Hydrogen-Bonding-Driven Enantioselective Resolution against the Kazlauskas Rule To Afford γ-Amino Alcohols by Candida rugosa Lipase

Most lipases resolve secondary alcohols in accordance with the “Kazlauskas rule” to give the R enantiomers. In a similar manner to other lipases, Candida rugosa lipase (CRL) exhibits R enantioselectivity towards heptan‐2‐ol, although the enantiomeric ratio (E) is low (E=1.6). However, unexpected enantioselectivity (i.e., S enantioselectivity, E=58) of CRL towards 4‐(tert‐butoxycarbonylamino)butan‐2‐ol, which has a similar chain length to heptan‐2‐ol, has been observed. To develop a deeper understanding of the molecular basis for this unusual enantioselectivity, we have conducted a series of molecular modeling and substrate engineering experiments. The results of these computational and experimental analyses indicated that a hydrogen bond between the Ser450 residue and the nitrogen atom of the carbamate group is critical to stabilize the transition state of the S enantiomer. Enantioselectivity reversal: Candida rugosa lipase (CRL) exhibits unexpected enantioselectivity (i.e., S selectivity, E=58) towards 4‐(tert‐butoxycarbonylamino)butan‐2‐ol. A molecular modeling study suggests that the formation of a hydrogen bond between the Ser450 residue and the carbamate nitrogen atom is essential for the observed selectivity.