An integrated process for the production of toxic catechols from toxic phenols based on a designer biocatalyst

We describe the biocatalytic production of 3‐phenylcatechol from 2‐phenylphenol with the whole cell biocatalyst Escherichia coli JM101 (pHBP461). The recombinant produces 2‐hydroxybiphenyl 3‐monooxygenase, an enzyme from Pseudomonas azelaica HBP1. This enzyme introduces a hydroxyl‐group at the C 3 ‐position of a variety of 2‐substituted phenols, such as 2‐phenylphenol. This permits the biocatalytic production of 3‐substituted catechols, which are difficult to synthesize chemically. Both 2‐phenylphenol and 3‐phenylcatechol are highly toxic to E. coli. The toxic effects of 2‐phenylphenol were minimized by feeding this substrate to the reactor at a rate slightly below the maximum biooxidation rate. As a result, the substrate concentration in the reactor remained below toxic levels during the bioconversion. The toxic product formed was removed by continuous adsorption on the solid resin Amberlite™ XAD‐4. To this end the reaction mixture, containing the biocatalyst, was pumped continuously through an external loop with a fluidized bed of the resin. This resin efficiently and quantitatively adsorbed both 3‐phenylcatechol and the remaining trace amounts of 2‐phenylphenol. Consequently, the concentrations of these compounds were kept at subtoxic levels (below 100 mg L −1 ) and gram amounts of 3‐phenylcatechol were produced with space–time yields of up to 0.39 g L −1 h −1 . The product was recovered from the resin by acidic methanol elution and purified by recrystallization from n ‐hexane resulting in overall yields exceeding 59%. The optimized system served as a surprisingly simple and efficient integrated process, that allows the bioconversion of toxic substrates to toxic products with whole cell biocatalysts. © 1999 John Wiley & Sons, Inc. Biotechnol Bioeng 62: 641–648, 1999.