Cleavage of O-glycosidic Bonds

Bochkov, A. F.; Заиков, Г. Е.

doi:10.1016/b978-0-08-022949-2.50011-3

Cited by 27 publications

(30 citation statements)

References 75 publications

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“…[29] Cycloaddition versus glycosidation: Anyone familiar with carbohydrate chemistry will recognize that the above-mentioned sugar-based nitroso acetals are in fact homologated Oglycosides. [30] Consequently, in spite of the theoretical inter- pretation provided in this work, it is still unclear if the stereocontrolled formation of nitroso acetals arises from a cycloaddition pathway or a stereospecific O-glycosidation involving ethanol as the glycosyl acceptor molecule. In the latter case, a hydroxyl-containing compound could be incorporated as the aglycone at the pseudoglycosidic centers of the five-and six-membered rings.…”

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confidence: 94%

Understanding Diastereofacial Selection in Carbohydrate-Based Domino Cycloadditions: Semiempirical and DFT Calculations

et al. 2000

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The sequential cycloaddition of nitroalkenes with methyl vinyl ether was investigated by semiempirical (PM3) and density functional methods (B3LYP/6-31G*). The asymmetric version was also examined with a threoconfigured carbohydrate auxiliary. This produces a larger, more flexible system that complicates the calculation. Most transition structures were then fully optimized at the PM3 level and further refinement was done at ab initio levels. This study represents a model case that enables the rationalization of the high facial selectivity observed in carbohydrate-based nitrone- and nitronate-alkene cycloadditions. The selective endo orientation of the [4+2] pathway results from Coulombic attraction and secondary orbital interactions in the transition state. The stereochemical outcome is largely influenced by a combination of steric shielding from the bulky chiral substituent at C4 and the anomeric effect that places the nitronate C6-alkoxy group in a pseudoaxial arrangement. The resulting conformation favors the subsequent exo approach of methyl vinyl ether to the less hindered re face of the nitronate. It is also remarkable to note that solvation energies stabilize significantly a particular transition structure, thereby explaining the marked stereoselection observed in a polar medium.

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confidence: 94%

Understanding Diastereofacial Selection in Carbohydrate-Based Domino Cycloadditions: Semiempirical and DFT Calculations

et al. 2000

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“…The achievement of high yields and complete stereocontrol is difficult due to the complexity of the glycosylation process that often proceeds along with a variety of side reactions. 5,6 However, a single-step glycosylation is not the only challenge researchers working on oligosaccharide synthesis face. Traditional linear approaches for the synthesis of oligosaccharides imply conversion of the disaccharide into second-generation glycosyl donors or acceptors.…”

Section: Introduction Chemical Glycosylation and Conventional Oligmentioning

confidence: 99%

Expeditious oligosaccharide synthesis via selective, semi-orthogonal, and orthogonal activation

Kaeothip

Demchenko

2011

Carbohydrate Research

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Traditional strategies for oligosaccharide synthesis often require extensive protecting and/or leaving group manipulations between each glycosylation step, thereby increasing the total number of synthetic steps while decreasing the efficiency of the synthesis. In contrast, expeditious strategies allow for the rapid chemical synthesis of complex carbohydrates by minimizing extraneous chemical manipulations. Oligosaccharide synthesis by selective activation of one leaving group over another is one such expeditious strategy. Herein, the significant improvements that have recently emerged in the area of the selective activation are discussed. The development of orthogonal strategy further expands the scope of the selective activation methodology. Surveyed in this article, are representative examples wherein these excellent innovations have been applied to the synthesis of various oligosaccharide sequences.

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“…The direction of the reaction depends on the relative configuration of C 1 and C 2 in the starting acylated chloroglucose and on the acceptor of the released HCl. Condensation of 1,2-cis-acylglycosylhalides with alcohols in the presence of Ag 2 CO 3 occurred mainly with C 1 configuration inversion, resulting in formation of 1,2-trans-glycosides [4].We performed quantum-chemical calculations using CS Mopac2000 Version 1.11 in order to justify theoretically the direction of the condensation of 1-chloro-2,3,4,6-tetra-O-acetyl-α-D-glucopyranose with the dibenzooxabicycloamine derivatives. Compounds were optimized before each AM1 (Austin Model 1) calculation by minimizing the energy using molecular mechanics (MM) and quantum-chemical methods [5].…”

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confidence: 99%

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Synthesis of some 1,2-trans-glucosides containing dibenzooxabicycloamines

et al. 2009

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Little has been published about carbohydrates containing heterocyclic compounds. However, such compounds are definitely of practical interest for synthesizing new types of 1,2-trans-glucosides [1][2][3].We propose a convenient method for synthesizing new types of heterocyclic derivatives of 1,2-trans-glucosides. Condensation of 1-chloro-2,3,4,6-tetra-O-acetyl-α-D-glucopyranose (1) with 4,4,8,8-tetramethyl-2,3,6,7-dibenzo-9-oxabicyclo-(3,3,1)-nonan-1-N-amino-5-ol (2); 4,4,8,8-tetramethyl-2,3,6,7-dibenzo-9-oxabicyclo-(3,3,1)-nonan-1-Nmethylamino-5-ol (3); 4,4,8,8-tetramethyl-2,3,6,7-dibenzo-9-oxabicyclo-(3,3,1)-nonan-1-N-ethylamino-5-ol (4); and 4,4,8,8-tetramethyl-2,3,6,7-dibenzo-9-oxabicyclo-(3,3,1)-nonan-1-N-tryptamin-5-ol (5) at room temperature in the presence of freshly prepared Ag 2 CO 3 catalyst in ether solution produced 6-9, respectively, according to Scheme 1.The course of reactions was monitored by TLC. The reactions took 14-16 h to produce mainly 1,2-trans-glycosides 6-9 although small quantities of the 1,2-cis-isomers were also observed. The products were yellow crystalline compounds that were soluble in CHCl 3 and alcohol (MeOH, EtOH). The yields of 2-5 decreased as the radical bonded to the heterocycle increased. This was probably due to steric factors.These are nucleophilic substitution reactions that occur through an S N 2 mechanismm. The direction of the reaction depends on the relative configuration of C 1 and C 2 in the starting acylated chloroglucose and on the acceptor of the released HCl. Condensation of 1,2-cis-acylglycosylhalides with alcohols in the presence of Ag 2 CO 3 occurred mainly with C 1 configuration inversion, resulting in formation of 1,2-trans-glycosides [4].We performed quantum-chemical calculations using CS Mopac2000 Version 1.11 in order to justify theoretically the direction of the condensation of 1-chloro-2,3,4,6-tetra-O-acetyl-α-D-glucopyranose with the dibenzooxabicycloamine derivatives. Compounds were optimized before each AM1 (Austin Model 1) calculation by minimizing the energy using molecular mechanics (MM) and quantum-chemical methods [5]. 1 2 -5 6 -9 R = -NH 2 (2, 6); -NHCH 3 (3, 7); -NHC 2 H 5 (4, 8); N H −NH−CH 2 −CH 2 (5, 9)

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Cleavage of O-glycosidic Bonds

Cited by 27 publications

References 75 publications

Understanding Diastereofacial Selection in Carbohydrate-Based Domino Cycloadditions: Semiempirical and DFT Calculations

Understanding Diastereofacial Selection in Carbohydrate-Based Domino Cycloadditions: Semiempirical and DFT Calculations

Expeditious oligosaccharide synthesis via selective, semi-orthogonal, and orthogonal activation

Synthesis of some 1,2-trans-glucosides containing dibenzooxabicycloamines

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