The role of Zn–OR and Zn–OH nucleophiles and the influence of para-substituents in the reactions of binuclear phosphatase mimetics
作者:Lena J. Daumann、Kristian E. Dalle、Gerhard Schenk、Ross P. McGeary、Paul V. Bernhardt、David L. Ollis、Lawrence R. Gahan
DOI:10.1039/c1dt11187f
日期:——
Analogues of the ligand 2,2â²-(2-hydroxy-5-methyl-1,3-phenylene)bis(methylene)bis((pyridin-2-ylmethyl)azanediyl)diethanol (CH3H3L1) are described. Complexation of these analogues, 2,6-bis(((2-methoxyethyl)(pyridin-2-ylmethyl)amino)methyl)-4-methylphenol (CH3HL2), 4-bromo-2,6-bis(((2-methoxyethyl)(pyridin-2-ylmethyl)amino)methyl)phenol (BrHL2), 2,6-bis(((2-methoxyethyl)(pyridin-2-ylmethyl)amino)methyl)-4-nitrophenol (NO2HL2) and 4-methyl-2,6-bis(((2-phenoxyethyl)(pyridin-2-ylmethyl)amino)methyl)phenol (CH3HL3) with zinc(II) acetate afforded [Zn2(CH3L2)(CH3COO)2](PF6), [Zn2(NO2L2)(CH3COO)2](PF6), [Zn2(BrL2)(CH3COO)2](PF6) and [Zn2(CH3L3)(CH3COO)2](PF6), in addition to [Zn4(CH3L2)2(NO2C6H5OPO3)2(H2O)2](PF6)2 and [Zn4(BrL2)2(PO3F)2(H2O)2](PF6)2. The complexes were characterized using 1H and 13C NMR spectroscopy, mass spectrometry, microanalysis, and X-ray crystallography. The complexes contain either a coordinated methyl- (L2 ligands) or phenyl- (L3 ligand) ether, replacing the potentially nucleophilic coordinated alcohol in the previously reported complex [Zn2(CH3HL1)(CH3COO)(H2O)](PF6). Functional studies of the zinc complexes with the substrate bis(2,4-dinitrophenyl) phosphate (BDNPP) showed them to be competent catalysts with, for example, [Zn2(CH3L2)]+, kcat = 5.70 ± 0.04 à 10â3 sâ1 (Km = 20.8 ± 5.0 mM) and [Zn2(CH3L3)]+, kcat = 3.60 ± 0.04 à 10â3 sâ1 (Km = 18.9 ± 3.5 mM). Catalytically relevant pKas of 6.7 and 7.7 were observed for the zinc(II) complexes of CH3L2â and CH3L3â, respectively. Electron donating para-substituents enhance the rate of hydrolysis of BDNPP such that kcatp-CH3 > p-Br > p-NO2. Use of a solvent mixture containing H2O18/H2O16 in the reaction with BDNPP showed that for [Zn2(CH3L2)(CH3COO)2](PF6) and [Zn2(NO2L2)(CH3COO)2](PF6), as well as [Zn2(CH3HL1)(CH3COO)(H2O)](PF6), the 18O label was incorporated in the product of the hydrolysis suggesting that the nucleophile involved in the hydrolysis reaction was a ZnâOH moiety. The results are discussed with respect to the potential nucleophilic species (coordinated deprotonated alcohol versus coordinated hydroxide).
描述了配体2,2-(2-羟基-5-甲基-1,3-亚苯基)双(亚甲基)双((吡啶-2-基甲基)氮烷二基)二乙醇(CH3H3L1)的类似物。这些类似物的络合,2,6-双(((2-甲氧基乙基)(吡啶-2-基甲基)氨基)甲基)-4-甲基苯酚(CH3HL2),4-溴-2,6-双(((2-甲氧基乙基)(吡啶-2-基甲基)氨基)甲基)苯酚(BrHL2)、2,6-双(((2-甲氧基乙基)(吡啶-2-基甲基)氨基)甲基)-4-硝基苯酚(NO2HL2)和4 -甲基-2,6-双(((2-苯氧基乙基)(吡啶-2-基甲基)氨基)甲基)苯酚(CH3HL3)与乙酸锌(II)得到[Zn2(CH3L2)(CH3COO)2](PF6) 、[Zn2(NO2L2)(CH3COO)2](PF6)、[Zn2(BrL2)(CH3COO)2](PF6) 和 [Zn2(CH3L3)(CH3COO)2](PF6),以及 [Zn4(CH3L2) )2(NO2C6H5OPO3)2(H2O)2](PF6)2 和 [Zn4(BrL2)2(PO3F)2(H2O)2](PF6)2。使用 1H 和 13C NMR 光谱、质谱、微量分析和 X 射线晶体学对配合物进行了表征。该配合物含有配位的甲基-(L2配体)或苯基-(L3配体)醚,取代了先前报道的配合物[Zn2(CH3HL1)(CH3COO)(H2O)](PF6)中潜在的亲核配位醇。锌配合物与底物双(2,4-二硝基苯基)磷酸酯 (BDNPP) 的功能研究表明它们是有效的催化剂,例如 [Zn2(CH3L2)]+, kcat = 5.70 ± 0.04 × 10â 3 s–1 (Km = 20.8 ± 5.0 mM) 和 [Zn2(CH3L3)]+, kcat = 3.60 ± 0.04 × 10–3 s–1 (Km = 18.9 ± 3.5 mM)。 CH3L2- 和 CH3L3- 的锌 (II) 配合物的催化相关 pKa 分别为 6.7 和 7.7。给电子对位取代基提高了 BDNPP 的水解速率,使得 kcatp-CH3 > p-Br > p-NO2。在与 BDNPP 的反应中使用含有 H2O18/H2O16 的溶剂混合物表明,对于 [Zn2(CH3L2)(CH3COO)2](PF6) 和 [Zn2(NO2L2)(CH3COO)2](PF6),以及 [Zn2 (CH3HL1)(CH3COO)(H2O)](PF6),18O标记被掺入水解产物中,表明参与水解反应的亲核试剂是Zn-OH部分。就潜在的亲核物质(配位去质子醇与配位氢氧化物)讨论了结果。