Expedient Synthesis of an Anomerically Modified Trisaccharide Component of the Capsular Polysaccharide from Streptococcus pneumoniae Type 19F
1995; Oxford University Press; Volume: 68; Issue: 5 Linguagem: Inglês
10.1246/bcsj.68.1449
ISSN1348-0634
AutoresEisuke Kaji, Eiko Matsui, Mie Kobayashi, Shonosuke Zen,
Tópico(s)Legume Nitrogen Fixing Symbiosis
ResumoA practical stereoselective synthesis is described for α-D-ManNAc-(1→4)-α-D-Glc-(1→2)-L-Rha, an anomerically modified trisaccharide component of the capsular polysaccharide of Streptococcus pneumoniae type 19F. The key intermediary disaccharide, 2-(benzoyloxyimino)-2-deoxyglycosyl-α(1→4)-glucoside, was prepared by α-selective glycosylation (AgOTf–TMU/CH2Cl2, 90%) of a suitably blocked p-methoxybenzyl 2,3,6-tri-O-benzyl-β-D-glucopyranoside with 3,4,6-tri-O-benzoyl-2-(benzoyloxyimino)-2-deoxy-α-D-arabino-hexopyranosyl bromide, and converted into an α-D-ManNAc-(1→4)-α-D-Glc-(1→MBn) derivative by means of a manno-selective reduction (BH3·THF → Ac2O, 55%). Consecutive anomeric activation (1-OMBn → 1-OH → 1-F, 45% over 2 steps), glycosylation (SnCl2–AgClO4/CH2Cl2, 71%, α : β = 2 : 1) of 2-OH of benzyl 3,4-di-O-benzyl-α-L-rhamnopyranoside, and deblocking (NaOMe → Pd-C/H2, 90%) gave the target trisaccharide.
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