- Novel phthalimide nucleosides for the specific recognition of a CG Watson-Crick base pair
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In an effort to extend the triple helix recognition code we have synthesized various substituted phthalimide-derived nucleosides that can recognize a CG Watson-Crick base pair. NMR experiments performed on the free nucleosides in methylene chloride at lowered temperatures indicate the strength and extent of H-bonding to the cytosine amino group of a CG base pair which strongly depend on the substituent of the phthalimide nucleobase. Consistent with the formation of an additional hydrogen bond to N7 of guanine, ureido-substituted nucleoside analogs show a higher overall affinity as compared to the 3-aminophthalimide nucleoside.
- Lengeler, David,Weisz, Klaus
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p. 1479 - 1481
(2007/10/03)
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- Studies on the origin of stereoselectivity in the synthesis of 1,2-trans glycofuranosyl azides
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The stereoselectivity of the 1,2-trans directed, Lewis acid-catalysed azidation of peracylated furanoses was found to depend on the reactivity of the azide donor (azide nucleophilicity) and the configuration at the anomeric centre relative to the neighbouring 2-O-acyl group. Reactions of 1,2-trans glycosyl esters with highly nucleophilic azide donors, generated from SnCl4 and Me3SiN3, were stereospecific. The results are interpreted in terms of the rapid reaction of the azide species with bicyclic 1,2-acyloxonium (1,2-O-alkyliumdiyl-D-glycofuranose) ions, which were the primarily formed reactive intermediates. When using 1,2-cis glycosyl esters as starting materials the selectivity was reduced (90-94% de); the same is true with 1,2-trans counterparts if less nucleophilic Me3SiN3 in combination with Me3SiOTf catalyst was used. This occurred due to the appearance of the more reactive but less selective oxocarbenium (glycofuranoxonium) ions either as primarily formed reactive intermediates in the former case or after equilibration with acyloxonium ions in the latter case. Protected 1,2-trans β-D-glycofuranosyl azides with ribo, xylo and 3-deoxy-erythro-pento configurations were best prepared from the corresponding glycosyl esters using 0.05 equivalents of SnCl4, i.e., under anomerization-free conditions. Azidation of methyl glycofuranosides proceeds with inferior (80-90% de) and less predictable selectivity irrespective of the starting anomeric configuration. Copyright (C) 2000 Elsevier Science Ltd.
- Stimac, Anton,Kobe, Joze
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p. 149 - 160
(2007/10/03)
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- 6-Methyl-5-azacytidine - Synthesis, conformational properties and biological activity. A comparison of molecular conformation with 5- azacytidine
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The title compound was prepared by the isocyanate procedure and the trimethylsilyl method. The measurement of 1H NMR spectrum of 6-methyl-5- azacytidine (1) revealed a preference of γ(t) (46%) rotamer around C(5')- C(4') bond, a predominance of N conformation of the ribose ring (K(eq) 0.33) and a preference of syn conformation around the C-N glycosyl bond. An analogous measurement of 5-azacytidine has shown a preference of γ+ (60%) rotamer around the C(5')-C(4') bond, a predominance of N conformation of the fibose ring (K(eq) 0.41) and a preference of anti conformation around the C- N glycosyl bond 6-Methyl-5-azacytidine (1) inhibits the growth of bacteria E coli to the extent of 85% at 4000 μM concentration and the growth of LoVo/L, a human colon carcinoma cell line, to the extent of 30% at 100 μM concentration but did not inhibit L1210 cells at ≤ 100 μM concentration 6- Methyl-5-azacytidine (1) exhibited no in vitro antiviral activity at ≤ 1 μM concentration.
- Hanna, Naeem B.,Zajicek, Jaroslav,Piskala, Alois
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p. 129 - 144
(2007/10/03)
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- Improved procedure for the regiospecific synthesis of 2'-deoxyribonucleosides
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2'-Deoxyribonucleosides are regiospecifically synthesized in high yields by catalyzing with KI-dibenzo-18-crown-6 PTC the condensation between unprotected silylated purines and pyrimidines and the appropriate easily available 2-deoxy-ribofuranosyl or pyranosyl sugar derivatives.
- Baud,Chavis,Lucas,Imbach
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p. 4437 - 4440
(2007/10/02)
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- Nucleoside Syntheses, XXII. Nucleoside Synthesis with Trimethylsilyl Triflate and Perchlorate as Catalysts
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The novel Lewis acids (CH3)3SiOSO2CF3 (5), (CH3)3SiOSO2C4F9 (6), and (CH3)3SiClO4 (4) are highly selective and efficient Friedel-Crafts catalysts for nucleoside formation from silylated heterocycles and peracylated sugars as well as for rearrangements of persilylated protected nucleosides.With basic silylated heterocycles these new catalysts give much higher yields of the natural N-1-nucleosides than with SnCl4.
- Vorbrueggen, Helmut,Krolikiewicz, Konrad,Bennua, Baerbel
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p. 1234 - 1255
(2007/10/02)
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- On the Synthesis of 5-(X-Methyl)ribofuranosyl-1,2,3-triazole Nucleosides
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The synthesis of the reactive 5-(bromomethyl)-1-(2',3',5'-tri-O-benzoyl-β-D-ribofuranosyl)-1,2,3-triazole (3) via 1,3-dipolar cycloaddition of the β-oxoalkylidenephosphorane 2 to the ribofuranosyl azide 1 under elimination of triphenylphosphane oxide is d
- Schoerkhuber, Wolfgang,Zbiral, Erich
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p. 3165 - 3169
(2007/10/02)
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