Enantiotopic differentiation in horse-liver alcohol-dehydrogenase-catalyzed oxidoreduction studied with novel substrates having organometallic moieties.
Horse-liver alcohol-dehydrogenase-catalyzed oxidation of 1,2-bis(hydroxymethyl)ferrocene (1) gave (1R)-(+)-1-formyl-2-hydroxymethylferrocene (3) (86 +/- 2% enantiomeric excess, e.e.), while the reduction of the corresponding dialdehyde 1,2-diformylferrocene (2) gave the antipode (1S)-(-)-3 (94 +/- 2% e.e.). This fact indicates that the pro-R group in both 1 and 2 was preferentially converted by the enzyme. When one of two substituents on the substrate was replaced by a methyl group or moved to the beta-site, the stereoselectivity in the reaction decreased as evidenced by the enantiomeric purity of the products (5-64% e.e.). Treatment of racemic 1-hydroxyethylferrocene (14) with horse-liver alcohol dehydrogenase (HLADH) gave optically pure (R)-(-)-14 together with acetylferrocene. The reduction of 2 with HLADH, NAD and (2H6)ethanol gave (-)-(1S,2R)-1-formyl-2-[(R)-hydroxy(2H1)methyl]ferrocene and that of 1,2-di[(2H)formyl]ferrocene with HLADH, NAD and ethanol gave (-)-(1S,2R)-1-(2H)formyl-2-[(S)-hydroxy(2H1)methyl]ferrocene. These configurations indicate that the enzymic reduction occurred on the re-face of pro-R formyl group. The re-face selectivity was also found in the enzymic reduction of (eta 6-benzaldehyde)tricarbonylchromium and its (2H)formyl analogue. Docking of 2 into the active site of HLADH was examined using computer graphics. It has been suggested that the enantioselectivity to the pro-R side in the oxidoreduction of 1 and 2 by HLADH is a natural consequence of the re-face selectivity, which is caused by a steric interaction between the ligand and the side chain of Phe-93 or the Zn complex and strengthened by an interaction between the unreactive polar alpha-substituent and the protein, probably by hydrogen bond formation.
Yamazaki
Y
Y
Fermentation Research Institute, Agency of Industrial Science and Technology, Tsukuba, Ibaraki, Japan.
Uebayasi
M
M
Hosono
K
K
D000426:Alcohol Dehydrogenase; D000818:Animals; D001665:Binding Sites; D005296:Ferrous Compounds; D006736:Horses; D008099:Liver / Q000201:enzymology*; D000075163:Metallocenes; D008968:Molecular Conformation; D009942:Organometallic Compounds; D010084:Oxidation-Reduction
D005296:Ferrous Compounds; D000075163:Metallocenes; D009942:Organometallic Compounds; D000426:Alcohol Dehydrogenase; C004998:ferrocene