1,4,7,10-tetraazacyclododecane metal complexes as potent promoters of carboxyester hydrolysis under physiological conditions

New 1,4,7,10-tetrazacyclododecane ([12]aneN4 or cyclen) ligands with different heterocyclic spacers (triazine and pyridine) of various lengths (bi- and tripyridine) or an azacrown pendant and their mono- and dinuclear Zn(II), Cu(II), and Ni(II) complexes have been synthesized and characterized. The pKa values of water molecules coordinated to the complexed metal ions were determined by potentiometric pH titrations and vary from 7.7 to 11.2, depending on the metal-ion and ligand properties. The X-ray structure of [Zn2L2]mu-OH(ClO4)3.CH3CN.H2O shows each Zn(II) ion in a tetrahedral geometry, binding to three N atoms of cyclen (the average distance of Zn-N = 2.1 A) and having a mu-OH bridge at the apical site linking the two metal ions (the average distance of Zn-O- = 1.9 A). The distance between the Zn(II) ion and the fourth N atom is 2.6 A. All Zn(II) complexes promote the hydrolysis of 4-nitrophenyl acetate (NA) under physiological conditions, while those of Cu(II) and Ni(II) do not have a significant effect on the hydrolysis reaction. The kinetic studies in buffered solutions (0.05 M Tris, HEPES, or CHES, I = 0.1 M, NaCl) at 25 degrees C in the pH range of 6-11 under pseudo-first-order reaction conditions (excess of the metal complex) were analyzed by applying the method of initial rates. Comparison of the second-order pH-independent rate constants (kNA, M-1 s-1) for the mononuclear complexes ZnL1, ZnL3, and ZnL8, which are 0.39, 0.27, and 0.38, respectively, indicates that the heterocyclic moiety improves the rate of hydrolysis up to 4 times over the parent Zn([12]aneN4) complex (kNA = 0.09 M-1 s-1). The reactive species is the Zn(II)-OH- complex, in which the Zn(II)-bound OH- acts as a nucleophile, which attacks intermolecularly the carbonyl group of the acetate ester. For dinuclear complexes Zn2L2, Zn2L4, Zn2L5, Zn2L6, and Zn2L7, the mechanism of the reaction is defined by the degree of cooperation between the metal centers, determined by the spacer length. For Zn2L7, having the longest triaryl spacer, the two metal centers act independently in the hydrolysis; therefore, the reaction rate is twice as high as the rate of the mononuclear analogue (kNA = 0.78 M-1 s-1). The complexes with a monoaryl spacer show saturation kinetics with the formation of a Michaelis-Menten adduct. Their hydrolysis rates are 40 times higher than that of the Zn[12]aneN4 system (kNA approximately 4 M-1 s-1). Zn2L6 is a hybrid between these two mechanisms; a clear saturation curve is not visible nor are the metal cores completely independent from one another. Some of the Zn(II) complexes show a higher hydrolytic activity under physiological conditions compared to other previously reported complexes of this type.     

Synthesis,crystal structures,and catalytic hydrolysis activities of four dinuclear complexes with 1,4,7,10-tetraazacyclododecane and succinate ligands

Four new dinuclear complexes of the type [M₂(cyclen)₂(suc)]Cl₂ · nH₂O (M = Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, cyclen = 1,4,7,10-tetraazacyclododecane, suc = succinate) have been obtained by the reaction of cyclen and succinate with the corresponding metal dichlorides in aqueous solution. All the complexes were characterized by physico-chemical and spectroscopic methods. The crystal structure of [Ni₂(cyclen)₂(suc)]Cl₂ · 2H₂O was determined. The four complexes have similar compositions and structures and are all bridged by succinate. Furthermore, the hydrolysis of bis(2,4-dinitrophenyl)phosphate (BDNPP) promoted by the four complexes was studied. The experimental results indicate that these complexes can efficiently catalyze hydrolysis of BDNPP, and their catalytic activities are in the order Ni > Zn > Cu > Co.     

