The synthesis of the tetrasaccharide repeating unit of the O-antigen of Escherichia coli O163 as its p-methoxyphenyl (PMP) glycoside was achieved followed by sequential glycosylation strategy through thioglycoside activation using sulfuric acid immobilized on silica (H 2 SO 4 -silica) in conjunction with N-iodosuccinimide as a Brønsted acid catalyst. The application of one-pot reaction conditions for two glycosylations and in situ PMB-group removal reduced the number of reaction steps significantly. The L-QuipNAc building block was obtained from known carbohydrate L-rhamnose precursors. The stereoselective outcomes of all glycosylation reactions were found to be very good. A late-stage TEMPO-mediated oxidation was performed for the formation of required uronic acid moiety. An analogue of the target tetrasaccharide was also prepared by using one-pot glycosylation approach. Such synthetic oligosaccharides could later be effectively conjugated with an appropriate protein to furnish glycoconjugate derivatives for their use in immunochemical studies.
We herein report a chemo-and regioselective 6-exo-dig catalytic cyclization of Ugi adducts N-substituted 2alkynamides to access functionalized morpholinone glycoconjugates in the presence of triphenylphosphine. This array allows an interesting multicomponent access to a library of functionalized morpholinone glycoconjugates under mild reaction conditions with regeneration of catalyst triphenylphosphine, supported by 31 P nuclear magnetic resonance studies. Density functional theory shows the 6-exo-dig oxocyclization pathway is preferred, which supports our experimental observation.Letter pubs.acs.org/OrgLett
Pentasaccharide moiety of starfish asterosaponin luidiaquinoside has been synthesized using sequential glycosylation strategy and its conformational analysis was carried out.
Direct triphenylphosphine mediated regioselective sulfenylation of glycals by using cheap and easily available various aryl sulfonyl chlorides as a sulfur source to generate different C2-S-aryl-glycosides was developed. Notably, features of...
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