Unsaturated Nucleosides Research Articles

Nucleic Acid Related Compounds. 105. Synthesis of 2',3'-Didehydro-2',3'-dideoxynucleosides from Ribonucleoside Cyclic 2',3'-(Sulfates or Phosphates) or 2',3'-Dimesylates via Reductive Elimination with Sodium Naphthalenide(1).

Treatment of purine ribonucleosides with thionyl fluoride resulted in formation of cyclic 2',3'-sulfite esters. Acetylation of the 5'-hydroxy group and Sharpless oxidation (NaIO(4)/RuCl(3)) gave the cyclic 2',3'-sulfate ester derivatives. Treatment of 5'-O-silyl-protected ribonucleosides with thionyl chloride followed by oxidation gave an alternative route to the cyclic 2',3'-sulfates. Reductive elimination with sodium naphthalenide (THF/-50 degrees C) gave the 2',3'-unsaturated nucleosides. Parallel treatment of adenosine cyclic 2',3'-phosphate gave the 2',3'-olefin. The adenine, hypoxanthine, and 2-amino-6-methoxypurine 2',3'-didehydro-2',3'-dideoxynucleosides were prepared efficiently (40-60% overall yields of crystalline, analytically pure products; 3-5 steps, some combined into one-flask procedures) by treatment of 5'-O-protected 2',3'-di-O-mesylribonucleosides with sodium naphthalenide. Reactions were performed at or below ambient temperature with readily available reagents and standard laboratory conditions.

Synthesis of Unsaturated Analogues of 9-[2(Phosphono- Methoxy)Propyl]Guanine as Antiviral Agents

The synthesis of 9-[2-(phosphonomethoxy)allyl]guanine (1) and 9-[2-(phosphonomethoxy)allyl]-8-aza-guanine (2), two new unsaturated acyclic phosphonate nucleosides analogues of the anti-HIV agents PMPG and 8-aza-PMPG, is described. Compounds 1 and 2 were evaluated for activity against human immunodeficiency virus (HIV-1 and HIV-2) and herpes simplex virus (HSV-1 and HSV-2).

Phosphodiester Amidates of Unsaturated Nucleoside Analogues as Anti-HIV Agents

Lipophilic phosphodiester L-alaninates of acyclic unsaturated nucleoside analogues 1d, 1e, 2d, 2e, 3d, 3e, 4d and 5d were prepared and their antiretroviral activity was examined in ATH8 cell culture infected with HIV-1. A possible mechanism of action of these analogues is discussed.

Phosphodiester amidates of unsaturated nucleoside analogues: synthesis and anti-HIV activity.

The effect of introduction of a lipophilic phosphodiester amidate moiety on the HIV activity of inactive unsaturated nucleoside analogues was investigated. Phosphodiester alaninates 5a, 5b, and 6 derived from unsaturated nucleoside analogues 3b, 3c, and 4a were synthesized and investigated as inhibitors of cytopathic effect and replication of HIV-1 in ATH-8 cells. Compound 5a is an inhibitor of HIV-1 whereas analogue 6 is inactive with cytotoxicity appearing above 10 microM and 5b is both inactive and nontoxic. Alkaline or enzymic hydrolysis of 5a gave phosphomonoester alaninate 14, a putative product of intracellular metabolism. Compound 14 as well as adenallene derivative 15c were devoid of anti-HIV activity, and they also failed to inhibit HIV reverse transcriptase. A new regioselective method for preparation of (Z)-4-(benzoyloxy)-1-hydroxy-2-butene, 7, a key intermediate for the synthesis of unsaturated nucleoside analogues of cis configuration such as 3a, 3b, and 3c, is also described.

Facile synthesis of 2′,3′-unsaturated nucleosides from 2-deoxyribose

A straightforward approach for the synthesis of 2′,3′-unsaturated nucleosides starting from 2-deoxyribose is described. This novel route involves two new methods; (1) preparation of 2-deoxy-1-thioribofuranoside by direct condensation of 2-deoxyribose and thiophenol, (2) formation of the nucleoside skeleton by the direct coupling of 2,3-unsaturated 1-thiopentofuranoside with pyrimidine bases.

