Synthesis of alkyl coumarate esters by celite-bound lipase of Bacillus licheniformis SCD11501

• A water-free reaction system was successfully employed to synthesize a series of alkyl coumarates by using a celite-immobilized lipase from B. licheniformis strain SCD11501.
• The optimal yields of methyl coumarate (69.0%), ethyl coumarate (63.1%), propyl coumarate (59.8%) and butyl coumarate (55.1%) were obtained.
• A high yield of methyl coumarate was achieved possibly because methyl group may cause relatively less stearic hindrance.
• Addition of molecular sieves to the reaction system had a modulatory effect on the ester synthesis.
• The characterization of synthesized esters was done by FTIR spectroscopy and 1H NMR spectra.

Coumaric acid and its derivatives are known to inhibit UV-induced melanogenesis, skin erythema, angiogenesis, platelet accumulation and osteoclastogenesis besides regulation of bone formation, anti-oxidant and anti-microbial activities. The present study is a novel piece of work in which the syntheses of a series of alkyl coumarates (methyl coumarate, ethyl coumarate, propyl coumarate and butyl coumarate) have been achieved using celite-immobilized lipase of Bacillus licheniformis strain SCD11501 in a water-free medium at 55 °C under shaking in a chemical reactor. The maximum yield(s) of coumaric acid based esters i.e. methyl coumarate (69.0%), ethyl coumarate (63.1%), n-propyl coumarate (59.8%) and n-butyl coumarate (55.1%) using celite-immobilized lipase could be achieved after optimizing various reaction parameters such as incubation time, incubation temperature, relative molar concentration of reactants, biocatalyst concentration and amount of molecular sieves added to the reaction system. Molecular sieves had an important effect on the ester synthesis resulting in an enhanced yield. Maximum yield was recorded for methyl coumarate (69.0%) possibly because methyl group causes less stearic hindrance to the catalytic site of the lipase due to which it becomes more accessible for immobilized lipase to undergo esterification. The characterization of synthesized esters was done through FTIR spectroscopy and 1H NMR spectra.

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