Natural Products and Glycotechnology Research Institute Inc. NPG

River Road, NC, United States

Natural Products and Glycotechnology Research Institute Inc. NPG

River Road, NC, United States

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Uriel C.,Institute Quimica Organica General IQOG CSIC | Ventura J.,Institute Quimica Organica General IQOG CSIC | Gomez A.M.,Institute Quimica Organica General IQOG CSIC | Lopez J.C.,Institute Quimica Organica General IQOG CSIC | Fraser-Reid B.,Natural Products and Glycotechnology Research Institute Inc. NPG
European Journal of Organic Chemistry | Year: 2012

Mannopyranose-derived methyl 1,2-orthoacetates (R = Me) and -benzoates (R = Ph) can function as glycosyl donors - upon BF 3·Et 2O activation in CH 2Cl 2 - in glycosylation reactions with monosaccharide acceptors to afford disaccharides in good yields. In the process, glycosylation is preferred to acid-catalyzed rearrangement leading to methyl mannopyranosides. Methyl 1,2-orthoesters can be also used in regioselective glycosylation protocols with monosaccharide diols, in which they display good regioselectivity. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Fraser-Reid B.,Natural Products and Glycotechnology Research Institute Inc. NPG | Lopez J.C.,Institute Quimica Organica General IQOG CSIC | Bernal-Albert P.,Institute Quimica Organica General IQOG CSIC | Gomez A.M.,Institute Quimica Organica General IQOG CSIC | And 2 more authors.
Canadian Journal of Chemistry | Year: 2013

n-Pentenyl glycosides (NPGs) and n-pentenyl orthoesters (NPOEs) have been transformed into glycosyl fluorides by a variety of methods. In the case of NPGs, Barluenga's reagent, bis(pyridinium)iodonium(I)tetrafluoroborate (IPy 2BF4), gives good yields of glycosyl fluorides when HF-pyridine complex is used as an additional fluoride source. NPOEs can be activated either by a combination of electrophilic iodonium (Barluenga's reagent) and HBF4 or by the action of HF-pyridine complex. The ensuing glycosyl fluorides form a semiorthogonal pair of glycosyl donors when confronted with NPGs. © 2012 Published by NRC Research Press.


Uriel C.,Institute Quimica Organica General IQOG CSIC | Gomez A.M.,Institute Quimica Organica General IQOG CSIC | Lopez J.C.,Institute Quimica Organica General IQOG CSIC | Fraser-Reid B.,Natural Products and Glycotechnology Research Institute Inc. NPG
Organic and Biomolecular Chemistry | Year: 2012

A branched Man5 oligosaccharide has been synthesized by sequential regioselective glycosylations on a mannose-tetraol with n-pentenyl orthoester glycosyl-donors promoted by NIS/BF3·Et 2O, in CH2Cl2. An extended n-pentenyl chain was incorporated into the tetraol acceptor to facilitate (a) the solubility of the starting tetraol in CH2Cl2, and (b) future manipulations at the reducing end of the Man5 oligosaccharide. © The Royal Society of Chemistry 2012.


Uriel C.,Institute Quimica Organica General IQOG CSIC | Ventura J.,Institute Quimica Organica General IQOG CSIC | Gomez A.M.,Institute Quimica Organica General IQOG CSIC | Lopez J.C.,Institute Quimica Organica General IQOG CSIC | Fraser-Reid B.,Natural Products and Glycotechnology Research Institute Inc. NPG
Journal of Organic Chemistry | Year: 2012

Mannopyranose-derived methyl 1,2-orthoacetates (R = Me) and 1,2-orthobenzoates (R = Ph) undergo stereoselective formation of 1α,1′β-disaccharides, upon treatment with BF 3•Et 2O in CH 2Cl 2, rather than the expected acid-catalyzed reaction leading to methyl glycosides by way of a rearrangement-glycosylation process of the liberated methanol. © 2011 American Chemical Society.


Fraser-Reid B.,Natural Products and Glycotechnology Research Institute Inc. NPG | Lopez J.C.,Natural Products and Glycotechnology Research Institute Inc. NPG | Lopez J.C.,Institute Quimica Organica General
Topics in Current Chemistry | Year: 2011

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. © 2011 Springer-Verlag Berlin Heidelberg.

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