In Vitro Cytotoxicity Testing of Potentially Active Anti-HIV Drugs with Cultured Cells

This study compared the ability of two continuous cell lines to predict the cytotoxicity of potentially active anti-HIV drugs. Human fetal lung fibroblasts (HFL1) and CD4+ T-lymphocytes (CEM-IW) were incubated in the absence or presence of increasing concentrations of 12 antiviral compounds. These six-membered unsaturated nucleoside analogues were stereospecifically synthesised in our laboratories, and were evaluated for cytotoxicity as well as for antiviral activity. Cells were incubated for six days and mitochondrial activity (XTT and MTT assays) was used to assess cytotoxicity. IC50 values were derived from concentration–effect curves after linear regression analysis. Comparison of the two sets of cytotoxicity data suggests that the experimental IC50 values from HFL1 cells correlate well with the values obtained in lymphocyte studies performed at the National Cancer Institute laboratories (r value = 0.93). For the 12 antiviral chemicals, and those we have tested previously, these methods probably detect basal cytotoxicity, i.e. the toxicity of a chemical to basic cellular functions and structures common to all mammalian specialised cells. However, as with any testing procedure, some chemicals may elude the cytotoxicity screen, as a result of false negatives due to solubility, miscibility and organ-specific effects, and could be mislabelled as having low toxic potential. It is therefore conceivable that tests involving continuous differentiated cell lines of various origins could be developed to cover a large percentage of toxic effects, thereby reducing the need to introduce many laborious assay systems with freshly-isolated primary cultures.

Allylic Substitution of 3‘,4‘-Unsaturated Nucleosides: Organosilicon-Based Stereoselective Access to 4‘-C-Branched 2‘,3‘-Didehydro-2‘,3‘-dideoxyribonucleosides

Reactions of organosilicon reagents (such as allyltrimethylsilane, silyl enol ethers, cyanotrimethylsilane) with 3‘,4‘-unsaturated nucleosides (of uracil, N4-acetylcytosine, and hypoxanthine) having an allyl ester structure were investigated in the presence of a Lewis acid in CH2Cl2. In the cases of uracil and N4-acetylcytosine derivatives, SnCl4 appeared to be suitable, whereas the use of EtAlCl2 was necessary for the hypoxanthine derivatives. The main pathway of these reactions was found to be α-face-selective SN2‘ allylic substitution, irrespective of the configuration of 2‘-O-acyl leaving group. As a result, a new stereoselective operation for C−C bonds formation leading to 4‘-carbon-substituted 2‘,3‘-didehydro-2‘,3‘-dideoxyribonucleosides has been disclosed for the first time. Stereochemistry of these 4‘-C-branched products can be assigned on the basis of 1H NMR spectroscopy in terms of the anisotropic shift of H-5 of the pyrimidine base (or H-8 of the hypoxanthine), which is caused by the 5‘-O-(tert-butyldiphenylsilyl) protecting group.

Synthesis of 2',3'-Didehydro-2',3'-dideoxynucleosides by Reaction of 5'-Protected Nucleoside 2',3'-Dimesylates with Telluride Dianion: A General Route from Cis Vicinal Diols to Olefins.

2',3'-Dimesylates of 5'-protected nucleosides are converted into the corresponding 2',3'-didehydro-2',3'-dideoxy compounds by treatment with telluride dianion in the form of the sodium or lithium salt. The method is well-suited to the preparation of unsaturated nucleosides that can be converted into compounds that are believed to be useful in the treatment of AIDS. The deoxygenation is general for vicinal dimesylates that have, or may adopt, a synperiplanar conformation. With straight chain compounds the reaction is stereospecific. In some cases, similar, but slower, deoxygenations can be performed with selenide dianion.

Synthesis of Novel Olefinic Carbocyclic Purine Nucleoside Analogues

Abstract The synthesis of optically pure unsaturated carbocyclic nucleoside analogues is described. (3,4S)-Bis(t-butyldiphenyl silyloxymethyl)-1R and 1S cyclopent-2-en-1-ol were coupled with 6-chloropurine and 2-amino-6-chloropurine respectively, using a modified Mitsunobu reaction. The products were reacted further using standard procedures to give compounds 12, 14, 16 and 18.

Synthesis of the β-2',3'-Unsaturated Pentopyranosyl Nucleosides and Their 3'-Hydroxymethyl Congeners

Abstract Fusion of the glycal 3 and purines/pyrimidines without acid catalyst provides anomeric mixtures of the 2′,3′-unsaturated pentopyranosyl nucleosides 4, which have been worked out to furnish the 3′-hydroxymethyl analogues, e.g. 5.

