Photochemical Glycosylation

Ragains, Justin R.

doi:10.1002/9783527696239.ch10

Cited by 3 publications

(3 citation statements)

References 51 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In spite of the many advances in chemical and enzymatic glycosidation, whether automated or classical, in recent years, − the stereocontrolled synthesis of many classes of glycosidic bond continues to be a significant challenge that retards the preparation of saccharides, oligosaccharides, and their conjugates for biomedical research. The problem arises because of the location of typical glycosylation reactions at the interface between S N 1 and S N 2 reactions where minor changes in structure and conditions cause major shifts in mechanism, − is compounded by the iterative nature of oligosaccharide synthesis, and is particularly significant in the preparation of the microbial glycans with their great structural diversity and complexity. − Indeed, notwithstanding the several spectacular syntheses published in recent years, − the surface of the microbial glycan problem has barely been scratched leaving many challenges for the ingenuity of the organic chemist.…”

Section: Introductionmentioning

confidence: 99%

Synthesis and Stereocontrolled Equatorially Selective Glycosylation Reactions of a Pseudaminic Acid Donor: Importance of the Side-Chain Conformation and Regioselective Reduction of Azide Protecting Groups

Dhakal

Crich

2018

J. Am. Chem. Soc.

View full text Add to dashboard Cite

Pseudaminic acid is an amino deoxy sialic acid whose glycosides are essential components of many pathogenic Gram-negative bacterial cell walls including those from Pseudomonas aeruginosa, Vibrio cholerae, Campylobacter jejuni, Campylobacter coli, Vibrio vulnificus, and Pseudoalteromonas distincta. The study of pseudaminic acid glycosides is however hampered by poor availability from nature, the paucity of good synthetic methods, and limited to no understanding of the factors controlling stereoselectivity. Conformational analysis of the side chains of various stereoisomeric sialic acids suggested that the side chain of pseudaminic acid would take up the most electron-withdrawing trans,gauche-conformation, as opposed to the gauche,gauche conformation of N-acetyl neuraminic acid and the gauche,trans-conformtion of 7-epi N-acetyl neuraminic acid, leading to the prediction of high equatorial selectivity. This prediction is borne out by the synthesis of a suitably protected pseudaminic acid donor from N-acetyl neuraminic acid in 20 steps and 5% overall yield, and by the exquisite equatorial selectivity it displays in coupling reactions with typical glycosyl acceptors. The selectivity of the glycosylation reactions is further buttressed by the development and implementation of conditions for the regioselective release of the two amines from the corresponding azides, such as required for the preparation of the lipopolysaccharides. These findings open the way to the synthesis and study of pseudaminic acid-based bacterial lipopolysaccharides and, importantly in the broader context of glycosylation reactions in general, underline the significant role played by side chain conformation in the control of reactivity and selectivity.

show abstract

Section: Introductionmentioning

confidence: 99%

Synthesis and Stereocontrolled Equatorially Selective Glycosylation Reactions of a Pseudaminic Acid Donor: Importance of the Side-Chain Conformation and Regioselective Reduction of Azide Protecting Groups

Dhakal

Crich

2018

J. Am. Chem. Soc.

View full text Add to dashboard Cite

show abstract

“…Photochemistry is a well‐established field with a plethora of applications for organic transformations [60] including glycosylation [61] . The first application of photochemically induced transformation of a thioglycoside was established by Griffin et al.…”

Section: Direct Activation Via the Interaction Of A Transition Metal ...mentioning

confidence: 99%

Transition‐Metal‐Mediated Glycosylation with Thioglycosides

Escopy

Demchenko

2022

Chemistry A European J

View full text Add to dashboard Cite

Thioglycosides are among the most common glycosyl donors that find broad application in the synthesis of glycans and glycoconjugates. However, the requirement for toxic and/or large access of activators needed for common glycosylations with thioglycosides remains a notable draw-back. Due to the increased awareness of the chemical waste impact on the environment, synthetic studies have been driven by the goal of finding non-toxic reagents. The main focus of this review is to highlight recent methods for thioglycoside activation that rely on transition metal catalysis.

show abstract

“…Because of their stability, however, thioglycoside activation typically requires the implementation of highly reactive electrophiles or reagent cocktails (e.g., NIS/HOTf, DMTST, MeOTf, PhSOTf). We and others have been successful in the development of alternative photochemical approaches to thio/selenoglycoside activation − while others have enjoyed considerable success in the area of electrochemical activation . However, the in situ generation of highly reactive and short-lived electrophiles that then react with thio/selenoglycosides is an underexplored area that interests us.…”

mentioning

confidence: 99%