STEREOSELECTIVE HYDROLYSIS BY ESTERASE - A STRATEGY FOR RESOLVING 2-(R,R'-PHENOXY)PROPIONYL ESTER RACEMATES

The stereoselective hydrolysis of 2-(R,R'-phenoxy)propionyl esters by carboxylesterase NP was investigated under different experimental cond itions to verify if their chiral resolution could be performed by this procedure. The reaction was performed on methyl, ethyl, isopropyl, is obutyl and benzyl esters 3-12 of 2-(3-methylphenoxy)propionic and 2-(2 ,3-dimethylphenoxy)propionic acids 1 and 2 in aqueous media and the co nversion was monitored by chiral HPLC analysis versus the reaction tim e. The best substrate for the biocatalytic resolution was the S enanti omer for the monomethyl-substituted compounds and the R enantiomer for the dimethyl-substituted ones. The 2-(3-methylphenoxy)propionyl ester s 3-7 hydrolyzed to a greater extent than the 2-(2,3-dimethylphenoxy)p ropionyl esters 8-12. The hydrolysis of isobutyl (6 and 11) and benzyl (7 and 12) derivatives suffered from poor enantioselectivity and long reaction times; this could be attributed to the steric hindrance (due to the non-acylic moiety) of interaction of the substrates with the a ctive site of the enzyme. Changes of pH (6.0, 7.2, 8.0), temperature ( 23 degrees and 37 degrees C) and substrate/enzyme ratio (S/enz = 250, 50, 25, 10) were assayed. The optimum for biocatalytic resolution was obtained when methyl ester 3 and isopropyl ester 10 were hydrolyzed at pH 7.2, 23 degrees C and S/enz 50. Finally the scaling up to preparat ive amounts of the enzymatic hydrolysis of 3 and 10 permitted us to ob tain satisfactory quantities of the acids 1 and 2 and the residual est ers with a good optical yield.