5-[4-(1-Hydroxyethyl)phenyl]-10,15,20-triphenylporphyrin as a probe of the transition-state conformation in hydrolase-catalyzed enantioselective transesterifications.
5-[4-(1-Hydroxyethyl)phenyl]-10,15,20-triphenylporphyrin (1a) and zinc porphyrin 1b were designed and synthesized to experimentally examine the validity of the transition-state model previously proposed for the lipase-catalyzed kinetic resolution of secondary alcohols. The lipases from Pseudomonas 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 degrees C). Subtilisin Carlsberg from Bacillus licheniformis (ChiroCLEC-BL) also showed high enantioselectivity for 1a (E = 140 at 30 degrees C), and the thermodynamic parameters were determined: DeltaDeltaH = -6.8 +/- 0.8 kcal mol(-1), DeltaDeltaS = -13 +/- 3 cal mol(-1) K(-1). Lipases and subtilisin showed R- and S-preference for 1, respectively. The mechanisms underlying the experimental observations are explained in terms of the transition-state models. The large secondary alcohol 1 is a powerful tool for investigating the conformation of the transition state of the enzyme-catalyzed reactions. The fact that 1 was resolved with high enantioselectivity strongly suggests that the gauche conformation, but not the anti conformation, is taken in the transition state, in agreement with the transition-state models involving the stereoelectronic effect.
Ema
Tadashi
T
Department of Applied Chemistry, Faculty of Engineering, Okayama University, Tsushima, Okayama 700-8530, Japan. ema@cc.okayama-u.ac.jp
Jittani
Masahito
M
Furuie
Kenji
K
Utaka
Masanori
M
Sakai
Takashi
T
D001407:Bacillus / Q000201:enzymology; D016956:Burkholderia cepacia / Q000201:enzymology; D002175:Candida / Q000201:enzymology; D002384:Catalysis; D002851:Chromatography, High Pressure Liquid; D018360:Crystallography, X-Ray; D004951:Esterification; D007700:Kinetics; D008049:Lipase / Q000378:metabolism*; D009682:Magnetic Resonance Spectroscopy; D008956:Models, Chemical; D008968:Molecular Conformation; D015394:Molecular Structure; D011166:Porphyrins / Q000737:chemistry*; D011550:Pseudomonas aeruginosa / Q000201:enzymology; D020103:Rhizomucor / Q000201:enzymology; D013237:Stereoisomerism; D013379:Substrate Specificity; D020860:Subtilisin / Q000378:metabolism*
C459319:5-(4-(1-hydroxyethyl)phenyl)-10,15,20-triphenylporphyrin; D011166:Porphyrins; D008049:Lipase; D020860:Subtilisin