Synthesis of cephalexin in organic medium at high substrate concentrations and low enzyme to substrate ratio

Abstract

The kinetically controlled synthesis of cephalexin (CEX) in ethylene glycol (EG) was previously optimized at moderate substrate concentrations and high enzyme to substrate ratio, obtaining yields close to stoichiometric. However, substrate concentrations were low and enzyme loads high enough for production purpose. The synthesis of cephalexin in 40% (v/v) ethylene glycol at 20 °C and pH 7.0 with glyoxyl-agarose immobilized penicillin acylase (GAPA) was studied at high substrates concentrations to the point of saturation and beyond. Phenylglycine methyl ester (PGME) was the acyl donor at a molar ratio of 3 with respect to nucleophile. At initially homogeneous conditions with nucleophile concentration close to its solubility and at low enzyme to substrate ratio, productivity increase eight times and specific productivity five times with respect to a control at moderate substrates concentrations and high enzyme to substrate ratio. At initially heterogeneous conditions with partially undissolved nucleophile and low enzyme to substrate ratio, increases in productivity and specific productivity were eleven and seven times, respectively. The biocatalyst was very stable under reaction conditions, so that a very high global productivity is anticipated, making the enzymatic process competitive with existing chemical synthesis.