| Abstract
| - 5-[4-(1-Hydroxyethyl)phenyl]-10,15,20-triphenylporphyrin (1a) and zinc porphyrin 1b were designedand synthesized to experimentally examine the validity of the transition-state model previouslyproposed for the lipase-catalyzed kinetic resolution of secondary alcohols. The lipases fromPseudomonas cepacia (lipase PS), Candida antarctica (CHIRAZYME L-2), Rhizomucor miehei(CHIRAZYME L-9), and Pseudomonas aeruginosa (lipase LIP) exhibited excellent enantioselectivity(E>100 at 30 °C). Subtilisin Carlsberg from Bacillus licheniformis (ChiroCLEC-BL) also showedhigh enantioselectivity for 1a (E = 140 at 30 °C), and the thermodynamic parameters weredetermined: ΔΔH⧧ = −6.8 ± 0.8 kcal mol-1, ΔΔS⧧ = −13 ± 3 cal mol-1 K-1. Lipases and subtilisinshowed R- and S-preference for 1, respectively. The mechanisms underlying the experimentalobservations are explained in terms of the transition-state models. The large secondary alcohol 1is a powerful tool for investigating the conformation of the transition state of the enzyme-catalyzedreactions. The fact that 1 was resolved with high enantioselectivity strongly suggests that the gaucheconformation, but not the anti conformation, is taken in the transition state, in agreement withthe transition-state models involving the stereoelectronic effect.
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