Research On Chemoenzymatic Production Of(R)-ethyl-2-(4-hydroxy-Phenoxy) Propanoate

(R)-ethyl-2-(4-hydroxyphenoxy)propionate((R)-EHPP)is key intermediate in the synthesis of aryloxyphenoxy propionate(APP)herbicides which were wildly used for the control of annual and perennial grasses in broadleaf crop field.The chiral APP herbicides have become more attractive recently due to features of safety,high effectiveness and low toxicity.Currently,Chemical routes are the main method for preparation of(R)-EHPP with strict operation condition?Serious environmental pollution and low purity.The use of biocatalysts for the industrial synthesis of chemicals has been attracting much attention as an environment-friendly synthetic method.Compared with chemical catalysts,whole-cell biocatalysts can be much more readily and inexpensively prepared on an industrial scale with better stability and adaptability.Chemical synthesis method of(R,S)-EHPP was established with hydroquinone and(R,S)-ethyl-2_chloropropionate as raw materials firstly in this paper,Major reaction parameters were investigated.The optimized reaction conditions were as follows:Hydroquinone(4.4 g,40 mmol)was dissolved in a solution of KOH(2.24 g,40 mmol)in 20 mL DMSO under N2 atmosphere,(R,S)-ethyl-2-chloropropionate(2.73 g,20 mmol)was then added dropwise at 0?.The mixture was kept at 30?35? for 4h,the yield of(R,S)-EHPP was about 69.8%,which was calculated based on(R,S)-ethyl-2-chloropropionate.Lyophilized mycelium of Aspergillus oryzae WZ007 was successfully developed to enantioselective hydrolysis of(R,S)-EHPP for production of(R)-EHPP in this paper.The key biocatalytic process parameters(cosolvent,temperature,pH,buffer ion concentration,rotation speed and substrate concentration)were optimized.The optimized reaction conditions were as follows:the concentration of substrate and A.oryzae WZ007 were 0.5 moll/L and 20 g/L,respectively.The reaction mixture was shaken(250 rpm)in a water bath shaking bed at 30? for 2h.the optical purity of(R)-EHPP was improved up to>99%when the conversion was above 50%.Further,we found dry mycelium of A.oryzae WZ007 maintains over 80%of its initial activity after eight repeating cycles.Finally,A 200 mL scale reaction was done under optimized reaction conditions,in order to explore high substrate concentration(0.25 mol/L)recycling reaction.Then an economical and efficient process was determined.Firstly,(R)-EHPP and(S)-2-(4-hydroxyphenoxy)propionic acid((S)-HPOPS)were separated and extracted by ethyl acetate,based on chemical properties between them,then the useless((S)-HPOPS)was racemized through chemical method,The e.e.t value 10%and yield 92%was obtained under the appropriate condition,and achieving a total yield of about 70.9%and a high optical purity of about 99.0%(based on(R,S)-EHPP)after four runs with recycling of(S)-HPOPS.