Phosphate Ester Cleavage Research Articles

Copper(II) Complexes of N‐Methylated Derivatives of ortho‐ and meta‐Xylyl‐Bridged Bis(1,4,7‐triazacyclononane) Ligands: Synthesis, X‐ray Structure and Reactivity as Artificial Nucleases

AbstractTwo new binucleating ligands, 1,3‐bis[(4,7‐dimethyl‐1,4,7‐triazacyclononan‐1‐yl)methyl]benzene (Lmemx) and 1,2‐bis[(4,7‐dimethyl‐1,4,7‐triazacyclononan‐1‐yl)methyl]benzene(Lmeox), have been prepared from 1,4,7‐triazatricyclo[5.2.1.04,10]decane and applied in the synthesis of the corresponding copper(II) complexes, [Cu2(μ‐AcO)2(Lmemx)](ClO4)2·H2O (Cm) and [Cu2(η2‐AcO)2(Lmeox)](ClO4)2 (Co). The X‐ray crystal structures confirmed the dinuclear nature of the complexes, with pairs of copper(II) centres residing in distorted square‐pyramidal coordination environments. The nitrogen donors on the ligands occupy three facially disposed coordination sites about each copper(II) centre, with two acetate ligands completing the copper(II) coordination spheres. For Cm, both acetate groups bridge the two metal centres, whilst in Co each acetate chelates to a single metal centre. To assess their utility as simple nuclease mimics, the metal complexes were tested for their phosphate ester cleavage ability using the model phosphodiester, bis(4‐nitrophenyl)phosphate (BNPP). It was found that Co exhibited the fastest rate of BNPP hydrolysis (kobsd. = 2.4 × 10–5 s–1), this rate being five times faster than that of the CuII complex of the non‐methylated analogue. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Phosphate Ester Cleavage with Binuclear Boron Chelates

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Microwave-assisted cleavage of phosphate, phosphonate and phosphoramide esters

A mild and rapid protocol for cleavage of phosphate, phosphonate and phosphoramide esters. The scope and limitations of this microwave-assisted reaction is explored here.

06/01716 Investigation of humic acid N with X-ray photoelectron spectroscopy: Effect of acid hydrolysis and comparison with 15N cross polarization/magic angle spinning nuclear magnetic resonance spectroscopy : Abe, T. et al. Organic Geochemistry, 2005, 36, (11), 1490–1497

Phosphoryl group transfer is central to genetic replication, cellular signalling and many metabolic processes. Understanding the mechanisms of phosphorylation and phosphate ester and anhydride cleavage is key to efforts towards biotechnological and biomedical exploitation of phosphate-handling enzymes. Analogues of phosphate esters and anhydrides are indispensable tools, alongside protein mutagenesis and computational methods, for the dissection of phosphoryl transfer mechanisms. Hydrolysable and non-hydrolysable phosphate analogues have provided insight into the nature and sites of phosphoryl transfer processes. Kinetic isotope effects and crystallography using transition state analogues have painted more detailed pictures of transition states and how enzymes work to stabilise them.

Synthesis, X-ray Crystal Structures, Magnetism, and Phosphate Ester Cleavage Properties of Copper(II) Complexes of N-Substituted Derivatives of 1,4,7-Triazacyclononane

Two new N-substituted derivatives of the 1,4,7-triazacyclononane (tacn) macrocycle, 1-benzyl-4,7-dimethyl-1,4,7-triazacyclononane (L2) and 1,4,7-tris(3-cyanobenzyl)-1,4,7-triazacyclononane (L3), have been prepared and, together with 1,4-dimethyl-1,4,7-triazacyclononane (L1), have been used to synthesize the corresponding hydroxo-bridged binuclear copper (II) complexes, [Cu2(mu-OH)2L2](ClO4)2.xH2O (1 L = L1, x = 0; 2 L = L2, x = 1; 3 L = L3, x = 2). The X-ray crystal structures of all three complexes reveal the presence of [Cu2(mu-OH)2]2+ cores capped by pairs of facially coordinating tacn ligands so that the Cu(II) centers reside in distorted square pyramidal coordination environments. Variable-temperature magnetic susceptibility measurements indicate weak antiferromagnetic coupling (J = -36.4 cm(-1)) between the Cu(II) centers in 1, while the centers in 2 and 3 have been shown to interact ferromagnetically (J = 11.2 and 49.3 cm(-1), respectively). The variation in the strength and sign of these interactions has been rationalized in terms of the differing geometries of the [Cu2(mu-OH)2]2+ cores. The ability of the Cu(II) complexes to cleave phosphate ester bonds has been probed using the model phosphate ester bis(4-nitrophenyl)phosphate (BNPP) at pH 7.4 and a temperature of 50 degrees C. The measured rate constant for 3 (3 x 10(-4) s(-1)) is significantly greater than those previously reported for the Cu(II) complexes of the fully alkylated tacn ligands, Me3tacn and iPr3tacn, which until now have been rated as the most effective tacn-based phosphate ester cleavage agents.

