Xinqi Xu,Fahui Xu,Jingjing Chen,Shumin Wang,Xialian Wang,Bingmei Su,Lian Xu,Juan Lin
Baeyer-Villiger monooxygenases (BVMOs) can catalyze the asymmetric sulfoxidation to form pharmaceutical prazoles in environmentally friendly approach. In this work, the thermostable BVMO named PockeMO had high sulfoxidation activity towards rabeprazole sulfide to form ( R )-rabeprazole but demonstrated significant overoxidation activity to form undesired sulfone by-product. To address this issue, the enzyme was engineered based on the computer assisted comparison for the substrate binding conformations. A mutant S482Y/L532Q (MU2) was obtained with much alleviated overoxidation activity and enhanced sulfoxidation activity towards rabeprazole sulfide. The catalytic efficiency for ( R )-rabeprazole oxidation decreased 35 folds and increased 40 folds for the sulfoxidation of lansoprazole sulfide. The structural mechanism for the selectivity improvement was illuminated to find a selectivity decision pocket that was conservatively present in BVMOs composed of 4 loops. In upscaled reaction system, the substrate loading for MU2 increased from 40 mM to 100 mM for the synthesis of enantiopure ( R )-rabeprazole. The sulfone content decreased from 16.6 % to 1.2 % compared to PockeMO. Lansoprazole sulfide could also be fully converted into enantiopure ( R )-lansoprazole at 50 mM in 4 h by MU2 while PockeMO almost did not have activity. This work indicated the synthetic applicability of MU2 for active pharmaceutical ( R )-prazoles.
Bingmei Su,Fahui Xu,Jinchang Zhong,Xinqi Xu,Juan Lin
S -omeprazole and R -rabeprazole are important proton pump inhibitors (PPIs) used for treating peptic disorders. They can be biosynthesized from the corresponding sulfide catalyzed by Baeyer-Villiger monooxygenases (BVMOs). During the development of BVMOs for target sulfoxide preparation, stereoselectivity and overoxidation degree are important factors considered most. In the present study, LnPAMO-Mu15 designed previously and TtPAMO from Thermothelomyces thermophilus showed high ( S )- and ( R )-configuration stereoselectivity respectively towards thioethers. TtPAMO was found to be capable of oxidating omeprazole sulfide (OPS) and rabeprazole sulfide (RPS) into R -omeprazole and R- rabeprazole respectively. However, the overoxidation issue existed and limited the application of TtPAMO in the biosynthesis of sulfoxides. The structural mechanisms for adverse stereoselectivity between LnPAMO-Mu15 and TtPAMO towards OPS and the overoxidation of OPS by TtPAMO were revealed, based on which, TtPAMO was rationally designed focused on the flexibility of loops near catalytic sites. The variant TtPAMO-S482Y was screened out with lowest overoxidation degree towards OPS and RPS due to the decreased flexibility of catalytic center than TtPAMO. The success in this study not only proved the rationality of the overoxidation mechanism proposed in this study but also provided hints for the development of BVMOs towards thioether substrate for corresponding sulfoxide preparation.
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