4 - Chloro - 3 - Hydroxybutyrate, Enzymatic Resolution And Its Dynamics,

The importance of chiral technology and the progress on the preparation of optical active compounds by lipase were reviewed. The preparation and resolution of ethyl 4-chloro-3-hydroxybutanoate (CHBE) was studied.CHBE is one of the important chiral building blocks which is a useful intermediate to L-camitine. It is reported that microbial, enzymes and BINAP-based Ru catalysts can be used to resolute CHBE. COBE which can be obtained from Aero company is a prochiral carbonyl compound of CHBE. (R.S)-CHBE was synthesized by reduction of COBE with NaBH4.We focused on the resolution of CHBE catalyzed by lipase and the kinetics of the resolution. The resolution of CHBE was realized by using lipase to catalyze the transesterification of CHBE and vinyl acetate. The scheme is :The concentration and enatiomeric excess (ee) of CHBE and the correspondent ester CASE (4-chloro-3-acetoxybutanoate ethyl) were analyzed by gas chromatography which was performed with a flame ionization detector and a glass column(HP Chiral 0.56mm by 25m) of 10%Permethylated B-cyclodextrin.The operational parameters were as follows: oven temperature, 79癈; detector temperature, 250癈; injector temperature, 250'C; nitrogen carrier, 1.3ml/min; hydrogen, 45ml/min; air, 400ml/min; split ratio 100:1.34 lipases were screened, lipase IX was found to be a best one to catalyze the transesterification of CHBE in organic media. The conversion of the substrate CHBE reached 65.9%, the enatiomeric excess (ee) of the substrate and product was 73.7% and 38.09%, respectively.Catalytic behavior of lipase IX was investigated, including the influence oftemperature, agitation, the concentration of substrate and the amount of enzyme.The reaction mechanism was hypothesized to be a ping-pong bi-bi reaction as a whole, disregard the R- and S-enatiomers. The rate equation isIf we take R- and S-enatiomer into consideration, using reversible uni-uni reaction model, the rate equation isThe deaction of the enzyme was considered. The deaction const obtained from the experiment is kdeact=2.0*10"4(min"1).The parameters of the Ping-pong model equation (1) were caculated. Vm=8.55*l(r4mM/min, KA=0.50mM, KB=1.0*10"4, KQA=3.0*l(r3,KBQA=l-0*10"6mM~1. The parameters of the uni-uni model equation (2) were also calculated. const=lmM , num1=1.94mM/min , num2=0.056mM/min , nuni3=0.83mM/irmu num4=0.0061mM/min> coefBr=1.2K coefQr=0.77> coefBs=7.23> coefQS=15.65oThe equation (1) with the parameters substituted was used to expect the concentration of the substrate and product at different substrate concentrations, and get satisfying result.The equations (2) with the parameters substituted was used to expect the concentration of R- and S-substrate at different substrate concentrations. We found that, at relatively low substrate concentration thses equations coincide with the experiment datas well.