Stereoselective α-glycosylation of C(6)-hydroxyl myo-inositols via nickel catalysis—application to the synthesis of GPI anchor pseudo-oligosaccharides

McConnell, Matthew S.; Mensah, Enoch A.; Nguyen, Hien M.

doi:10.1016/j.carres.2013.09.006

Cited by 14 publications

(11 citation statements)

References 57 publications

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“…For the O -glycosyl trichloroacetimidate activation, also quite a few Lewis acidic metal salts were investigated and the same reaction course was envisaged. Worth mentioning are Ni(II) − and Pd(II) salts, − ZnBr 2 , and MgBr 2 ·Et 2 O in the presence and absence of a Brønsted acid, AuCl, InCl 3 , InBr 3 , In(OTf) 3 , Sm(OTf) 3 , Yb(OTf) 3 , Sn(OTf) 2 , and AgOTf. , …”

Section: Introductionmentioning

confidence: 99%

An Alternative Reaction Course in O-Glycosidation with O-Glycosyl Trichloroacetimidates as Glycosyl Donors and Lewis Acidic Metal Salts as Catalyst: Acid–Base Catalysis with Gold Chloride-Glycosyl Acceptor Adducts

Peng

Schmidt

2015

J. Am. Chem. Soc.

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Gold(III) chloride as catalyst for O-glycosyl trichloroacetimidate activation revealed low affinity to the glycosyl donor but high affinity to the hydroxy group of the acceptor alcohol moiety, thus leading to catalyst-acceptor adduct formation. Charge separation in this adduct, increasing the proton acidity and the oxygen nucleophilicity, permits donor activation and concomitant acceptor transfer in a hydrogen-bond mediated S(N)2-type transition state. Hence, the sequential binding between acceptor and catalyst and then with the glycosyl donor enables self-organization of an ordered transition-state. This way, with various acceptors, even at temperatures below -60 °C, fast and high yielding glycosidations in high anomeric selectivities were recorded, showing the power of this gold(III) chloride acid-base catalysis. Alternative reaction courses via hydrogen chloride or HAuCl4 activation or intermediate generation of glycosyl chloride as the real donor could be excluded. With partially O-protected acceptors, prone to bidentate ligation to gold(III) chloride, particularly high reactivities and anomeric selectivities were observed. Gold(I) chloride follows the same catalyst-acceptor adduct driven acid-base catalysis reaction course.

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Section: Introductionmentioning

confidence: 99%

An Alternative Reaction Course in O-Glycosidation with O-Glycosyl Trichloroacetimidates as Glycosyl Donors and Lewis Acidic Metal Salts as Catalyst: Acid–Base Catalysis with Gold Chloride-Glycosyl Acceptor Adducts

Peng

Schmidt

2015

J. Am. Chem. Soc.

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“…Consistent with our hypothesis that the reaction proceeds through the same intermediate, the resonance at δ 6.15 was detected in both α- and β-imidate 5 upon addition of TfOH (Figure c,f) at −60 °C. This also rules out anomerization of the imidate leaving group, as the anomeric resonance β-imidate was not detected in the spectrum of the α-counterpart and vice versa . Since the chemical shift and coupling constant of this proton corresponds to the range of the previously reported anomeric proton resonance of α-glycosyl triflates (δ 6.0–6.5), it was tentatively assigned as α-triflate 12 (Figure ).…”

Section: Results and Discussionmentioning

confidence: 64%

“…This also rules out anomerization of the imidate leaving group, as the anomeric resonance β-imidate was not detected in the spectrum of the α-counterpart and vice versa. 30 Since the chemical shift and coupling constant of this proton corresponds to the range of the previously reported anomeric proton resonance of α-glycosyl triflates (δ 6.0−6.5), 49 it was tentatively assigned as α-triflate 12 (Figure 3). A COSY 2D-NMR experiment of this putative glycosyl triflate intermediate indicated the resonance at δ 6.15 to be at the C(1) position (Figure S8a).…”

Section: ■ Results and Discussionmentioning

confidence: 79%

“…As part of the effort to develop catalytic stereoselective glycosylations, ,− we recently identified a novel, scalable method to address many of the synthetic limitations previously associated with the construction of 1,2- cis -2-aminoglycosides (Scheme ). ,,,− In our studies, we examined an array of glycosyl electrophiles and metal salts. From this evaluation, we discovered that the combination of C(2)- N -substituted trifluoromethylbenzylideneamino N -phenyl trifluoroacetimidate electrophiles 1 and nickel triflate, Ni(OTf) 2 , provided high α-selectivity for 1,2- cis -amino linkage formation.…”

Section: Results and Discussionmentioning

confidence: 99%

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Are Brønsted Acids the True Promoter of Metal-Triflate-Catalyzed Glycosylations? A Mechanistic Probe into 1,2-cis-Aminoglycoside Formation by Nickel Triflate

Sletten

Schlegel

et al. 2019

ACS Catal.

