Targeted Glycosyl Donor Delivery for Site-Selective Glycosylation<sup>,</sup><sup>1</sup>

Anilkumar, G.; Nair, Latha G.; Fraser‐Reid, Bert

doi:10.1021/ol0001214

Cited by 43 publications

(25 citation statements)

References 15 publications

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“…In contrast, the armed counterpart 81 was promiscuous, although going to O2 mainly to give 82 as the major product (Scheme 13a). When acceptor diol 80 was presented simultaneously to both donors 79 and 81, the product 83 was the only trisaccharide obtained (Scheme 13b), each donor having gone to its preferred-OH as previously revealed in Scheme 13a [92].…”

Section: Secondary Versus Secondary Hydroxyl Groups In Diolssupporting

confidence: 53%

Armed–Disarmed Effects in Carbohydrate Chemistry: History, Synthetic and Mechanistic Studies

Fraser‐Reid¹,

López

2010

Reactivity Tuning in Oligosaccharide Assembly

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This chapter begins with an account of the serendipitous events that led to the development of n-pentenyl glycosides (NPGs) as glycosyl donors, followed by the chance events that laid the foundation for the armed-disarmed strategy for oligosaccharide assembly. A key mechanistic issue for this strategy was that, although both armed and disarmed entities could function independently as glycosyl donors, when one was forced to compete with the other for one equivalent of a halonium ion, the disarmed partner was found to function as a glycosyl acceptor. The phenomenon was undoubtedly based on reactivity, but further insight came unexpectedly. Curiosity prompted an examination of how ω-alkenyl glycosides, other than n-pentenyl, would behave. Upon treatment with wet N-bromosuccinimide, allyl, butenyl, and hexenyl glucosides gave bromohydrins, whereas the pentenyl analog underwent oxidative hydrolysis to a hemiacetal. Although the answer was definitive, an in depth comparison of n-pentenyl and n-hexenyl glucosides was carried out which provided evidence in support of the transfer of cyclic bromonium ion between alkenes in a steady-state phenomenon. It was found that for two ω-alkenyl glycosides having a relative reactivity ratio of only 2.6:1, nondegenerate bromonium transfer enabled the faster reacting entity to be converted completely to product, while the slower reacting counterpart was recovered completely. This nuance suggests that in the armed/disarmed coupling, such a nondegenerate steady-state transfer is ultimately responsible for determining how the reactants are relegated to donor or acceptor roles.Development of chemoselective armed/disarmed coupling led to another phase in the sequence of serendipities. During experiments to glycosylate an acceptor diol, it was found that armed and disarmed donor's glycosylated different hydroxyl groups. This observation caused us to embark on studies of regioselective glycosylation. One of these studies showed that it is possible to activate selectively n-pentenyl orthoesters (NPOEs) over other n-pentenyl donors, and that this chemoselective process enables regioselective glycosylation. As a result, reaction partners can be so tuned that glycosylation of an acceptor with nine free hydroxyl groups by an n-pentenyl orthoester donor carrying two free hydroxyl groups is able to furnish a single product in 42% yield. Experiments such as the latter suggest that the donor favors a particular hydroxyl group, and/or that a particular hydroxyl favors the donor. Either option implies that the principle of reciprocal donor acceptor selectivity (RDAS) is in operation.Such examples of regioselective glycosylation provide an alternative to the traditional practice of multiple protection/deprotection events to ensure that the only free hydroxyl group among glycosyl partners is the one to be presented to the donor. By avoiding such protection/deprotections, there can be substantial savings of time and material - as well as nervous anxiety.

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Section: Secondary Versus Secondary Hydroxyl Groups In Diolssupporting

confidence: 53%

Armed–Disarmed Effects in Carbohydrate Chemistry: History, Synthetic and Mechanistic Studies

Fraser‐Reid¹,

López

2010

Reactivity Tuning in Oligosaccharide Assembly

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“…On the other hand, when the Lewis acid was scandium triflate the yield was higher but the reaction was complicated by the formation of a trisaccharide (41). Although the reaction conditions and the donor were the same as in the previous example the yields were notably higher, especially with Yb(OTf) 3 as Lewis acid (33). With both Yb(OTf) 3 and Sc(OTf) 3 excellent regioselectivities were observed, but again the reactions were complicated by the formation of a trisaccharide 44 in the case of the more potent Lewis acid (Scheme 16).…”

Section: Regioselective Glycosylation Of Diolsmentioning

confidence: 76%

Double Diastereoselection, Regioselectivity, and the Importance of Donor-Acceptor Complementarity in the Stereoselectivity of Glycosylation Reactions

Bohé¹,

Crich²

2010

TIGG

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Glycosylation is a process involving the union of two chiral partners, a donor and an acceptor, and is therefore formally subject to double diastereodifferentiation. In this review, we discuss, through the presentation of suitable examples, double diastereoselection in glycosylation reactions based on the "matched and mismatched concept". We also discuss the related but more widely appreciated concept of regioselective glycosylation of diols and illustrate through select examples how this may vary on the basis of donor and even promoter. Finally, we diverge from the usual course of representation of glycosylation stereoselectivity as a simple ratio, and also represent it in terms of diastereomeric excess to facilitate comparison with other branches of organic chemistry.

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“…This facilitated the possibility of performing iterative glycosylations in the synthesis of larger oligosaccharide building blocks . In a comparative study, it was illustrated that n ‐pentenyl glycosides gave a mixture of products, whereas NPOE yielded strictly the equatorial product in a clean reaction with a higher conversion ratio. Mathew et al.…”

Section: Glycosylationsmentioning

confidence: 99%

Chemical O‐Glycosylations: An Overview

2016

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The development of glycobiology relies on the sources of particular oligosaccharides in their purest forms. As the isolation of the oligosaccharide structures from natural sources is not a reliable option for providing samples with homogeneity, chemical means become pertinent. The growing demand for diverse oligosaccharide structures has prompted the advancement of chemical strategies to stitch sugar molecules with precise stereo‐ and regioselectivity through the formation of glycosidic bonds. This Review will focus on the key developments towards chemical O‐glycosylations in the current century. Synthesis of novel glycosyl donors and acceptors and their unique activation for successful glycosylation are discussed. This Review concludes with a summary of recent developments and comments on future prospects.

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Targeted Glycosyl Donor Delivery for Site-Selective Glycosylation^,¹

Cited by 43 publications

References 15 publications

Armed–Disarmed Effects in Carbohydrate Chemistry: History, Synthetic and Mechanistic Studies

Armed–Disarmed Effects in Carbohydrate Chemistry: History, Synthetic and Mechanistic Studies

Double Diastereoselection, Regioselectivity, and the Importance of Donor-Acceptor Complementarity in the Stereoselectivity of Glycosylation Reactions

Chemical O‐Glycosylations: An Overview

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Targeted Glycosyl Donor Delivery for Site-Selective Glycosylation,1

Cited by 43 publications

References 15 publications

Armed–Disarmed Effects in Carbohydrate Chemistry: History, Synthetic and Mechanistic Studies

Armed–Disarmed Effects in Carbohydrate Chemistry: History, Synthetic and Mechanistic Studies

Double Diastereoselection, Regioselectivity, and the Importance of Donor-Acceptor Complementarity in the Stereoselectivity of Glycosylation Reactions

Chemical O‐Glycosylations: An Overview

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Targeted Glycosyl Donor Delivery for Site-Selective Glycosylation^,¹