A Study on the Influence of the Structure of the Glycosyl Acceptors on the Stereochemistry of the Glycosylation Reactions with 2‐Azido‐2‐Deoxy‐Hexopyranosyl Trichloroacetimidates

Cid, M. B.; Alfonso, Francisco; Martín‐Lomas, Manuel

doi:10.1002/chem.200400746

Cited by 27 publications

(5 citation statements)

References 37 publications

(27 reference statements)

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“…The extrapolation of the stereoselectivity of benzylidene glucose donors to their glucosazide counterparts suggests that benzylidene or analogously protected glucosazides might represent an attractive class of 1,2- cis -selective glucosamine donor synthons. 20,21 …”

Section: Introductionmentioning

confidence: 99%

“…The in-depth research conducted on conformationally restricted benzylidene mannose and glucose donors has provided important insight into the glycosylation mechanisms of this type of 1,2- cis -selective donor. − To construct 1,2- cis linkages of glucosamine donors, the C-2-amino group is most commonly masked as the nonparticpating azide. , Notably, benzylidene glucosazides have not been systematically investigated with respect to the stereoselectivity of glycosylations in which they are employed. The extrapolation of the stereoselectivity of benzylidene glucose donors to their glucosazide counterparts suggests that benzylidene or analogously protected glucosazides might represent an attractive class of 1,2- cis -selective glucosamine donor synthons. , …”

Section: Introductionmentioning

confidence: 99%

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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: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Stereoselectivity of Conformationally Restricted Glucosazide Donors

et al. 2017

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“…The reactivity of the nucleophile can vary widely due to a combination of steric, stereoelectronic and inductive effects. 137,138,[190][191][192][193][194][195][196][197] The nature of the glycosyl acceptor can influence the outcome of a glycosylation reaction, both in terms of isolated yield and stereoselectivity. 198 When all groups are equatorial, as is the case of a glucose acceptor, in the 1 C 4 -conformation, the following reactivity order is observed: 6-OH 4 3-OH 4 2-OH 4 4-OH.…”

Section: Influence Of Protecting Groups On the Nucleophilementioning

confidence: 99%

Advances in glycoside and oligosaccharide synthesis

Crawford,

Seeberger

2023

Chem. Soc. Rev.

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“…5.34) with different glycosyl donors, in particular 2-azido-2-deoxy-glycopyranosyl trichloroacetimidates. In an attempt to extend the applicability of the double stereodifferentiation principle [59] to glycosylation reactions [60], Martin-Lomas et al studied the stereoselectivity of the glycosylation of D-and L-chiro-inositol derivatives with several glycosyl donors [61]. The authors observed that when differently protected 1,2-diols, derived from both chiroinositol enantiomers, are used as acceptors, both the absolute configuration of the acceptor as well as the nature of the donor's and acceptor's protecting groups plays a key role in the regiochemistry of the coupling.…”

Section: Regio-and Stereoselectivity In Glycosylationmentioning

confidence: 99%

Armed-Disarmed Concept in the Synthesis of Glycosidic Bond

Miljković

2013

Electrostatic and Stereoelectronic Effects in Carbohydrate Chemistry

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-Reid et al. reported [1] that n-pentenyl glycosides undergo chemospecific cleavage 1 ! 2 ! 3, with N-bromosuccinimide under conditions that leave a wide variety of other protecting groups unaffected ( Fig. 5.1).According to the proposed mechanism ( Fig. 5.1), the addition of water to the reaction mixture will lead to hydrolysis but the addition of alcohol or another sugar having a free hydroxyl group will lead to the formation of glycoside or a disaccharide. In the course of these studies, Fraser-Reid et al. [1] observed that sugar molecules having an acyloxy group at the C2 carbon (6 in Fig. 5.2) hydrolyzed much more slowly than if they had an alkoxy group (7 in Fig. 5.2). This observation suggested that the n-pentenyl glycoside could be made more or less reactive (it could be armed or disarmed) by the type of protecting group placed on the C2 oxygen.The ability of the C2 acyloxy group to disarm the n-pentenyl glycoside was rationalized as shown in Fig. 5.3. Thus, it can be assumed that the cyclic halonium ions 8 and 9 are formed reversibly [2] and that the electron density on the glycosidic oxygen is depleted in 2-O-acyl derivatives so that nucleophilic attack of this oxygen on the halonium ion is less favored than in the 2-O-alkyl counterpart 9. The reason for this is that the electron-withdrawing group at the C2 carbon makes the C2 carbon slightly positively charged so that the formation of another positive charge at the C1 carbon is not a favorable process [there cannot exist two positive charges on two neighboring carbons (C1 and C2) (Fig. 5.3).].Consequently, the armed glycosyl donors react with electrophiles faster than the disarmed ones, and therefore in a solution containing both an armed and disarmed glycosyl donor molecules, whereby disarmed glycosyl donor molecules have one free hydroxyl group, the reaction with an electrophile will result in crosscoupling and not self-coupling, i.e., an armed glycosyl donor will react with the disarmed one, whereas a disarmed donor will not react with itself [3] as illustrated in Fig. 5.5. The promoters for the activation of n-pentenyl group [4,5] are iodonium dicollidine perchlorate (IDCP) and N-iodosuccinimide/triethylsilyl triflate (NIS/Et 3 SiOTf).M. Miljkovic, Electrostatic and Stereoelectronic Effects in Carbohydrate Chemistry,

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A Study on the Influence of the Structure of the Glycosyl Acceptors on the Stereochemistry of the Glycosylation Reactions with 2‐Azido‐2‐Deoxy‐Hexopyranosyl Trichloroacetimidates

Cited by 27 publications

References 37 publications

Stereoselectivity of Conformationally Restricted Glucosazide Donors

Stereoselectivity of Conformationally Restricted Glucosazide Donors

Advances in glycoside and oligosaccharide synthesis

Armed-Disarmed Concept in the Synthesis of Glycosidic Bond

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