192706-01-7Relevant academic research and scientific papers
Synthesis of a single repeat unit of type VIII group B Streptococcus capsular polysaccharide
Eichler, Eva,Jennings, Harold J.,Whitfield, Dennis M.
, p. 385 - 411 (2007/10/03)
We have synthesized a single repeat unit of type VIII Group B Streptococcus capsular polysaccharide, the structure of which is {L-Rhap(ss1-→4)-D-Glcp(ss1→4)[Neu5Ac(α2→3)]-D- Galp(ss1→4)}n. The synthesis presented three significant synthetic challenges namely: the L-Rhap(ss1→4)-D-Glcp bond, the Neu5Ac(α2→3)-D-Galp bond and 3,4-D-Galp branching. The L-Rhap bond was constructed in 60% yield (α:ss 1:1.2) using 4-O-acetyl-2,3-di-O-benzoyl-α-L-rhamnopyranosyl bromide 6 as donor, silver silicate as promotor and 6-O-benzyl-2,3-di-O-benzoyl-1-thio-ss-D-glucopyranoside as acceptor to yield disaccharide 18. The Neu5Ac(α2→3) linkage was synthesized in 66% yield using methyl [phenyl 5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-2-thio-D-glycero-D-galacto- nonulopyranosid]onate as donor and triol 2-(trimethylsilyl) ethyl 6-O-benzyl-ss-D-galactopyranoside as acceptor to give disaccharide 21. The 3,4-D-Galp branching was achieved by regioselective glycosylation of disaccharide diol 21 by disaccharide 18 in 28% yield to give protected tetrasaccharide 22. Tetrasaccharide 22 was deprotected to give as its 2-(trimethylsilyl)ethyl glycoside the title compound 1a. In addition the 2-(trimethylsilyl)ethyl group was cleaved and the tetrasaccharide coupled by glycosylation (via tetrasaccharide trichloroacetimidate) to a linker suitable for conjugation.
