Synthetic Nucleosides and Nucleotides. XX1. Synthesis of Various 1-β-D-Xylofuranosyl-5-Alkyluracils and Related Nucleosides

Abstract

Treatment of D-xylose (1) with 0.5% methanolic hydrogen chloride under controlled conditions followed by benzoylation and acetolysis afforded crystalline 1-O-acetyl-2, 3, 5-tri-O-benzoyl-α-D-xylofuranose (4) in good yield. Coupling of 4 with 2, 4-bis-trimethylsilyl derivatives of 5-alkyluracils (methyl, ethyl, propyl and butyl) (5a-5d), 5-fluorouracil (5e) and uracil (5f) in acetonitrile in the presence of stannic chloride gave 1-(2,3,5-tri-O-benzoyl-β-D-xylofuranosyl)-nucleosides (6a-6f). Saponification of 6 with sodium methoxide afforded 1-β-D-xylofuranosyl-5-substituted uracils (7a-7f). Condensation of 4 with free adenine in similar fashion and deblocking gave carcinostatic 9-β-D-xylofuranosyladenine (7g).     

Nucleosides. LXV. Synthesis of New Pteridine–N8–Nucleosides

A general synthetic approach to various isoxanthopterin‐nucleosides starting from 6‐methyl‐2‐methylthio‐4(3H), 7(8H)‐pterdinedione (1) has been developed. Ribosylation with 1‐O‐acetyl‐2,3,5‐tri‐O‐benzoyl‐β‐d‐ribofuranose via the silyl‐method led to 2 and reaction with 1‐chloro‐2‐deoxy‐3,5‐di‐O‐p‐toluoyl‐α‐d‐ribofuranose using the DBU‐method afforded 28. Protection of the amide function at O⁴ by benzylation to 5 and by a Mitsunobu reaction with 2‐(4‐nitrophenyl)ethanol to 29 gave soluble intermediates which can be oxidized to the corresponding 2‐methylsulfonyl derivatives 8 and 30, respectively. Nucleophilic displacement reactions of the highly reactive 2‐methylsulfonyl functions by various amines proceeded under mild conditions to isoxanthopterin‐N₈‐ribo‐ (11–17) and 2′‐deoxyribomucleosides (31–33). Debenzylation can be achieve by Pd‐catalyzed hydrogenation (9 to 19) and cleavage of the npe‐protecting group (31, 32 to 34, 35) works well with DBU by β‐elimination.     

Nucleosides. LIV1 Synthesis and Properties of 3′-Azido- and 2′,3′-Dideoxy-6,7-diphenyllumazine Nucleosides

Abstract

The best approach for the synthesis of1-(3-azido-2,3-dideoxy-β-D-erythro-pento-furanosyl)lumazine (5) and its 6,7-dimethyl- (4) and 6,7-diphenyl derivatives (3) has been found in the interconversion of the corresponding 1-(2-deoxy- β-threo-pentofuranosyl)-lumazines. Monomethoxytritylation at the 5′-position (1 7, 3 4, 4 9) followed by mesylation at the 3′-OH group and subsequent nucleophilic displacement by lithium azide afforded 1 9, 2 9 and 4 7 which were deprotected by acid treatment to give 3–5 in good yields. The syntheses of 1-(2,3-dideoxy-β-D-glycero-pentofuranosyl)-6,7-diphenyllumazine (6) and its 6,7-dimethyl derivative (7) were achieved from 1-(2-deoxy-β-D-erythro-pentofuranosyl)-6,7-diphenyllumazine and the corresponding 6,7-dimethyllumazine (2 6) via their 5′-O-p-toluoyl- (2 0, 3 0), and 3′-deoxy-3′-iodo derivatives (2 4, 3 1) to form, after radical dehalogenation and final deprotection, 6 and 7. The newly synthesized lumazine nucleosides have been characterized by elemental analyses, UV-and NMR spectra.     

