Ab Initio Study of Lowest-Energy Conformers of Lewis X (Lex) Trisaccharide
Ab Initio Study of Lowest-Energy Conformers of Lewis X (Lex) Trisaccharide
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Lewis X (Lex) 三糖最低能量构象的从头算研究
DOI：
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发表时间：
2000
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通讯作者：
I. Csizmadia
中科院分区：
文献类型：
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作者：
G. Csonka;C. Sosa;I. Csizmadia
本文首次对Gal-β-1,4-[Fuc-α-1,3]- glcnac -β- och3和Gal-β-1,4-[Fuc-α-1,3]- glcnac -β- oh三糖（Lewis x）在气相中的构象进行了从头计算研究。首先通过MM2*-SUMM构象搜索技术选择它们的最低能量构象。对于这两种相似的化合物，MM2*相对能的顺序不同。在HF/6-31G(d)理论水平上进一步分析了最低能转子（缩醛7个，半缩醛11个）的分子几何形状和能量。从头算方法得到的两种分子的旋转体的能量顺序相同，但前7个旋转体的能量差异相当大：MM2*方法提供0.3 ~ 0.5 kcal/mol，而HF/6-31G(d)方法提供4.5 kcal/mol。在最稳定的MM2*结构中，半乳糖（逆时针方向）和焦（顺时针方向）的氢键链是不连接的。Gal（O6H）是氢键供体(顺时针方向直接…
This paper presents the first ab initio conformational study of the Gal-β-1,4-[Fuc-α-1,3]-GlcNAc-β-OCH3 and Gal-β-1,4-[Fuc-α-1,3]-GlcNAc-β-OH trisaccharides (Lewis x) in the gas phase. Their lowest-energy conformers were selected first by the MM2*-SUMM conformational search technique. MM2* relative energies do not follow the same order for the two similar compounds. The molecular geometries and energies of the lowest-energy rotamers (7 of the acetal and 11 of the hemiacetal) were further analyzed at the HF/6-31G(d) level of theory. The ab initio method yields the same energetic order for the rotamers of the two molecules with considerably larger energetic differences for the first 7 rotamers: the MM2* method provides 0.3−0.5 kcal/mol, whereas the HF/6-31G(d) method provides 4.5 kcal/mol. In the most stable MM2* structures the hydrogen-bonded chains of galactose (in counterclockwise direction) and fucose (in clockwise direction) are not connected. The Gal(O6H) is a hydrogen bond donor (in clockwise direct...