Bacterial pseudaminic acids (Pse)
are present on the surface of many pathogenic
bacteria. Herein, we report a robust methodology for the stereocontrolled
chemical glycosylation of
pseudaminic acid to afford both α- (axial) and β- (equatorial) glycosides reliably
with complete stereoselectivity, using a common glycosyl donor (7<i>N-</i>Cbz/5<i>N</i>-azido Pse thioglycoside) simply by changing the reaction
conditions (DCM-DMF, -40 <sup>o</sup>C and
DCM/MeCN, -78 <sup>o</sup>C, respectively). Examples of such bimodal
selectivity are both sparse and highly sought-after in carbohydrate chemistry.
This method enables efficient access to pseudaminylated molecules, which will
open up various opportunities in chemical glycobiology research of bacterial
pseudaminic acids and carbohydrate-based antibacterial vaccine development.