Zinc(ii) complexes with intramolecular amide oxygen coordination as models of metalloamidases
作者:Juan C. Mareque Rivas、Emiliano Salvagni、Ravi Prabaharan、Rafael Torres Mart�n de Rosales、Simon Parsons
DOI:10.1039/b312221b
日期:——
Polydentate ligands (6-R1-2-pyridylmethyl)–R2
(R1
= NHCOtBu, R2
= bis(2-pyridylmethyl)amine L1, bis(2-(methylthio)ethyl)amine L2 and N(CH2CH2)2S L3) form mononuclear zinc(II) complexes with intramolecular amide oxygen coordination and a range of coordination environments. Thus, the reaction of Zn(ClO4)2·6H2O with L1–3 in acetonitrile affords [(L)Zn](ClO4)2
(L =
L1, 1; L2, 2) and [(L3)Zn(H2O)(NCCH3)](ClO4)23. The simultaneous amide/water binding in 3 resembles the motif that has been proposed to be involved in the double substrate/nucleophile Lewis acidic activation and positioning mechanism of amide bond hydrolysis in metallopeptidases. X-ray diffraction, 1H and 13C NMR and IR data suggests that the strength of amide oxygen coordination follows the trend 1 > 2 > 3. L1–3 and 1–3 undergo cleavage of the tert-butylamide upon addition of Me4NOH·5H2O (1 equiv.) in methanol at 50(1)
°C. The rate of amide cleavage follows the order 1 > 2
≫
3, L1–3. The extent by which the amide cleavage reaction is accelerated in 1–3 relative to the free ligands, L1–3, is correlated with the strength of amide oxygen binding and Lewis acidity of the zinc(II) centre in 1–3 deduced from the X-ray, NMR and IR studies.
多齿配体 (6-R1-2-pyridylmethyl)-R2 (R1 = NHCOtBu,R2 = 双(2-吡啶甲基)胺 L1、双(2-(甲硫基)乙基)胺 L2 和 N(CH2CH2)2S L3)形成具有分子内酰胺氧配位和一系列配位环境的单核锌(II)配合物。因此,Zn(ClO4)2-6H2O 与 L1-3 在乙腈中反应生成 [(L)Zn](ClO4)2 (L = L1,1;L2,2)和 [(L3)Zn(H2O)(NCCH3)](ClO4)23 。3 中的酰胺/水同时结合类似于金属肽酶中酰胺键水解的双底物/亲核路易斯酸活化和定位机制中的图案。X 射线衍射、1H 和 13C NMR 以及 IR 数据表明,酰胺氧配位的强度遵循 1 > 2 > 3 的趋势。在 50(1) ℃ 的甲醇中加入 Me4NOH-5H2O(1 等份)后,L1-3 和 1-3 的叔丁酰胺发生裂解。酰胺裂解的速率按照 1 > 2 ≫ 3 的顺序进行,L1-3。相对于游离配体 L1-3,酰胺裂解反应在 1-3 中的加速程度与酰胺氧结合强度和 1-3 中锌(II)中心的路易斯酸度有关,这是从 X-射线、核磁共振和红外研究中推断出来的。