P-64 含リン脱離基法を用いるO18抗原の合成研究(ポスター発表の部)
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概要
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The β-linked 2-acetamido-2-deoxy-D-mannosides are present in bacterial capsular polysaccharides and lipopolysaccharides. As part of a program to extend the glycosidation method that capitalizes on phosphorus-containing leaving groups, we addressed the stereoselective construction of 2-azido-2-deoxy-β-D-mannosidic linkages by exploiting a direct glycosidation using 2-azido-2-deoxy-D-mannosyl donors. Since TMSOTf-promoted reaction of the 4,6-O-benzylidene-protected mannosyl diethyl phosphite 1 with alcohols furnished mannosides in good yields with high β-selectivities (eq 1), we decided to investigate the glycosidation of 2-azido-3-O-benzy1-4,6-O-benzylidene-2-deoxy-D-mannosyl donors. We found that the modest β-selectivity (α: β=18: 82) could be obtained by the TMSOTf-promoted reaction of diphenyl phosphate 6α with 6-O-unprotected glycoside alcohol 7 in CH_2Cl_2 at -30℃ in the presence of molecular sieves 4A (Table 1). The present glycosidation method offered a facile and high-yielding route to 2-azido-2-deoxy-β-mannosides with a variety of acceptor alcohols, wherein the α: β ratios ranged from 19: 81 to 8: 92 (Table 2). To demonstrate the effectiveness of the present method, we then undertook the synthesis of the repeating unit of the polymeric O antigen isolated from Acinetobacter baumannii serogroup O18. The synthesis commenced with the glycosidation of diphenyl phosphate 6α with 4-O-unprotected galactoside 15, affording the disaccharide in 88% yield with an α: β ratio of 8: 92 (Scheme 3). After separation of the anomers, conversion of the azido group in β-anomer 18 to an acetamide was followed by deprotection of the allyl glycoside and introduction of a diphenyl phosphate as a leaving group to give disaccharide donor 13 in 45% overall yield. Disaccharide acceptor 14 was obtained by the direct glycosidation of 2-acetamido-2-deoxygalactosyl diethyl phosphite 16 with 3-O-unprotected galactoside 17, followed by oxidative deprotection of the MPM ether (Scheme 4). The crucial coupling of 13 with 14 could be attained by the use of TMSClO_4 as a promoter, providing tetrasaccharide 21 in 60% yield (eq 2). Further efforts to improve the efficiency of the coupling reaction between the disaccharides are in progress, and will be reported in the symposium.
- 天然有機化合物討論会の論文
- 2006-09-15
著者
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橋本 俊一
北大院薬
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中村 精一
北大院薬
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在原 僚一
北大院薬
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山田 和弘
北大院薬
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津田 敏史
北大院薬
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橋本 俊一
Fac. Of Pharmaceutical Sciences Hokkaido Univ. Sapporo 060-0812 Jpn
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中村 精一
Faculty Of Pharmaceutical Sciences Hokkaido University
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