- Stereospecific synthesis of methyl 2-amino-2-deoxy-(6S)-deuterio-α,β-D-glucopyranoside and methyl 2,6-diamino-2,6-dideoxy-(6R)-deuterio-α,β-D-glucopyranoside: Side chain conformations of the 2-amino-2-deoxy and 2,6-diamino-2,6-dideoxyglucopyranosides
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The stereospecifically labeled 6-monodeuterio methyl 2,6-diamino-2,6-dideoxy-α- and β- D-glucopyranosides were synthesized with a view to determining their side chain conformations. NMR studies in D2O at pH 5 and pH 11 reveal both anomers to adopt very predominantly the gt conformation consistent with the gauche conformation of 2-aminoethanol and its acetate salt. In contrast, as also revealed with the help of stereospecifically-labelled monodeuterio isotopomers, the methyl 2-amino-2-deoxy-α- and β- D-glucopyranosides are an approximately 1:1 mixture of gg and gt conformers as is found in glucopyranose itself.
- Kato, Takayuki,Vasella, Andrea,Crich, David
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- Synthesis of unstable 4-benzoyl-1,6-anhydro-3-keto-β-D-mannopyranose via stereoselective photobromination of 2,3-isopropylidene-4-benzoyl-1,6-anhydro-β-D-mannopyranose
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Stereoselective photobromination of 1,6-anhydro-β-D-glucopyranose derivatives occurs at exo-H6. However, photobromination of 4-benzoyl-2,3-isopropylidene-1,6-anhydro-β-D-mannopyranose 6 produced unstable 4-benzoyl-1,6-anhydro-3-keto-β-D-mannopyranose 7. The mechanism of stereoselective oxidation at C-3 could be attributed to the facile radical proton abstraction at C-3, followed by the subsequent bromination of the isopropylidene group, which was subsequently eliminated during the aqueous workup. Thus, the aim of this article is to identify the molecular structure of the unstable compound 7.
- Mahdi, Jassem G.,Dawoud, Hanaa M.,Manning, Abigail J.,Lieberman, Harvey F.,Kelly, David R.
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- Photobromination of Carbohydrate Derivatives. VI. Funcionalization at C6 of 2,3,4-tri-O-acetyl-1,6-anhydro-β-D-glucopyranose
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Photobromination of 2,3,4-tri-O-acetyl-1,6-anhydro-β-D-glucopyranose gives the syrupy 6S (exo) bromide in high yield; further reaction leads to secondary bromination at this position.The monobromide reacts with methanol and thiophenol under conditions of kinetic control to give mainly the endo-methoxy and phenylthio derivatives formed by direct nucleophilic displacement, and from the latter the exo-methoxy acetal was obtained by a second nucleophilic substitution.Acetolysis of these compounds can lead to the coresponding exo-6-acetoxy ester or monocyclicproducts formed by opening of the five-membered rings.
- Ferrier, Robert J.,Furneaux, Richard H.
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p. 1025 - 1036
(2007/10/02)
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