Evidence for Endocyclic Cleavage of Conformationally Restricted Glycopyranosides

Manabe, Shino; Ishii, Kazuyuki; Hashizume, Daisuke; Koshino, Hiroyuki; Ito, Yukishige

doi:10.1002/chem.200900064

Cited by 50 publications

(40 citation statements)

References 68 publications

(32 reference statements)

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“…[16] By using similar conditions to those described above, dimethyl(ethyl)silane/Cu(OTf) 2 in CH 3 CN [17] at room temperature gave a significant amount of anomerized product 8 in 38 % yield together with dimethylethylsilylated compound 9 in 52 % yield. After chloroacetylation of the hydroxy group, the thioglycosides 10 and 11 were used as glycosyl donors.…”

Section: Resultsmentioning

confidence: 93%

“…When the β-glycoside 22b was submitted to the same reaction conditions used in entry 6, it was recovered unchanged in 89 % yield. [16,28] Unfortunately, fluoridated glycoside 12 was not activated under Suzuki conditions even at 40°C in CH 2 Cl 2 (entry 11). [29] Bromide donor 13 was not activated by the weak activators Ag 2 O (entry 12) or Ag 2 CO 3 (entry 13), but was activated by AgOTf.…”

Section: Resultsmentioning

confidence: 99%

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N‐Benzyl‐2,3‐trans‐Carbamate‐Bearing Glycosyl Donors for 1,2‐cis‐Selective Glycosylation Reactions

2010

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Glycosyl donors for the preparation of 1,2‐cis glycosides of amino sugars have been developed. The 2,3‐trans‐cyclic‐carbamate‐carrying glycosyl donors were readily prepared from the corresponding known trichloroethyl carbamate protected amino sugars under standard hydroxy group benzylation conditions. The donors exhibit high 1,2‐cis stereoselectivity towards secondary hydroxy group substrates. In the case of primary hydroxy acceptors, high stereoselectivities were achieved with the aid of the dioxane effect. After glycosylation, the carbamate was removed under alkaline conditions. Importantly, these glycosyl donors can be used in polymer‐supported and solid‐phase synthesis.

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Section: Resultsmentioning

confidence: 93%

Section: Resultsmentioning

confidence: 99%

N‐Benzyl‐2,3‐trans‐Carbamate‐Bearing Glycosyl Donors for 1,2‐cis‐Selective Glycosylation Reactions

2010

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“…Probably, this mode of anomerization is promoted by ring strain induced by the cyclic protecting group. Evidence for endocyclic cleavage was obtained by intra- and intermolecular Friedel-Crafts reactions, chloride addition, and reduction of the generated cation 92. Interestingly, it is important to that pyranosides are lock in a chair conformation for endocyclic opening because pyranosides with the distorted conformations did not undergo this reaction.…”

Section: Anomeric Control In Glycosylationsmentioning

confidence: 99%

Opportunities and challenges in synthetic oligosaccharide and glycoconjugate research

2009

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Synthetic oligosaccharides and glycoconjugates are increasingly used as probes for biological research and as lead compounds for drug and vaccine discovery. These endeavors are, however, complicated by a lack of general methods for the routine preparation of this important class of compounds. Recent development such as one-pot multi-step protecting group manipulations, the use of unified monosaccharide building blocks, the introduction of stereoselective glycosylation protocols, and convergent strategies for oligosaccharide assembly, are beginning to address these problems. Furthermore, oligosaccharide synthesis can be facilitated by chemo-enzymatic methods, which employ a range of glycosyl transferases to modify a synthetic oligosaccharide precursor. Glycosynthases, which are mutant glycosidases, that can readily form glycosidic linkages are addressing a lack of a wide range glycosyltransferases. The power of carbohydrate chemistry is highlighted by an ability to synthesize glycoproteins.There is a growing appreciation that posttranslational modifications, such as glycosylation, dramatically increase protein complexity and function. [1][2][3][4][5][6] For example, almost all cell surface and secreted proteins are modified by covalently-linked carbohydrate moieties and the glycan structures on these glycoproteins have been implicated as essential mediators in processes such as protein folding, cell signaling, fertilization, embryogenesis, neuronal development, hormone activity, and the proliferation of cells and their organization into specific tissues. In addition, overwhelming data supports the relevance of glycans in pathogen recognition, inflammation, innate immune responses, and the development of autoimmune diseases and cancer. [7][8][9][10] The importance of protein glycosylation is also underscored by the developmental abnormalities observed in a growing number of human disorders known as Congenital Disorders of Glycosylation caused by defects in the glycosylation machinery. 11Polysaccharides are major constituents of the microbial cell surfaces and, for example, the bacterial cell wall can contain relatively large amounts of capsular polysaccharides (CPS) or lipopolysaccharides (LPS). 12 These components are important virulence factors by promoting bacterial colonization, blocking phagocytosis, and interfering with leukocyte migration and adhesion. CPS and LPS can be recognized by receptors of the innate immune system leading to the production of cytokines, chemokines, and cellular adhesion molecules.13 -16 With a few exceptions, bacterial polysaccharides can induce an adaptive immune response and, not surprisingly, bacterial saccharides have been employed for the development of vaccines for several pathogens.17 -20

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“…This glycosyl triflate intermediate reacted with alcohols of high reactivity to afford β-glycosides as kinetic products. The α-products were also obtained at elevated temperatures after anomerization of the β-products, as both Oscarson and our group have previously reported [18,22–24]. Namely, α- and β-glycosides were obtained from 2,3-oxazolidinone donors by changing the reaction conditions.…”

Section: Resultsmentioning

confidence: 71%

“…On the other hand, the corresponding α-isomer of disaccharide 8α was obtained as a major product together with the anomerized donor 9 when the reaction was performed at 0 °C in the absence of DTBMP (Table 3, entry 4). These anomerizations may be caused by the endocyclic cleavage reaction [22–24], which is often observed for pyranosides with a 2,3- trans carbamate group, under acidic conditions. The yield of disaccharide 8 was improved by raising the temperature to 0 °C after the completion of electrolysis at −78 °C (Table 3, entry 5).…”

Section: Resultsmentioning

confidence: 99%

Electrochemical generation of 2,3-oxazolidinone glycosyl triflates as an intermediate for stereoselective glycosylation

Nokami¹,

Shibuya²,

Saigusa³

et al. 2012

Beilstein J. Org. Chem.

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SummaryGlycosyl triflates with a 2,3-oxazolidinone protecting group were generated from thioglycosides by low-temperature electrochemical oxidation. The glycosyl triflates reacted with alcohols to give the corresponding glycosides β-selectively at low temperatures. However, α-selectivity was observed in the absence of base at elevated reaction temperatures. In situ generated triflic acid promotes the isomerization of β-products to α-products.

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Evidence for Endocyclic Cleavage of Conformationally Restricted Glycopyranosides

Cited by 50 publications

References 68 publications

N‐Benzyl‐2,3‐trans‐Carbamate‐Bearing Glycosyl Donors for 1,2‐cis‐Selective Glycosylation Reactions

N‐Benzyl‐2,3‐trans‐Carbamate‐Bearing Glycosyl Donors for 1,2‐cis‐Selective Glycosylation Reactions

Opportunities and challenges in synthetic oligosaccharide and glycoconjugate research

Electrochemical generation of 2,3-oxazolidinone glycosyl triflates as an intermediate for stereoselective glycosylation

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