained. The nucleoside IX was further acetylated, brominated with Br₂/CCl₄ and deblocked with methanolic ammonia to give 6-aza-5[2-(5-bromothienyl)]-2′-deoxyuridine[XIV].     

CycloSaligenyl Pronucleotides of 5-Iodo and 5-Trifluoromethyl-1-(2-deoxy-β-D-ribofuranosyl)-2,4-difluorobenzene Mimics of Thymidine: Synthesis and Evaluation of this Pronucleotide Monophosphate Delivery System for Compounds with Potential Anticancer Activity

Abstract

A group of unnatural 1-(2-deoxy-β-D-ribofuranosyl)-2,4-difluorobenzenes possessing a 5-I or 5-CF₃ substituent, that were originally designed as thymidine mimics, were coupled via their 5′-OH group to a cyclosaligenyl (cycloSal) ring system having a variety of C-3 substituents (Me, OMe, H). The 5′-O-cycloSal-pronucleotide concept was designed to effect a thymidine kinase-bypass, thereby providing a method for the intracellular delivery and generation of the 5′-O-monophosphate for nucleosides that are poorly phosphorylated. The 5′-O-cycloSal pronucleotide phosphotriesters synthesized in this study were obtained as a 1:1 mixture of two diastereomers that differ in configuration (S _P or R _P) at the asymmetric phosphorous center. The (S _P)- and (R _P)-diastereomers for the 5′-O-3-methylcycloSal- and 5′-O-3-methoxycycloSal derivatives of 1-(2-deoxy-β-D-ribofuranosyl)-2,4-difluoro-5-iodobenzene were separated by silica gel flash column chromatography. This class of cycloSal pronucleotide compounds generally exhibited weak cytotoxic activities in a MTT assay (CC₅₀ values in the 10^?3 to 10^?4 M range), against a number of cancer cell lines (143B, 143B-LTK, EMT-6, Hela, 293), except for cyclosaligenyl-5′-O-[1′-(2,4-difluoro-5-iodophenyl)-2′-deoxy-β-D-ribofuranosyl]phosphate that was more potent (CC₅₀ values in the 10^?5 to 10^?6 M range), than the reference drug 5-iodo-2′-deoxyuridine (IUDR) which showed CC₅₀ values in the 10^?3 to 10^?5 M range.     

Synthesis and Anti-cancer Activity of Some Novel 5-Azacytosine Nucleosides

Abstract

1-O-Acetyl-2-deoxy-3,5-di-O-toluoyl-4-thio-D-erythro-pentofuranose and 2-deoxy-1,3,5-tri-O-acetyl-4-thio-L-threo-pentofuranose were coupled with 5-azacytosine to obtain α and β anomers of nucleosides. All four nucleosides were reduced to the corresponding dihydro derivatives and deblocked to give target compounds. All eight target compounds were evaluated in a series of human cancer cell lines in culture. Only 2′-deoxy-4′-thio-5-azacytidine (3β) was found to be cytotoxic in all the cell lines and was further evaluated in vivo. Details of the synthesis and biological activity are reported.     

Photochemistry of the O-Nitrobenzyl Protecting Group in RNA Synthesis

Abstract

UV irradiation of 2′-O (o-nitrobenzyl)adenylyl(3′-5′)uridine in the presence of O₂ yields the corresponding nitrobenzoyl derivative in addition to the expected A-U. A mechanism proposed for this oxidation involves the successive removal of the two benzylic protons with a hydroperoxide as the intermediate between the two steps.     

Synthesis of Branched-Chain and Bicyclic Thiosugar Nucleosides

Abstract

The synthesis of strategically protected nucleosides bearing β-mercaptoethyl chains at the α-C-3′ position from 1,2-di-O-acetyl-2′-S-acetyl-5-t?butyldiphenylsilyl-3-deoxy-3-C-(2′-mercaptoethyl)-α-D-ribofuranose 1 is described. It was found that treatment of the 5-O-methanesulfonyl sugar 19 or nucleoside 5 with either benzylmercaptan or methoxide resulted in rapid cleavage of the thiolester followed by intramolecular cyclization. This was used to prepare the novel trans?fused oxathiahydrindane nucleosides 7 and 27 as well as the cAMP analogue 29.     

Reactions of Some 2,3-Anhydro Pyrimidine Nucleosides with Dilithium Tetrahalocuprates

Abstract

The reaction of 1-(2,3-anhydro-5-0-trityl-β-D-lyxofuranosyl)-2-0-methyluracil (2a) and its thymine analogue (2b) with dilithium tetrahalocuprates (Li₂CuX₄) revealed an excellent to perfect regioselectivity, yielding 2,2′-anhydro-3′-halonucleosides (3a-d), while the same reactions with 2,3-anhdro uracil and thymine nucleosides (5a,b) gave arabinosyl (6a-d) and xylosyl halohydrins (7a-d) with respective product ratios of 7:3 to 8:2 which were estimated after mesylation to 8a-d and 9a-d.     

Synthesis,Conformational Analysis,and Biological Activity of a Rigid Carbocyclic Analogue of 2′-Deoxy Aristeromycin Built on a Bicyclo[3.1.0]hexane Template

Abstract

A new chiral synthesis of the pseudosugar synthon (1R,2S,4R,5S)-1-[(benzyloxy)methyl]-2-tert-butyloxy-4-hydroxybicyclo[3.1.0]hexane (12) is reported. This compound was used as a template for the construction of carbocyclic nucleoside 4, a conformationally rigid analogue of 2′-deoxyaristeromycin. The X-ray structure and ¹H NMR analysis confirmed the exclusive North [2′-exo (₂E)] conformation of 4 which is vastly different from that of other non-rigid carbocyclic nucleosides. Compound 4 showed good in vitro antiviral activity against human cytomegalovirus and EBV with minimal cytotoxicity.

     

Systematic Synthesis and Antiviral Evaluation of α-L-Arabinofuranosyl and 2′-Deoxy-α-L-Erythro-Pento-Furanosyl Nucleosides of the Five Naturally Occurring Nucleic Acid Bases

Abstract

The α-L-arabinofuranosyl and 2′-deoxy-α-L-erythro-pentofuranosyl analogues of the naturally occurring nucleosides have been synthesized and their antiviral properties examined. The α-L-arabinofuranosyl nucleosides were prepared by glycosylation of purine and pyrimidine aglycons with a suitably peracyl-α-L-arabinose, followed by removal of the protecting groups. Their 2′-deoxy derivatives were obtained by sequential selective 2′-O-deacylation and deoxygenation. All the prepared compounds were tested for their activity against a variety of RNA and DNA viruses, but they did not show significant antiviral activity.     

2′- and 3′- Cholesterol-Conjugated Adenosine and Cytosine Nucleoside Building Blocks: Synthesis of Lipidic Nucleic Acids

Abstract

Recently our laboratory introduced¹ chemistries to synthesize 2′- and 3′- cholesteroluridine conjugates which were incorporated into several antisense oligonucleotides. We have now extended this chemistry to other nucleosides (adenosine and cytosine) and synthesized antisense oligonucleotide conjugates for several disease targets. Synthesis of these cholesterol nucleosides was carried out hy condensing choleskrol chloroformate with 2′-O-alkylamine or 3′-O-alkylamine of the appropriate nucleoside. The 2′-O-alkylamines were deiived from direct alkylation procedure.