Application and limitations of the methyl imidate protection strategy of N-acetylglucosamine for glycosylations at O-4: synthesis of Lewis A and Lewis X trisaccharide analogues

被引:25
作者
Hendel, Jenifer L. [1 ]
Cheng, Anderson [1 ]
Auzanneau, France-Isabelle [1 ]
机构
[1] Univ Guelph, Dept Chem, Guelph, ON N1G 2W1, Canada
基金
加拿大创新基金会; 加拿大自然科学与工程研究理事会;
关键词
Methyl imidate; Lewis A; Lewis X; N-Acetylglucosamine acceptor; Thioglycoside donor; Tricholoroacetimidate donor;
D O I
10.1016/j.carres.2008.08.025
中图分类号
Q5 [生物化学]; Q7 [分子生物学];
学科分类号
071010 ; 081704 ;
摘要
We describe here the synthesis of the allyl Le(3) trisaccharide antigen as well as that of an analogue of the Le(x) trisaccharide antigen, in which the galactose residue has been replaced by a glucose unit. Although successful fucosylations at O-4 of N-acetylglucosamine acceptors have been reported using perbenzylated thioethyl fucosyl donors under MeOTf activation, such conditions led in our case to the conversion of our acceptor to the corresponding alkyl imidates. Indeed, in this synthesis of the Le(3) analogue, we demonstrate that the temporary protection of the N-acetyl group as a methyl imidate is advantageous to fucosylate at O-4. In contrast, we report here that glucosylation at O-4 of an N-acetylglucosamine monosaccharide acceptor using the alpha-trichloroacetimidate of peracetylated glucopyranose as a donor proceeded in better yields under activation with excess BF3 center dot OEt2 than that of the corresponding methyl imidate. Therefore, we conclude that activation of thioglycoside donors by MeOTf to glycosylate at O-4 of a glucosamine acceptor is best accomplished following the temporary protection of the N-acetyl group as a methyl imidate, especially when the donors are highly reactive and prone to degradation. In contrast, if donor and acceptor can withstand multiple equivalents of BF3 center dot OEt2, glycosylations at O-4 of a glucosamine acceptor with a trichloroacetimidate donor does not benefit from the temporary protection of the N-acetyl group as a methyl imidate. (C) 2008 Elsevier Ltd. All rights reserved.
引用
收藏
页码:2914 / 2923
页数:10
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