Syntheses of Novel 3-Substituted-2′-deoxy-3-deazauridine Nucleosides

Syntheses of novel 3-ethynyl (8), 3-vinyl (10) and 3-acetoxy (13)-2′-deoxy-3-deazauridine analogs starting from the protected 2′-deoxy-3-deazauridine derivative 4 are described.     

A new synthesis of 3′-deoxy-3′-fluoroadenosine,a key intermediate of cyclic dinucleotide

A new synthesis of 3′-deoxy-3′-fluoroadenosine for use as an important intermediate of antitumor-active cyclic dinucleotide is disclosed. The synthesis started with the known 5-O-TBDPS-D-lyxofuranose 1,2-acetonides, which was first transformed into a fluorinated compound after the DAST reaction. Desilylation and acidic methanolysis were then finished in one pot. After a sequence of triflation, displacement by OBz as well as benzoylation, perbenzoylated 3-deoxy-3-fluoro-D-ribofuranoside was obtained, which would be transformed to 3′-deoxy-3′-fluoroadenosine as the key intermediate of cyclic dinucleotide after ammonolysis.     

Thermal analysis of 5′-deoxy-5′-iodo-2′,3′-O-isopropylidene-5-fluorouridine

The melting temperature, melting enthalpy, and specific heat capacities (C _p) of 5′-deoxy-5′-iodo-2′,3′-O-isopropylidene-5-fluorouridine (DIOIPF) were measured using DSC-60 Differential Scanning Calorimetry. The melting temperature and melting enthalpy were obtained to be 453.80 K and 33.22 J g^?1, respectively. The relationship between the specific heat capacity and temperature was obtained to be C _p/J g^?1 K^?1 = 2.0261 – 0.0096T + 2 × 10^?5 T ² at the temperature range from 320.15 to 430.15 K. The thermal decomposition process was studied by the TG–DTA analyzer. The results showed that the thermal decomposition temperature of DIOIPF was above 487.84 K, and the decomposition process can be divided into three stages: the first stage is the decomposition of impurities, the mass loss in the second stage may be the sublimation of iodine and thermal decomposition process of the side-group C₄H₂O₂N₂F, and the third stage may be the thermal decomposition process of both the groups –CH₃ and –CH₂OCH₂–. The obtained thermodynamic basic data are helpful for exploiting new synthetic method, engineering design, and commercial process of DIOIPF.     

Synthesis of 5′-deoxy-5′-[18F]fluoro-adenosine by Radiofluorination of 5′-deoxy-5′-haloadenosine Derivatives

5-Deoxy-5-[¹⁸F]fluoro-adenosine was synthesised by nucleophilic radiofluorination reactions of 5-deoxy-5-haloadenosines. The homogeneous isotope exchange in 5-deoxy-5-fluoro-adenosine was also investigated. The conversion of these reactions was found to be rather low and depends on the strength of the halogen-carbon bond: 0.248% for chloride-, 0.488% for bromide- and 1.070% for iodide-derivative; there was no reaction observed in the case of fluoro-compound.     

Synthesis of 2′-deoxy-2′-fluororibo- and 2′-deoxy-2′,2′-difluororibonucleosides derived from 6-(het)aryl-7-deazapurines

A series of novel sugar-modified derivatives of cytostatic 6-hetaryl-7-deazapurine ribonucleosides (2′-deoxy-2′-fluororibo- and 2′-deoxy-2′,2-difluororibonucleosides) bearing an aryl or hetaryl group in position 6, was prepared and screened for biological activity. The fluororibo derivatives were prepared by aqueous palladium catalyzed cross-coupling reactions of the corresponding 6-chloro-7-deazapurine 2′-deoxy-2′-fluororibonucleoside 11 with (het)arylboronic acids. The key intermediate 11 was prepared by a six-step sequence from the corresponding arabinonucleoside by selective protection of 3′- and 5′-hydroxyls by acid-labile groups followed by stereoselective S_N2 fluorination and deprotection. The difluororibo-series was prepared by non-stereoselective glycosidation of 6-chloro-7-deazapurine with benzoyl-protected 2-deoxy-2,2-difluoro-d-erythro-pentofuranosyl-1-mesylate followed by cross-couplings, separation of anomers and deprotection. The title nucleosides did not show considerable cytostatic or antiviral activity.     

