Development of Artificial Sugar-Transformation Systems by Biomimic Multimetallic Centers

阐明碳水化合物与金属离子之间的相互作用在生物无机化学中具有重要意义，因为许多糖代谢酶和一些糖结合蛋白与多种二价金属离子如Mg ^2+、Mn ^2+、Co ^2+、Zn ^2+和Ca ^2+一起发挥作用。在某些情况下，在许多水解金属酶中普遍存在的羧基桥联的二价双金属中心也通过与碳水化合物的相互作用发挥重要作用。MCl_2-nH_2O与N，N'-bis的反应（D-吡喃葡萄糖基）-1，4，7-三氮杂环壬烷（D-Glc）_2-tacn），合成了一系列含有两个β-D-吡喃葡萄糖基的单核二价金属配合物[M {（D-Glc）_2-tacn} Cl] Cl（M = Zn（11），Cu（12），Ni（13），Co（14））。配合物11 - 14通过分析和光谱测量以及X射线晶体学表征为具有被五配位N-糖苷配体连接的扭曲八面体M（II）中心， ...更多信息 （b-D-吡喃葡萄糖基）2-tacn和氯阴离子。每个D-葡萄糖部分通过具有tacn的b-N-糖苷键连接到金属中心，并且另外通过C-2羟基配位，产生λ-gauche五元螯合环。化合物11（M = Zn）与[Zn（XDK）（H_2O）]（21）或[Cu（XDK）（py）_2]（22）（H_2XDK =间苯二甲胺双（肯普三酸酰亚胺））反应，生成了均和异三金属配合物[Zn_2M ′ {（D-Glc）_2-tacn}_2（XDK）] Cl_2（M ′ = Zn（31），Cu（32））。化合物12（M = Cu）与配合物21或22进行类似的反应，得到[Cu_2M ′ {（D-Glc）_2-tacn}_2（XDK）]-Cl_22（M ′ = Cu（33），Zn（34））。X射线晶体学研究表明，配合物31和34具有由XDK的两个羧酸基团和两个D-吡喃葡萄糖残基桥接的Zn ^3或Cu ^Zn ^Cu ^3三金属中心。<II><II><II><II>M... M '的间距为3.418（3）-3.462（3）&lt;$（31）和3.414（1）-3.460（1）&lt;$（34），M... M'... M角为155.18（8）°（31）和161.56（6）°（34）。末端金属离子通过（D-Glc）2-tacn配体通过tacn的三个氮原子、碳水化合物的C-2羟基的两个氧原子和XDK配体的羧酸根氧原子进行八面体配位。中心金属离子位于（D-Glc）_2-tacn配体中糖残基的4个氧原子和XDK分子中的2个羧基氧原子的扭曲八面体环境中，C-2羟基上的去质子化β-D-吡喃葡萄糖基单元将末端和中心离子与C-2 μ-烷氧基、C-1 N-糖苷氨基和C-3羟基连接起来。络合物31 - 34是其中D-葡萄糖单元充当桥连配体的金属络合物的第一个实例。这些结构可能是非常有用的木糖或葡萄糖异构酶的底物结合模型，其通过使用由谷氨酸残基桥接的二价双金属中心来促进D-葡萄糖D-果糖异构化。<->少

Elucidation of interactions between carbohydrates and metal ions is of importance in bioinorganic chemistry, since many sugar-metabolizing enzymes and some sugar-binding proteins function with a variety of divalent metal ions such as Mg^<2+>, Mn^<2+>, Co^<2+>, Zn^<2+>, and Ca^<2+>. In some cases, carboxylate-bridged divalent dimetal centers, a ubiquitous motif in many hydrolytic metalloenzymes, also play important roles via interactions with carbohydrates.Reactions of MCl_2-nH_2O with N,N'-bis (D-glucopyranosyl)-1, 4, 7-triazacyclononane (D-Glc)_2-tacn), which was formed from D-glucose and 1, 4, 7-triazacyclononane (tacn) in situ, afforded a series of mononuclear divalent metal complexes with two β-D-glucopyranosyl moieties, [M{(D-Glc)_2-tacn}Cl]Cl (M=Zn (11), Cu (12), Ni (13), Co (14)). Complexes 11-14 were characterized by analytical and spectroscopic measurements and X-ray crystallography to have a distorted octahedral M(II) center ligated by the pentacoordinate N-glycoside ligand, … More (b-D-glucopyranosyl) 2-tacn, and a chloride anion. Each D-glucose moiety is tethered to the metal center through the b-N-glycosidic bond with tacn and additionally coordinated via the C-2 hydroxyl group, resulting in a λ-gauche five-membered chelate ring. Reactions of 11 (M=Zn) with [Zn (XDK)(H_2O)] (21) or [Cu(XDK)(py)_2] (22) (H_2XDK=m-xylylenediamine bis (Kemp's triacid imide)) yielded homo-and heterotrimetallic complexes formulated as [Zn_2M'{(D-Glc)_2-tacn}_2(XDK)] Cl_2 (M'=Zn (31), Cu (32)). The similar reactions of 12 (M=Cu) with complex 21 or 22 afforded [Cu_2M'{(D-Glc)_2-tacn}_2(XDK)]-Cl_22 (M'=Cu (33), Zn (34)). X-ray crystallographic study revealed that complexes 31 and 34 have a Zn^<II>_3 or Cu^<II>Zn^<II>Cu^<II> trimetallic centers bridged by two carboxylate groups of XDK and two D-glucopyranosyl residues. The M…M' separations are 3.418 (3)-3.462 (3) Å (31) and 3.414 (1)-3.460 (1) Å (34) and the M…M'…M angles are 155.18 (8) ° (31) and 161.56 (6)°(34). The terminal metal ions are octahedrally coordinated by the (D-Glc)2-tacn ligand through three nitrogen atoms of tacn, two oxygen atoms of C-2 hydroxyl groups of the carbohydrates, and a carboxylate oxygen atom of XDK ligand. The central metal ions sit in a distorted octahedral environment ligated by four oxygen atoms of the carbohydrate residues in the (D-Glc)_2-tacn ligands and two carboxylate oxygen atoms of XDK.The deprotonated β-D-glucopyranosyl unit at C-2 hydroxyl group bridges the terminal and central ions with the C-2 μ-alkoxo group and with the C-1 N-glycosidic amino and the C-3 hydroxyl groups coordinating to each metal center. Complexes 31-34 are the first examples of metal complexes in which D-glucose units act as bridging ligands. These structures could be very useful substrate binding models of xylose or glucose isomerases, which promote D-glucose <-> D-fructose isomerization by using divalent dimetallic centers bridged by a glutamate residue. Less