Ester Complexes Research Articles

A study of the intermolecular interactions of tolmetin/N-acetyl- l-tyrosine ethyl ester complex

The formation of tolmetin/N-acetyl- l-tyrosine ethyl ester (ATEE) complex has been reported by means of both theoretical and experimental studies, including quantum mechanical calculations as well as UV–vis absorption, fluorescence and time-resolved spectroscopy measurements. It has been found that the fluorescence of ATEE is quenched due to the formation of a non-fluorescent complex between ATEE and tolmetin in the ground state. The geometrical parameters of ATEE/tolmetin complex have been determined with the use of the DFT method applying the B3LYP correlation-exchange functional and 6-31G(d) basis set. The results of experiments indicated the static ATEE quenching by tolmetin. Additionally, the experimental and theoretically predicted Gibbs free energy of complexation has been calculated.

Efficient synthesis of (1 R,2 S) and (1 S,2 R)-2-aminocyclopentanecarboxylic acid ethyl ester derivatives in enantiomerically pure form

A 4-step synthesis of an optically active synthetic intermediate [(1 R,2 S)-2-(4′-fluorobenzylamino)cyclopentanecarboxylic acid ethyl ester complex with ( S)-(+)-mandelic acid; compound 12, >99% de] required for the preparation of a promising HCV NS5B polymerase inhibitor is reported. This process utilizes mandelic acid as a resolving agent, which can be recovered in good yield by a simple extraction. An optimized version of the chemistry described avoids the use of chromatographic purifications making it suitable for large-scale applications. In addition, the straightforward conversion of compound 12 to enantiomerically pure (1 R,2 S)-2-aminocyclopentanecarboxylic acid ethyl ester and the corresponding Boc and Cbz derivatives is reported. The preparation of the enantiomer of 12 (compound 15) in enantiomerically pure form and the conversion of this entity to (1 S,2 R)-2-aminocyclopentanecarboxylic acid ethyl ester and the corresponding Boc and Cbz derivatives is also described.

A Sodium Supported Borate Ester: Synthesis, Spectral Characterization and Crystal Structure of dimeric Sodium Organoborate Complex [Na(py)][B(hyncaH−2)2

A dimeric sodium supported borate complex, [Na(py)][B(hyncaH−2)2]2 (1) (py = pyridine, hynca = 1-hydroxynaphthalene-2-carboxylic acid), has been synthesised by the reaction of NaBH4 with two equivalents of hynca in anhydrous THF and following crystallization from py/H2O solution afforded borate ester derivative. The complex has been fully characterized by FT-IR in the solid state and by NMR (1H and 13C) spectroscopy and electrospray ionization mass spectrometry in solution. The molecular structure of the title compound was determined by single crystal X-ray diffraction. Structure analysis of complex 1 confirmed the presence of an anionic complex [B(hyncaH−2)2]− in which boron atom is coordinated simultaneously by two hynca ligands utilising both alkoxide and carboxylate groups for bonding. The Na atom is six- coordinate to five O atoms of hydroxy carboxylic acid and one pyridine N atom. Crystal data: crystal system, monoclinic, a = 10.971(3) A, b = 6.839(3) A, c = 30.545(5) A, β = 92.20(2)°, space group P21/c (#14), V = 2,290(1) A3, Z = 4. There are limited examples of alkali metal supported borate ester complexes.

Terpene Conjugates of Diaminedichloridoplatinum(II) Complexes: Antiproliferative Effects in HL‐60 Leukemia, 518A2 Melanoma, and HT‐29 Colon Cancer Cells

Twenty-eight [6-(aminomethyl)nicotinate]dichloridoplatinum(II) complexes 1 esterified with various terpene alcohols either directly or via alkyl spacers were tested for antiproliferative activity in human 518A2 melanoma and HL-60 leukemia cells. Generally, conjugates with menthanes and polycyclic sesquiterpenes attached via propane-1,2-diyl spacers were most active. In the melanoma cells, the propane-1,2-diyl-spacered conjugates of (-)-menthol (1a(2')), (+)-neomenthol (1b(2')), (-)-carvomenthol (1h(2')), and (-)-isolongifolol (1n(2')) displayed growth inhibition at IC(50)<4 microM which is ten times smaller than that of cisplatin. The stationary diamino ligand was also crucial. The (-)-menthyl ester complexes with 2,3-diaminopropanoate (9a) and 2,4-diaminobutanoate (10a) ligands caused a greater and persistent growth inhibition in HT-29 colon cancer cells upon long-term exposure when compared to the 6-(aminomethyl)nicotinate analogue 1a. The cedrenyl ester 1l and the menthoxyisopropyl ester 1a(2') proved most efficacious in all three tumor cell lines. The DNA binding of complexes 1 was assessed by electrophoretic band-shift experiments and found correlated to the terpene structure but not to the observed antiproliferative activities.

