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[摘要]：The biantennary complex-type N-glycans bearing LacNAc and LacdiNAc as the nonreducing end motif were synthesized in a protected form suitable to use in the Fmoc solid-phase peptide synthesis studies. Two approaches for the nonasaccharide synthesis were examined by taking advantage of the highly beta-selective glycosylation with GlcNTCA (N-phenyl)trifluoroacetimidate. An earlier approach, which involved the reaction of the trisaccharide donor (Gal-GlcNTCA-Man) and trisaccharide acceptor (Man-GlcNPhth(2)-N-3), produced a mixture of nonasaccharide isomers. On the other hand, mannosylation of the trisaccharide acceptor (Man-GlcNPhth(2)-N-3) stereoselectively afforded the known pentasaccharide (Man(3)-GlcNPhth(2)-N-3), which was reacted with the disaccharyl glycosyl donor (Gal-GlcNTCA or GalNTCA-GlcNTCA) to produce the desired nonasaccharide as a single stereoisomer. Selective dephthaloylation followed by N-acetylation furnished the GlcNAc(2) functionality. The resulting nonasaccharyl azides were condensed with Fmoc-Asp(OPfp)-OBut or Fmoc-Asp(OPfp)-OPac in the presence of Ph(CH3)(2)P and HOOBt. Finally, the Zn reduction and cleavage of the tert-butyl ester or Zn reduction alone produced the targeted nonasaccharyl Asn building blocks. |
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