- Lanthanum trifluoromethane-sulfonate-catalyzed facile synthesis of per-O-acetylated sugars and their one-pot conversion to S-aryl and O-alkyl/aryl glycosides
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Lanthanum trifluoromethanesulfonate-catalyzed solvent-free per-O-acetylation with stoichiometric acetic anhydride proceeds in high yield (95%-99%) to afford exclusively pyranose products as anomeric mixtures. Subsequent anomeric substitution employing borontrifluoride etherate and thiols or alcohols furnished the corresponding 1,2-trans-linked thioglycosides and O-glycosides, respectively, in good to excellent overall yield (75%-85%). Alternatively, reaction of free sugars in neat alcohol employing the same catalyst at elevated temperature gives the corresponding 1,2-cis-linked O-glycosides (along with 1,2-trans-linked glycosides as minor product) in good yield (73%-80%). Anomeric mixtures of compounds thus produced were characterized as their per-O-acetylated derivatives.
- Dasgupta, Somnath,Rajput, Vishal Kumar,Roy, Bimalendu,Mukhopadhyay, Balaram
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- Mild and efficient method for the cleavage of benzylidene acetals using HClO4-SiO2 and direct conversion of acetals to acetates
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HClO4-SiO2 has been used successfully for the deprotection of benzylidene acetals and the direct conversion of benzylidene acetals to the corresponding di-O-acetates. The reactions are very fast and yields are excellent.
- Agnihotri, Geetanjali,Misra, Anup Kumar
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p. 3653 - 3658
(2007/10/03)
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- 'Armed-disarmed' glycosidation strategy based on glycosyl donors and acceptors carrying phosphoroamidate as a leaving group: A convergent synthesis of globotriaosylceramide
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A stereocontrolled synthesis of globotriaosylceramide with three different glycosidic linkages has been accomplished by linear and convergent routes exploiting 'armed-disarmed' glycosidation methodology based on glycosyl donors and acceptors carrying tetramethylphosphoroamidate as a leaving group. In particular, the convergent strategy featuring a coupling of a galactosyl(1→4)-galactosyl donor with a glucosylceramide derivative has proven to be extremely efficient.
- Hashimoto, Shun-Ichi,Sakamoto, Hiroki,Honda, Takeshi,Abe, Hiroshi,Nakamura, Sei-Ichi,Ikegami, Shiro
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p. 8969 - 8972
(2007/10/03)
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- Conversion of p-methoxyphenyl glycosides into the corresponding glycosyl chlorides and bromides, and into thiophenyl glycosides
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p-Methoxyphenyl (pMP) β-D-glycopyranosides (Glc, Gal, GlcNPhth, GalNPhth, GlcNTroc, Galβ4Glc, Galα4Gal) were prepared from the corresponding 1-O-acetyl sugars in 79-90% yield, using boron trifluoride etherate as promoter. Treatment of the pMP glycosides with acyl chlorides or bromides in the presence of various Lewis acids gave the corresponding glycosyl chlorides and bromides in 81-98% yield. Treatment of the acyl-protected pMP glycosides with thiophenol and boron trifluoride etherate gave the corresponding thioglycosides in 80-100% yield and high (> 20:1) β/α selectivity. The stability of pMP glycosides was investigated against a series of reagents.
- Zhang, Zhiyuan,Magnusson, Goeran
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- Cyclo-glycosylation of (1→4)-linked glycohexaoses: Synthesis of cyclolactohexaose
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Cyclo-glycosylation of (2,3,6-tri-O-benzyl-β-D-galactopyranosyl)-{(1→4)-(2,3,6-tri-O-benzyl- β-D-glucopyranosyl)-(1→4)-(2,3,6-tri-O-benzyl-α-D- galactopyranosyl)}2-(1→4)-(2,3,6-tri-O-benzyl-α/ β-glucopyranosyl fluoride and subsequent deprotection of the product gave an excellent yield of cyclo-lactohexaose.
- Kuyama, Hiroki,Nukada, Tomoo,Nakahara, Yoshiaki,Ogawa, Tomoya
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p. 2171 - 2174
(2007/10/02)
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