Complexes of Alkyl Esters of Ethylidenediphosphonic Acids with Lanthanide Nitrates

The lanthanide complexes LnL2(NO3)3 3a‐c and 5a‐c, where Ln is La, Ce and Sm and L are tetraethyl esters of ethylidenediphosphonic acid 1 (for complexes 3) and tetraisopropyl esters of ethylidenediphosphonic acid 4 (for complexes 5) were synthesized and characterized by elemental analysis, IR and NMR spectroscopy. The crystal structure of DyL2(NO3)3 7 (L is tetraisopropyl ester of methylenediphosphonic acid) was determined by single crystal X‐ray diffraction. The complex 7 crystallized in the monoclinic space group P21/n with a=14.196(2)Å, b= 18.013(2)Å, c=17.929(2)Å, β=103.723(3)°, V=4453.7(8)Å3, Z=4, ρcalc=1.547 g/cm3, R=0.0290, wR2=0.0555, S=0.995 for 10 233 reflections. The dysprosium atom in 7 is surrounded by nine oxygen atoms where four are delivered from the two bidentate chelating nitrate ions, one from the monodentate nitrate group and four from the bidentate phosphonate ligands.

Complexation of amino acids derivatives in water by calix[4]arene phosphonic acids

Series of the calix[4]arene phosphonic acids with various substituents at the lower rim was synthesized. Complexing properties of these receptors towards methyl esters of six amino acids strongly depended on the calix[4]arene conformation flexibility. The complex formation processes were monitored using 1H NMR spectroscopy (deuterated phosphate buffer at pD 7.3, 22 °C) and association constant values were evaluated. Inherently mobile calix[4]arene molecule 3 occurred in cone conformation in aqueous solution turned out to be more effective in complexation of the basic amino acids methyl esters compared to the rigid 2 and flexible 4. Mixed 1:2 and 2:1 (host–guest) complexes were observed for compound 1 with all amino acids methyl esters.

Molecular interaction of alkanols with acrylic esters: A spectroscopic study

Using FTIR spectroscopy, the complexation of alkanols viz. n-pentanol, sec-pentanol and tert-pentanol with acrylic esters viz. methyl methacrylate (MMA), ethyl methacrylate (EMA) and butyl methacrylate (BMA) in organic solvents viz. n-heptane, CCl 4 and benzene has been studied. The formation constants and free energy changes of the complexation were determined. It was observed that n-pentanol forms stronger complexes with acrylic esters than tert-pentanol in the latter systems, which is attributed to the difference in steric hindrance. The strength and the nature of interaction between the molecules of pentanol with esters and acrylic esters have been discussed. The effect of solvent on the formation of the alkanol–ester complexes is also discussed.

Treatment of Diabetes in Experimental Animals by Metallocomplexes

The number of patients suffered from diabetes mellitus has increased over the decades probably because of both lifestyle- and diet-changes. There are two types of diabetes mellitus. Type 1 diabetes mellitus is due to the autoimmune-mediated destruction of pancreatic B cells, which results in absolute insulin deficiency, thus the patients require insulin injections. Type 2 diabetes mellitus is due to the insulin resistance and abnormal insulin secretion, thus the patients require exercise, diet control and/or oral hypoglycemic medicines. Each treatment, however, has some problems involving physical and mental burden, and formation of self-antibodies for insulin injections, and the severe side effects and discontinuation of insulin synthesis in the pancreas for hypoglycemic medicines. To overcome these important problems and find the replacements for the insulin injections and synthetic medicines, we attempted to develop new antidiabetic metallocomplexes with novel structures and mechanisms. In 1990, we first presented orally active vanadyl (+4 oxidation state of oxo-vanadium) complexes including vanadyl-cysteine methyl ester complex, which normalized hyperglycemia in the streptozocin (STZ)-induced type 1 diabetic rats. Based on these findings, we have developed a wide variety of vanadyl complexes with different coordination environments around vanadyl ion. Following the study, we also challenged to develop orally active zinc complexes since 2002. This review focuses on our recent development of vanadyl and zinc complexes for anti-diabetic and anti-metabolic syndromes, together with the propose for the possible action mechanism of these complexes in adipocytes.

