A flexible approach to azasugars: asymmetric total syntheses of (+)-castanospermine, (+)-7-deoxy-6-epi-castanospermine, and (+)-1-epi-castanospermine.
A flexible approach to azasugars: asymmetric total syntheses of (+)-castanospermine, (+)-7-deoxy-6-epi-castanospermine, and (+)-1-epi-castanospermine.
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DOI：
10.1002/chem.200903490
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发表时间：
2010-05
期刊：
影响因子：
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通讯作者：
Gang Liu;Tian-jun Wu;Yuanping Ruan;Pei‐Qiang Huang
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文献类型：
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作者：
Gang Liu;Tian-jun Wu;Yuanping Ruan;Pei‐Qiang Huang
天然氮杂糖（+）-栗精胺、（+）-7-脱氧-6-表栗精胺和合成的（+）-1-表栗精胺的不对称全合成从一个共同的手性结构单元（S）-8开始，经过9 ~ 10步完成。该方法的特点是一个强大的手性中继策略，包括一个高度非对映选择性的乙烯基-Mukaiyama型反应与手性或非手性醛（>或= 95% de; de=非对映异构体过量）和非对映异构体的还原tetramic酸，这允许形成三个连续的立体中心，具有高非对映选择性。该方法还提供了对5-（α-羟烷基）特特拉姆酸（例如17/34）和5-（α-羟烷基）-4-羟基-2-吡咯烷酮（例如18和25/35 a）结构阵列的灵活访问。该方法首次实现了具有挑战性的手性配体A和D，从而以高度对映选择性的方式实现了方案1中所示的概念上有吸引力的逆合成分析。
The asymmetric total synthesis of natural azasugars (+)-castanospermine, (+)-7-deoxy-6-epi-castanospermine, and synthetic (+)-1-epi-castanospermine has been accomplished in nine to ten steps from a common chiral building block (S)-8. The method features a powerful chiral relay strategy consisting of a highly diastereoselective vinylogous Mukaiyama-type reaction with either chiral or achiral aldehydes (> or = 95% de; de=diastereomeric excess) and a diastereodivergent reduction of tetramic acids, which allows formation of three continuous stereogenic centers with high diastereoselectivities. The method also provides a flexible access to structural arrays of 5-(alpha-hydroxyalkyl)tetramic acids, such as 17/34, and 5-(alpha-hydroxyalkyl)-4-hydroxyl-2-pyrrolidinones, such as 18 and 25/35 a. The method constitutes the first realization of the challenging chiral synthons A and D and thus of the conceptually attractive retrosynthetic analysis shown in Scheme 1 in a highly enantioselective manner.