Synthesis and X-ray crystal structure of 3-deoxy-3-fluoro-β-D-allopyranoside

The synthesis of a novel compound, 3-deoxy-3-fluoro--d-allopyranoside, is described. It involves blocking the 4- and 6-positions of allose to cause fluorination only at the 3-position. This six-step synthesis gave pure crystalline compound in a 5% overall yield. The crystal structure, determined by X-ray diffraction, confirmed the chemical formula and configuration of the product. It showed that the C-F bond isaxial, while the C-(OH) bonds areequatorial. The overall conformation of this fluoroallose is similar to that of allose (Acta Cryst.1984,C40, 1863) (with OH instead of F), but the packing in the two crystals is different in the region of C3, the site of chemical variation.     

Synthesis of 2-O-ethyl analogues of 3′-azido- and 3′-fluoro-2′,3′-dideoxyuridines and evaluation of their biological activity against HIV

Summary 2-O-Ethyluracil and 2-O-ethylthymine were silylated with 1,1,1,3,3,3-hexamethyldisilazane and condensed in the presence ofTMS triflate with 2,3-dideoxy-3-fluoro-D-erythro-pentofuranoside, 3-azido-2,3-dideoxy-D-erythro-pentofuranoside, and 2,3-dideoxy-3-phthalimido--D-erythro-pentofuranose derivatives to give the corresponding 2-O-ethyl nucleosides. Deprotection with saturated methanolic ammonia afforded the 2,3-dideoxy-3-fluoro-2-O-ethyluridines, whereas 3-azido-2,3-dideoxy-3-O-ethyluridine was obtained by deprotection with tetrabutylammonium fluoride in tetrahydrofuran. 3-Amino-2,3-dideoxy-3-O-ethyluridine could be obtained only by treatment of the corresponding 3-azido nucleoside with triphenylphosphine in pyridine. 3-Deoxy-2-O-ethyl-3-fluorothymidine (6b) showed moderate activity against HIV-1.

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Synthese von 2-O-Ethyl-Analogen von 3-Azido- und 3-Fluor-23-dideoxyuridinen und Bestimmung ihrer biologischen Aktivität gegenüber HIV

Zusammenfassung 2-O-Ethyluracil und 2-O-Ethylthymin wurden mit 1,1,1,3,3,3-Hexamethyldisilazan silyliert und in Gegenwart vonTMS-triflat mit 2,3-Dideoxy-3-fluoro-D-erythro-pentofuranosid, 3-Azido-2,3-dideoxy-D-erythro-pentofuranosid und 2,3-Dideoxy-3-phthalimido--D-erythro-pentofuranosederivaten zu den entsprechenden 2-O-Ethyl-Nucleosiden umgesetzt. Entfernung der Schutzgruppe mit gesättigter methanolischer Ammoniaklösung lieferte 2,3-Dideoxy-3-fluor-2-O-ethyluridin; 3-Azido-2,3-dideoxy-3-O-ethyl-uridin wurde durch Entschützung mit Tetrabutylammoniumfluorid in Tetrahydrofuran erhalten. 3-Amino-2,3-dideoxy-3-O-ethyl-uridin konnte nur durch Behandeln des entsprechenden 3-Azido-Nucleosids mit Triphenylphosphin in Pyridin hergestellt werden. 3-Deoxy-2-O-ethyl-3-fluor-thymidin (6b) zeigt geringe Aktivität gegenüber HIV-1.

     

Diastereoselective and enantioselective synthesis of 4′-aza analogues of 2′,3′-dideoxynucleosides

A diastereo- and enantioselective synthesis of 4′-aza analogues of 2′,3′-dideoxynucleosides has been designed by the strategy of the 1,3-dipolar cycloaddition reaction of a Vasella-type nitrone. The reaction leads to (1′R)- and (1′S)-4′-aza analogues of 2′,3′-dideoxythimidine and fluorouridine, in enantiomerically pure forms.     

