Abstract
Hydrophilic ionic liquids (ILs) were employed as green solvents to construct an IL-containing co-solvent system for improving the asymmetric reduction of 4-(trimethylsilyl)-3-butyn-2-one by immobilized Candida parapsilosis cells. Among 14 hydrophilic ILs examined, 1-(2′-hydroxyl)ethyl-3-methylimidazolium nitrate (C2OHMIM·NO3) was considered as the most suitable IL for the bioreduction with the fastest initial reaction rate, the highest yield and the highest product e.e., which may be due to the good biocompatibility with the cells. For a better understanding of the bioreduction performed in the C2OHMIM·NO3-containing co-solvent system, the effects of several crucial variables were systematically investigated. The optimal C2OHMIM·NO3 content, substrate concentration, buffer pH, co-substrate concentration and temperature were 10% (v/v), 3.0 mmol/L, 5.0, 98.1 mmol/L and 30°C, respectively. Under the optimal conditions, the initial reaction rate, the maximum yield and the product e.e. were 17.3 µmol/h gcell, 95.2% and >99.9%, respectively, which are much better than the corresponding results previously reported. Moreover, the immobilized cells remained more than 83% of their initial activity even after being used repeatedly for 10 batches in the C2OHMIM·NO3-containing system, exhibiting excellent operational stability.
Highlights
Silicon-containing compounds play an important role in asymmetric synthesis and functional materials, and in the preparation of silicon-containing drugs, such as Zifrosilone, Cisobitan and TAC-101{4-[3,5-bis(trimethylsilyl)benzamido] benzoic acid} [1,2,3]
In order to explore the effect of ionic liquids (ILs) with different combination of cation and anion, the bioreduction of TMSB to (S)-TMSBOL with immobilized C. parapsilosis cells were conducted in various hydrophilic IL-containing co-solvent systems
In the BF42-based IL-containing co-solvent systems, the substrate TMSB disappeared completely after reaction for 1 h without any desired product TMSBOL found in the reaction medium
Summary
Silicon-containing compounds play an important role in asymmetric synthesis and functional materials, and in the preparation of silicon-containing drugs, such as Zifrosilone, Cisobitan and TAC-101{4-[3,5-bis(trimethylsilyl)benzamido] benzoic acid} [1,2,3]. These silicon-containing compounds generally possess greater pharmaceutical activity, higher selectivity and lower toxicity than their carbon counterparts due to the unique physical and chemical characteristics of the silicon atom, such as its larger atomic radius and smaller electronegativity than the carbon atom [4]. The major advantages of using whole cells rather than isolated enzymes as the biocatalysts are that cells provide a natural environment for the enzymes, preventing conformational changes in the protein structure that would lead to loss of activity in nonconventional medium, and are able to efficiently regenerate cofactors [8]
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