Influence of protecting groups on O- and C-glycosylation with neuraminyl and ulosonyl dibutylphosphates
作者:Riku Ogasahara、Shuay Abdullayev、Vikram A. Sarpe、Appi Reddy Mandhapati、David Crich
DOI:10.1016/j.carres.2020.108100
日期:2020.10
The adamantanyl thioglycosides of 5-isothiocyano and 5-azido 5-desamino-4,7,8,9-tetra-O-acetylneuraminic acid methyl ester were converted into the corresponding dibutyl phosphates, which proved to be excellent alpha-selective donors for O-sialidation with a range of typical acceptors, and good donors for reaction with allyltributylstannane, albeit without significant anomeric selectivity. In the KDN series the dibuylphosphate derived from a donor carrying a 4,5-cyclic carbonate protecting group afforded the corresponding C-glycoside with excellent alpha-selectivity on activation in the presence of allyltributylstannane, whereas the corresponding donor carrying acetate esters at the 4and 5-positions was unselective. Overall, it is revealed that while the strongly electron-withdrawing isothiocyanato and azido groups are sufficient to promote highly alpha-selective O-sialidation, they are inadequate when faced with less reactive nucleophiles when mixtures of anomers are obtained.