Add time:09/01/2019         Source:sciencedirect.com

Perbenzylated methyl α-l-fucopyranosyl-(1→2)-β-d-galactopyranosides having a single free OH group at position C-2′, C-3′ or C-4′ have been synthesized. Methyl 3,4,6-tri-O-benzyl-β-d-galactopyranoside was glycosylated either with phenyl 3,4-di-O-benzyl-2-O-(2-naphthyl)methyl-, phenyl 2,4-di-O-benzyl-3-O-(2-naphthyl)methyl- or phenyl 2,3-di-O-benzyl-4-O-(2-naphthyl)methyl-1-thio-β-l-fucopyranoside. The 2-ONAP ether functioned well as a non-participating group. The yields of the glycosylation reactions, promoted by NIS/TfOH, were above 80% and the stereoselectivity was 8:1 to 10:1 in favour of the α-anomers. The 2-ONAP ether was obtained by (2-naphthyl)methylation, the 3-ONAP and the 4-ONAP ethers were prepared either by hydrogenolysis of the 3,4-O-(2-naphthyl)methylene acetals of β-l-fucopyranoside or by tin acetal-mediated alkylations. The latter procedure afforded higher yields. The ONAP ethers from the disaccharides were removed by oxidative cleavage with DDQ.

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