Bioinorganic Chemistry of Group 12 Complexes Supported by Tetradentate Tripodal Ligands Having Internal Hydrogen‐Bond Donors

AbstractInspired by the proposed role of secondary hydrogen‐bonding interactions in modulating the chemistry of mononuclear zinc centers in metalloenzymes, zinc complexes supported by tetradentate tripodal ligands having one or more internal hydrogen‐bond donors have been prepared, characterized, and investigated for biologically relevant reactivity. Complexes of this class have been examined in terms of water activation and CO2 reactivity, alcohol/alkoxide coordination, and amide methanolysis and phosphate ester hydrolysis reactivity. The results of these studies indicate that the presence of internal hydrogen‐bond donors will lower the pKa of a zinc‐bound water molecule, stabilize zinc alkoxide species with respect to hydrolysis, and enhance the phosphate ester cleavage reactivity of mononuclear zinc complexes. In addition, use of tripodal ligands having a single internal hydrogen‐bond donor has enabled the isolation of a novel cadmium hydroxide complex and examination of its CO2 chemistry, as well as the identification of a novel amide cleavage reaction which proceeds by initial formation of a deprotonated amide intermediate. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Comparing a mononuclear Zn(ii) complex with hydrogen bond donors with a dinuclear Zn(ii) complex for catalysing phosphate ester cleavage

Introducing ligand based hydrogen bond donors to increase the activity of a mononuclear Zn(II) complex for catalysing phosphate ester cleavage can be a more effective strategy than making the dinuclear analogue.

Catalytic destruction of paraoxon by metallomicelle layers of Co(II) and Cr(III)

AbstractTwo micellized ion complexes, Co(II) and Cr(III), were synthesized and found to possess good catalytic activity in cleaving the paraoxon/cobalt (chromate) complex phosphate ester. The complexes orm metallomicelles, which bind the substrate by coordinating with the phosphorus in the paraoxon (which is chemically similar to the nerve agents sarin and soman). Possible reasons for the acceleration include enhanced electrophilicity of the micellized metals, enhanced surface activity, and the recognized ability of cationic micelles to accelerate the cleavage of phosphate ester. The results of kinetic data (half‐lives) for paraoxon degradation were 16.5 and 28.9 min in the presence of Co(II) and Cr(III) metallomicelle layers, respectively. The higher the value of the stability constant, the more stable the Co(II) and Cr(III) complexes.

Kinetics and Mechanism of Hydrolysis of a Model Phosphate Diester by [Cu(Me3tacn)(OH2)2]2+ (Me3tacn = 1,4,7-Trimethyl-1,4,7-triazacyclononane)

The kinetics of hydrolysis of bis(p-nitrophenyl)phosphate (BNPP) by [Cu(Me3tacn)(OH2)2]2+ has been studied by spectrophotometrical monitoring of the release of the p-nitrophenylate ion from BNPP. The reaction was followed for up to 8000 min at constant BNPP concentration (15 microM) and ionic strength (0.15 M) and variable concentration of complex (1.0-7.5 mM) and temperature (42.5-65.0 degrees C). Biphasic kinetic traces were observed, indicating that the complex promotes the cleavage of BNPP to NPP [(p-nitrophenyl)phosphate] and then cleavage of the latter to phosphate, the two processes differing in rate by 50-100-fold. Analysis of the more amenable cleavage of BNPP revealed that the rate of BNPP cleavage is among the highest measured for mononuclear copper(II) complexes and is slightly higher than that reported for the close analogue [Cu(iPr3tacn)(OH2)2]2+. Detailed analysis required the determination of the pKa for [Cu(Me3tacn)(OH2)2]2+ and the constant for the dimerization of the conjugate base to [(Me3tacn)Cu(OH)2Cu(Me3tacn)]2+ (Kdim). Thermodynamic parameters derived from spectrophotometric pH titration and the analysis of the kinetic data were in reasonable agreement. Second-order rate constants for cleavage of BNPP by [Cu(Me3tacn)(OH2)(OH)]+ and associated activation parameters were obtained from initial rate analysis (k = 0.065 M(-1) s(-1) at 50.0 degrees C, deltaH = 56+/-6 kJ mol(-1), deltaS = -95+/-18 J K(-1) mol(-1)) and biphasic kinetic analysis (k = 0.14 M(-1) s(-1) at 50.0 degrees C, deltaH = 55+/-6 kJ mol(-1), deltaS = -92+/-20 J K(-1) mol(-1)). The negative entropy of activation is consistent with a concerted mechanism with considerable associative character. The complex was found to catalyze the cleavage of BNPP with turnover rates of up to 1 per day. Although these turnover rates can be considered low from an application point of view, the ability of the complexes to catalyze phosphate ester cleavage is clearly demonstrated.

