Catching elusive glycosyl cations in a condensed phase with HF/SbF5 superacid

Martin, Amélie; Ardá, Ana; Désiré, Jérôme; Martin‐Mingot, Agnès; Probst, Nicolas; Sînaÿ, Pierre; Jiménez‐Barbero, Jesús; Thibaudeau, Sébastien; Blériot, Yves

doi:10.1038/nchem.2399

Cited by 134 publications

(118 citation statements)

References 38 publications

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“…53 The studies described here support a mechanism of glycosylation of donors having a ( S )-phenylthiomethylbenzyl ether at C-2, in which initially an anomeric sulfonium ion intermediate is formed as a trans -decalin system that undergoes an S N 2-like glycosylation reaction indicated by donor–acceptor complexation via hydrogen bonding leading to the selective formation of an α -glycoside. The results of glycosylations with analogs in which the thiophenyl moiety of the auxiliary was replaced by an anisoyl or benzyl moiety indicate that it is not the inherent chirality of the auxiliary that controls anomeric selectivity of glycosylations of an oxocarbenium ion intermediate.…”

Section: Discussionsupporting

confidence: 66%

Mechanism of Glycosylation of Anomeric Sulfonium Ions

Fang

Huang

et al. 2016

J. Am. Chem. Soc.

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Anomeric sulfonium ions are attractive glycosyl donors for the stereoselective installation of 1,2-cis glycosides. Although these donors are receiving increasing attention, their mechanism of glycosylation remains controversial. We have investigated the reaction mechanism of glycosylation of a donor modified at C-2 with a (1S)-phenyl-2-(phenylsulfanyl)ethyl chiral auxiliary. Preactivation of this donor results in the formation of a bicyclic β-sulfonium ion that after addition of an alcohol undergoes 1,2-cis-glycosylation. To probe the importance of the thiophenyl moiety, analogs were prepared in which this moiety was replaced by an anisoyl or benzyl moiety. Furthermore, the auxiliaries were installed as S- and R-stereoisomers. It was found that the nature of the heteroatom and chirality of the auxiliary greatly influenced the anomeric outcome and only the one containing a thiophenyl moiety and having S-configuration gave consistently α-anomeric products. The sulfonium ions are sufficiently stable at a temperature at which glycosylations proceed indicating that they are viable glycosylation agents. Time-course NMR experiments with the latter donor showed that the initial rates of glycosylations increase with increases in acceptor concentration and the rate curves could be fitted to a second order rate equation. Collectively, these observations support a mechanism by which a sulfonium ion intermediate is formed as a trans-decalin ring system that can undergo glycosylation through a bimolecular mechanism. DFT calculations have provided further insight into the reaction path of glycosylation and indicate that initially a hydrogen-bonded complex is formed between sulfonium ion and acceptor that undergoes SN2-like glycosylation to give an α-anomeric product.

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Section: Discussionsupporting

confidence: 66%

Mechanism of Glycosylation of Anomeric Sulfonium Ions

Fang

Huang

et al. 2016

J. Am. Chem. Soc.

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“…As the oxocarbenium ion [21] is in equilibrium with the commonly observed [22] α-glycosyl triflate this stabilization results in a longer lifetime of the oxocarbenium ion and looser ion pairs leading to a reduction in selectivity (Scheme 5). [23] This rationale is consistent with computational work by Woerpel suggesting that pyranosyl oxocarbenium ions are stabilized when the side chain adopts the gg conformation.…”

Section: Resultsmentioning

confidence: 99%

Determination of the Influence of Side‐Chain Conformation on Glycosylation Selectivity using Conformationally Restricted Donors

Suresh

Crich

2016

Chemistry A European J

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The synthesis of a series of conformationally locked mannopyranosyl thioglycosides in which the C6-O6 bond adopts either the gauche,gauche, gauche,trans, or trans,gauche conformation is described, and their influence on glycosylation stereoselectivity investigated. Two 4,6-O-benzylidene protected mannosyl thioglycosides carrying axial or equatorial methyl groups at the 6-position were also synthesized and the selectivity of their glycosylation reactions studied to enable a distinction to be made between steric and stereoelectronic effects. The presence of an axial methoxy group at C6 in the bicyclic donor results in a decreased preference for formation of the β-mannoside whereas an axial methyl group has little effect on selectivity. The result is rationalized in terms of through space stabilization of a transient intermediate oxocarbenium ion by the axial methoxy group resulting in a higher degree of SN1-like character in the glycosylation reaction. Comparisons are made with literature examples and exceptions are discussed in terms of pervading steric effects layered on top of the basic stereoelectronic effect.

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“…These undesired isomerizations can be limited through optimization of reaction conditions17363738. Thus, we conducted a series of optimization experiments including solvents, temperature and catalyst loading, and found that when reactions were conducted under anhydrous conditions with diethyl ether/tetrahydrofuran (2:1, v/v) using 0.05 equiv TMSOTf as catalyst at −30 °C, no isomerization was found by NMR and the desired protected β-glucoside 2 was obtained with 60% yield, [α] D = +15.2 ( c 1.14, CHCl 3 ).…”

Section: Resultsmentioning

confidence: 99%

Synthesis of Chrysogeside B from Halotolerant Fungus Penicillium and Its Antimicrobial Activities Evaluation

Liu

Wang²,

et al. 2017

Sci Rep

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Chrysogeside B, a natural cerebroside, was efficiently synthesized from commercial feedstocks. The bioassays showed that compounds 4, 5 and 6 exhibited enhanced biological activities compared Chrysogeside B. Further studies revealed that free hydroxyl groups and glycosidic bond have significant impact on the antimicrobial activities. The synthesis of Chrysogeside B and analogues designed to allow identification of the features of this glycolipid required for recognition by tested bacteria and Hela cells is described.

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Catching elusive glycosyl cations in a condensed phase with HF/SbF5 superacid

Cited by 134 publications

References 38 publications

Mechanism of Glycosylation of Anomeric Sulfonium Ions

Mechanism of Glycosylation of Anomeric Sulfonium Ions

Determination of the Influence of Side‐Chain Conformation on Glycosylation Selectivity using Conformationally Restricted Donors

Synthesis of Chrysogeside B from Halotolerant Fungus Penicillium and Its Antimicrobial Activities Evaluation

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