Abstract
(R)-mandelic acid is an industrially important chemical, especially used for producing antibiotics. Its chemical synthesis often uses highly toxic cyanide to produce its racemic form, followed by kinetic resolution with 50% maximum yield. Here we report a green and sustainable biocatalytic method for producing (R)-mandelic acid from easily available styrene, biobased L-phenylalanine, and renewable feedstocks such as glycerol and glucose, respectively. An epoxidation-hydrolysis-double oxidation artificial enzyme cascade was developed to produce (R)-mandelic acid at 1.52 g/L from styrene with > 99% ee. Incorporation of deamination and decarboxylation into the above cascade enables direct conversion of L-phenylalanine to (R)-mandelic acid at 913 mg/L and > 99% ee. Expressing the five-enzyme cascade in an L-phenylalanine-overproducing E. coli NST74 strain led to the direct synthesis of (R)-mandelic acid from glycerol or glucose, affording 228 or 152 mg/L product via fermentation. Moreover, coupling of E. coli cells expressing L-phenylalanine biosynthesis pathway with E. coli cells expressing the artificial enzyme cascade enabled the production of 760 or 455 mg/L (R)-mandelic acid from glycerol or glucose. These simple, safe, and green methods show great potential in producing (R)-mandelic acid from renewable feedstocks.
Highlights
Biosynthesis of high-value chemicals from renewable feedstocks for sustainable manufacturing of chemicals has received an increasing attention in attribution to the change of the global climate and oil depletion (Biermann et al 2011; Christensen et al 2008; Tuck et al 2012; Vennestrøm et al 2011)
We report the development of novel artificial enzyme cascades for (R)-MA production from cheap and available styrene, bio-based L-Phe (Fig. 1a), as well as the combination of natural L-Phe biosynthesis pathway and the artificial enzyme cascade for the Scheme 1 Enzyme cascades for the bioproduction of (R)-mandelic acid from L-Phe, glucose or glycerol. a The five-enzyme artificial cascade containing phenylalanine ammonia lyase (PAL), Phenylacrylic acid decarboxylase (PAD), Styrene monooxygenase (SMO), Epoxide hydrolase (StEH), and alditol oxidase (AldO) for the conversion of L-Phe to (R)-MA. b Biotransformation of glycerol or glucose to (R)-MA by combining L-Phe biosynthesis pathway with five-enzyme artificial cascade production of (R)-MA from glucose or glycerol in single strain (Fig. 1b) and coupled cells biotransformation (Fig. 1c), respectively
VLB120 and epoxide hydrolase (StEH) from Solanum tuberosum was developed for converting styrene to (R)-PED
Summary
Biosynthesis of high-value chemicals from renewable feedstocks for sustainable manufacturing of chemicals has received an increasing attention in attribution to the change of the global climate and oil depletion (Biermann et al 2011; Christensen et al 2008; Tuck et al 2012; Vennestrøm et al 2011). The replacement (R)-mandelic acid (MA) is an important and useful chiral molecule for the production of antibiotics such as cephalosporins, semi-synthetic penicillins (Bhatia et al 2014; Jiang et al 2016; Zhang et al 2010), as well as antitumor (Surivet and Vatèle 1999) and anti-obesity agents (Mills et al 1983). It is intensively applied in the resolution of both racemic amines (Kinbara et al 1996) and alcohols (Whitesell and Reynolds 1983) as the chiral resolving agent.
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