Is an acyl group at O-3 in glucosyl donors able to control α-stereoselectivity of glycosylation? The role of conformational mobility and the protecting group at O-6

Komarova, Bozhena S.; Orekhova, Maria V.; Tsvetkov, Yury E.; Nifantiev, Nikolay E.

doi:10.1016/j.carres.2013.11.016

Cited by 73 publications

(48 citation statements)

References 64 publications

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“…The 1,2- cis selectivity generally observed for these donors can be completely changed to selectively give the α-linked products by installing a C-3- O -acyl group in the donor. 58,59 The difference between the benzylidene mannose and benzylidene glucose series can be found in the different geometries that the oxocarbenium ions adopts. For the benzylidene mannose system, a B 2,5 -like structure is one of the lower-energy oxocarbenium ion conformers.…”

Section: Resultsmentioning

confidence: 99%

Stereoselectivity of Conformationally Restricted Glucosazide Donors

et al. 2017

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Glycosylations of 4,6-tethered glucosazide donors with a panel of model acceptors revealed the effect of acceptor nucleophilicity on the stereoselectivity of these donors. The differences in reactivity among the donors were evaluated in competitive glycosylation reactions, and their relative reactivities were found to be reflected in the stereoselectivity in glycosylations with a set of fluorinated alcohols as well as carbohydrate acceptors. We found that the 2-azido-2-deoxy moiety is more β-directing than its C-2-O-benzyl counterpart, as a consequence of increased destabilization of anomeric charge development by the electron-withdrawing azide. Additional disarming groups further decreased the α-selectivity of the studied donors, whereas substitution of the 4,6-benzylidene acetal with a 4,6-di-tert-butyl silylidene led to a slight increase in α-selectivity. The C-2-dinitropyridone group was also explored as an alternative for the nonparticipating azide group, but this protecting group significantly increased β-selectivity. All studied donors exhibited the same acceptor-dependent selectivity trend, and good α-selectivity could be obtained with the weakest acceptors and most reactive donors.

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Section: Resultsmentioning

confidence: 99%

Stereoselectivity of Conformationally Restricted Glucosazide Donors

et al. 2017

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“…A doubled quantity of stereodirecting groups in the donor does not always mean the highest selectivity. This is evident on comparison of the glucosylations of primary acceptor 56 and secondary acceptor 61 with variously protected glucosyl donors 42 – 46 , 55 (Table 5) . The coupling of the acceptor 56 , which can be considered as reactive due to the presence of electron‐donating benzyl protection and primary hydroxyl, with a perbenzylated glucosyl donor 42 demonstrates moderate 1,2‐ trans ‐selectivity (Table 5, entry 1).…”

Section: Design Of α‐Selective Glycopyranosyl Donors Relying On Remotmentioning

confidence: 96%

“…Before starting the synthesis of the pentasaccharide 165 , the selectivity of the 3‐O‐glucosylation of glucosyl acceptors with donors bearing one and two stereodirecting acyl groups at O‐3 and O‐6 was investigated (Table 5) . It was shown in these experiments that, in the case of glycosylation of secondary OH‐3, only one stereodirecting group at O‐6 is sufficient to induce decent 1,2‐ cis ‐selectivity.…”

Section: Design Of α‐Selective Glycopyranosyl Donors Relying On Remotmentioning

confidence: 99%

Design of α-Selective Glycopyranosyl Donors Relying on Remote Anchimeric Assistance

Komarova

Tsvetkov

Nifantiev

2016

The Chemical Record

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102

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Oligosaccharides have a variety of versatile biological effects, but unlike peptides and oligonucleotides, investigation of the roles of oligosaccharides is not easy. Since biosynthesis of oligosaccharides does not comply with direct genetic control, their isolation from natural sources and biotechnological preparation are complicated, due to the heterogeneous composition of raw carbohydrates. Oligosaccharide synthesis is needed for the establishment or confirmation of the structure of natural glycocompounds. Also, synthetically prepared, defined oligosaccharides and their derivatives are becoming increasingly important tools for many biological and immunological research projects. The key step of oligosaccharide synthesis involves glycosylation, a reaction that builds glycosidic bonds. Usually, construction of 1,2-trans-bonds is easy, and therefore, this reaction can even be included into automated syntheses. At this time, installation of the 1,2-cis-bond remains simultaneously frustrating and compelling. In our and other laboratories, a strategy of α-selective (1,2-cis) glycosylation, relying on remote anchimeric assistance with acyl groups, is studied. The state of the art in this work is summarized in this review.

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“…Contributing to the continued discussion on participation by remote ester groups in glycosylation reactions, 20 Kalikanda and Li computed (QM) the relative energies of a series of 2-azido-2-deoxygalactopyranosyl oxocarbenium ions and their bridged counterparts derived by participation of a remote ester group. Not surprisingly, in view of the greater delocalization of the positive charge the bridged species uniformly were found to be the more stable.…”

Section: Computational Work On Glycosyl Oxocarbenium Ionsmentioning

confidence: 99%

A propos of glycosyl cations and the mechanism of chemical glycosylation; the current state of the art

Bohé

Crich

2015

Carbohydrate Research

125

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An overview of recent advances in glycosylation with particular emphasis on mechanism is presented. The mounting evidence for both the existence of glycosyl oxocarbenium ions as fleeting intermediates in some reactions, and the crucial role of the associated in counter ion in others is discussed. The extremes of the SN1 and SN2 manifolds for the glycosylation reaction are bridged by a continuum of mechanisms in which it appears likely that most examples are located.

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Is an acyl group at O-3 in glucosyl donors able to control α-stereoselectivity of glycosylation? The role of conformational mobility and the protecting group at O-6

Cited by 73 publications

References 64 publications

Stereoselectivity of Conformationally Restricted Glucosazide Donors

Stereoselectivity of Conformationally Restricted Glucosazide Donors

Design of α-Selective Glycopyranosyl Donors Relying on Remote Anchimeric Assistance

A propos of glycosyl cations and the mechanism of chemical glycosylation; the current state of the art

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