α-Selective Glycosylation of 3,6-O-o-Xylylene-Bridged Glucosyl Fluoride

Motoyama, Atsushi; Arai, Tomoki; Ikeuchi, Kazutada; Aki, Kazuya; Wakamori, Shinnosuke; Yamada, Hidetoshi

doi:10.1055/s-0036-1590927

Cited by 12 publications

(2 citation statements)

References 7 publications

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“…Among these promoters Sn(II) species (SnCl 2 -AgX, X = ClO 4 or B(C 6 F 5 ) 4 ) [6,18], group IVB metallocenes (Cp 2 MCl 2 -AgClO 4 , M = Zr, Hf, Ti) [19][20][21], BF 3 •OEt 2 [22] and protic acids (TfOH, HClO 4 , HB(C 6 F 5 ) 4 ) [23] are the most frequently used. During the last decade, apart from reports on novel promoters (Hf(OTf) 4 [24], InI 3 [25], In(OTf) 3 [26], B(C 6 F 5 ) 3 [27]) and coupling partners [28], great attention has been paid to a stereoselective glycosylation by sterically fixed glycosyl fluorides as glycosyl donors [29][30][31]. The enhanced stability of glycosyl fluorides has also allowed to develop a straightforward protecting-group-free strategy towards oligosaccharides and glycopeptides under basic aqueous conditions [32,33].…”

Section: Introductionmentioning

confidence: 99%

Metal-free glycosylation with glycosyl fluorides in liquid SO₂

Gulbe¹,

Lugiņina²,

Jansons³

et al. 2021

Beilstein J. Org. Chem.

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Liquid SO2 is a polar solvent that dissolves both covalent and ionic compounds. Sulfur dioxide possesses also Lewis acid properties, including the ability to covalently bind Lewis basic fluoride ions in a relatively stable fluorosulfite anion (FSO2 −). Herein we report the application of liquid SO2 as a promoting solvent for glycosylation with glycosyl fluorides without any external additive. By using various temperature regimes, the method is applied for both armed and disarmed glucose and mannose-derived glycosyl fluorides in moderate to excellent yields. A series of pivaloyl-protected O- and S-mannosides, as well as one example of a C-mannoside, are synthesized to demonstrate the scope of the glycosyl acceptors. The formation of the fluorosulfite species during the glycosylation with glycosyl fluorides in liquid SO2 is proved by 19F NMR spectroscopy. A sulfur dioxide-assisted glycosylation mechanism that proceeds via solvent separated ion pairs is proposed, whereas the observed α,β-selectivity is substrate-controlled and depends on the thermodynamic equilibrium.

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Section: Introductionmentioning

confidence: 99%

Metal-free glycosylation with glycosyl fluorides in liquid SO₂

Gulbe¹,

Lugiņina²,

Jansons³

et al. 2021

Beilstein J. Org. Chem.

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“…We have previously reported β-selective glycosylation using ethyl 6-O-pivaloyl-1-thio-2,3,4-tri-O-triisopropylsilyl (TIPS)-β-D-glucopyranoside (1) via the conformational lock strategy [35][36][37][38][39][40][41][42][43][44] based on the steric bulk of silyl-protecting groups 45) (Fig. 1b).…”

Section: Introductionmentioning

confidence: 99%

β-Selective Glycosylation Using Axial-Rich and 2-<i>O</i>-Rhamnosylated Glucosyl Donors Controlled by the Protecting Pattern of the Second Sugar

Bando

Kawasaki

Nagata

et al. 2021

CHEMICAL & PHARMACEUTICAL BULLETIN

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Herein, we describe two counterexamples of the previously reported β/α-selectivity of 96/4 for glycosylation using ethyl 2-O-[2,3,4-tris-O-tert-butyldimethylsilyl (TBS)-α-L-rhamnopyranosyl]-3,4,6-tris-O-TBS-thio-β-D-glucopyranoside as the glycosyl donor. Furthermore, we investigated the effects of protecting group on the rhamnose moieties in the glycosylation with cholestanol and revealed that β-selectivity originated from the two TBS groups at the 3-O and 4-O positions of rhamnose. In contrast, the TBS group at the 2-O position of rhamnose hampered the β-selectivity. Finally, the β/α-selectivity during the glycosylation was enhanced to ≥99/1. The results obtained herein suggest that the protecting groups on the sugar connected to the 2-O of a glycosyl donor with axial-rich conformation can control the stereoselectivity of glycosylation.

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Display of Rich Reactivities of Endo‐ and Exocyclic Unsaturated Sugars that Parallel the Native Sugars

Jayaraman

2021

The Chemical Record

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Unsaturated monosaccharides expand the scope of reactivities in a sugar, directly leading to the development of newer methodologies, molecular structures and functional entities. The unsaturation as a reactive moiety can either be within the molecule, namely, endocyclic, or as a pendant moiety around the molecule, namely, exocyclic. One carbon homologations aided by reactions at the unsaturated moiety expand the molecular structures in both endo‐ and exocyclic sugars and lead to structures that are largely hitherto unknown. Molecular shifts and rearrangements permit interchanging the reactivities from one carbon to the other in unsaturated sugars. Activations of exocyclic unsaturated sugars also find newer possibilities to reactions central to the sugar chemistry, namely, the glycosylations. The personal reflections result from a couple of decades of explorations that traverse through the unsaturated sugars from different vantage points.

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α-Selective Glycosylation of 3,6-O-o-Xylylene-Bridged Glucosyl Fluoride

Cited by 12 publications

References 7 publications

Metal-free glycosylation with glycosyl fluorides in liquid SO₂

Metal-free glycosylation with glycosyl fluorides in liquid SO₂

β-Selective Glycosylation Using Axial-Rich and 2-<i>O</i>-Rhamnosylated Glucosyl Donors Controlled by the Protecting Pattern of the Second Sugar

Display of Rich Reactivities of Endo‐ and Exocyclic Unsaturated Sugars that Parallel the Native Sugars

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α-Selective Glycosylation of 3,6-O-o-Xylylene-Bridged Glucosyl Fluoride

Cited by 12 publications

References 7 publications

Metal-free glycosylation with glycosyl fluorides in liquid SO2

Metal-free glycosylation with glycosyl fluorides in liquid SO2

β-Selective Glycosylation Using Axial-Rich and 2-<i>O</i>-Rhamnosylated Glucosyl Donors Controlled by the Protecting Pattern of the Second Sugar

Display of Rich Reactivities of Endo‐ and Exocyclic Unsaturated Sugars that Parallel the Native Sugars

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Metal-free glycosylation with glycosyl fluorides in liquid SO₂

Metal-free glycosylation with glycosyl fluorides in liquid SO₂