Partition and substrate concentration effect in the enzymatic synthesis of cephalexin in aqueous two-phase systems (original) (raw)

2010, Process Biochemistry

The kinetically controlled synthesis of cephalexin in aqueous two-phase systems was studied, using immobilized penicillin acylase, 7-amino 3-desacetoxycephalosporanic acid as nucleophile and phenylglycine methyl ester as acyl donor. The organic phases used were 80% (v/v) polyethyleneglycol 400 and 600 and the aqueous phase was 2.5 M (NH 4 ) 2 SO 4 . 7-amino 3-desacetoxycephalosporanic acid and cephalexin partition coefficients were determined at pH 7.4 and 7.8, at 14 • C and 20 • C. Highest partition coefficient for cephalexin was obtained for polyethyleneglycol 400-(NH 4 ) 2 SO 4 at pH 7.4 and 20 • C, while the lowest partition coefficient for 7-amino desacetoxycephalosporanic acid was obtained in the same system at pH 7.8 and 14 • C. No significant effect of pH was observed on conversion yield and productivity of cephalexin synthesis; however, higher values were obtained with polyethyleneglycol 400 as organic phase. Higher conversion yields with both biphasic systems were obtained at the lowest temperature, where product hydrolysis was lower; volumetric productivity was higher for the fully aqueous medium (control), being higher at 20 • C. All parameters of synthesis were improved at higher substrates concentrations, obtaining conversion yields of 78.2% and 65.4%, with 60 mM 7-amino desacetoxycephalosporanic acid for the polyethyleneglycol 400-(NH 4 ) 2 SO 4 system and the control, respectively. (C. Aguirre), aillanes@ucv.cl (A. Illanes).