Geometry-dependent phosphodiester hydrolysis catalyzed by binuclear copper complexes

Two isomeric binuclear ligands PBTPA and MBTPA and their copper(II) complexes were prepared and examined for hydrolysis of a model phosphodiester substrate: bis(p-nitrophenyl)phosphate. A bell-shaped pH vs rate profile, which is in agreement with one mechanism proposed for bimetallonucleases/phosphatases, was observed for the binuclear complex of copper(II) and PBTPA. At pH 8.4, a maximum rate of 1.14 x 10(-6) s(-1)--more than 10(4)-fold over uncatalyzed reactions--was achieved. However, the analogous complex of MBTPA did not show significant rate enhancement. The binuclear complex of copper(II) and PBTPA also showed 10-fold acceleration over mononuclear complex of copper(II) and tris(2-pyridylmethyl)amine (TPA) catalyzed reaction. A phage phiX174 DNA assay showed that the complex of copper(II) and PBTPA promoted supercoiled phage phiX174 DNA relaxation under both aerobic and anaerobic conditions, in contrast to the hydrolytic inactivity of the mononuclear complex of copper(II) and TPA.     

Short and straightforward synthesis of 1,7-dimethyl-1,4,7,10-tetraazacyclododecane

A novel, cost-effective, and efficient process for the synthesis of 1,7-dimethyl-1,4,7,10-tetraazacyclododecane 1 has been developed. The two-step process involved the selective conversion of commercially available cyclen to N1,N7-diethylcarbamate cyclen 3 that afforded the title compound in high yield after the reduction step.     

Synthesis and acid-base and complex-forming properties of 1,4,7,10-tetrakis(dihydroxyphosphorylmethyl)-1,4,7,10-tetraazacyclododecane

Conclusions A new complexone, 1,4,7,10-tetrakis(dihydroxyphosphorylmethyl)-1,4,7,10-tetraazacyclododecane, has been synthesized and its acid-base and complex-forming properties have been studied. It shows a very high complexing capability and marked selectivity for cations of large ionic radius (Cd²⁺, Hg²⁺, Pb²⁺, La³⁺).Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 844–849, April, 1984.     

Solvent effects and alkali metal ion catalysis in phosphodiester hydrolysis

The kinetics of the alkaline hydrolysis of bis(p-nitrophenyl) phosphate (BNPP) have been studied in aqueous DMSO, dioxane, and MeCN. In all solvent mixtures the reaction rate steadily decreases to half of its value in pure water in the range of 0-70 vol % of organic cosolvent and sharply increases in mixtures with lower water content. Correlations based on different scales of solvent empirical parameters failed to describe the solvent effect in this system, but it can be satisfactorily treated in terms of a simplified stepwise solvent-exchange model. Alkali metal ions catalyze the BNPP hydrolysis but do not affect the rate of hydrolysis of neutral phosphotriester p-nitrophenyl diphenyl phosphate in DMSO-rich mixtures. The catalytic activity decreases in the order Li+ > Na+ > K+ > Rb+ > Cs+. For all cations except Na+, the reaction rate is first-order in metal ion. With Na+, both first- and second-order kinetics in metal ions are observed. Binding constants of cations to the dianionic transition state of BNPP alkaline hydrolysis are of the same order of magnitude and show a similar trend as their binding constants to p-nitrophenyl phosphate dianion employed as a transition-state model. The appearance of alkali metal ion catalysis in a medium, which solvates metal ions stronger than water, is attributed to the increased affinity of cations to dianions, which undergo a strong destabilization in the presence of an aprotic dipolar cosolvent.     

A new,facile synthesis of 1,4,7,10-tetraazacyclododecane: cyclen

This report outlines a new and efficient synthesis of cyclen (1,4,7,10-tetraazacyclododecane, 1) utilizing bis-imidazoline, 6 (1,1'-ethylenedi-2-imidazoline), with 1,2-dibromoethane. General conditions were developed, allowing for the simple, three-step synthesis of 1 at the multigram scale with an isolated overall yield approaching 65%. The cyclization of 6 produced by the condensation of triethylene tetraamine (TETA) with N,N-dimethylformamide dimethyl acetal, gave the twelve-membered, imidazolinium, cyclized intermediate bromide salt, 7 (2,3,4,5,6,7,8,8c-octahydro-1H-4a,6a,8a-triaza-2a-azoniacyclopent[fg]acenaphthylene), which hydrolyzed to 1 with the use of hot, aqueous caustic. Hydrolysis of 7 under milder conditions formed the 1,4,7,10-tetraazabicyclo[8.2.1]tridecan-13-one (20). Mechanistically, the formation of 7 may be rationalized as involving a diaminocarbene that undergoes an intramolecular carbon-hydrogen insertion.     