Nanozymes: Gold‐Nanoparticle‐Based Transphosphorylation Catalysts

Particularly effective: The self-assembly of triazacyclonane-functionalized thiols on the surface of nanosize gold particles provides a facile entry to functional gold nanoparticles that, upon complexation with ZnII, turn into powerful catalysts for the cleavage of phosphate esters (see scheme). Because of their RNase-like behavior they are dubbed nanozymes.

Plasmid relaxation induced by copper metalated diglycine conjugates under heterogeneous reaction conditions

This paper reports synthesis and plasmid modification activities of a new class of insoluble copper-metalated diglycine conjugates, containing aliphatic linkers of varying length. Besides providing significant rate enhancement for model phosphate ester cleavage, these constructs also displayed efficient supercoiled plasmid scission, in the absence of co-oxidants, under heterogeneous catalytic conditions.

PH dependent phosphate hydrolysis by a lanthanide EF-hand peptide

A 20-mer peptide comprising an EF-hand calcium-binding sequence was shown to bind Eu(III) ions and promote phosphate ester cleavage in a pH dependent manner. The hydrolysis rate of bisnitrophenyl phosphate (BNPP) was followed over a 6.9–9.0 pH range, and the rate increases sharply at pH 8.2. This rate increase, which may correlate to the p K a of an inner sphere water of an Eu-EF-hand motif, is discussed in the context of coordinate water p K a values for a variety of small molecule Eu complexes.

A peptide template as an allosteric supramolecular catalyst for the cleavage of phosphate esters.

The heptapeptide H-Iva-Api-Iva-ATANP-Iva-Api-Iva-NHCH(3) (P1a), where Iva is (S)-isovaline, Api is 4-amino-4-carboxypiperidine, and ATANP is (S)-2-amino-3-[1-(1,4,7-triazacyclononane)]propanoic acid, has been synthesized. Its conformation in aqueous solution is essentially that of a 3(10)-helix. By connecting three copies of P1a to a functionalized Tris(2-aminoethyl)amine (Tren) platform a new peptide template, [T(P1)(3)], was obtained. This molecule is able to bind up to four metal ions (Cu(II) or Zn(II)): one in the Tren subsite and three in the azacyclononane subunits. The binding of the metals to the Tren platform induces a change from an open to a closed conformation in which the three short, helical peptides are aligned in a parallel manner with the azacyclonane units pointing inward within the pseudocavity they define. T(P1)(3) shows a peculiar behavior in the transphosphorylation of phosphate esters; the tetrazinc complex is a catalyst of the cleavage of 2-hydroxypropyl-p-nitrophenyl phosphate (HPNP), whereas the free ligand is a catalyst of the cleavage of an oligomeric RNA sequence with selectivity for pyrimidine bases. In the case of HPNP, Zn(II) acts as a positive allosteric effector by enhancing the catalytic efficiency of the system. In the case of the polyanionic RNA substrate, Zn(II) switches off the activity, thus behaving as a negative allosteric regulator. It is suggested that the opposite behavior of the catalyst induced by Zn(II) is associated with the change of conformation of the Tren platform, and consequently of the relative spatial disposition of the three linked peptides, that occurs after binding of the metal ion.

Hydrolytically active Eu(III) and Ce(IV) EF-hand peptides

A chimeric peptide (P4) has been designed to incorporate an EF-hand metal-binding loop into the context of the helix-turn-helix DNA binding motif of the engrailed homeodomain. This construct binds lanthanides, and in the presence of these metals, promotes the cleavage of supercoiled DNA and model phosphate esters (bisnitrophenyl phosphate). P4 binds lanthanides with moderate affinities (Eu(III), log Ka=4.85; and Ce(IV), log Ka=5.23). The structure of P4 is enhanced by metal binding, but the increase in secondary structure observed by CD is small, and suggests the metallopeptide is also quite flexible. Despite this flexibility, the efficient cleavage of DNA at low concentrations is dependent on the metallopeptide, and not on peptide or metal alone. This enhanced reactivity suggests the designed DNA-binding EF-hand peptides deliver the metal to the DNA for catalysis, even without rigid secondary structure.

