- Scope of the DMC mediated glycosylation of unprotected sugars with phenols in aqueous solution
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Activation of reducing sugars in aqueous solution using 2-chloro-1,3-dimethylimidazolinium chloride (DMC) and triethylamine in the presence of para-nitrophenol allows direct stereoselective conversion to the corresponding 1,2-Trans para-nitrophenyl glycosides without the need for any protecting groups. The reaction is applicable to sulfated and phosphorylated sugars, but not to ketoses or uronic acids or their derivatives. When applied to other phenols the product yield was found to depend on the pKa of the added phenol, and the process was less widely applicable to 2-Acetamido sugars. For 2-Acetamido substrates an alternative procedure in which the glycosyl oxazoline was pre-formed, the reaction mixture freeze-dried, and the crude product then reacted with an added phenol in a polar aprotic solvent system with microwave irradiation proved to be a useful simplification.
- Fairbanks, Antony J.,Qiu, Xin
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p. 7355 - 7365
(2020/10/13)
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- Synthesis of aryl α-O-L-rhamnopyranoside by two-step reaction in one pot
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The title compounds were conveniently synthesized by a phase transfer catalyzed approach in two steps and one pot using the rhamnopyranosyl chloride as key intermediate. The twostep one-pot procedure is more convenient and environmentally friendly, compared to the published synthetic routes. Besides, the structure-reactivity relationship and the plausible mechanism for this base-catalyzed glycosylation were discussed bymeans of the Hammett equation.
- Liu, Nianping,Tian, Xiangguang,Ding, Zekun,Zhou, Yongda,Zhang, Wan,Wang, Qingbing,Zhang, Yi,Gu, Yijun,Zhang, Jianbo
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p. 220 - 234
(2017/11/10)
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- Carbohydrate-carbohydrate interactions in water with glycophanes as model systems
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The synthesis and conformational properties of glycophanes 2 and 3 (cyclodextrin-cyclophane hybrid receptors containing two maltose units linked by (4-hydroxymethyl) benzoic acid spacer) are described. The binding properties in water of these receptors with a series of 4-nitrophenyl glycosides with α- and β-configurations at the anomeric center have been studied using 1H NMR spectroscopy and molecular mechanics calculations. A comparison of these properties with those of glycophane 1 (an α,α-trehalose containing glycophane) and α-cyclodextrin (αCD) using the same glycosides shows the existence of a stabilizing contribution to the free energy of binding in the case of of glycophanes but not in the case of the αCD system. This contribution is due to carbohydrate-carbohydrate interactions between both host and guest lipophilic sugar surfaces. Glycophanes 1, 2, and 3 show similar α/β selectivity on binding the ligands, despite the great flexibility of 3 related to 1 and 2. Parallels are drawn between the thermodynamic behavior of these model systems and that proposed for sugar- protein interactions.
- Morales, Juan Carlos,Zurita, Dacil,Penades, Soledad
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p. 9212 - 9222
(2007/10/03)
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