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J Kobe

Publications and source records attributed to J Kobe.

8 recordsLinked to original sources
PubMed2001

Reactivity of anomeric 1alpha- and 1beta-pentofuranosyl azide derivatives in ammonia chemical ionization.

Electron impact (EI), fast atom bombardment (FAB) and ammonia chemical ionization [CI(NH3)] mass spectrometry were applied with the aim of differentiating between the anomeric 1alpha- and 1beta-azidopentofuranosyl derivatives. Calculated ammonium affinities [AA(M)] and proton affinities [PA(M)] show that beta-anomers have higher affinities for H+ and NH4+ ions than alpha-azides. Protonated molecules, obtained by CI(NH3) of azidofuranosyl derivatives, lose HN3 giving abundant furanosyl (S+) ions. Ammonia solvation of MH+ ions competes with the previous reaction producing the [SNHN2NH3]+ ion, a competitive product to the ammonium-attached [SN3NH4]+ ion. The fragmentation pathways of the stable and metastable [MNH4]+, MH+ ions, and several other important fragment ions, were determined using mass analyzed ion kinetic energy spectrometry (MIKES). The abundance of the [SN3NH4]+ and/or [SNHN2NH3]+ ions was found to correlate inversely with the exothermicity of ammonia solvation of the MH+ ion. The abundance of the fragment ions [SNHNH3]+, [SNH3]+ and SNH+ in some examples correlates with the exothermicity of the corresponding [MNH4]+ and MH+ parent ion formation. The fragment ions SNH3+ and SNHNH3+ can be formed, at least in part, in the ammonia solvation reaction of the S+ and SNH+ ions taking place within the high-pressure region of the CI ion source.

Journal Article↗
PubMed2000

Stereoselective synthesis of 1,2-cis- and 2-deoxyglycofuranosyl azides from glycosyl halides.

Protected 1,2-cis glycofuranosyl azides with alpha-D-ribo, beta-D-arabino and 2-deoxy-2-fluoro-beta-D-arabino configurations were efficiently prepared from the appropriate 1,2-trans glycosyl halides bearing non-participating 0-2 substituent by inversion with sodium azide under phase transfer catalytic conditions (80-85% yields, 90-96% de). The same method failed to result in sufficiently good beta-selectivity starting from 2-deoxy-3,5-di-O-(p-toluoyl)-alpha-D-ery-thro-pentofuranosyl chloride (5alpha) (40% de). The selectivity in favour of the protected 2-deoxy-beta-D-erythro-pentofura-nosyl azides was greatly improved (74-80% de) by treating 5alpha and its p-chlorobenzoyl analog 6alpha with cesium or potassium azide in dimethylsulfoxide at room temperature (83-85% yields).

Azides↗
PubMed2000

Studies on the origin of stereoselectivity in the synthesis of 1,2-trans glycofuranosyl azides.

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 beta-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.

Azides↗
PubMed2000

Methyl 1-

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Journal Article↗
PubMed1982

Conformation and structure of 2-amino-8-(beta-D-ribofuranosyl)imidazo [1,2-a]-s-triazin-4-one(5-aza-7-deaza guanosine), a potent antiviral nucleoside.

The crystal and molecular structure of one imidazo[1,2-a]-s-triazine nucleoside and its antiviral activity are described. The crystal structure of 2-amino-8-(beta-D-ribofuranosyl)imidazo[1,2-a]-s-triazin-4-one monohydroate (C10H13N5O5.H2O) was solved by X-ray counter data. The compound crystallizes in the monoclinic space group P21 with cell dimensions a = 7.353 (1), b = 6.465 (1), c = 13.701 (1) A, B = 104.64 (1) degrees. The structure was solved by direct methods and refined by full matrix least-squares technique to a final value of the conventional R-factor of 0.049 using 1998 observed intensities. The orientation of the base relative to the sugar ring defined in terms of rotating about the C(1')-N(8) glycosyl bond is anti (47.8 degrees). The ribose moiety exhibits C(2')-endo, E conformation. The conformation around C(4')-C(5') is gauche-. Molecular packing is dominated by hydrogen bonds. Base stacking occurs long the b axis. 5-Aza-7-deazaguanosine has shown a marked antiviral activity in vitro against herpes simplex virus despite the fact that N(3) is effective as the hydrogen acceptor only.

Antiviral Agents↗
PubMed1982

Synthesis and antiviral activities of 2-substituted azino-3-(D-arabinofuranosyl)-5-carboxymethylene-thiazolidine-4-ones.

2-(1-Isopropylidene)azino-3-beta and 3-alpha-D-arabinofuranosyl-5-methoxycarbonylmethylenethiazolidine-4-ones (III) and (IV) have been synthesized by condensation of benzylated alpha-chloro-D-arabinofuranose (V) with o-(trimethylsilyl)-2-(1-isopropilidene)azino-5-methoxycarbonylmethylen- thiazolidine-4-one (VI) in the presence of SnCl4 or molecular sieves. Condensation of benzoylated alpha, beta-bromo-D-arabinose (VII) with (VI) led exclusively to the alpha anomer (VIII). 2-(1-Isopropylidene)azino-3-alpha-D-arabinofuranosyl-5-carbamoylmethylene- thiazolidine-4-one (IX) has been synthesized from (IV) (R, R1, R2 = CH3). 1H-N.M.R. and 13C-N.M.R. data confirmed the structures of (III) and (IV) (R, R1, R2 = CH3 and R, R1 = CH3, R2 = Ph). Antiviral activities were tested on monolayer cultures of KB-cells. Whereas previously tested beta-D-ribofuranosyl derivatives had moderate activity, alpha and/or beta-D-arabinofuranosyl derivatives are totally inactive against herpes simplex and poliovirus.

Antiviral Agents↗