Chemical Conversion of Uridine to 3′-Branched Sugar Nucleosides (Nucleosides and Nucleotides. 421.)

Abstract

Deamination of 1-(3-amino-3-deoxy-β-D-glucopyranosyl)-uracil gave a ring contracted nucleoside, 3′-deoxy-3′-formyluridine as a hemiacetal form, and uracil. Similar treatment of the 2′-deoxyderivative, 1-(3-amino-2,3-dideoxy-β-D-glucopyranosyl)uracil, gave the corresponding 2′,3′-dideoxy-3′-formyluridine in high yield. The 3′-epimerization of the 3′-formyluridine derivative was achieved and after reduction of the formyl groups, 2′,3′-dideoxy-3′(R and S)-hydroxymethyluridine were obtained.     

Nucleosides and Nucleotides. 125. Synthesis and Biological Evaluation of 2′,3′-Dideoxy-3′-fluoro-2′-methylidene Pyrimidine Nucleosides

Abstract

Reaction of 2′-deoxy-2′-methylidene-5′-O-trityluridine (1) with diethylamino-sulfur trifluoride (DAST) in CH₂Cl₂ resulted in the formation of a mixture of (3′R)-2′,3′-dideoxy-3′-fluoro-2′-methylidene derivative 3 and 2′,3′-didehydro-2′,3′-dideoxy-2′-fluoromethyl derivative 4 (3:4 = 1:1.5) in 65% yield. A similar treatment of 1-(2-deoxy-2-methylidene-5-O-trityl-β-D-threo-pentofuranosyl)uracil (19) with DAST in CH₂Cl₂ afforded (3′S)-2′,3′-dideoxy-3′-fluoro-2′-methylidene derivatives 20 and 4 in 38% and 17% yields respectively. Transformation of the uracil nucleosides 4, 12, and 20 into cytosines followed by deprotection furnished the corresponding cytidine derivatives 29, 18, and 25, respectively. The corresponding thymidine congener 27 was also synthesized in a similar manner. All of the newly synthesized nucleosides were evaluated for their inhibitory activities against HIV and for their antiproliferative activities against L1210 and KB cells.     

Mechanistic and Synthetic Aspects of the C-1′ Radicals in Modified Nucleosides

Abstract

The direct and indirect production of C-1′ radicals has been achieved through the synthesis of modified nucleosides. Product studies and spectroscopic investigations have been used to study the structure and fate of C-1′ radical species under anoxic or aerobic conditions. The results are of fundamental importance in understanding the mechanism of DNA cleavage via C-1′ radicals. The mechanistic schemes of some very recent synthetic applications have also been revisited.     

Nucleosides and Nucleotides. 140. Synthesis and Antileukemic Activity of 5-Carbon-Substituted 1-β-d-Ribofuflranosylimidazole-4-Carboxamides

Abstract

Synthesis of 5-carbon-substituted 1-β-d-ribofuranosylimidazole-4-carboxamides are described. Treatment of 5-iodo derivative 8 with methyl acrylate in the presence of palladium catalyst gave (E)-5-(2-carbomethoxyvinyl)-1-(2,3,5-tri-O-acetyl-β-D-ribofuranosyl)imidazole-4-carboxamide (9), followed by appropriate manipulations to afford various 5-carbon-substituted imidazole derivatives 1–7. The antileukemic activities of these imidazole nucleosides are also described.

