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本通过对几种拆分手性药物的方法的列举,比较几种方法,详细介绍了几种方法的特点,以及它们的不同作用。各个方法中又列出了不同的线索,根据这些线索来研究这几种拆分的方法,它们的优缺点以及针对这些缺点的解决方法,最后给出了几个典型的用该方法的实验,以辨别它们的效用。 相似文献
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Vitamin B12 (cobalamin) is among the largest known non-polymeric natural products, and the only vitamin synthesized exclusively by microorganisms. The biosynthesis of the lower ligand of vitamin B(12), 5,6-dimethylbenzimidazole (DMB), is poorly understood. Recently, we discovered that a Sinorhizobium meliloti gene, bluB, is necessary for DMB biosynthesis. Here we show that BluB triggers the unprecedented fragmentation and contraction of the bound flavin mononucleotide cofactor and cleavage of the ribityl tail to form DMB and D-erythrose 4-phosphate. Our structural analysis shows that BluB resembles an NAD(P)H-flavin oxidoreductase, except that its unusually tight binding pocket accommodates flavin mononucleotide but not NAD(P)H. We characterize crystallographically an early intermediate along the reaction coordinate, revealing molecular oxygen poised over reduced flavin. Thus, BluB isolates and directs reduced flavin to activate molecular oxygen for its own cannibalization. This investigation of the biosynthesis of DMB provides clarification of an aspect of vitamin B12 that was otherwise incomplete, and may contribute to a better understanding of vitamin B12-related disease. 相似文献
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针对多年来农业院校传统的普通化学实验课教学,进行了教学模式、教学内容、考核方式和实验管理体系等全方位的改革探索和实践.结果表明,经过实验教学改革与实践使学生的实验基本技能、综合素质能力和实验水平有了很大的提高,取得了满意的教学效果. 相似文献
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