The hexasaccharide repeating unit corresponding to the capsular polysaccharide of
Streptococcus pneumoniae type 7A has been synthesized in good yield using [3+2+1] block synthetic strategy.
The synthetic strategy involved a number of challenging stereoselective glycosylation
steps, which include β-selective glycosylation of l-rhamnosyl thioglycoside donor, α-selective glycosylations of 2-azido-2-deoxy-d-glucopyranosyl thioglycoside donor and d-galactopyranosyl donor together with the formation of β-glycoside of d-galactosamine moiety and α-glycoside of l-rhamnosyl moiety. Suitably functionalized thioglycosides have been used as glycosyl
donors and a combination of N-iodosuccinimide (NIS) and trimethylsilyl trifluoromethanesulfonate (TMSOTf) has
been used as glycosylation promoter.
Key words
carbohydrates - glycosylation - glycoside - oligosaccharide - synthesis -
Streptococcus pneumoniae