Microwave Synthesis, Characterization and Theoretical Study of para-Toluenesulfonic Acid Threonine Salt and Its Ester Derivatives

Some new amino acid ionic liquids (ILs) derived from threonine (Thr) were studied. The para-toluenesulfonic acid threonine and its methyl ester (ThrC1-TsOH) and ethyl ester (ThrC2-TsOH) derivatives were synthesized with one-step microwave synthesis method, and their physicochemical properties, including the IR spectra, melting points, and thermostability, were studied experimentally. Quantum chemistry calculations were also performed to study the influence of the esterification of cation on the melting point. Geometry optimizations on the single molecules of the Thr complex and its methyl and ethyl ester complexes in gas phase were performed with DFT B3LYP/6-311++G** method, and the vibration frequencies of each optimized molecule were analyzed at the same level method. The binding energies between ions were calculated and the basis set superposition error (BSSE) was corrected with counterpoise method (CP). It was found that the esterification of cation would weaken not only the intermolecular hydrogen bond interaction, but also the intramolecular interaction between ions obviously. And so the decrease of the melting point is caused by the two factors, and the weakenness of intramolecular interaction should be the main factor for the titled compound to be an ionic liquid.

Electrokinetic probes for single-step screening of polyol stereoisomers: the virtues of ternary boronate ester complex formation

Electrokinetic probes based on the differential migration of ternary boronate ester complexes permit the selective analysis of micromolar levels of UV-transparent polyol stereoisomers in urine samples via dynamic complexation-capillary electrophoresis that is applicable to single-step screening of in-born errors of sugar metabolism, such as galactosemia.

Structures of complexes of benzyl and allyl esters of monensin A with Mg 2+, Ca 2+, Sr 2+, Ba 2+ cations studied by ESI-MS and PM5 methods

Benzyl ester of monensin A (MON3) and allyl ester of monensin A (MON4) were synthesized and their ability of forming complexes with divalent cations was studied by ESI mass spectrometry and by PM5 semi empirical calculations. The ESI-MS spectra indicate that MON3 as well as MON4 form stable 1:1 complexes with the divalent cations used in this study. The complexes of MON3 are stable to cv = 50 V and after this cv value no m/ z signals are more observed in the spectra. In contrast, with increasing cone voltage values, a fragmentation process of the MON4 complexes is simultaneously observed, where dehydration processes are the main events. The structures of the complexes are discussed in detail on the basis of conformational analysis together with the PM5 semiempirical calculations.

Transcriptional regulation of phospholipid biosynthesis is linked to fatty acid metabolism by an acyl-CoA-binding-protein-dependent mechanism in Saccharomyces cerevisiae

In the present study, we have used DNA microarray and quantitative real-time PCR analysis to examine the transcriptional changes that occur in response to cellular depletion of the yeast acyl-CoA-binding protein, Acb1p. Depletion of Acb1p resulted in the differential expression of genes encoding proteins involved in fatty acid and phospholipid synthesis (e.g. FAS1, FAS2, ACC1, OLE1, INO1 and OPI3), glycolysis and glycerol metabolism (e.g. GPD1 and TDH1), ion transport and uptake (e.g. ITR1 and HNM1) and stress response (e.g. HSP12, DDR2 and CTT1). In the present study, we show that transcription of the INO1 gene, which encodes inositol-3-phosphate synthase, cannot be fully repressed by inositol and choline, and UAS(INO1) (inositol-sensitive upstream activating sequence)-driven transcription is enhanced in Acb1p-depleted cells. In addition, the reduction in inositol-mediated repression of INO1 transcription observed after depletion of Acb1p appeared to be independent of the transcriptional repressor, Opi1p. We also demonstrated that INO1 and OPI3 expression can be normalized in Acb1p-depleted cells by the addition of high concentrations of exogenous fatty acids, or by the overexpression of FAS1 or ACC1. Together, these findings revealed an Acb1p-dependent connection between fatty acid metabolism and transcriptional regulation of phospholipid biosynthesis in yeast. Finally, expression of an Acb1p mutant which is unable to bind acyl-CoA esters could not normalize the transcriptional changes caused by Acb1p depletion. This strongly implied that gene expression is modulated either by the Acb1p-acyl-CoA ester complex directly or by its ability to donate acyl-CoA esters to utilizing systems.