     

Nucleosides. 140. Stereoselectivity of the Reaction of 1-(2,3-Anhydro-5-O-Benzoyl-β-D-Lyxofuranosyl) Uracil with Ammonium Azide. Isolation and Characterization of 2-Azido-Xylo-Nucleoside Derivatives

Abstract

The composition of the products of reaction of 1-(2,3-anhydro-5-O-benzoyl-β-D-lyxofuranosyl)uracil (1) with NH₄N₃ was studied by a reverse-phase HPLC system which was found to separate the 3-azido-arabino 2 and 2-azido-xylo 3 isomers that were formed. The use of a 10:1 ratio of NH ₄ N ₃ to 1 in refluxing EtOH was found to minimize ring opening at C-2 (7%). The higher stereoselectivity of ring opening produced by using a large excess of NH ₄ N ₃ was suppressed by conducting the reaction in DMF. Preventing the escape of the NH ₃ by-product only resulted in debenzoylation. The isolation of pure, crystalline 3 was achieved by reverse-phase preparative HPLC. Separation from the arabino isomer was also effected by debenzoylation and selective acetonide formation with the xylo isomer, which allowed facile isolation of the latter by normal phase chromatography. Hydrolysis of the acetonide 7 provided unprotected 2-azido-xylo nucleoside 6, which was also obtained by NaOMe treatment of 3. The mechanistic basis for the stereoselectivity of epoxide opening is discussed.     

Nucleosides and Nucleotides. 232. Synthesis of 2′-C-Methyl-4′-thiocytidine: Unexpected Anomerization of the 2′-Keto-4′-thionucleoside Precursor

The synthesis of 2′-C-methyl-4′-thiocytidine (16) is described. Since the 2′-keto-4′-thiocytidine derivative 2β unexpectedly isomerized to 2α and the methylation of 2β proceeded predominantly from the less hindered α-face to give 7, the desired product 16 was synthesized via the Pummerer reaction of the sulfoxide 14 and N ⁴ -benzoylcytosine.     

Synthesis of 2′-N-Formamido Nucleosides and Biological Evaluation

The 2′-N-formamide derivatives of adenosine, cytidine, and 9-β-d-arabinofuranosyladenine were synthesized and tested (as triphosphate) for their substrate capacities for the HCV NS5B polymerase.     

Synthesis of 4′-C-Ethynyl and 4′-C-Cyano Purine Nucleosides from Natural Nucleosides and Their Anti-HIV Activity

Abstract

Purine 2′-deoxynucleosides bearing an ethynyl or a cyano group at C-4′ of the sugar moiety were synthesized from the corresponding 2′-deoxynucleosides. These compounds exhibited very potent anti-HIV activity, and remained active against drug resistant HIV strains.     

Nucleosides. 140. Stereoselectivity of the Reaction of 1-(2,3-Anhydro-5-O-Benzoyl-β-D-Lyxofuranosyl)Uracil with Ammonium Azide. Isolation and Characterization of 2-Azido-XYLO-Nucleoside Derivatives.1

Abstract

The composition of the products of reaction of 1-(2,3-anhydro-5-O-benzoyl-β-D-lyxofuranosyl)uracil (1) with NH₄N₃ was studied by a reverse-phase HPLC system which was found to separate the 3-azido-arabino 2 and 2-azido-xylo 3 isomers that were formed. The use of a 10:1 ratio of NH₄N₃ to 1 in refluxing EtOH was found to minimize ring opening at C-2 (7%). The higher stereoselectivity of ring opening produced by using a large excess of NH₄N₃ was suppressed by conducting the reaction in DMF. Preventing the escape of the NH₃ by-product only resulted in debenzoylation. The isolation of pure, crystalline 3 was achieved by reverse-phase preparative HPLC. Separation from the arabino isomer was also effected by debenzoylation and selective acetonide formation with the xylo isomer, which allowed facile isolation of the latter by normal phase chromatography. Hydrolysis of the acetonide 7 provided unprotected 2-azido-xylo nucleoside 6, which was also obtained by NaOMe treatment of 3. The mechanistic basis for the stereo-selectivity of epoxide opening is discussed.     

