Stereoselectivity of glycosylations of conformationally restricted mannuronate esters

Codée, Jeroen D. C.; Jong, Ana R. de; Dinkelaar, Jasper; Overkleeft, Herman S.; Marel, Gijsbert A. van der

doi:10.1016/j.tet.2009.02.067

Cited by 20 publications

(11 citation statements)

References 33 publications

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“…Structure I* arranges three substituents in sterically unfavorable axial positions and does not benefit from a stabilizing anomeric effect. This conformation is in line with the structural preference of the related mannuronate ester oxacarbenium ion, which preferentially adopts a 3 H 4 half chair or closely related conformation. ,,, Because the anomeric carbon is quite electron depleted, the α-triflate I* takes up a structure closely mimicking the structure of the 3 H 4 -like oxacarbenium ion, which is best stabilized by an equatorial substituent at C-2 and by axial substituents at C-3, C-4, and C-5. Treatment of the conformational mixture of anomeric α-triflates I / I* with a 25-fold excess of MeOH- d 4 at −80 °C rapidly provided methyl mannoside 8 with high β-selectivity (see Table , entries 1 and 3).…”

Section: Resultssupporting

confidence: 56%

Mannosazide Methyl Uronate Donors. Glycosylating Properties and Use in the Construction of β-ManNAcA-Containing Oligosaccharides

et al. 2010

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Mannosazide methyl uronate donors equipped with a variety of anomeric leaving groups (β- and α-S-phenyl, β- and α-N-phenyltrifluoroacetimidates, hydroxyl, β-sulfoxide, and (R(s))- and (S(s))-α-sulfoxides) were subjected to activating conditions, and the results were monitored by (1)H NMR. While the S-phenyl and imidate donors all gave a conformational mixture of anomeric α-triflates, the hemiacetal and β- and α-sulfoxides produced an oxosulfonium triflate and β- and α-sulfonium bistriflates, respectively. The β-S-phenyl mannosazide methyl uronate performed best in both activation experiments and glycosylation studies and provided the 1,2-cis mannosidic linkage with excellent selectivity. Consequently, an α-Glc-(1→4)-β-ManN(3)A-SPh disaccharide, constructed by the stereoselective glycosylation of a 6-O-Fmoc-protected glucoside and β-S-phenyl mannosazide methyl uronate, was used as the repetitive donor building block in the synthesis of tri-, penta-, and heptasaccharide fragments corresponding to the Micrococcus luteus teichuronic acid.

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Section: Resultssupporting

confidence: 56%

Mannosazide Methyl Uronate Donors. Glycosylating Properties and Use in the Construction of β-ManNAcA-Containing Oligosaccharides

et al. 2010

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“…15,16 Significant effort, particularly in carbohydrate synthesis, has been expended to develop conditions that favor a single pathway in a predictive manner. 7,17-23 For example, changes in the pyranosyl donor, 17,22-24 nucleophile, 25-28 activator, 3,24 and solvent 29 can alter the predominant mechanistic pathway and the resulting stereoselectivity.…”

Section: Introductionmentioning

confidence: 99%

Correlations Between Nucleophilicities and Selectivities in the Substitutions of Tetrahydropyran Acetals

2009

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Selectivities that deviate from SN1 stereoelectronic models in the nucleophilic substitutions of tetrahydropyran acetals were investigated. When weak nucleophiles were employed, stereoselectivities conformed to known SN1 stereoelectronic models. In contrast, stereoselectivities in the substitutions of acetals with strong nucleophiles depended on reaction conditions. Erosions in selectivities were observed when strong nucleophiles were employed in the absence of coordinating counterions. These erosions in selectivities are attributed to rates of nucleophilic additions to oxocarbenium ion intermediates that approach the diffusion limit. When triflate counterions were present, however, SN2-like pathways became accessible with strong nucleophiles. In most cases examined, the major stereoisomers formed from reactions that proceeded through SN2-like pathways were opposite to the major stereoisomers formed from the analogous reactions that proceeded through SN1 pathways.

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“…In parallel to their work on the synthesis of β-mannosides using torsionally disarming 4,6- O -benzylidene groups, in 2000, the Crich group demonstrated that conformationally restricting 2,3- O -cyclic and 3,4- O- cyclic protecting groups are highly α-directing using mannosyl thioglycoside donors 45 and 46 (Scheme a) . Codée and co-workers subsequently reported the same α-selectivity using conformationally restricted mannuronate donors (Scheme b) . Thioglycosides 50 and 51 , protected with either a 2,3- O -isopropylidene or a 3,4-butanedimethylacetal group, respectively, were shown to be α-selective when glycosylated under Ph 2 SO/Tf 2 O preactivation conditions.…”

Section: Glycosylations Using Torsionally Disarmed Glycosyl Donorsmentioning

confidence: 95%

“…54 Codeé and co-workers subsequently reported the same α-selectivity using conformationally restricted mannuronate donors (Scheme 9b). 55 Thioglycosides 50 and 51, protected with either a 2,3-O-isopropylidene or a 3,4butanedimethylacetal group, respectively, were shown to be αselective when glycosylated under Ph 2 SO/Tf 2 O preactivation conditions. In contrast, monocyclic mannuronate donor 52 gave rise to the β-linked products.…”

Section: Glycosylations Using Torsionallymentioning

confidence: 99%

Conformationally Constrained Glycosyl Donors as Tools to Control Glycosylation Outcomes

2020

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Stereoselectivity of glycosylations of conformationally restricted mannuronate esters

Cited by 20 publications

References 33 publications

Mannosazide Methyl Uronate Donors. Glycosylating Properties and Use in the Construction of β-ManNAcA-Containing Oligosaccharides

Mannosazide Methyl Uronate Donors. Glycosylating Properties and Use in the Construction of β-ManNAcA-Containing Oligosaccharides

Correlations Between Nucleophilicities and Selectivities in the Substitutions of Tetrahydropyran Acetals

Conformationally Constrained Glycosyl Donors as Tools to Control Glycosylation Outcomes

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