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Metal triflates have been utilized to catalytically facilitate numerous glycosylation reactions under mild conditions. In some methods, the metal triflate system provides stereocontrol during the glycosylation, rather than the nature of protecting groups on the substrate. Despite these advances, the true activating nature of metal triflates remains unclear. Our findings indicated that the in situ generation of trace amounts of triflic acid from metal triflates can be the active catalyst species in the glycosylation. This fact has been mentioned previously in metal triflate-catalyzed glycosylation reactions; however, a thorough study on the subject and its implications on stereoselectivity has yet to be performed. Experimental evidence from control reactions and 19F NMR spectroscopy have been obtained to confirm and quantify the triflic acid released from nickel triflate, for which it is of paramount importance in achieving a stereoselective 1,2-cis-2-amino glycosidic bond formation via a transient anomeric triflate. A putative intermediate resembling that of a glycosyl triflate has been detected using variable temperature NMR (1H and 13C) experiments. These observations, together with density functional theory calculations and a kinetic study, corroborate a mechanism involving triflic acid-catalyzed stereoselective glycosylation with N-substituted trifluoromethylbenzylideneamino protected electrophiles. Specifically, triflic acid facilitates formation of a glycosyl triflate intermediate which then undergoes isomerization from the stable α-anomer to the more reactive β-anomer. Subsequent SN2-like displacement of the reactive anomer by a nucleophile is highly favorable for the production of 1,2-cis-2-aminoglycosides. Although there is a previously reported work regarding glycosyl triflates, none of these reports have been confirmed to come from the counter ion of the metal center. Our work provides supporting evidence for the induction of a glycosyl triflate through the role of triflic acid in metal triflate-catalyzed glycosylation reactions.

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“…The Ni(4-F-PhCN) 4 (OTf) 2 catalyst has since been employed by the Nguyen group, − notably in the synthesis of mycothiol which had previously proved challenging since the required 1,2- cis couplings are difficult to synthesize (Scheme ). During these studies it was confirmed that the β-TCA donor was unreactive toward the Ni(II) catalyst as previously reported, whereas only the α-TCA donor facilitated the formation of a glycoside with excellent α-selectivity.…”

Section: Glycosyl Imidate Donorsmentioning

confidence: 95%

Catalytic Glycosylations in Oligosaccharide Synthesis

2018

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Catalytic glycosylation has been a central reaction in carbohydrate chemistry since its introduction by Fischer 125 years ago, but it is only in the past three to four decades that catalytic methods for synthesizing oligosaccharides have appeared. Despite the development of numerous elegant and ingenious catalytic glycosylation methods, only a few are in general use. This review covers all methods of catalytic glycosylation with the focus on the development and application in oligosaccharide synthesis and provide an overview of the scope and limitations of these. The review also includes relevant mechanistic studies of catalytic glycosylations. The future of catalytic glycosylation chemistry is discussed, including specific, upcoming methods and possible directions for the field of research in general.

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Stereoselective α-glycosylation of C(6)-hydroxyl myo-inositols via nickel catalysis—application to the synthesis of GPI anchor pseudo-oligosaccharides

Cited by 14 publications

References 57 publications

An Alternative Reaction Course in O-Glycosidation with O-Glycosyl Trichloroacetimidates as Glycosyl Donors and Lewis Acidic Metal Salts as Catalyst: Acid–Base Catalysis with Gold Chloride-Glycosyl Acceptor Adducts

An Alternative Reaction Course in O-Glycosidation with O-Glycosyl Trichloroacetimidates as Glycosyl Donors and Lewis Acidic Metal Salts as Catalyst: Acid–Base Catalysis with Gold Chloride-Glycosyl Acceptor Adducts

Are Brønsted Acids the True Promoter of Metal-Triflate-Catalyzed Glycosylations? A Mechanistic Probe into 1,2-cis-Aminoglycoside Formation by Nickel Triflate

Catalytic Glycosylations in Oligosaccharide Synthesis

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