The lipase-catalysed kinetic resolution of rac-4-phenyl-2-azetidinone was investigated in supercritical carbon dioxide (scCO(2)). Water (0.5 mol equivalent) was used as nucleophilic donor. The effects of pressure and temperature were studied in a batch reactor (internal volume: 30 mL). The optimum pressure and temperature of the beta-lactam ring-opening reaction proved to be 14 MPa and 70 degrees C. Under optimum conditions, full conversion was achieved in 120 h. The resulting (R)-beta-phenylalanine (ee >= 98%) and (S)4-phenyl-2-azetidinone (ee >= 99%) could be easily separated by scCO(2) extraction of the (S)-beta-lactam and subsequent washing of the enzyme with hot water to recover the amino acid. (C) 2010 Elsevier B.V. All rights reserved.