Reactivity pathways for nitric oxide and nitrosonium with iron complexes in biologically relevant sulfur coordination spheres

The interaction of nitric oxide (NO) with iron–sulfur cluster proteins results in the formation of dinitrosyl iron complexes (DNICs) coordinated by cysteine residues from the peptide backbone or with low molecular weight sulfur-containing molecules like glutathione. Such DNICs are among the modes available in biology to store, transport, and deliver NO to its relevant targets. In order to elucidate the fundamental chemistry underlying the formation of DNICs and to characterize possible intermediates in the process, we have investigated the interaction of NO (g) and NO+ with iron–sulfur complexes having the formula [Fe(SR)4]2−, where R=tBu, Ph, or benzyl, chosen to mimic sulfur-rich iron sites in biology. The reaction of NO (g) with [Fe(StBu)4]2− or [Fe(SBz)4]2− cleanly affords the mononitrosyl complexes (MNICs), [Fe(StBu)3(NO)]− (1) and [Fe(SBz)3(NO)]− (3), respectively, by ligand displacement. Mononitrosyl species of this kind were previously unknown. These complexes further react with NO (g) to generate the corresponding DNICs, [Fe(SPh)2(NO)2]− (4) and [Fe(SBz)2(NO)2]− (5), with concomitant reductive elimination of the coordinated thiolate donors. Reaction of [Fe(SR)4]2− complexes with NO+ proceeds by a different pathway to yield the corresponding dinitrosyl S-bridged Roussin red ester complexes, [Fe2(μ-StBu)2(NO)4] (2), [Fe2(μ-SPh)2(NO)4] (7) and [Fe2(μ-SBz)2(NO)4] (8). The NO/NO+ reactivity of an FeII complex with a mixed nitrogen/sulfur coordination sphere was also investigated. The DNIC and red ester species, [Fe(S-o-NH2C6H4)2(NO)2]− (6) and [Fe2(μ-S-o-NH2C6H4)2(NO)4] (9), were generated. The structures of 8 and 9 were verified by X-ray crystallography. The MNIC complex 1 can efficiently deliver NO to iron–porphyrin complexes like [Fe(TPP)Cl], a reaction that is aided by light. Removal of the coordinated NO ligand of 1 by photolysis and addition of elemental sulfur generates higher nuclearity Fe/S clusters.

Comparative study of the synthesis of CoFe2O4 and NiFe2O4 in silica through the polymerized complex route of the sol–gel method

In this work the synthesis of CoFe2O4-SiO2 and NiFe2O4-SiO2 nanocomposites was studied via the sol–gel method, using the polymerized complex route. The polymerized precursors obtained by the reaction of citric acid, ethylene glycol, tetraethylorthosilicate, ferric nitrate, and cobalt nitrate or nickel chloride were characterized by nuclear magnetic resonance (NMR) and infrared (IR) spectroscopy. NMR and IR spectra of the precursors, without and with metallic ions, show the formation of polymeric chains with ester and ether groups and complexes of metal-polymeric precursor. The nanocomposites were obtained by the thermal decomposition of the organic fraction and characterized by X-ray diffraction (XRD) and vibrating sample magnetometry (VSM). XRD patterns show the formation of CoFe2O4 and NiFe2O4 in an amorphous silica matrix above 400 °C in both cases. When the calcination temperature was 800 °C the particle size of the crystalline phases, calculated using the Scherrer equation, reached ∼35 nm for the two oxides. VSM plots show the ferrimagnetic behavior that is expected for this type of magnetic material; the magnetization at 12.5 KOe of the CoFe2O4-SiO2 and NiFe2O4-SiO2 compounds was 29.5 and 17.4 emu/g, respectively, for samples treated at 800 °C.

Synthesis and structural characterization of cross-linked histidine–phenol Cu(ii) complexes as cytochrome c oxidase active site models

Tridentate cross-linked histidine-phenol Cu(ii) ether and ester complexes, chemical analogs of the active site of several heme-copper oxidases, have been synthesized and crystallized.

Templating Photodimerization of trans-Cinnamic Acid Esters with a Water-Soluble Pd Nanocage

A water-soluble octahedral Pd nanocage acting as a reaction vessel templates the photodimerization of substituted trans-cinnamic acid methyl esters in water. Irradiation of the host-guest complexes of trans-cinnamic acid methyl esters with the Pd nanocage resulted in selective formation of a syn head-head dimer in addition to the corresponding cis isomer. These results suggest that the guest molecules are preoriented in a selective fashion with the hydrophilic ester group facing water and the hydrophobic aryl group tucked within the cavity of the host. Such an orientation occurs at the hydrophobic-hydrophilic interface between the nanocage exterior and interior. Weak intermolecular C-H-pi and pi-pi interactions between the host and the guest(s) are likely to be responsible for the lack of mobility of the reactant olefins during their short excited-state lifetime.

