Conformational analysis of nitrilium intermediates in glycosylation reactions

Synthesis and intramolecular glycosylation of sialyl mono-esters of o-xylylene glycol. The importance of donor configuration and nitrogen protecting groups on cyclization yield and selectivity; isolation and characterization of a N-sialyl acetamide indicative of participation by acetonitrile

“…This rationale follows that advanced for the formation of equatorial glycosides from simple perbenzyl protected glycopyranosyl donors when reactions are conducted in acetonitrile. 42–43 However, unlike the case of the simple α-glucopyranosyl nitrilium ions for which ample evidence exists from inter- and intramolecular trapping experiments, 44–49 and NMR spectroscopic investigations, 50–51 unequivocal evidence for the existence of the sialyl nitrilium ions has yet to be provided.…”

Neighboring‐Group Participation by C‐2 Ether Functions in Glycosylations Directed by Nitrile Solvents

“…mediates. [11][12][13] Some evidence of the presence of such nitrilium species has emerged in the past. Hindsgaul, for example, applied an intramolecular trapping technique to detect the presence of nitrilium species, [14] whereas Crich reported the formation of an imidate side product on nucleophilic addition of an alcohol to the nitrilium species.…”

Antitumor Vaccines Based on Synthetic Mucin Glycopeptides

“…After careful deacetylation of T N -antigen-Fmoc-threonine Kunz 1994, 1997b;Zemplen and Kuntz 1923) 6, the resulting product 12 is sialylated regio-and stereoselectively in the 6-position using of xanthate 11 activated by MeSOTf (Dasgupta and Garegg 1988) in an acetonitrile containing solvent. At low temperature (À65 C), only the kinetically favored equatorial product is formed due to assistance of the nitrile solvent (Braccini et al 1993;Loenn and Stenvall 1992;Schmidt et al 1990). Further transformations include peracetylation of 13 and cleavage of the t-Bu-ester 14 to give the Fmoc-SPPS-building block 15 (Liebe and Kunz 1997a) (Scheme 11.2).…”