含氮不饱和大环铈配合物催化磷酸二酯降解的研究

本文利用含氮不饱和大环铈配合物催化BNPP水解。通过改变温度、pH等方法测定含氮大环铈配合物催化对硝基苯酚磷酸二酯的反应速率。整个实验过程保持含氮大环铈配合物浓度高于底物浓度10倍以上,以使反应为一级反应。结果表明:其水解反应的最佳温度在45℃左右,最佳pH在8.0左右。     

Quinone methide phosphodiester alkylations under aqueous conditions

A detailed analysis of the alkylation of phosphodiesters with a p-quinone methide under aqueous conditions has been accomplished. The relative rates of phosphodiester alkylation and hydrolysis have been examined by (1)H NMR analysis of the reaction of 2,6-dimethyl-p-quinone methide in a buffered diethyl phosphate/acetonitrile solution (1:9 v/v, pH 4.0). The rate of hydrolysis of the quinone methide was confirmed by UV analysis in 28.5% solutions of aqueous inorganic phosphate in acetonitrile at pH 4.0 and 7.0. Similarly, the rate of phosphodiester alkylations by the quinone methide was also confirmed by UV analysis in 28.5% solutions of aqueous dibenzyl, dibutyl, or diethyl phosphate in acetonitrile at pH 4.0 and 7.0. These kinetic studies further establish that the phosphodiester alkylation reactions are acid-catalyzed, second-order processes. The rate constant for phosphodiester alkylation was found to range from approximately 370-3700 times the rate constant of quinone methide hydrolysis with diethyl and dibenzyl phosphate, respectively (pH 4.0, 28.5% aqueous acetonitrile).     

On the Synthesis of 1,4,7-Tris(tert-butoxycarbonylmethyl)-1,4,7,10-tetraazacyclododecane

1,4,7-Tris(tert-butoxycarbonylmethyl)-1,4,7,10-tetraazacyclododecane is widely used as an intermediate in the preparation of medically important DO3A and DOTA metal chelators. Despite its commercial availability and importance, the literature describing the preparation and properties of the free base is limited and sometimes unclear. We present herein an efficient synthesis of the hydrobromide salt of 1,4,7-tris(tert-butoxycarbonylmethyl)-1,4,7,10-tetraazacyclododecane, characterize this compound spectroscopically and by X-ray crystallographic analysis, describe its simple conversion to the corresponding free base, characterize this compound spectroscopically and by X-ray crystallographic analysis, and make observations on the reactivity of this interesting and useful compound.     

Synthesis and Crystal Structure of 1,4,7,10-Tetrakis-（2-（2,3-difluorophenyl）-ethyl）-1,4,7,10-tetraazacyclododecane

The new compound 1,4,7,10-tetrakis-(2-(2,3-difluorophenyl) ethyl) -1,4,7,10-tetra-zacyclododecane 2 has been synthesized and structurally characterized by single-crystal X-ray diffraction. The molecule turned into diamond crystals grown from CH3CN by slow diffusion at room temperature. It crystallizes in the triclinic system,space group P1 with a = 9.543(2) ,b = 10.507(3) ,c = 10.734(3) ,α = 60.979(3) ,β = 81.870(4) ,γ = 84.279(4) o,V = 931.1(4) 3,Z = 1,Dc = 1.307 g/cm3,C40H44F8N4,Mr = 732.79,F(000) = 384,μ = 0.105 mm-1,T = 296(2) K,MoKa radiation(λ = 0.71073) ,R = 0.0494 and wR = 0.0989 for 1589 observed reflections with I > 2σ(I) . Hydrogen bonds and C-H···π stacking interactions in 2 contribute to a supramolecular structure. Moreover,compound 2 has been determined by 1H NMR,13C NMR,MS,IR spectra and elemental analysis.     

Selective monoprotection of 1,4,7,10-tetraazacyclododecane via direct reaction with 4-nitrophenyl active esters

A simple, one-pot preparation of monoprotected 1,4,7,10-tetraazacyclododecanes via an efficient acylation reaction with 4-nitrophenyl active esters has been developed.     

