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K. Beran

Bio: K. Beran is an academic researcher. The author has an hindex of 1, co-authored 1 publications receiving 11 citations.

Papers
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Journal ArticleDOI
TL;DR: In this article, ein and zweiwertigen Pheeol (Brenzcatechin) wurde sowohl die Einfuhrung eines als auch zweier Zuckerreste vorgenommen.
Abstract: Es wurde gefunden, das durch Zusatz vonBorfluorid zu benzolischen Losungen von β-Pentaacetylglucose und ein- und zweiwertigen Phenolen eine schon bei Zimmertemperatur in guter Ausbeute vor sich gehende Bildung von Phenol-β-pentaglucosidacetaten eingeleitet wird. Im gegensatz zu den anderen Verfahren, bei welchen stets einUberschus der Phenolkomponente verwendet werden mus, liesen sich bei Verwendung von Borfluorid auch bei Einsatz aquimolekularer Mengen der beiden Reaktionspartner in einfacher Weise die gewunschten Glucosidacetate isolieren. An einem. zweiwertigen Pheeol (Brenzcatechin) wurde sowohl die Einfuhrung eines als auch zweier Zuckerreste vorgenommen. Wie bei den anderen sauren Kondensationsmitteln durften auch bei der Borfluoridmethode die Ausbeuten am gewunschten Reaktionsprodukt durch das Isomerisierungsvermogen des Kondensationsmittels auf Penta-acetylglucose bzw. gebildetes Glucosid begrenzt sein.

11 citations


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Book ChapterDOI
TL;DR: The chapter focuses on the reactions of O -acyl derivatives of sugars, glycosides, and glycosyl halides because these substances play the central role in carbohydrate chemistry.
Abstract: Publisher Summary This chapter discusses some implications of the theories relating to the mechanisms of replacement reactions in the carbohydrate chemistry. It discusses the significance of new concepts from the field of theoretical organic chemistry and thus helps to stimulate the advance. The chapter focuses on the reactions of O -acyl derivatives of sugars, glycosides, and glycosyl halides because these substances play the central role in carbohydrate chemistry. The chapter presents the correlation of both stability and reactivity with structure. This requires the complete structure of each compound considered to be established unequivocally. Several experiments carried out by different scientists are discussed. The chapter reviews the nature and activating effect of neighboring-group participation in reactions at the lactol carbon atom. General considerations of anomerization are presented. Acetylated aldoses, O -acetylglycosyl halides, and acetylated alkyl glycosides are reviewed in detail in the chapter.

83 citations

Book ChapterDOI
TL;DR: This chapter discusses the methyl and phenyl glycosides of the common sugars and the O -acetylglycosyl bromides (“acetobromosugars”) are by far the most commonly employed.
Abstract: Publisher Summary This chapter discusses the methyl and phenyl glycosides of the common sugars. Several new general methods or modified procedures for glycoside synthesis have been introduced. The O -acylglycosyl halides, where the acyl group at the potential reducing group in a fully acylated reducing sugar has been replaced by halogen, are the most generally useful intermediates in the synthesis of alkyl and aryl glycosides, and the O -acetylglycosyl bromides (“acetobromosugars”) are by far the most commonly employed. They are more reactive than the chlorides and more stable than the iodides. In some instances, however, the bromide is so unstable that the chloride is preferred. Yields of O -acetylglycosyl bromides obtained from other sugars by this method were: lactose 85%, arabinose 50%, maltose 60%, cellobiose 72%, and galactose 75%. With cellobiose, some glacial acetic acid has to be added at the start to maintain solution. In general, the products are pure enough to be used without recrystallization in the next stage of glycoside synthesis. Apart from their use as starting materials for the preparation of O -acetyl-glycosyl halides, polyacetylated sugars are employed extensively in glycoside synthesis by the Helferich reaction, in which they are condensed directly with low-melting phenols.

53 citations

Journal ArticleDOI
TL;DR: From the yellow flowers of Chrysanthemum indicum, a new flavone glycoside, acacetin 7-O-β- d -galactopyranoside was isolated and its structure established from spectral evidence and synthesis.

28 citations

Journal ArticleDOI
TL;DR: In this paper, the C-1-spiroorthoesters were readily available in a "one-pot synthesis" starting from glucosyl halides, where the starting glycoside had CH2OH, the cyclization was regio-and stereo-specific by α-attack.

23 citations

Journal ArticleDOI
TL;DR: In this paper, 13C NMR spectroscopy was used to study the stereoselectivity of glycosylation of phenols with the α and β anomers of penta-O-acetyl-D-glucopyranose.
Abstract: 13C NMR spectroscopy was used to study the stereoselectivity of glycosylation of phenols with the α and β anomers of penta-O-acetyl-D-glucopyranose, penta-O-trifluoroacetyl-D-glucopyranose, and 2,3,4,6-tetra-O-acetyl-1-O-trifluoroacetyl-D-glucopyranose in the presence of boron trifluoride etherate at varied temperature, time, and catalyst amount. The boron trifluoride etherate-catalyzed reaction of penta-O-acetyl-β-D-glucopyranose and 2,3,4,6-tetra-O-acetyl-1-O-trifluoroacetyl-β-D-glucopyranose with phenols occurs with a high stereocontrol to give, depending on conditions, predominantly 1,2-cis- or 1,2-trans-arylglycosides. This reaction can be used for preparative synthesis of the α- and β-anomeric forms of glycosides of a wide range of phenols.

20 citations