Abstract
This work describes the chemoselective bioreduction of (1E,4E)-1,5-bis(4-methoxyphenyl)-1,4-pentadien-3-one (1) mediated by baker's yeast (BY, Saccharomyces cerevisiae cells) in an aqueous/organic solvent biphasic system. The biotransformation of this compound was chemoselective and formed only the corresponding saturated ketone 1,5-bis(4-methoxyphenyl)-3-pentanone (2). The influence of various factors which may alter the bioreduction of 1, such as the type and percentage of co-solvents, use of six different S. cerevisiae yeast samples (four commercial and two industrial), variations in the substrate and yeast concentrations, temperature, pH and volume of aqueous and organic phases, was investigated. The best reaction conditions were 66.7 g L-1 of Fleischmann BY, 8.3 × 10-3 mol L-1 of substrate, pH 6.5 at 35 oC in the presence of 2.5% (v/v) of N,N-dimethyl sulfoxide (DMSO) as an additive and a Vaq/Vorg ratio of 70/30. Under these conditions, the product 2 was recovered in conversions of 82% in 5 h reaction.
Highlights
The use of whole cells or isolated enzymes in organic chemistry to mediate the reduction of ketones, β-ketoesters, imines and α,β-unsaturated systems with C=C activated by strongly polarizing groups such as nitro, carbonyl or hydroxyl groups is the subject of extensive study.[1,2,3,4,5,6]
It is well known that biotransformation of an α,β-unsaturated carbonyl compound in many cases gives a mixture of saturated ketone or aldehyde, saturated alcohol or allylic alcohol, indicating that several enzymes may catalyze the reduction of C=C and C=O double bond competitively
In the first step of this study, (1E,4E)-1,5-bis(4methoxyphenyl)-1,4-pentadien-3-one (1) was synthesized by the aldol condensation reaction between the 4-methoxybenzaldehyde and acetone under basic conditions. This compound was used as a substrate in the bioreduction reaction using S. cerevisiae cells in aqueous/ organic solvent biphasic systems formed with n-hexane and potassium phosphate/citric acid buffer
Summary
The use of whole cells or isolated enzymes in organic chemistry to mediate the reduction of ketones, β-ketoesters, imines and α,β-unsaturated systems with C=C activated by strongly polarizing groups such as nitro, carbonyl or hydroxyl groups is the subject of extensive study.[1,2,3,4,5,6] It is well known that biotransformation of an α,β-unsaturated carbonyl compound in many cases gives a mixture of saturated ketone or aldehyde, saturated alcohol or allylic alcohol, indicating that several enzymes may catalyze the reduction of C=C and C=O double bond competitively. Different strategies to improve the conversion into product, varying the substrate and yeast concentrations, temperature, pH, and volume of aqueous and organic phases, were considered.
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