Abstract
Biocatalytic oxidations mediated by laccases are gaining importance due to their versatility and beneficial environmental effects. In this study, the oxidation of 1,4-dihydropyridines has been performed using three different types of bacterial laccase-based catalysts: purified laccase from Bacillus licheniformis ATCC 9945a (BliLacc), Escherichia coli whole cells expressing this laccase, and bacterial nanocellulose (BNC) supported BliLacc catalysts. The catalysts based on bacterial laccase were compared to the commercially available Trametes versicolor laccase (TvLacc). The oxidation product of 2,6-dimethyl-1,4-dihydropyridine-3,5-dicarboxylate was obtained within 7–24 h with good yields (70–99%) with all three biocatalysts. The substrate scope was examined with five additional 1,4-dihydropyridines, one of which was oxidized in high yield. Whole-cell biocatalyst was stable when stored for up to 1-month at 4 °C. In addition, evidence has been provided that multicopper oxidase CueO from the E. coli expression host contributed to the oxidation efficiency of the whole-cell biocatalyst. The immobilized whole-cell biocatalyst showed satisfactory activity and retained 37% of its original activity after three biotransformation cycles.
Highlights
Regarded as a green and sustainable technology, biocatalysis has found numerous applications in organic synthesis [1]
A Isolated yield of the product. b CuSO4 was added during the production of the recombinant protein. c Reaction run in the absence of ABTS. d Absence of enzyme and ABTS. e Absence of enzyme, ABTS added
The presence of ABTS as a mediator was proven to be beneficial for the displayed activity of B. licheniformis ATCC 9945aTM laccase (BliLacc) towards DHPy1, with its absence causing a drop in yield by nearly 60% (Table 1, Entry 10)
Summary
Regarded as a green and sustainable technology, biocatalysis has found numerous applications in organic synthesis [1]. Whether in pure form, as part of a cell lysate, or whole cells, enzymes are increasingly being developed as biocatalysts in industrial settings [2]. As such, they can provide substantial reduction of the cost of goods, number of synthetic steps and environmental impact, as well as improved safety and selectivity [3]. Due to the fact that these enzymes only require oxygen as a co-substrate, and they release water as the only by-product laccases have received much interest as suitable biocatalysts in various waste valorization efforts [5] and other biotechnological applications [6,7]. Compared with fungal enzymes, which are frequently used as biocatalysts, bacterial laccases are often more
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