Yamazaki Y, Uebayasi M, Hosono K
Fermentation Research Institute, Agency of Industrial Science and Technology, Tsukuba, Ibaraki, Japan.
Eur J Biochem. 1989 Oct 1;184(3):671-80. doi: 10.1111/j.1432-1033.1989.tb15065.x.
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.
马肝醇脱氢酶催化的1,2-双（羟甲基）二茂铁（1）的氧化反应生成了（1R）-（+）-1-甲酰基-2-羟甲基二茂铁（3）（对映体过量86±2%，e.e.），而相应的二醛1,2-二甲酰基二茂铁（2）的还原反应生成了其对映体（1S）-（-）-3（对映体过量94±2%，e.e.）。这一事实表明，1和2中的前手性R基团均优先被该酶转化。当底物上的两个取代基之一被甲基取代或移至β位时，反应中的立体选择性降低，这可由产物的对映体纯度证明（对映体过量5 - 64%）。用马肝醇脱氢酶（HLADH）处理外消旋的1-羟乙基二茂铁（14）得到光学纯的（R）-（-）-14以及乙酰基二茂铁。用HLADH、NAD和（2H6）乙醇还原2得到（-）-（1S,2R）-1-甲酰基-2-[(R)-羟基(2H1)甲基]二茂铁，用HLADH、NAD和乙醇还原1,2-二[(2H)甲酰基]二茂铁得到（-）-（1S,2R）-1-(2H)甲酰基-2-[(S)-羟基(2H1)甲基]二茂铁。这些构型表明酶促还原发生在前手性R甲酰基的Re面。在（η6-苯甲醛）三羰基铬及其（2H）甲酰基类似物的酶促还原反应中也发现了Re面选择性。使用计算机图形学研究了2在HLADH活性位点的对接情况。有人提出，HLADH对1和2氧化还原反应中前手性R侧的对映选择性是Re面选择性的自然结果，Re面选择性是由配体与苯丙氨酸-93侧链或锌配合物之间的空间相互作用引起的，并通过未反应的极性α-取代基与蛋白质之间的相互作用（可能是通过氢键形成）而增强。