Synthesis and Anti-HIV Evaluation of 3′-Triazolo Nucleosides

A series of hitherto unknown 3′-α-[1,2,3]-substituted triazolo-2′,3′-dideoxypyrimidine nucleoside analogues of the anti-HIV 3′-azido-3′-deoxythymidine (AZT) were synthesized through catalyzed alkyne-azide 1,3-dipolar cycloaddition (Huisgen reaction). Those 3′-[1,2,3]-triazolo analogues bearing an azido alkyl chain were evaluated for their anti-HIV activity against HIV-1 in primary human lymphocytes as well as for their cytotoxicity in different cells. None of them inhibit HIV replication (EC₅₀ > 20 μM); two of them were converted to their triphosphate form to evaluate their HIV-RT inhibition.     

Alternate Approaches to the Synthesis of 2′-O-Me Nucleosides

Abstract

Three different approaches to the synthesis of 2′-O-methyl nucleosides starting from the corresponding nucleoside or commercially available 1,2:5,6-di-O-isopropylidene-α-D-allofuranose 1 are described.     

Nucleosides. LXII. Synthesis of 6-Methyl-8-(2-deoxy-β-D-ribofuranosyl)-isoxanthopterin and Derivatives

Abstract

The syntheses of 6-methyl-8-(2-deoxy-ß-D-ribofuranosyl)isoxanthopterin (21) and its protected 3′-O-phosphoramidite 23 were achieved from 6-methyl-2-methylthio-8-(2-deoxy-3,5-di-O-p-toluoyl-ß-D-ribofuranosyl)-3H,8H-pteridine-4,7-dione (8) in several steps. The new building block for oligonucleotide syntheses is highly fluorescent and can be considered as a substitute for 2′-deoxyguanosine.     

Modified Nucleosides. II.1 Economical Synthesis of 2′,3′-Dideoxycytidine

Abstract

An economical two pot synthesis of 2′,3′-dideoxycytidine (2) from N⁴-acetyl-cytidine (4) has been developed. The key feature of this sequence is the in situ reductive elimination of a mixture of 1-(3-bromo-3-deoxy-2,5-di-O-acetyl-β-D-xylofuranosyl)-N⁴-acetylcytosine (5) and 1-(2-bromo-3-deoxy-3,5-di-O-acetyl-β-D-arabinofuranosyl)-N⁴-acetylcytosine (6) and subsequent hydrogenation of the resultant olefin over palladised charcoal.     

Nucleosides. 124. 3-Amino-3-deoxyhexopyranosyl Nucleosides. 7. 1-(3-Deoxy-3-Nitro-β-D-glucopyranosyl) Uracil and Its Galactopyranosyl Isomer1

Abstract

Crystalline 1-(3-deoxy-3-nitro-β-D-glucopyranosyl) uracil (3), originally prepared by nitromethane condensation of “uridine dialdehyde,” was found to contain the galactosyl isomer (4). Each isomer was obtained in pure form by 4′,6′-O-benzylidenation of the mixture of 3 and 4, followed by chromatographic separation and subsequent O-debenzylidenation. The structure of each isomer was established by chemical conversion of the isomer into the corresponding known 3′-acetamido-2′,4′,6′-tri-O-acetyl derivative.     

Antileukemic Activities and Mechanism of Action of 2′-Deoxy-4′-methylcytidine and Related Nucleosides

Abstract

Antileukemic activity of several analogues containing 2′-deoxy-4′-methylcytidine and its araC counterpart were evaluated against murine leukemic P388 cells in vitro and in vivo. Both compounds showed significant cytostatic activity (both IC₅₀=0.4 μM) in vitro and the former compound administered intraperitoneally at a dose of 3 mg/kg/day × 5 showed high activity (T/C=175%) in vivo. The mechanism of action of these 5′-triphosphates on DNA polymerases in detail will be also described.     

Synthesis of 2′-Deoxy-6,2′-Ethano-Cyclouridine1 (Nucleosides and Nucleotides. Part 57)

Abstract

Synthesis of a carbon-bridged cyclouridine,2′-deoxy-6,2′-ethano-cyclouridine, was accomplished starting from a 2′-ketouridine via the 2′-deoxy-2′-iodoethyl-5-chlorouridine derivative through a radical cyclization.