Enzymatic catalysis of formation of Z-aspartame in ionic liquid - An alternative to enzymatic catalysis in organic solvents

We present the first report of enzymatic catalysis in an ionic liquid. The virtually nonexistent vapor pressure makes ionic liquids an exciting new al ternative for enzyme-catalyzed syntheses in environmentally friendly enviro nments. Z-aspartame was synthesized in a thermolysin-catalyzed reaction of carbobenzoxy-L-aspartate and L-phenylalanine methyl ester hydrochloride in 1-butyl-3-methylimidazolium hexafluorophosphate (BP6). Ionic liquids such a s BP6 are thermally stable and have a remarkable range of temperatures over which they remain liquid (300 degreesC). With an initial rate of 1.2 +/- 0 .1 nmol min(-1) mg(-1), we observed a competitive rate in comparison to tha t of enzymatic synthesis in organic solvent. Additionally, the enzyme exhib its outstanding stability, which would normally require immobilization.