“…While many strategies have evolved to address these problems with regard to pyranoside synthesis, methods for the construction of the furanosidic linkage have only recently begun to attract significant attention. This is due primarily to the current interest in the chemistry − and biology of β- d -galactofuranosides owing to the widespread occurrence of this moiety in lower organisms.…”
Treatment of the peracetylated ethyl dithioacetals of D-glucose, D-galactose, and D-mannose with acetyl chloride and boron trifluoride diethyl etherate at reflux yields the known acyclic 1-chloro-1-(ethylthio) derivatives. These compounds are shown to effectively glycosylate a variety of carbohydrate acceptors using silver trifluoromethanesulfonate as the promotor, affording stereospecifically the corresponding acyclic O,S-acetals in good to excellent yield. Furthermore, following deacetylation, treatment of these O,S-acetals with a mixture of mercuric salts in either methanol or dimethylformamide gives rise to disaccharides terminating in D-furanosyl residues.
“…While many strategies have evolved to address these problems with regard to pyranoside synthesis, methods for the construction of the furanosidic linkage have only recently begun to attract significant attention. This is due primarily to the current interest in the chemistry − and biology of β- d -galactofuranosides owing to the widespread occurrence of this moiety in lower organisms.…”
Treatment of the peracetylated ethyl dithioacetals of D-glucose, D-galactose, and D-mannose with acetyl chloride and boron trifluoride diethyl etherate at reflux yields the known acyclic 1-chloro-1-(ethylthio) derivatives. These compounds are shown to effectively glycosylate a variety of carbohydrate acceptors using silver trifluoromethanesulfonate as the promotor, affording stereospecifically the corresponding acyclic O,S-acetals in good to excellent yield. Furthermore, following deacetylation, treatment of these O,S-acetals with a mixture of mercuric salts in either methanol or dimethylformamide gives rise to disaccharides terminating in D-furanosyl residues.
“…This disaccharide serves as an anchor that couples arabinan and galactan chains of AG. The known precursor 11 was converted into a dibutylstannyl acetal by refluxing with Bu 2 SnO in toluene followed by addition of 1.0 equiv of BnBr to give rise to the tribenzyl derivative 21 (Scheme ). 4 …”
Syntheses of the ethyl glycosides of 5-O-(beta-D-galactofuranosyl)-beta-D-galactofuranose and 5-O-(alpha-D-arabinofuranosyl)-6-O-(beta-D-galactofuranosyl)-beta-D-galactofuranose present in motifs D and E of Mycobacterium tuberculosis arabinogalactan, respectively, have been presented. The pentenyl-mediated O-glycosylation reaction was utilized to obtain the disaccharide of motif D. The first coupling reaction to prepare the inner disaccharide portion of motif E was accomplished by trichloroacetamidate method while the installation of the terminal sugar by pentenyl glycosylation approach was successful.
Scope and limitations of 1,4-anhydro sugars as precursors of glycofuranosyl building blocks are described. The experiments revealed that the choice of the substituents is very important for an efficient preparation as well as a successful ring-opening reaction of 1,4-anhydro sugars. DFT Calculations suggest that selective protonation of 1,4-anhydro sugars is the key to the selective ring opening in order to afford only furanosides.
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