Synthesis of fully protected α-l-fucopyranosyl-(1→2)-β-d-galactopyranosides with a single free hydroxy group at position 2′, 3′ or 4′ using O-(2-naphthyl)methyl (NAP) ether as a temporary protecting group
作者:Zoltán B. Szabó、Anikó Borbás、István Bajza、András Lipták
DOI:10.1016/j.tetasy.2004.11.056
日期:2005.1
Perbenzylated methyl alpha-L-fucopyranosyl-(1-->2)-beta-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-beta-D-galactopyranoside was glyco-sylated 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-beta-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 alpha-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 beta-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. (C) 2004 Elsevier Ltd. All rights reserved.