Candida antarctica lipase B-catalyzed hydrolysis of carbocyclic 5–8-membered cis β-amino esters was carried out in green organic media, under solvent-free and ball-milling conditions. In accordance with the high enantioselectivity factor (E > 200) observed in organic media, the preparative-scale resolutions of β-amino esters were performed in tBuOMe at 65 °C. The unreacted β-amino ester enantiomers (1R,2S) and product β-amino acid enantiomers (1S,2R) were obtained with modest to excellent enantiomeric excess (ee) values (ees > 62% and eep > 96%) and in good chemical yields (>25%) in one or two steps. The enantiomers were easily separated by organic solvent/H2O extraction.
An efficient and novel enzymatic method has been developed for the synthesis of β-fluorophenyl-substituted β-amino acid enantiomers through lipase PSIM (Burkholderia cepasia) catalyzed hydrolysis of racemic β-amino carboxylic ester hydrochloride salts 3a–e in iPr2O at 45 °C in the presence of Et3N and H2O. Adequate analytical methods were developed for the enantio-separation of racemic β-amino carboxylic ester hydrochlorides 3a–e and β-amino acids 2a–e. Preparative-scale resolutions furnished unreacted amino esters (R)-4a–e and product amino acids (S)-5a–e with excellent ee values (≥99%) and good chemical yields (>48%).
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