Spatial effects of oxovanadium-immobilized mesoporous silica on racemization of alcohols and application in lipase-catalyzed dynamic kinetic resolution
Spatial effects of oxovanadium-immobilized mesoporous silica on racemization of alcohols and application in lipase-catalyzed dynamic kinetic resolution
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DOI：
10.1039/c6cy00257a
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发表时间：
2016-01-01
影响因子：
5
通讯作者：
Akai, Shuji
中科院分区：
文献类型：
--
作者：
Sugiyama, Koji;Oki, Yasuhiro;Akai, Shuji
我们最近报道了一种新的动态动力学拆分（DKR）方法，该方法基于脂肪酶催化外消旋醇的动力学拆分和v - mps3催化低反应性醇对映体的原位外消旋相结合。在V-MPS3中，氧化钒部分共价结合在介孔二氧化硅（MPS）的内表面，孔径约为3 nm。V-MPS3的催化活性远高于相关钒化合物；然而，我们既不能解释其异常高的活性，也不能证实外消旋作用主要发生在V-MPS孔内。因此，在本研究中，我们分别从孔径约为2 nm和4 nm的相应MPS中制备了V-MPS2和V-MPS4，并使用不同分子大小和极性的旋光性醇，比较了它们与V-MPS3的外消旋活性。我们发现V-MPS的孔径大小与底物消旋速率以及MPS孔隙的高极性呈正相关。结果表明，外消旋作用主要发生在V-MPS的孔隙中，而小孔径（2 ~ 4nm）是形成V-MPS极性环境的必要条件，这可能是通过促进钒酸盐中间体的C-O键断裂而加速了外消旋作用。使用孔径适合每种底物的V-MPS，脂肪酶/氧化钒组合催化的DKR可以应用于更广泛的醇类，包括烯丙醇、苯甲酸醇和丙炔醇，以优异的分离收率和对映选择性得到相应的酯类。
We recently reported a new dynamic kinetic resolution (DKR) method based on the combination of lipase-catalyzed kinetic resolution of racemic alcohols and the V-MPS3-catalyzed in situ racemization of less reactive alcohol enantiomers. In V-MPS3, oxovanadium moieties were covalently bound to the inner surface of mesoporous silica (MPS) with a pore size of about 3 nm. The catalytic activity of V-MPS3 was much higher than that of related vanadium compounds; however, we could neither explain its unusually high activity nor confirm that the racemization predominantly occurred inside the V-MPS pores. Therefore, in this study, we prepared V-MPS2 and V-MPS4 from the corresponding MPS with pore diameters of approximately 2 nm and 4 nm, respectively and compared their racemization activities with that of V-MPS3 using some optically active alcohols with different molecular sizes and polarities. We discovered a positive correlation between the pore size of V-MPS and substrate racemization rate as well as the high polarity of the MPS pores. The results suggested that the racemization predominantly occurs in the pores of V-MPS and that a small pore size (2-4 nm) is essential to generate the polar environment of V-MPS, which probably accelerates the racemization by facilitating the C-O bond cleavage of the vanadate intermediates. Using V-MPS with a pore size suitable for each substrate, lipase/oxovanadium combo-catalyzed DKR could be applied to a wider range of alcohols including allyl alcohols, benzylic alcohols, and propargyl alcohols to give the corresponding esters in excellent isolated yields and enantioselectivities.