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© Valérie Choumet
Mosquitoes were orally infected with the chikungunya virus. Midguts were dissected at day 5 post-infection, fixed and permeabilised. Virus is shown in red (anti-E2 protein, cyanine 3), the actin network in green (phalloidin 548) and nuclei in blue (DAPI).
Publication : Journal of Carbohydrate Chemistry

First synthesis of a branched pentasaccharide representative of the repeating unit of the Shigella flexneri serotype 5a O-antigen

Scientific Fields
Diseases
Organisms
Applications
Technique

Published in Journal of Carbohydrate Chemistry - 01 Jan 2000

Mulard LA, Ughetto-Monfrin J

J Carbohydr Chem 2000; 19: 193-220

Based on the use of a 2-deoxy-2-trichloroacetamido-D-glucopyranosyl donor, a stepwise synthesis of methyl a-L-rhamnopyranosyl-(l—»3)-2-acetamido-2-deoxy-b-Dglucopyranosyl-(l->2)-a-L- rhamnopyranosyl-(l-»2)-[a-D-glucopyranosyl-(l-»3)]-a-Lrhamnopyranoside (CDA(E)B-OMe, 3) is described. This branched pentasaccharide constitutes a methyl glycoside representative of the repeating unit of the O-antigen of Shigella flexneri serotype 5a. Two routes to 3 were undertaken. Route 1 involved the coupling of a rhamnopyranosyl trichloroacetimidate (7) to a DA(E)B acceptor bearing an N-trichloroacetyl functionality at position 2 of residue D. Transformation of the trichloroacetamide moiety into an acetamide group was performed either by radical dechlorination or by catalytic hydrogenation. In route 2, the latter conversion was performed at the tetrasacchande stage by Zemplen deacylation and subsequent acetylation of the free amino group. Coupling of the resulting DA(E)B to 7 gave the fully protected 2-acetamido pentasacchande intermediate. The reactivity of the two tetrasacchande acceptors differed, the acetamido one requiring harsher coupling conditions. Besides, when perfonned at the tetrasaccharide stage, conversion of the trichloroacetamide group into the desired acetamide group was rather delicate. For these reasons, route 1 was preferred. In any case, distortion of several signals in the C NMR spectra of many synthetic intermediates showed that steric hindrance had a major impact on the outcome of the
glycosylation steps.