Synthesis of a trisaccharide‐ribitol‐phosphate analogue of the repeating unit of the complex polysaccharide, C‐substance, from Streptococcus pneumoniae type 1

Abstract

AbstractThe synthesis of analogue 14f (Scheme 2) of a fragment of the S. pneumoniae type 1 C‐substance antigen (Fig. 1, Ia) is presented. The protected disaccharide 5 and trisaccharide 7 (Scheme 1) were prepared by silver trifluoromethanesulfonate‐catalyzed α‐glycosylation of 2c with 4b (54%) and 2d with 6b (59%), respectively. A silver‐silicate‐catalyzed β‐glycosylation of ribitol derivative 9 with trisaccharide bromide 8b gave 10a (55%). The selectively deprotected trisaccharideribitol 10b was coupled with spacer 11 (Scheme 2) using phosphorylating reagent 12 to give the fully protected phosphotriester derivative 14a (98%). The stepwise deprotection of 14a, including conversion of the azide functions into acetamido groups, turned out to be troublesome and afforded 14f in low yield.