Synthesis of 2′,3′-didehydro-3′-deoxythymidine and its activity against HIV

2,3-Didehydro-3-deoxythymidine has been obtained with an overall yield of 10% by the condensation of 1,2-di-O-acetyl-3,5-di-O-benzoyl-D-xylofuranose with bis-(dimethylsilyl)thymine and a series of subsequent transformations. The anti-HIV activity of the compound obtained was studied on the model of MT-4 lymphoid cells primarily infected with HIV-1. It was found that the substance effectively inhibits the reproduction of HIV-1 in a cell culture.Institute of Organic Chemistry, Ural Branch, Russian Academy of Sciences, Ufa. Vector Scientific-Production Association, Kil'tsovo, Novosibirsk Province. Institute of the Chemistry of Plant Substances, Uzbek SSR Academy of Sciences, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 133–136, January–February, 1993.     

Fully automated and simplified radiosynthesis of [<Superscript>18</Superscript>F]-3′-deoxy-3′-fluorothymidine using anhydro precursor and single neutral alumina column purification

[¹⁸F]-3′-deoxy-3′-fluorothymidine ([¹⁸F]FLT) is an established positron emission tomograph (PET)—radiopharmaceutical to study cell-proliferation rate in tumors. Very low practical yield, uncertain and time-consuming high performance liquid chromatography (HPLC) purification, are the main obstacles for the routine use of [¹⁸F]FLT in clinical PET. To obviate these difficulties, we have developed a fully automated radiosynthesis procedure for [¹⁸F]FLT using 5′-O-(4,4′-dimethoxytriphenylmethyl)-2,3′-anhydro-thymidine (DMTThy) and simplified single neutral alumina column purification. The [¹⁸F]FLT yield was 8.48 ± 0.93% (n = 5) (without radioactive decay correction) in a synthesis time of 68 ± 3 min. The radiochemical purity was greater than 95% as confirmed by analytical HPLC using reference standard FLT and also free of non-radioactive impurity. Soluble aluminum in the final product was much below the permissible limits. Di-methyl sulfoxide (DMSO), the reaction medium, could be detected in the final product in trace amounts, well below the permissible levels. The synthesized [¹⁸F]FLT was sterile and bacterial endotoxin free by appropriate tests. PET imaging study in normal rabbits showed distinct localization of [¹⁸F]FLT in organs having rapid cell division rate like bone marrow, guts and snout and the excretion was through the renal route. There were no significant uptakes in bone and brain. The former finding confirms the in vivo stability of the [¹⁸F]FLT. This simplified radiosynthesis procedure can easily be adapted in any commercial or indigenous [¹⁸F]FDG synthesis module for routine [¹⁸F]FLT synthesis without the need of additional automation for HPLC purification.     

Differentiation of 2′-O- and 3′-O-methylated Ribonucleosides by tandem mass spectrometry

Recent studies revealed that the 3'-terminal nucleotides in plant microRNAs were methylated on the ribose at the 2' or 3' hydroxyl groups. Here we examined the fragmentation of the electrospray-produced [M + H]+ and [M - H]- ions of 2'- and 3'-O-methylated ribonucleosides. It turned out that the predominant fragmentation pathway for the [M + H]+ ions of ribose-methylated nucleosides was the neutral loss of the methylated ribose, which made it impossible to distinguish 2'-O-methylation from 3'-O-methylation by positive-ion MS/MS. However, characteristic fragment ions, resulting from the cleavage through the ribose rings, were produced for the [M - H]- ions of each pair of ribose-methylated nucleosides. In this respect, the neutral loss of a 90-Da fragment (C3H6O3) was observed for 2'-O-methylated cytidine, guanosine and adenosine, but not for their 3'-O-methylated counterparts. On the other hand, the neutral loss of a 60-Da fragment (C2H4O2) was found for 3'-O-methyluridine, but not for 2'-O-methyluridine.     

Structure and stability of molecular and ionic complexes of AlCl3 with pyrazine and 4,4′-bipyridyl

Structural and thermodynamic characteristics of molecular and ionic complexes of aluminum trichloride with pyrazine (pyz) and 4,4′-bipyridyl (bipy) are calculated at the RI-BP86/def2-SVP level. It is found that for molecular 2AlCl₃·3L and 4AlCl₃·3L complexes an energy difference between isomers does not exceed 4 kJ/mol, and the rotation barrier of the AlCl₃ moiety relative to the N-Al-N bond does not exceed 24 kJ/mol. A comparison of the stability of molecular and ionic complexes of aluminum in the gas phase shows that the maximum energy difference is ～60 kJ/mol. For L = pyz the molecular complex is more stable whereas for L = bipy it is the ionic one.     

