Intramolekulare Wasserstoffbrücken in substituierten Gluco‐ bzw. Fructopyranosen und ‐furanosen

Bartsch, Jürgen; Prey, V.

doi:10.1002/jlac.19687170121

Cited by 2 publications

(1 citation statement)

References 18 publications

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“…A specific solvation of the substrate through hydrogen bonds between the sugar and the solvent and its impact on intramolecular hydrogen bonds in the substrate could thus also explain the observed regioselectivities. Intramolecular hydrogen bonds in sugars are weak, typically on the order of 1-3 RT (i.e., less than 1.8 kcal/mol), but are well established by 1 H NMR studies, even in DMSO-d 6 , which is even more polar ( ) 48.9) than DMA ( ) 37.78) [45][46][47] and have also been proposed on the basis of solution-state IR 48,49 and theoretical studies. 50 Intramolecular hydrogen bonds are also inferred to be the origin of regioselectivity in the DMAP-catalyzed acetylation of octyl hexopyranosides in CHCl 3 .…”

Section: Discussionmentioning

confidence: 99%

Regioselective Silylation of Sugars through Palladium Nanoparticle-Catalyzed Silane Alcoholysis

et al. 2002

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Palladium(0)-catalyzed silane alcoholysis was applied to sugars for the first time using tert-butyldimethylsilane (TBDMS-H) and Ph(3)SiH as the silanes. The catalyst is a colloidal solution of Pd(0) generated in situ from PdX(2) (X = Cl(-), OAc(-)) and TBDMS-H in N,N-dimethylacetamide. The colloid has been characterized by dynamic light scattering and transmission electron microscopy and consists of catalytically highly active nanoparticles of approximately 2 nm diameter. The silane alcoholysis reaction is an effective method for the regioselective silylation of methyl and phenyl glycosides and generates hydrogen gas as the only side product. For many of the sugar substrates investigated, the distribution of regioisomers obtained is complementary to that of the traditional R(3)SiCl/base (base = pyridine, imidazole) methodology and gives convenient access to the 3,6- rather than the 2,6-silylated pyranosides, obtained as the main product by the silyl chloride method. The method also allows a selective axial silylation of levoglucosan and 1,3,5-O-methylidene-myo-inositol. In an attempt to rationalize the observed regioselectivities, ab initio predictions (HF/3-21G) have been made on the relative energies of some of the silylated products. They suggest that the observed regioselectivities do not reflect a kinetic vs thermodynamic product distribution but are induced by the silylation agent employed. Models for the possible origin of the observed regioselectivity in both silylation methods (silane- and silyl chloride-based) are discussed.

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Section: Discussionmentioning

confidence: 99%

Regioselective Silylation of Sugars through Palladium Nanoparticle-Catalyzed Silane Alcoholysis

et al. 2002

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Barrieren der behinderten Rotation um die N‐glycosidische Bindung, IV. 1‐(β‐D‐Ribofuranosyl)isocyanursäuren

Wegner¹,

Jochims²

1979

Chem. Ber.

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Es werden Synthesen der ~-Ribofuranosylnucleoside 5 a -c und 6b, c beschrieben. Die Temperaturabhangigkeiten der 'Hund 13C-NMR-Spektren lassen sich nur als Folge behinderter Rotation um die N-glycosidische Bindung deuten ''. Die Gibbsschen Aktivierungsenergien (43 -46 kJmol . I ) sind unabhPngig von einer Acetylierung der OH-Gruppen des Furanoseringes oder einer Einschrlnkung \on dessen Flexibilitat durch Bildung eines 2',3'-lsopropylidenderirates und liegen erheblich tiefer als die entsprechenden Werte (um 69 kJmol-I ) der Glucopyranosylnucleoside 7b, c. Die Aktivierungsentropien sind gering. Die Befunde werden gedeutet.Barriers to Hindered Rotation Around the N-Glycosidic Bond, IV ') 1-( P-D-Ribofuranosyl)isocyanuric AcidsThe 8-ribofuranosyl nucleosides 5 a -c and 6b, c are synthesized. The temperature dependency of the 'Hand I3C-NMR spectra can only be interpreted as hindered rotation around the Nglycosidic bond 'I, The Gibbs activation energies (43 -46 kJmoI ~ I ) are independent of acetylation of the OH groups of the furanose ring or restriction of its flexibility through formation of a 2 ' 3isopropylidene derivative, and are considerably lower than the corresponding data (about 69 kJmol-I) of the glucopyranosyl nucleosides 7b, c. The actibation entropies are small. The results are interpreted.

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Intramolekulare Wasserstoffbrücken in substituierten Gluco‐ bzw. Fructopyranosen und ‐furanosen

Cited by 2 publications

References 18 publications

Regioselective Silylation of Sugars through Palladium Nanoparticle-Catalyzed Silane Alcoholysis

Regioselective Silylation of Sugars through Palladium Nanoparticle-Catalyzed Silane Alcoholysis

Barrieren der behinderten Rotation um die N‐glycosidische Bindung, IV. 1‐(β‐D‐Ribofuranosyl)isocyanursäuren

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