HYDROPHOBIC VITAMIN-B-12 .12. PREPARATION, CHARACTERIZATION AND ENANTIOSELECTIVE ALKYLATION OF STRAPPED HYDROPHOBIC VITAMIN-B-12
HYDROPHOBIC VITAMIN-B-12 .12. PREPARATION, CHARACTERIZATION AND ENANTIOSELECTIVE ALKYLATION OF STRAPPED HYDROPHOBIC VITAMIN-B-12
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DOI：
10.1039/p29950001175
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发表时间：
1995-06-01
期刊：
影响因子：
--
通讯作者：
NISHIOKA, T
中科院分区：
文献类型：
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作者：
MURAKAMI, Y;HISAEDA, Y;NISHIOKA, T
通过在咕啉B环的外围位置引入1，3-苯二乙酰基部分，对氰钴胺进行了修饰，以提供束缚的疏水性维生素B-12。通过各种光谱方法和循环伏安法对修饰后的配合物进行了表征，并与不含束缚基团的简单疏水维生素B-12的相应数据进行了比较。在甲醇中，疏水维生素B-12衍生物与外消旋3-溴-2-甲基丙酸酯在β-轴位上的烷基化反应进行了研究，并通过H-1 NMR光谱检测了对映选择性的程度。发现束缚的疏水性维生素B-12和简单的疏水性维生素B-12比相应的R-对映体更容易与（S）-3-溴-2-甲基丙酸酯反应;最高的S-选择性（75%. ee）与束缚的疏水维生素B-12一起观察到。通过分子力学和动力学计算，对烷基化疏水维生素B-12进行了构象搜索，从立体化学的角度讨论了S-对映选择性.
Cyanocobalamin has been modified to afford a strapped hydiophobic vitamin B-12 by introducing a 1,3-phenylenediacetyl moiety into the peripheral site-of the corrin's B ring. The modified complex was characterized by various spectroscopic methods and cyclic voltammetry in comparison with the corresponding data for a simple hydrophobic vitamin B-12 without a strapping moiety, The alkylation of hydrophobic vitamin B-12 derivatives with racemic 3-bromo-2-methylpropionic esters at the beta-axial site was carried out in methanol, and extents of the enantioselectivity were examined by H-1 NMR spectroscopy. The strapped hydrophobic vitamin B-12 and a simple hydrophobic vitamin B-12 were found to react with (S)-3-bromo-2-methylpropionates more readily than the, corresponding R-enantiomers; the highest S-selectivity (75%. ee) was observed with the strapped hydrophobic vitamin B-12. The S-enantioselectivity was discussed from a stereochemical viewpoint based on the conformational search for the alkylated hydrophobic vitamin B-12 by means of molecular mechanics and dynamics calculations.