I have spoken about catalytic enzyme reactions in the microwave before, largely in relation to enantioselective options in the synthetic arsenal. It has been a small percentage option for a very long time….and that is largely because unless you dedicate your time to enzyme mechanisms, there is a severe experimental curve — aqueous/or organic solvents, temperature of denaturization or decomposition — and even conformation fit. The general feeling on the street when we come face to face with a resolution need or selective process is that we are going to have to spend weeks with a suite of enzymes (lipases, esterases, etc) to find one or two) — temp, and the like to find hope without a return. It’s enough to bang your head against the hood. And to boot, most chemists accept sensitive reactions with enzymes and sugars (carbohydrates) and small added temperature effects as a bad thing — like there is no energy change within 4-5C — probably forgot their physics.

Not that I have pontificated — here is a book reference where one would start to see approaches taken followed by a  few selected reaction strategies for your interest.

Aqueous Microwave Assisted Chemistry: Synthesis and Catalysis Microwave-assisted enzymatic reactions in aqueous media: Ch 5 Hua Zhao

Org. Biomol. Chem. 2007 Probing the effects of microwave irradiation on enzyme-catalyzed organic tranformations: the case of lipase-catalyzed transesterification reactions. (N. Leadbeater)

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Ind. Eng. Chem. Res., 2014, 53 (21), pp 8706–8713 Microwave Irradiated Lipase Catalyzed Synthesis of Alkyl Benzoate Esters by Transesterification: Mechanism and Kinetic Modeling

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Current Organic Chemistry 2013

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Tett Lett 2013

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Journal of Chemical Technology and Biotechnology 2007

Isoniazid is a useful antitubercular drug widely employed in combination therapy with rifampicin. The synthesis of isoniazid from ethyl isonicotinate and hydrazine hydrate was studied in non-aqueous media via lipase-catalyzed hydrazinolysis under both conventional heating and microwave irradiation by using different supported lipases. Among three different commercial lipases used, namely Novozym 435 (Candida antarctica lipase), Lipozyme RM IM (Rhizomucor miehei lipase) and Lipozyme TL IM (Thermomyces lanuginosus lipase), Novozym 435 was found to be the most effective, with conversion of 54% for equimolar concentrations at 50 °C in 4 h. The rate of reaction as well as final conversion increased synergistically under microwave irradiation in comparison with conventional heating, which showed 36.4% conversion, even after 24 h, for the control experiment. Effects of various process parameters such as speed of agitation, catalyst loading, substrate concentration, product concentration and temperature were studied. A kinetic model is also described.

For my next post I will review the design work in a specific enzyme-catalyzed reaction to provide some takeaways on the things to think about when using a combination of mw and enzyme as a solution to synthetic endeavors. Happy reading!

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