Catalysis and inhibition of ester hydrolysis in the presence of resorcinarene hosts functionalized with dimethylamino groups

AbstractComplexation and catalysis of two calixresorcinarene (RES) derivatives with nucleophilic N,N‐dimethylamino functions attached to their upper rims in the hydrolysis of carboxylate and sulfonate esters of 4‐nitrophenol and 2,4‐dinitrophenol have been investigated. Rate constants obey the complexation equation: Values of the dissociation constant (Ks) of the complexes are within the range exhibited by other systems such as cyclodextrins–ester complexes. The reactions of sulfonate esters only exhibit inhibition by the macrocyclic hosts. The reactions of the carboxylate esters exhibit catalysis and inhibition depending on the pH of the system. It is proposed that the dimethylamino function in RES3 and RES5 behaves as a nucleophile to form a reactive acylammonium species which subsequently decomposes and regenerates the catalytic amine.In the reaction of substituted phenyl acetates with RES3 the effective charge on the leaving oxygen in the complexed state (+0.88) is slightly more positive than that in the free ester (+0.70). The effective charge on the leaving oxygen in the transition structure is substantially more positive (+0.04 units) than in a model intramolecular reaction of tertiary dimethylamines with aryl esters (−0.53 units). The influence of the host on the reaction in the complex includes an electronic component which is ascribed to solvation of the transition structure of the rate‐limiting step by water molecules located within the cavity of the host. It is suggested that this solvation is stronger than that occurring in the transition state for the model intramolecular reaction. Copyright © 2006 John Wiley &amp; Sons, Ltd.

A novel lipopathic Cr(VI) oxidant for organic substrates: Kinetic study of oxidation of benzyl alcohol

AbstractA novel lipopathic oxidizing agent, cetyltrimethylammonium dichromate, was used for oxidation of benzyl alcohol in various organic solvents and in surfactant systems. The reaction kinetics was investigated with change in [acid], [substrate], [oxidant], [surfactant], and temperature. The rate constant values led to propose that the reaction occurs in a reversed micellar system produced by the oxidant, akin to an enzymatic environment. The rate variation with variation in [surfactant] and solvent isotope effect suggest that the path of reaction to be through the formation of an ester complex, the decomposition of which is the rate‐determining step. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 651–656, 2006

Oxidation of Cholesterol by a Biomimetic Oxidant, Cetyltrimethylammonium Dichromate

The oxidation of cholesterol by cetyltrimethylammonium dichromate (CTADC) in dichloromethane (DCM) yielded 7-dehydrocholesterol, while with addition of acetic acid in DCM the product was found to be 5-cholesten-3-one. The kinetics of oxidation of cholesterol by CTADC in DCM, in the presence of acid, was investigated with change in [acid], [cholesterol], [CTADC], [surfactant], temperature, and solvents. The reaction was found to be first order with acetic acid and fractional order with CTADC and cholesterol. Michaelis-Menten-type kinetics was observed with respect to cholesterol. The solvent isotope effect was found to be k(D2O)/k(H2O) = 0.72. The observed experimental data suggest that the reaction occurs in reversed micellar system, akin to an enzymatic environment, and the reaction path involves the intermediate formation of an ester complex, which undergoes decomposition to give the product.

Polyoxaalkyl esters of phenylboronic acids as new podands

Three oxaalkyl esters of phenylboronic acid and one oxaalkyl ester of phenyldiboronic acid have been synthesized and their ability to form complexes with Li + and Na + cations has been studied using multinuclear NMR, ESI mass spectrometric and PM5 semiempirical methods. It has been demonstrated that the esters of phenylboronic acid form 1:1 complexes with Li + and Na + cations whereas the ester of phenyldiboronic acid can additionally form complexes of 1:2 stoichiometry. The stability constants of these complexes have been determined to show that with increasing number of oxygen atoms in the oxaalkyl chains the complexes of increasing stability are formed. The exemplary 1:1 and 1:2 structures of the complexes of esters with Li + and Na + cations, respectively, are given. They show that the cations are coordinated within a pseudo-crown structures formed by oxaalkyl chains.