Enzyme-Catalysed Optical Resolution Of Mandelic Acid

Enantiomers of mandelic acid which is also named a-hydroxy styrene, and their derivatives are valuable chemicals which is used as a precursor for the manufacture of semi-synthetic penicillin and cephalosporin. They have been utilized extensively for synthetic purposes as well as stereo-chemical investigations. Enzyme catalysis will get prominence in chiral drug synthesis and purification for their high enantio-selectivity and wide substrate specificity.It was studied that lipase catalyses optical resolution of R-mandelic acid via RS-ethyl mandelate in non-aqueous media. Lipase N435 was screened as catalyst, and tert-butanol as solvent. When lipase N435 was 2.5 g·L^-1, RS-ethyl mandelate was 0.250 mol·L^-1, water to RS-ethyl mandelate was 5:1, temperature was 40℃, the speed of agitation was 200 r/min, the R-ethyl mandelate conversion will reach to 41.6 %, and e.e was 84.0 % after 24 h.Enzyme concentration, RS(-|+)-ethyl mandelate concentration, speed of agitation andtemperature were determined with cross-over method. The best results were: N435 was 3.0 g.L^-1, RS-ethyl mandelate was 0.050 mol·L^-1, temperature was 50 °C, and the speed of agitation was 200 r/min, the R-ethyl mandelate conversion will reach to 45.9 %, and e.e was 85.2 % after 24 h. The reaction rate could be described in terms of the Michaelis-Menten equation with the ordered bi-bi mechanism. Studied inhibition by substrate and product, the kinetic model which follows quasi-steady state was built. The values of the apparent kinetic parameters were computed as : V_max= 186 μmol·(L·min·g enzyme)^-1;K_mA= 0.0434 mol(Lg enzyme)¹;K_mB = 2.67 mol-(L-g enzyme)^-1;K_ia= 0.0126 mol·(L·g enzyme)^-1;K_iq= 0.0144 mol·(L·g enzyme)^-1. Model results were found to fit the initial rate data very well.