Efficient Production of (S)-Naproxen with (R)-Substrate Recycling Using an Overexpressed Carboxylesterase BsE-NP01

An (S)-enantioselective esterase from Bacillus subtilis ECU0554, named BsE-NP01, has been cloned and over-expressed in a heterologous host Escherichia coli BL21. BsE-NP01 was shown to be a carboxylesterase with a molecular mass of about 32 kDa, and temperature and pH optima at 50 °C and 8.5, respectively. It could catalyze the selective hydrolysis of the (S)-enantiomer of racemic naproxen methyl ester, giving optically pure (S)-naproxen with 98% enantiomeric excess. A mechanic-grinding approach to substrate dispersion was also reported, which was considered to be an alternative to take the place of deleterious surfactants such as Tween-80, with improved performance of the hydrolysis reaction. Batch production of (S)-naproxen was repeatedly carried out in a solid-water biphasic system at 2-L scale, achieving an average total yield of about 85% after ten runs with complete recycling of (R)-substrate.