Nucleoside analogues. Synthesis of 2′,3′-dideoxy and 2′,3′-unsaturated ribofuranonucleosides of 5,6-dichloro-2-mercaptobenzimidazole as potential antiviral agents

Novel benzimidazole nucleoside derivatives structurally related to 5,6-dichloro-1-(β-D-ribofuranosyl)benzimidazole (DRB) and to tetrahydroimidazobenzodiazepinethione (TIBO) compounds have been synthesized and their antiviral properties examined. The 2′,3′-unsaturated nucleoside was obtained following chemical transformations of the corresponding β-D-ribofuranonucleoside, whereas the 2′,3′-dideoxynucleoside was synthesized by a glycosylation reaction between a suitably protected 2,3-dideoxy-D-glycero-pentofuranose and silylated 5,6-dichloro-2-mercaptobenzimidazole. The prepared compounds were tested for their activity against HIV and against a variety of RNA and DNA viruses, but they did not show significant antiviral activity.

Highly efficient synthesis of 2,2′-anhydro-1-(3′-bromo-3′-deoxy-5′-O-trityl-β-D-arabinofuranosyl)thymine and its derivatives from an unsaturated thymine nucleoside

Reaction of 5′-O-trityl-2′,3′-thymidinene 1 with hypobromous acid gave (5R,6R)-2,2′-anhydro-5-bromo-1-(3′-bromo-3′-deoxy-5′-O-trityl-β-D-arabinofuranosyl)-6-hydroxy-5, 6-dihydrothymine 3a and its (5S,6S)-trans isomer 4a. Similarly, 6-methoxy analogues (3b and 4b) and 6-acetoxy analogues (3c and 4c) of 3a and 4a were synthesized. Compounds 3a and 4a were converted into the corresponding 5,6-epoxy derivatives, 5 and 6. Deoxygenation of oxiranes 5 and 6 with Ph3P gave 2,2′-anhydro-1-(3′-bromo-3′-deoxy-5′-O-trityl-β-D-arabinofuranosyl)thymine 7, which was also obtainable in excellent yields from compounds 3a, b or/and 4a, b by treatment with Ph3PNaHCO3, or directly from unsaturated furanose 1 by one-pot synthesis via methyl ethers 3b and 4b or acetates 3c and 4c. Compound 7 was deprotected to give the mother compound 8 and was also converted into the 2, 3-lyxo epoxy thymine furanosides, 11 and 12, in high yields.

New acetenyl acyclic nucleosides synthesis of 1-(propargyloxymethyl) derivatives of uracil

Alkylation of trimethylsilyl derivatives of uracil, thymine, 5-fluorouracil, and 6-methyluracil with propargyloxymethyl chloride afforded the corresponding 1-(propargyloxymethyl) derivatives, new unsaturated acyclic nucleosides having an end carbon-carbon triple bond.

Allylic alcohol transpositions in the carbohydrate moiety of pyrimidine nucleosides.

The reagent system chlorodiphenylphosphine, imidazole, and iodine, is shown to be useful in a novel transposition reaction of allylic alcohols to provide access to a new class of 2′,3′-unsaturated nucleoside analogues.

Uracil and adenine nucleosides having a 2′,3′-bromovinyl structure: highly versatile synthons for the synthesis of 2′- C- and 3′- C-Branched 2′,3′-Unsaturated Derivatives

Preparation of 2′- and 3′-bromo derivatives of 2′,3′-unsaturated uracil and adenine nucleosides has been carried out starting from the corresponding β-hydroxyselenides by way of bromination and successive selenoxide elimination. These compounds have been shown to serve as versatile synthons for the preparation of anti-HIV candidates, 2′-C- and 3′-C-branched 2′,3′-unsaturated nucleosides, through palladium-catalyzed cross-coupling and halogen-lithium exchange reactions.

A Short Synthesis of 2′,3′-Didehydro-3′-deoxythymidine

Abstract Reaction of sodium metal in HMPA-THF with 2,3′-anhydrothymidine la, results in an elimination to give the 2′,3′-unsaturated nucleoside 3a, This process was utilized in a synthesis of the antiviral drug D4T from thymidine.

