- High-throughput five minute microwave accelerated glycosylation approach to the synthesis of nucleoside libraries
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The Vorbrueggen glycosylation reaction was adapted into a one-step 5 min/130 °C microwave assisted reaction. Triethanolamine in acetontrile containing 2% water was determined to be optimal for the neutralization of trimethylsilyl inflate allowing for direct MPLC purification of the reaction mixture. When coupled with a NH3/methanol deprotection reaction, a high-throughput method of nucleoside library synthesis was enabled. The method was demonstrated by examining the ribosylation of 48 nitrogen containing heteroaromatic bases that included 25 purines, four pyrazolopyrimidines, two 8-azapurines, one 2-azapurine, two imidazopyridines, two benzimidazoles, three imidazoles, three 1,2,4-triazoles, two pyrimidines, two 3-deazapyrimidines, one quinazolinedione, and one alloxazine. Of these, 32 yielded single regioisomer products, and six resulted in separable mixtures. Seven examples provided inseparable regioisomer mixtures of -two to three compounds (16 nucleosides), and three examples failed to yield isolable products. For the 45 single isomers isolated, the average two-step overall yield ± SD was 26 ± 16%, and the average purity ± SD was 95 ± 6%. A total of 58 different nucleosides were prepared of which 15 had not previously been accessed directly from glycosylation/deprotection of a readily available base.
- Bookser, Brett C.,Raffaele, Nicholas B.
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p. 173 - 179
(2007/10/03)
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- Synthesis and stability of GNRA-loop analogs
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Nebularinc, 9-(β-D-ribofuranosyl)-9H-purin-2-amine, and inosine phosphoramidites 8, 16, and 17, respectively, were synthesized and incorporated into the GNRA tetraloop at different positions (see Scheme, Table, and Fig. 4). The oligomers were investigated by means of UV and CD spectroscopy to address the question of how the individual base-modified N- nuclcosides contribute to changes in H-bonding and base-stacking interactions within the loop. Several CD spectra are given and compared with each other (Figs 5 and 6). The exchange of the loop sequence in position 4 and 7 results in a distinct change in base stacking. CD-Band shifting allows us to advance the hypothesis that a transition from a GNRA-type towards a UNCG-type base stacking is observed.
- Woerner, Karlheinz,Strube, Thorsten,Engels, Joachim W.
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p. 2094 - 2104
(2007/10/03)
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- Oxidative Transformations of Minor Components of Nucleic Acids. An Anomalous Reaction Course of Oxidation of N6,N6-Dialkyladenosines and Related Compounds with m-Chloroperoxybenzoic Acid
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Oxidation of N6-methyladenosine (1a) or the corresponding tribenzoate 1b with m-chloroperoxybenzoic acid gave N1-oxides 2a and 2b whereas N6,N6-dimethyladenosine tribenzoate (3a) afforded 2',3',5'-tri-O-benzoylinosine (4a) and N6-methyl-N6-formyl derivative 5.The N6,N6-diethyladenosine 3b and piperidine derivative 3c yielded only 4a, but N6,N6-dibenzyl compound 3d was not oxidized.N,N-Dimethyl-2,4-dinitroaniline (6a) was oxidized with m-chloroperoxybenzoic acid to give N-methyl-N-formyl derivative 7a, N-methyl-2,4-dinitroaniline (8a), N-oxide 10a, and only traces of 2,4-dinitrophenol (9a).By contrast, 2-(dimethylamino)-5-nitropyridine (6b) afforded 5-nitro-2-pyridone (9b) and N-demethylated N1-oxide 11. 2-(Dimethylamino)pyridine (6c) and 2-(methylamino)-5-nitropyridine (8b) gave the respective N2- and N1-oxides 10c and 11.The reaction of 6-chloropurine nucleosides 15a and 15b with N,N-dimethylhydroxylamine gave inosine 4a or 4b accompanied by a smaller amount of 3a or 3e. 2,4-Dinitrofluorobenzene (16) afforded O-(2,4-dinitrophenyl)-N,N-dimethylhydroxylamine (17).Mass spectra of compounds 10a, 10c, and 17 provided evidence for Meisenheimer rearrangement and subsequent cyclic transformation.The N-oxide 10a and hydroxylamino derivative 17 gave 2,4-dinitrophenol (9a), and N2-oxide 10c afforded fragments belonging to 2-pyridone (9c).Compound 17 is thermally stable whereas N-oxide 10a yielded at 100 deg C a mixture of 8a, 8b, 9a, and 17.
- Endo, Takeshi,Zemlicka, Jiri
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p. 1887 - 1894
(2007/10/02)
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- The preparation of 14C-Labeled Ribosyl-trans-zeatin and Its cis Isomer
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14C-Labeled ribosyl-trans-zeatin and its cis isomer have been prepared from inosine by facile reactions.
- Nakajima, Hiromitsu,Yokota, Takao,Watanabe, Naoharu,Takahashi, Nobutaka
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p. 2717 - 2720
(2007/10/02)
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