Synthesis of two analogues of a fragment of the complex polysaccharide C substance from Streptococcus pneumoniae type 1

Abstract The syntheses of two (spacer‐containing and choline‐phosphate‐deficient) analogues ( 12e and 12h , Scheme 2) of a fragment of the C substance from S. pneumoniae type 1 are presented. Starting from 1,6:2,3‐dianhydro‐ß‐D‐talopyranose ( la ), the “building block” 1‐ O ‐(3,6‐di‐ O ‐acetyl)‐2‐azido‐4‐ O ‐benzyl‐2‐deoxy‐ß‐D‐galactopyranosyl)‐2,3,4‐tri‐ O ‐benzyl‐D‐ribitol ( 6b ) was obtained in six steps (Scheme 1). A second “building block” ( 9e ), containing a protected propanolamine spacer, was prepared in five steps, starting from 2,3,4,6‐tetra‐ O ‐acetyl‐α‐D‐glucopyranosyl bromide ( 7 ). The building blocks 6b and 9e were coupled (Scheme 2) using bis (1‐benzotriazolyl) 2‐chlorophenyl phosphate ( 10 ) to give the fully protected phosphotriester derivative 12a . Complete deprotection of compound 12a via two different routes afforded β‐D‐GalNH 2 p ‐(1 ŕ l)‐ribitol‐5‐phosphate‐6‐β‐D–Glc p ‐[1 ŕ O ‐(CH 2 ) 3 ‐NH 2 ] ( 12h , an analogue of structure Ia ) and its β‐D‐GalNA cp derivative 12e (corresponding to Ib ).