| Abstrakt: |
A new approach to the lipase-catalyzed hydrolytic resolution of ( R, S)-azolyl carbamates for obtaining chiral azolyl carbamates and alcohol is described. With ( R, S)-1-phenylethyl azolyl carbamates as the model substrates, the best reaction condition of using ( R, S)-1-phenylethyl 4-bromopyrazole carbamate ( 1) as the substrate in water-saturated diisopropyl ether at 45 °C is selected. The kinetic constants, and hence enantiomeric ratio of 124, are then estimated from the kinetic analysis by considering the alcohol inhibition effect, with which theoretical time-course conversions for both enantiomers are numerically solved and agree with the experimental data. The thermodynamic parameters −ΔΔ H and −ΔΔ S satisfying a linear enthalpy-entropy compensation relationship of −ΔΔ S = −38.84 + 3.29(−ΔΔ H) are further estimated. An extension of the resolution platform to ( R, S)-4-bromopyrazole carbamates derived from other ( R, S)-alcohols ( 4, 5, 7) is also addressed. [ABSTRACT FROM AUTHOR] |
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