Evaluation of the radiochemical impurities arising during the competitive fluorination of nosyl group during the synthesis of 3′-deoxy-3′-fluorothymidine, [18F]FLT

The study is aimed at the analysis and identification of radiochemical and chemical impurities present in [¹⁸F]FLT synthesized by a simplified combination-column purification procedure, instead of the currently used HPLC purification. HPLC analysis of the final product showed an anionic radioactive byproduct, which was established as [¹⁸F]4-FBSA. The identity of the product was also confirmed by the radiofluorination of nosyl chloride. Mass spectrum analysis of both a decayed sample of [¹⁸F]FLT and fluorinated nosyl chloride showed a major peak at 242. We have also investigated the possible interference of this byproduct during PET-imaging in rabbits.     

Synthesis of 5-substituted-3-[(2′S,3′S)-3′-hydroxy-2′-hydroxymethyltetrahydrofuran-3′-yl]-1,2,4-oxadiazoles and their epimers

5-Phenyl-3-[(2′R,3′S)-3′-hydroxy-2′-dimethoxymethyltetrahydrofuran-3′-yl]-1,2,4-oxadiazole 10a and its epimer 11a, 5-methyl-3-[(2′R,3′S)-3′-hydroxy-2′-dimethoxymethyltetrahydrofuran-3′-yl]-1,2,4-oxadiazole 10b and its epimer 11b were synthesized from cyanohydrin benzoates 8a, 9a and cyanohydrin acetates 8b, 9b, respectively, by treatment with hydroxylamine in methanol via intramolecular transacylation and subsequent cyclization of the corresponding amidoximes. Hydrolysis and reduction of the dimethoxymethyl groups in the above compounds gave the desired compounds 12a, 13a, 12b and 13b.     

Transformations of β-d-xylofuranosyl nucleosides. Synthesis of 3′-azido-3′-deoxythymidine

A modified synthesis of 3′-azido-3′-deoxythymidine starting fromD-xylose is proposed. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2062–2063, October, 1998.     

Concise Synthesis and Cellular Evaluation of 3′-Formyl-4′,6′-dihydroxy-2′-methoxy-5′-methylchalcone (FMC) and Its Analogues

3′-Formyl-4′,6′-dihydroxy-2′-methoxy-5′-methylchalcone (FMC) was a natural product isolated from Cleistocalyx operculatus. A four-step synthetic strategy toward FMC and its four analogues (1b–1e) was first developed. All compounds were synthesized from commercially available 2,4,6-trihydroxyacetophenone; formylation at 3′ position under Vilsmeier–Haack conditions was followed by the introduction of a methyl group at 5′ position. The key step of selective methylation at 2′ position was achieved by trimethylsilyldiazomethane (TMSCHN₂). Then substituted aromatic aldehydes were condensed through Claisen–Schmidt reaction in the presence of potassium hydroxide. All structures were confirmed by ¹H NMR, ¹³C NMR, and high-resolution mass spectra. FMC and analogues were screened for their antiproliferative activity.     

Calorimetric study of 2′-methylacetophenone and 4′-methylacetophenone

Values of the condensed phase standard (p = 0.1 MPa) molar enthalpy of formation for 2′- and 4′-methylacetophenones were derived from the standard molar energies of combustion, in oxygen, at T = 298.15 K, measured by static bomb combustion calorimetry. The values of the standard molar enthalpy of vaporization, at T = 298.15 K, were measured by Calvet microcalorimetry. Combining these two values, the following enthalpies of formation in the gas phase, at T = 298.15 K, were then derived: 2′-methylacetophenone, –(115.7 ± 2.4) kJ · mol⁻¹, and 4′-methylacetophenone, –(122.6 ± 2.4) kJ · mol⁻¹. Substituent effects are discussed in terms of stability and compared with other similar compounds. The value of the standard molar enthalpy of formation for 3′-methylacetophenone was estimated from isomerization schemes.