Catalytic promiscuity of Escherichia coli BioH esterase: Application in the synthesis of 3,4-dihydropyran derivatives

Enzymatic catalytic promiscuity has received increasing attention in the past decade. In this research, ten enzymes were investigated for the promiscuous activity in catalysis of the Michael addition-cyclization cascade reaction of p-nitrobenzalacetone with 1,3-cyclohexanedione to prepare 2-hydroxy-2-methyl-4-(4-nitrophenyl)-3,4,7,8-tetrahydro-2H-chromen-5(6H)-one in anhydrous media, and control experiments were conducted to exclude false positive results. The highest yield (46.1%) was observed with Escherichia coli BioH esterase and the optimal reaction condition was: 1 mmol α,β-unsaturated ketone, 1 mmol 1,3-dicarbonyl compound, 20 mg E. coli BioH esterase, 20 ml N,N-dimethylformamide at 37 °C for 120 h. To preliminarily investigate the mechanism, site-directed mutagenesis was performed on the hydrolysis catalytic triad of BioH, and the results indicated “alternate-site enzyme promiscuity”. When a series of substituted benzalacetones and 1,3-cyclic diketones were used as the reactants, yields of up to 76.3% were achieved. These results imply the potential industrial application of E. coli BioH in the preparation of dihydropyran derivatives.