Identification of sugar degradation intermediates in a metalloporphyrin mediated DNA cleavage resulting from hydroxylation at C-5′

Hydroxylation of poly(dA)·poly(dT) at the 5′ position of the deoxyribose units by the chemical nuclease Mn-TMPyP–KHSO5[Mn–TMPyP = manganese(III) complex of meso-tetrakis(4-N-methylpyridiniumyl)porphyrin] followed by an additional thermal step provides 5′-aldehyde-3′,4′-unsaturated nucleosides which can be reduced by sodium borohydride and then hydrogenated with palladium on charcoal giving 2′,3′-dideoxyribonucleosides having the natural β or the non-natural α configuration at 4′.

Towards fluorinated nucleosides — tales of the unexpected

There is much current interest in the preparation of nucleoside analogues as potential anti-viral agents against a wide range of viral infections, the work being stimulated by the search for agents active against HIV. Much of this work has been done by groups without access to some techniques available to fluorine chemists and we thus turned our attention to this problem in collaboration with the Birmingham nucleoside group. It is proposed to cover three aspects of our study; firstly, the fluorination of intact nucleosides with elemental fluorine; secondly, the reaction of 5′-hydroxy and formyl derivatives of nucleosides with DAST; and thirdly, the reaction of pentofuranoses with DAST. In the first part of the work the fluorination of a wide range of unsaturated nucleosides will be discussed as well as a new method of obtaining these important intermediates. The surprising case of the reaction and the unusual nature of the major products will be outlined and mechanistic details of the processes leading to the products will be covered. The second two parts will cover some related reactions in attempts to prepare 5′-fluorinated pyrimidine nucleosides and sugar derivatives related to these. Some unexpected and exceptional rearrangements we have observed will be described and details of the mechanism of these will be discussed.

Synthesis and anti-HIV activity of 4'-azido- and 4'-methoxynucleosides.

A series of nucleosides were synthesized in which the 4'-hydrogen was substituted with either an azido or a methoxy group. The key steps in the syntheses of the 4'-azido analogues were the stereo- and regioselective addition of iodine azide to a 4'-unsaturated nucleoside precursor followed by an oxidatively assisted displacement of the 5'-iodo group. The 4'-methoxynucleosides were made via epoxidation of 4'-unsaturated nucleosides with in suit epoxide opening by methanol. Reaction-mechanism considerations, empirical conformation rules, NMR-based conformational calculations, and NOE experiments suggest that the 4'-azidonucleosides prefer a 3'-endo (N-type) conformation of the furanose moiety. When evaluated for their inhibitory effect on HIV in A3.01 cell culture, all the 4'-azido-2'-deoxy-beta-D-nucleosides exhibited potent activity. IC50's ranged from 0.80 microM for 4'-azido-2'-deoxyuridine (6c) to 0.003 microM for 4'-azido-2'-deoxyguanosine (6e). Cytotoxicity was detected at 50-1500 times the IC50's in this series. The 4'-methoxy-2'-deoxy-beta-D-nucleosides were 2-3 orders of magnitude less active and less toxic than their azido counterparts. Modifications at the 2'- or 3'-position of the 4'-substituted-2'-deoxynucleosides tended to diminish activity. Further evaluation of 4'-azidothymidine (6a) in H9, PBL, and MT-2 cells infected with HIV demonstrated a similar inhibitory profile to that of AZT. However, 4'-azidothymidine (6a) retained its activity against HIV mutants which were resistant to AZT.

Suppression of murine retroviral disease as a model for AIDS by 2′,3′-dideoxy-2′,3′-didehydrothymidine (D4T) : R. W. Sidwell, K. J. Okleberry, R. A. Burger, R. P. Warren, and J. D. Morrey. Institute for Antiviral Research, Utah State University, Logan, UT, USA

Synthesis of the 4′-ethynyl and 4′-cyano phosphonates 8–11, which mimic the 5′-monophosphate of 4′-branched 2′,3′-didehydro-2′,3′-dideoxy nucleosides, was investigated by employing the 3′,4′-unsaturated nucleosides (13 and 28) as the starting material. The synthesis was initiated by the electrophilic addition of NIS/(EtO)2P(O)CH2OH to these unsaturated nucleosides. After introduction of the 2′,3′-double bond, the 4′-hydroxylmethyl group of the resulting adducts was transformed into the ethynyl or cyano group. While the 4′-cyano phosphonates 9 and 11 were not sufficiently stable to be isolated, the 4′-ethynyl counterparts (8 and 10) were obtained as their mono-ammonium salts. The adenine derivative 8 showed almost comparable anti-HIV-1 activity to that of d4T.