Ruthenium-metallated adenine nucleobase polymers as novel reagents for catalytic cleavage of phosphate esters

A ruthenium-impregnated resin has been used for the catalytic cleavage of model phosphate ester (P-ester) substrates and highly efficient hydrolytic rate enhancements were obtained. Remarkably, million-fold rate acceleration was observed for a phosphodiester substrate. A thorough Michaelis–Menten kinetic analysis of this resin-catalyzed hydrolytic reaction, using three different phosphate monoester and diester substrates, is presented in this communication.

Attachment of Sugar Phosphates and Nucleotide Derivatives to Pyrazolylborate-Zinc Units

Phosphate derivatives which model intermediates of enzymatic glycoside and nucleotide transformations were reacted with the hydrolytically active zinc-hydroxide species Tp*Zn−OH (Tp* = 3,5-disubstituted tris(pyrazolyl)borates). Depending on the substrate or the reaction conditions, either phosphate ester cleavage or deprotonation of a nucleobase NH was observed. As a result, the Tp*Zn units were attached to the phosphate part or/and to the nucleobase part of the substrate. Nucleobase adducts were found of three uridine monophosphate derivatives. Phosphate adducts were found of a hydroxyacetone monophosphate, of a ribose phosphate, and of uridine and N-methyluridine monophosphates. The products were identified by crystallographic and spectroscopic methods as tetrahedral Tp*Zn−X complexes. Crystals of TpCum,MeZn−OPO(OC6H4NO2)(O-hydroxyacetone dimethyl ketal) are monoclinic, space group P21/n, with a = 13.221(1) Å, b = 13.738(1) Å, c = 30.303(3) Å, β = 99.57(1)°, Z = 4; those of TpCum,MeZn−OPO(OC6H4NO2)(O-2,3-isopropylidene-5-methylribose) are monoclinic, space group P21, with a = 16.179(6), Å, b = 16.206(5) Å, c = 21.192(14) Å, β = 101.02(5)°, Z = 2; those of TpPic,MeZn(H2O)−OPO(OC6H4NO2)(O-2,3-isopropylidene-5-methylribose) are triclinic, space group P1, with a = 13.106(4) Å, b = 13.676(5) Å, c = 17.021(6) Å, α = 84.10(3)°, β = 88.37(3)°, γ = 62.43(3)°, Z = 1.

(Pyrazolylborate)zinc Organophosphate Complexes Resulting from Hydrolytic Cleavage of Phosphate Esters

Five different (pyrazolylborate)zinc hydroxide complexes Tp*Zn−OH (1) were used as hydrolytic reagents towards esters of various acids of phosphorus. Trimethyl phosphate and trimethyl phosphite could not be cleaved. Dimethyl and diphenyl phosphite yielded TptBu,MeZn−OPHO(OR) (2, 3). Triphenyl phosphate reacted slowly producing moderate yields of Tp*Zn−OPO(OPh)2 (4). Tris(p-nitrophenyl) phosphate was cleaved rapidly, forming Tp*Zn−OPO(OC6H4NO2)2 (5) and Tp*Zn−OC6H4NO2 (6). Alkylbis(p-nitrophenyl) phosphates showed intermediate reactivity, losing p-nitrophenolate upon hydrolysis and producing Tp*Zn−OPO(OR)(OC6H4NO2) (7, 8). When phosphorus acid diesters were employed, condensation between the Zn−OH and P−OH functions occurred. This proved to be the convenient way of preparing the organophosphate complexes Tp*Zn−OPO(Ph)2 (9), Tp*Zn−OPO(OPh)2 (4), and Tp*Zn−OPO(OC6H4NO2)2 (5). Six structure determinations showed the structural variability of the resulting complexes.

Solid phase synthesis of peptides containing a phosphoserine - sulfur mustard adduct

Solid phase synthesis of peptides containing a serine thiodiglycol phosphate residue has been achieved by following a global on-resin phosphorylation strategy with a functionalized benzyl phosphoramidite. To preclude cleavage of the acid labile thiodiglycol phosphate ester during deprotection, the thioether functionality was temporarily protected as a sulfoxide.

Phosphate ester cleavage with a zinc hydroxide complex. Formation and crystal structure of a dinuclear zinc complex bridged with a phosphate monoester

The P–O bond in tris- or bis-phosphate ester is cleaved by a hydroxo zinc(II) complex to give a dinuclear µ-phosphate monoester complex 3, monomeric phosphate diester complex 4 and phenoxo complex 5.

Multiple reductive cleavage of calixarene diethyl phosphate esters: a route to [1 n ]metacyclophanes

The OH groups of p-t-butylcalix[n]arene (n= 4 and 8) were converted into diethyl phosphate esters and reductively cleaved by treatment with K/NH3 to yield tetra-p-t-butyl[14]- and octa-p-t-butyl[18]metacyclophanes (4) and (7).