Stereoselective Synthesis of 2-C-Branched (Acetylmethyl) Oligosaccharides and Glycoconjugates: Lewis Acid-Catalyzed Glycosylation from 1,2-Cyclopropaneacetylated Sugars

Abstract

/npsi/ctrl?action=rtdoc&an=17364211&lang=en http://nparc.cisti-icist.nrc-cnrc.gc.ca/npsi/ctrl?action=rtdoc&an=17364211&lang=fr READ THESE TERMS AND CONDITIONS CAREFULLY BEFORE USING THIS WEBSITE.http://nparc.cisti-icist.nrc-cnrc.gc.ca/npsi/jsp/nparc_cp.jsp?lang=en Vous avez des questions? Nous pouvons vous aider. Pour communiquer directement avec un auteur, consultez la première page de la revue dans laquelle son article a été publié afin de trouver ses coordonnées. Si vous n'arrivez pas à les repérer, communiquez avec nous à PublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca. Questions?Contact the NRC Publications Archive team at PublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca. If you wish to email the authors directly, please see the first page of the publication for their contact information. NRC Publications Archive Archives des publications du CNRCThis publication could be one of several versions: author's original, accepted manuscript or the publisher's version. / La version de cette publication peut être l'une des suivantes : la version prépublication de l'auteur, la version acceptée du manuscrit ou la version de l'éditeur. For the publisher's version, please access the DOI link below./ Pour consulter la version de l'éditeur, utilisez le lien DOI ci-dessous.http://doi.org/10.1021/jo1016579Journal Of Organic Chemistry, 76, 4, pp. 1045Chemistry, 76, 4, pp. -1053Chemistry, 76, 4, pp. , 2011 1,2-Cyclopropaneacetylated sugars as glycosyl donors reacted with a series of glycosyl acceptors (monosaccharides, amino acids, and other alcohols) in the presence of Lewis acid to produce oligosaccharides and glycoconjugates containing 2-C-acetylmethylsugars. Galactosyl donor gave good to excellent R-selectivities with TMSOTf as a catalyst, whereas galactosyl donor offered moderate to good β-selectivities when BF 3 3 Et 2 O was used as a catalyst. However, glucosyl donors produced β-exclusive selectivity under both conditions. The stereoselectivities of glycosylation depend on the reactivity of donor sugars and Lewis acid catalyst, which effectively dictated the glycosylation pathways. The evidence suggests that galactosyl donors (e.g., 7) can undergo S N 1 pathway with a strong Lewis acid (TMSOTf) and S N 2 pathway under BF 3 3 Et 2 O, whereas the glucosyl donors (e.g., 8 and 10) followed S N 2 pathway. The stereoselectivity was also consequential to the formation of a C2 0 -acetal intermediate formed via the 2-C-acetylmethyl group and the anomeric carbonium intermediate in glycosylation.

An ultra-low thiourea catalyzed strain-release glycosylation and a multicatalytic diversification strategy

“…This investigation was initiated by utilizing a ( D )-furanoxylose, ( D )-Xyl f derived strained glycosyl donor 19a and a ( D )-Galactose derived acceptor 21a as the model furanosylation reaction (Table 1 ) 50 – 52 . We hypothesize that utilizing such cyclopropane fused furanosides might provide an advantage in activating the furanosyl donor via thermodynamic strain release, and the ketone functionality provides a functional handle for thiourea to activate via bidendate hydrogen bonding.…”

Recent advances in the stereoselective synthesis of carbohydrate 2-C-analogs

“…Very recently, Hu and Shao realized the opening of suitably substituted 1,2-cyclopropanated sugars 44 in the presence of different Lewis acids (Scheme 12). 37 Their strategy afforded carbohydrate 2-C-analogs 45 and 46 in high yields. Interestingly, TMSOTf as catalyst gave high α-selectivities with the galactoisomer, whereas the gluco-configured starting material yielded β-anomers as sole products under the same conditions.…”

“…Contradictorily, BF 3 •Et 2 O operates by a S N 2 reaction and the β-anomers are formed due to a neighboring group participation. Such Lewis acid-catalyzed ring-openings were applied for the stereoselective synthesis of di-or trisaccharides, glycosyl amino acids and other diverse 2-C-acetylmethylglycosides, 37 which opened a convenient entry to functionalized carbohydrate 2-C-analogs.…”

Bimolecular nature of boron trifluoride catalyzed glycosylation of a galactosyl donor: The role of the acceptor

“…An enolic zwitterion Z (Fig. ) has been previously suggested as a putative intermediate linking D and E . However, Z has a quite dubious structure.…”

“…Core step of this novel chemical glycosylation is the donor's 2‐acetyl neighboring participation (Fig. ) . Enol ether E is the neighboring participating intermediate, and is a nexus connecting reactants to both the main glycosylation product and the ketal intermediate by‐product.…”