A chemo-enzymatic transformation of linalyl acetate to estragole, a phenyl propanoid ether using recombinant esterase in acetone reaction system

Abstract

The esterase gene from Bacillus subtilis E9 was expressed in E. coli BL21 (DE3) using the pTAC Bs-est recombinant plasmid and the enzyme was purified to determine its biocatalytic ability on the natural ester, linalyl acetate. The substrate affinity of the esterase enzyme was confirmed through docking studies on the interaction between the modelled esterase protein with the ligand. Recombinant esterase transformed linalyl acetate both in buffer and acetone containing reaction system to an alcohol, linalool through hydrolysis within four hours of incubation. This enzymatic hydrolysis involved the release of acetic acid, making the environment acidic. However, after 20 h of enzyme treatment, unlike that of aqueous reaction system, in acetone reaction system this acid condition favoured further chemical conversion of linalool to a cyclic phenyl propanoid ether, estragole. The presence of organic solvent-acetone in the reaction phase could have contributed to the structural modification of the enzyme, facilitating the hydrolysis of linalyl acetate to form linalool and further cyclization to estragole. The overall substrate conversion rate of linalyl acetate to the transformed products, linalool and estragole in acetone containing reaction system was 84 %.