Catalytic hydrolysis of phosphodiesters by nucleophilic ions in gemini micellar media

The catalytic hydrolysis of bis(4‐nitrophenyl)phosphate (BNPP) and bis(2,4‐dinitrophenyl)phosphate (BDNPP) catalyzed by α‐nucleophiles in gemini micellar media was investigated at 27 °C. The cationic gemini surfactants, i.e., alkanediyl‐α‐ω‐bis(hydroxyethylmethylhexadecylammonium bromide) (16‐s‐16 MEA 2Br^?, where s = 4 and 6) were used. Nucleophilic reactivity of α‐nucleophiles such as hydroperoxide (HOO^?), acetohydroxamate (AHA^?), and butane 2,3‐dione monoximate ions (BDMO^?) were compared. The kinetic rate data were treated by applying the pseudophase model. The cationic gemini surfactants show unusual rate acceleration toward the cleavage of phosphodiesters with nucleophiles. These studies reveal that the hydroperoxide ion shows the highest catalytic activity reported so far with an unprecedented acceleration rate, 10⁷ times faster than that of the uncatalyzed reaction. The possible mechanism for the BNPP and BDNPP cleavage promoted by α‐nucleophiles is proposed on the basis of kinetic analysis. Copyright © 2014 John Wiley & Sons, Ltd.     

Intramolecular Participation of Amino Groups in the Cleavage and Isomerization of Ribonucleoside 3′‐Phosphodiesters: The Role in Stabilization of the Phosphorane Intermediate

A dinucleoside‐3′,5′‐phosphodiester model, 5′‐amino‐4′‐aminomethyl‐5′‐deoxyuridylyl‐3′,5′‐thymidine, incorporating two aminomethyl functions in the 4′‐position of the 3′‐linked nucleoside has been prepared and its hydrolytic reactions studied over a wide pH range. The amino functions were found to accelerate the cleavage and isomerization of the phosphodiester linkage in both protonated and neutral form. When present in protonated form, the cleavage of the 3′,5′‐phosphodiester linkage and its isomerization to a 2′,5′‐linkage are pH‐independent and 50–80 times as fast as the corresponding reactions of uridylyl‐3′,5′‐uridine (3′,5′‐UpU). The cleavage of the resulting 2′,5′‐isomer is also accelerated, albeit less than with the 3′,5′‐isomer, whereas isomerization back to the 3′,5′‐diester is not enhanced. When the amino groups are deprotonated, the cleavage reactions of both isomers are again pH‐independent and up to 1000‐fold faster than the pH‐independent cleavage of UpU. Interestingly, the 2′‐ to 3′‐isomerization is now much faster than its reverse reaction. The mechanisms of these reactions are discussed. The rate accelerations are largely accounted for by electrostatic and hydrogen‐bonding interactions of the protonated amino groups with the phosphorane intermediate.     

La（III）催化磷酸二（4－硝基苯酚）酯水解研究

The catalytic hydrolysis of bis（4-nitrophenyl）phosphate （BNPP） by lanthanum（Ⅲ） ion in the presence of amino-alcoholic ligands： diethanolamine （DEA） and triethanolamine （TEA）, was investigated kinetically at 30 ℃. The results indicated that the dinuclear dihydroxo complexes formed by lanthanum（Ⅲ） ion with aminoalcoholic ligands might be the catalytically active species which catalyze the hydrolysis of BNPP to different extents and the catalytic mechanism was believed to involve the synergism of double Lewis acid activation of the substrate and an intramolecular nucleophilic attack of a bridging oxo ligand.     

Synthesis and Crystal Structures of Two Di-Cu(Ⅱ) Complexes Based on an Asymmetric Dinucleating Ligand

Two new dicopper(II) complexes [Cu2L(OAc)2](ClO4)·H2O(1) and [Cu2L(BPP)2]-(ClO4)(2) using an asymmetric dinucleating ligand HL and auxiliary ligands such as acetate(OAc) and bisphenyl phosphate(BPP) have been synthesized and characterized by elemental analysis, IR and single-crystal X-ray diffraction. Complex 1 crystallizes as blue single crystals that belong to the triclinic crystal system and P1 space group, while complex 2 crystallizes in a monoclinic P21/c space group. Single-crystal X-ray diffraction analysis reveals that the two copper ions in complexes 1 and 2 reside within the adjacent ligand compartments and are bridged by the endogenous phenoxo-O from ligand L and the introduction of two desired exogenous carboxylates or phosphates in the bidentate μ-1,3-bridged mode. The coordination geometries of Cu(1) and Cu(2) are both distorted square pyramids.     

Hydrolysis of phosphate esters in aqueous solution promoted by cobalt(III)-tetraamine metallohydrolases: Chromatographic and spectroscopic studies

A combination of chromatographic and spectroscopic (Q-ToF/MS; FTIR) studies were conducted to further understand hydrolytic processes in reactions of phosphate mono- and phosphodiesters with model Cobalt(III)-tetraamine metallohydrolases of the type [CoL(OH)(OH₂)]²⁺; L?=?(en)₂, (tn)₂; en?=?1,2-diaminoethane, tn?=?1,3-diaminopropane.

