Biocatalyzed irreversible esterification in the preparation of S-naproxen

Dimethyl carbonate was used as alcohol donor in the esterification of naproxen in the presence of immobilised lipase B from Candida antarctica (Novozym 435). The conjugation of hydrolysis of dimethyl carbonate and esterification of acid, created irreversible operative conditions so permitting the recovery of S-naproxen in high ee (>98%). The adopted procedure has a general use.