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首页> 外文期刊>Chemistry: A European journal >Epimerization of Glycal Derivatives by a Cyclopentadienylruthenium Catalyst: Application to Metalloenzymatic DYKAT
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Epimerization of Glycal Derivatives by a Cyclopentadienylruthenium Catalyst: Application to Metalloenzymatic DYKAT

机译：环戊二烯基钌催化剂对糖基衍生物的差向异构化：在金属酶DYKAT中的应用

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摘要

Epimerization of a non-anomeric stereogenic center in carbohydrates is an important transformation in the synthesis of natural products. In this study an epimerization procedure of the allylic alcohols of glycals by cyclopentadienylruthenium catalyst 1 is presented. The epimerization of 4,6-O-benzylidene-d-glucal 4 in toluene is rapid, and an equlibrium with its d-allal epimer 5 is established within 5 min at room temperature. Exchange rates for allal and glucal formation were determined by 1D ~1H EXSY NMR experiments to be 0.055 s~(-1) and 0.075 s~(-1), respectively. For 4-O-benzyl-l-rhamnal 8 the epimerization was less rapid and four days of epimerization was required to achieve equilibration of the epimers at room temperature. The epimerization methodology was subsequently combined with acylating enzymes in a dynamic kinetic asymmetric transformation(DYKAT), giving stereoselective acylation to the desired stereoisomers 12, 13, and 15. The net effect of this process is an inversion of a stereogenic center on the glycal, and yields ranging from 71% to 83% of the epimer were obtained.
机译：碳水化合物中非异源立体异构中心的差向异构化是天然产物合成中的重要转变。在该研究中，提出了环戊二烯基钌催化剂1对缩醛的烯丙基醇进行差向异构化的方法。 4，6-O-亚苄基-d-葡糖醛4在甲苯中的差向异构反应是快速的，并且在室温下5分钟内建立了与其d-alal差向异构体5的平衡。通过1D〜1H EXSY NMR实验确定的所有和葡萄糖形成的交换速率分别为0.055 s〜（-1）和0.075 s〜（-1）。对于4-O-苄基-1-rhamnal 8，差向异构化的速度较慢，并且需要四天的差向异构化以在室温下实现差向异构体的平衡。该差向异构化方法随后在动态动力学不对称转化（DYKAT）中与酰化酶结合，对所需的立体异构体12、13和15进行了立体选择性酰化。此过程的净效果是将立体异构中心转化为糖基，获得了差向异构体的71％至83％的产率。

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