Natural deep eutectic solvents are viable solvents for plant cell culture-assisted stereoselective biocatalysis

Abstract

We report a plant (Beta vulgaris L. subsp. vulgaris.) cell culture-mediated reduction of prochiral 1-(3,4-dimethylphenyl)ethanone into the chiral alcohol (1R)-1-(3,4-dimethylphenyl)ethanol in natural deep eutectic solvents (NADES). To the best of our knowledge, this is the first report on plant culture cell behaviour during incubation in these solvents, where the novelty is transformation in callus culture. Three different choline chloride-based NADES (aqueous solutions containing 30, 50 and 80 % water [w/w]) containing sugar (glucose) or polyalcohols (glycerol and ethylene glycol) were screened for conversion and enantiomeric excess during the bioreduction. Both the conversion and the enantiomeric excess differed considerably when using different hydrogen bond donors, with the (R)-alcohol configuration predominating in the reactions conducted in most NADES. Changing the water content in NADES also altered the enantioselectivity. Testing the biocompatibility of NADES with sugar beet cell cultures revealed that NADES cause permeabilisation of cell membranes, leading to stress conditions that change plant metabolism. The potential for recycling and reusing plant biomass was tested for sugar beet cell cultures. The results indicate that recycling may be possible after 3–7 days of incubation, but longer incubations lead to too high a toxicity to cellular metabolism.