Armed/disarmed effects in glycosyl donors: rationalization and sidetracking

Fraser‐Reid, Bert; Wu, Zufan; Udodong, Uko E.; Ottosson, Håkan

doi:10.1021/jo00312a004

Cited by 258 publications

(162 citation statements)

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“…Both species were found to be more energetically favoured than the non-coordinated oxocarbenium ion. Optimizing experiments were first conducted with common activating conditions, such as NIS/AgOTf, NIS/TMSOTf and Ph 2 SO/Tf 2 O/TTBP ( In general, the structure of glycosyl acceptors only shows complementary effects 28 on stereoselectivity of a glycosylation reaction, compared with the structure of donors [29][30][31] , and other factors such as temperature or solvents. Glycosyl acceptors bearing electron-withdrawing substituents should diminish the nucleophilicity of the hydroxyl group, resulting in a decrease of reaction rate 29,32 .…”

Section: Resultsmentioning

confidence: 99%

The intriguing dual-directing effect of 2-cyanobenzyl ether for a highly stereospecific glycosylation reaction

Hoang

Liu

2014

Nat Commun

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The diverse presence as well as their very specific bio-responses of glycoconjugates found in all living species requires scientists to synthesize the precise structure of these complex oligosaccharides for various studies on glycoscience. Very few approaches were able to offer the sole a-or b-glycosylated products, even at the cost of complicating the preparative route or usage of exotic chiral auxiliaries to drive the stereoselectivity. In this report, the unification of solvent assistance and neighbouring group participation concepts have led us to the use of 2-cyanobenzyl ether as the dual-directing auxiliary for stereospecific construction of a-and b-glycosidic bonds from a single starting material, and both isomers can be obtained in exclusive stereoselectivity. This work demonstrates the difference in reactivities of glycosyl acceptors can be employed to completely drive the stereoselectivity, drawing the parallel comparison with the arming/disarming concept, which has been exclusively confined to glycosyl donors.

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Section: Resultsmentioning

confidence: 99%

The intriguing dual-directing effect of 2-cyanobenzyl ether for a highly stereospecific glycosylation reaction

Hoang

Liu

2014

Nat Commun

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“…The reaction of 5a with 1.5 molar equivalent of 1a as a sialosyl donor using 3.0 molar equivalent of N-iodosuccinimide (NIS) and 0.5 eq of triethylsilyl triflate (TESOTf) 15) in CH 3 CN at room temperature gave the expected glycosides 6a in 68% yield with a-anomer as the major product (a/bϭ2 : 1) (entry 1, Table 1). The a/b ratio was determined by integration of the H-3eq 1 H-NMR signal.…”

Section: Resultsmentioning

confidence: 99%

Preparation of 4-Pentenoic Acid Ester of Neu5Ac and 4-Pentenyl Glycoside of Neu5Ac and Their Application to Glycosylation

et al. 2005

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N-Acetylneuraminic acids (Neu5Ac), sialic acids are most frequently found as a-glycosidically linked terminal residues of glycoproteins and glycolipids. There are a wide range of biological properties endowed by sialic acids on natural glycoconjugate structure and function, often involved in important cell surface communications and infection processes. 1-3)The development of the efficient method of O-sialylation has been a challenging task in the field of sialic acid chemistry. 4,5) Fraser-Reid and his co-workers introduced a 4-pentenyl group as a new and effective leaving group at the anomeric center of the glycosyl donor.6) The attractiveness of 4-pentenyl glycosides is enhanced by the fact that they can be applied to the armed/disarmed methodology of oligosaccharide synthesis.7) 4-Pentenyl glycosides are of interest for studying various biological and physiological phenomena of carbohydrates.8) To the best of our knowledge, there has been no report on the synthesis of 4-pentenoic acid ester of Neu5Ac (1a). A few reports 9,10) on the synthesis of 4-pentenyl glycoside of Neu5Ac (1b) have been reported, however application of 1b to O-sialylation has not been studied. As a part of our program aimed at the development of new O-sialylation, 11,12) we are interested in finding out whether 1a, b would be suitable for stereoselective O-sialylation. This paper describes the synthesis of 1a, b and their application to O-sialylation. Results and DiscussionWe first focused on an efficient synthesis of 1a having 4-pentenoyloxy group at the 2-position of Neu5Ac as a leaving group. Treatment of per-O-acetylated Neu5Ac 2 with hydrogen chloride in AcCl-AcOH (1 : 1) gave 2-chloro derivative 3 in a quantitative yield. Compound 3 was treated with silver carbonate in acetone-H 2 O (9 : 1) to afford 2-hydroxy derivative 4 13) in 88% yield. Acylation of 4 was achieved by 4-pentenoic anhydride and pyridine and N,N-dimethylaminopyridine (DMAP) in CH 2 Cl 2 to give 1a in a quantitative yield as an anomeric mixture with b-anomer as the major product (Chart 1). Next, we focused on a search for an efficient method of synthesizing 1b. When silver salicylate was used as a promoter in the presence of 4-penten-1-ol in CH 2 Cl 2 , 1b was obtained in 80% yield.9) The best result was obtained when the reaction was performed by Koenigs-Knorr condi- * To whom correspondence should be addressed. e-mail: ikeda@u-shizuoka-ken.ac. Novel sialosyl donors, 4-pentenoic acid ester of N-acetylneuraminic acids (Neu5Ac) (1a) and 4-pentenyl glycoside of Neu5Ac (1b) were successfully prepared from the corresponding per-O-acetylated 2-hydroxy and 2-chloro derivatives of Neu5Ac, respectively and applied to the synthesis of O-sialosides.

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“…A significant development in stereoselective glycosylation chemistry was made a quarter century ago when the idea of matched/mismatched donors and acceptors based on the armed or disarmed reactivity of glycosyl donors was proposed by Fraser-Reid. 50 Fraser-Reid demonstrated for the first time that competitive glycosylation between armed and disarmed donors could be chemoselective with an armed donor reacting preferentially to give a mixture of glycosides (a/b 2:1) while a disarmed donor would remain unreactive. Subsequently other groups have expanded on this concept to show that armed/disarmed reactivity could be modulated to achieve stereoselectivity in the glycosylation reaction.…”

Section: Methodsmentioning

confidence: 99%

Great South African molecules: the case for mycothiol

Nkambule

2017

S.Afr.j.chem.

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South Africa has one of the oldest chemical societies in the world and has a long history of natural products, synthetic, and medicinal chemistry yet the visibility of molecules discovered or synthesized in South Africa is very low. Is this because South African scientists are incapable of discovering influential and celebrated molecules, or is there inadequate publicity of such discoveries? Perspective profiles on the discovery and scope of research on 'Great South African Molecules' should be a good start to redress this state of affairs. One such molecule deserving publicity is the antioxidant mycothiol which is produced by mycobacteria. This is a molecule of interest not only because of its medicinal potential in the fight against tuberculosis, but also from synthetic methodology and enzyme inhibition studies. This review aims to illuminate the scope of research in mycothiol chemistry for the purpose of promoting multidisciplinary investigations related to this South African molecule.

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Armed/disarmed effects in glycosyl donors: rationalization and sidetracking

Cited by 258 publications

References 0 publications

The intriguing dual-directing effect of 2-cyanobenzyl ether for a highly stereospecific glycosylation reaction

The intriguing dual-directing effect of 2-cyanobenzyl ether for a highly stereospecific glycosylation reaction

Preparation of 4-Pentenoic Acid Ester of Neu5Ac and 4-Pentenyl Glycoside of Neu5Ac and Their Application to Glycosylation

Great South African molecules: the case for mycothiol

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