High resolution mass spectroscopic (HRMS) analysis of the reaction fragments indicates that the monoester substrates undergo initial coordination to the metal center followed by an intramolecular hydroxyl attack on phosphorus, a process that is concerted with liberation of the bound alcoholic leaving group. The Co^III(tn)₂ complex displays twice as more reactivity towards both mono- and phosphodiesters compared to the (en)₂ analog under similar conditions, a behavior that is discussed in terms of the structural differences in the coordinated amine ligands. Plausible mechanisms for Co(III)-promoted hydrolysis of both the mono- and phosphodiesters are proposed.     

A Novel Lanthanide Complex with Remarkable Phosphodiester Transesterification Activity and DNA-Conjugatable Functionality

Encapsulated lanthanide complexes like the TCMC complexes are highly stable under physiological conditions. With the ultimate goal being an in vivo application of these complexes as a sequence-selective RNA/DNA cleaving agent (artificial RNAse/DNAse), kinetic stability of the complex would be a distinct advantage. We have synthesized a novel lanthanide complex with such stability and which displays high transesterification activity. The most important attribute of this compound is the nitrophenyl group which would allow further derivatization and conjugation to a DNA oligomer, thus creating a potential for the sequence selective hydrolysis of its target.     

Effective Homogeneous Hydrolysis of Phosphodiester and DNA Cleavage by Chitosan‐copper Complex

We aimed to explore the role of chitosan‐based metal complexes in catalyzing the hydrolysis of phosphodiesters. To this end, we performed detailed studies on the kinetics of the chitosan copper complex (CSCu)‐catalyzed hydrolysis of bis(4‐nitrophenol) phosphate (BNPP) in Tris‐H⁺ buffer and in an organic solvent. A significant enhancement in the rate of reaction (up to 3×10⁵‐fold acceleration) was observed at pH 8.0 (25°C). The pH dependence of BNPP hydrolysis at pH 5.5–9.5 and the UV spectra revealed that the copper‐bounded water molecules underwent deprotonation to form the active catalytic species CSCu‐OH. The kinetic behavior of BNPP catalytic hydrolysis in the Tris‐H⁺ buffer was consistent with that predicted by the Michaelis‐Menten kinetics model. An intramolecular nucleophilic attack by the copper‐bonded hydroxide group on the same activated phosphodiester substrate was proposed as the catalytic mechanism for CSCu‐catalyzed reaction system. The results of DNA binding and cleavage experiments indicated electrostatic binding mode of CSCu to DNA as well as the strong capability of CSCu to disturb the supercoiled strand of DNA and cleave it to nicked circular form.     

DNA Binding and Cleavage Activity of Zinc(II) Complex of N,N′‐Bis(2‐guanidinoethyl)‐2,6‐pyridinedicarboxamide

The interaction of zinc(II) complex of N,N′‐bis(guanidinoethyl)‐2,6‐pyridinedicarboxamide (Gua) with DNA was studied by CD spectroscopy and agarose gel electrophoresis analysis. The results indicate that the DNA binding affinity of Zn²⁺‐Gua is stronger than that of Gua and the Zn²⁺‐Gua can promote the cleavage of phosphodiester bond of supercoiled DNA under a physiological condition, which is ～10⁶ times higher than DNA natural degradation. The hydrolysis pathway was proposed as the possible mechanism for DNA cleavage promoted by the Zn²⁺‐ Gua. The acceleration is due to cooperative catalysis of the zinc cation center and the functional groups (bisguanidinium groups).     

A Novel Fluorescent Probe for Lead Ions

A new fluorescent probe for lead ions, p-nitrophenyl 3H-phenoxazin-3-one-7-yl phosphoric acid (NPPA), has been synthesized by linking resorufLn (serving as a fluorophore and electron acceptor) to p-nitrophenol (serving as a fluorescence quencher and electron donor) through phosphodiester bonds. When NPPA was irradiated with light, intramolecular fluorescence self-quenching took place due to the PET (photoinduced electron transfer) from the donor to the acceptor. However, upon addition of Pb^Ⅱ, the phosphate ester bonds in the probe were cleaved and the fluorophore was released, accompanying the retrievement of fluorescence.     

低pH毛细管区带电泳法分离寡核苷酸和硫代反义寡核苷酸

在低pH条件下采用毛细管区带电泳法对寡核苷酸(PO-ODNs)及具有药用价值的硫代反义寡核苷酸(PS-ODNs)药物“癌泰得”系列样品(18~20 mers)进行分离,并系统考察优化了缓冲溶液的pH、缓冲溶液的种类及浓度、添加剂的种类及浓度、电压、温度等因素对样品单碱基分离的影响。其中缓冲溶液的pH对分离起决定性的作用,而添加剂尿素的加入显著提高了PS-ODNs样品的分离度。结果表明,采用未涂层弹性石英毛细管(50 μm,总长49.0 cm,有效长度40.7 cm),以50 mmol/L磷酸二氢钠-磷酸(pH 2.24)-7 mol/L尿素为缓冲溶液,压力进样(2 kPa×10 s),负极进样,正极检测,在分离电压20 kV、柱温25 ℃、检测波长260 nm条件下,可实现寡核苷酸及硫代反义寡核苷酸混合样品的单碱基分离。PO-ODNs的18～19 mers及19~20 mers样品的平均分离度分别为4.68,3.20;PS-ODNs的18～19 mers及19~20 mers样品的平均分离度分别为1.23及0.81。该法操作简单,重现性好,可为反义寡核苷酸药物的分析提供借鉴。