AN EFFICIENT SYSTEM FOR THE ASYMMETRIC ACYLATION OF (R,S)-3-n-BUTYLPHTHALIDE CATALYZED BY NOVOZYME 435

Abstract

Novozyme 435 could be a highly efficient catalyst in the asymmetric acylation of (R,S)-3-n-butylphthalide in tetrahydrofuran–hexane solvents. The effect of various reaction parameters such as agitation velocity, water content, mixed media, temperature, concentration of Novozyme 435, molar ratio of acetic anhydride to (R,S)-3-n-butylphthalide, reaction time, enantiomeric excess of substrate (eeS), enantiomeric excess of product (eeP), and enantioselective ratio (E) were studied. Tetrahydrofuran markedly improved (R,S)-3-n-butylphthalide conversion, enantiomeric excess of remaining 3-n-butylphthalide, and enantiomeric ratio. The optimum media were 50% (v/v) tetrahydrofuran and 50% (v/v) hexane. Other ideal reaction conditions were an agitation velocity of 150 rpm, 0.4% (v/v) water content, temperature of 30°C, 8 mg/mL dosage of Novozyme 435, 8:1 (0.4 mmol: 0.05 mmol) molar ratio of acetic anhydride to (R,S)-3-n-butylphthalide, and a reaction time of 48 hr. Under the optimum conditions, 96.4% eeS and 49.3% conversion of (R,S)-3-n-butylphthalide were achieved. In addition, enantiomeric excess of the product was above 98.0%.