Monte Carlo simulation of a 1,4,7,10-tetraazacyclododecane/lithium complex in aqueous solution

Monte Carlo simulations have been carried out for the system consisting of a 1,4,7,10-tetraazacyclododecane (cyclen)-lithium complex in 201 water molecules. The volume of the periodic cube was calculated using the experimental density of pure water at 298 K and 1 atm of 1 g.cm(-)(3), plus additional space occupied by the complex. The geometry of the complex is the alternated form, where the ion is located at the center of the cyclen. The complex-water interaction was represented by the cyclen-water and lithium-water pair potentials, both of which were developed on the basis of ab initio calculations. The results show two layers of solvation shells consisting of 2 and 6.9 water molecules. Two water molecules in the first solvation shell (O(1) and O(2)) bind directly to the ion in which the ion-oxygen distance is 2.38 A, the dipole vector points to the ion, and rotation takes place around the ion-oxygen axis. In the next layer, 4 water molecules coordinate simultaneously to the first 2 water molecules in the first shell and the NH functional groups of cyclen. The remaining 2.9 water molecules in the second layer are also coordinated to be in the first half-hydration shell of O(1) and O(2).     

Synthesis and Crystal Structure of 1,4,7,10-Tetrakis （2-（（4-hydroxy）phenoxy）ethyl）-1,4,7,10- tetraazacyclododecane

A novel molecule tetra-N-alkylation of cyclen （1,4,7,10-tetraazacyclododecane）, 1,4,7,10-tetrakis（2-（（4-hydroxy）phenoxy）ethyl）-1,4,7,10-tetraazacyclododecane 2, was synthesized and structurally characterized by single-crystal X-ray diffraction. The molecule turned into chiral helical compound crystals grown from EtOH by slow diffusion at room temperature and three of the four hydroquinone groups of the benzene ring formed a g-electron-rich cavity by C-H…π stacking interaction. The crystal belongs to the monoclinic system, space group P21/C with a = 13.9192（9）, b = 13.2871（6）, c = 22.1894（15）A^°, β = 91.4600（10）°, V = 4102.5（4）A^°3, Z = 4, Dc = 1.219 g/cm^3, C40H52N4O8, Mr = 752.89, F（000） = 1616,μ = 0.088 mm^-1, MoKa radiation （λ = 0.71073）, R = 0.0578 and wR = 0.1389 for 5588 observed reflections with I 〉 2σ（I）. Moreover, compound 2 was characterized with ^1H NMR, ^13C NMR, IR spectra and MS.     

Carboxylic acid functionalized cobalt(III) cyclen complexes for catalytic hydrolysis of phosphodiester bonds

4-(1,4,7,10-Tetraazacyclotetradec-1-yl)methylbenzoic acid (cycmba, 1) has been synthesized, as a step towards the eventual development of sequence-specific hydrolytic complexes. A cobalt(III) complex of 1, [Co(cycmba)Cl2]Cl.1.5H2O (.1.5H2O) was found to be active against both an activated phosphodiester compound, bis(nitrophenyl)phosphate (BNPP), and supercoiled DNA. The presence of the benzoate group depresses the rate of hydrolysis of the ligand-Co(III) system at neutral pH, as confirmed by the kinetics results of a methyl ester analog. The ability of (2.1.5H2O) to bind to solid substrates and remain active was also demonstrated by attachment of the molecule to agarose beads.     

Synthesis,structure and antitumor activities of a new macrocyclic ligand with four neutral pendent groups: 1,4,7,10-tetrakisbenzyl-1,4,7,10-tetraazacyclododecane (L) and its Co,Ni and Cu complexes

A new macrocyclic ligand, 1,4,7,10-tetrakisbenzyl-1,4,7,10-tetraazacyclododecane (L) and its three new divalent metal complexes of general formula: M(NO₃)₂(L)nH2O [M = Co(1), Ni(2), n = 0; M = Cu(3), n = 1.5] have been synthesized and characterized by elemental analysis, i.r., EI mass spectra and molecular conductance. Complex (2) has been characterized by X-ray diffraction. In complex (2), the central Ni^II atom coordinatively bonds to four nitrogen atoms of the macrocyclic ligand and two oxygen atoms of nitrate anion, to form a distorted octahedron. X-ray diffraction indicated that the bonds Ni–N(1), Ni–N(2), Ni–N(3) and Ni–N(4) are of almost equal length, i.e. 2.11(1), 2.12(1), 2.10(1) and 2.17(1)Å, respectively. Bond lengths of Ni–O(1) and Ni– O(2) are 2.11(1) and 2.10(1)Å. Preliminary pharmacological tests show that these complexes have high antitumor activity towards HL-60 tumor cell lines.