Kun Zhang,Zhiyou Pan,Zhoujian Diao,Shuli Liang,Shuangyan Han,Suiping Zheng,Ying Lin
Kinetic resolution of sec -alcohols is a green process with biocatalyst. Candida antarctica lipase B (CALB) displayed on Pichia pastoris cell-surface (Pp-CALB) was characterized in kinetic resolution of sec -alcohols with different structures. The reaction parameters including acyl donors, molar ratio of substrates, solvents and temperatures were examined with 2-octanol as model substrate. 47.4% molar conversion of 2-octanol and 99.7% ee p were obtained after a 5 h reaction with Pp-CALB, and 90% of its original activity still remained after being reused for 10 cycles. Pp-CALB was then used to several sec -alcohols and it showed great enzymatic activity and enantioselectivity to all tested sec -alcohols, more than 93.1% of ee p . The enantioselective characteristics of Pp-CALB catalysed sec -alcohols with different structures were compared with Novozyme 435 which was almost the same. Solvent free system as one way of green chemistry was applied to Pp-CALB and Pp-CALB showed great catalytic activity and enantioselectivity. Pp-CALB was potential biocatalyst of high enzymatic activity and enantioselectivity using in resolution of sec -alcohols.
Graphical A dynamic double kinetic resolution (DDKR) strategy under the co-catalysis of Raney nickel and Candida antarctica lipase B (CAL-B) was established for the one-pot simultaneous resolution of primary amines and secondary alcohols. Herein, we have established a dynamic double kinetic resolution (DDKR) strategy under the co-catalysis of Raney nickel and Candida antarctica lipase B (CAL-B) for the one-pot simultaneous resolution of primary amines and secondary alcohols (or esters). The DDKR strategy was successfully applied to the resolution of a series of racemic amines and secondary alcohols (or esters) as well as mexiletine, an important antiarrhythmic agent. The catalysts could be recycled and reused several times with the same high activity. Scale-up experiments were also successful. As a more atom-economical and efficient process than traditional simple kinetic resolutions, the DDKR strategy can be widely used to prepare optically pure amines and alcohols.
In this paper, uniform H-β nanozeolite microsphere (β-ZMS) prepared by polymerization-induced colloid aggregation, combined with an immobilized lipase B from Candida antarctica (commercially available Novozym® 435), is applied as a racemization catalyst to the one-pot dynamic kinetic resolution (DKR) of aromatic sec -alcohols. The DKRs of various aromatic sec- alcohols can be carried out with high selectivity and conversion under optimum conditions. Importantly, it is found that, compared to commercial zeolites β (C-β), β-ZMSs display high selectivity for small sec- alcohol molecules because their shorter microporous channels reduce the diffusion time of substrate/product in the three-dimensional framework, and thereby decrease the possibility of secondary reactions. However, the β-ZMSs show a high racemization rate in the DKR of large sec- alcohol molecules, such as racemic 1-(1-naphthyl)-ethanol, thanks to their abundant accessible active sites. This observation will not only benefit the performance of acidic zeolite catalysts in one-pot DKR systems but also provide a new perspective on the application of nanozeolites in catalysis.
In this paper, the chiral surfactants bearing two long alkyl chains with hydroxyl groups at their terminals were synthesized and employed to encapsulate a catalytically efficient polyoxometalate through electrostatic interaction. The obtained chiral surfactant-encapsulated polyoxometalate complexes, in which a defined chiral microenvironment surrounds the inorganic cluster, were covalently immobilized into the silica matrix via a sol–gel process. Kinetic resolution of racemic aromatic alcohols was selected as the model reaction to evaluate the chiral supramolecular hybrid catalysts. Up to 89% enantiomeric excess was obtained by varying the reaction conditions. Importantly, the change of loading values of the chiral surfactant-encapsulated polyoxometalates leads to mutative inner microstructures ranging from uniform dispersion to subsequent formation of nanocrystalline domains in the silica matrix. Such a structural evolution differentiates the density and stability of the chiral microenvironment, resulting in a regular change of enantioselectivity of the prepared asymmetric catalysts. Moreover, the fixation of the chiral microenvironment surrounding the polyoxometalates by covalent immobilization was proved to have a promoting effect on enantioselectivity. The present research uncovers the unique effect of immobilization on the kinetic resolution. The strategy helps to understand the influencing factors of enantioselectivity, and provides a convenient and efficient approach for the construction of supramolecular asymmetric catalysts based on chiral surfactant-encapsulated polyoxometalate complexes.
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