Propionic Acid Substituents Research Articles

Preferential Solvation of 4-Carboxyl-2, 6-Dinitrophenylazohydroxynaphthalenes in Mixed Hydroxylic Solvents

Background: The applications of a group of 4-carboxyl-2,6-dintrophenylazohydroxynaphathalenes, AZ-01 to 04, as colourants, chemosensors or synthetic intermediates have been limited by their solubility.Aim: To investigate the effect of solvent mixture composition on the solubility, solution thermodynamics and position of equilibrium processes of the dyes.Method: The UV-visible spectral patterns of the dyes in binary mixtures including Methanol:Water, Ethanol:Water, Methanol:Ethanol, Methanol:Propan-1-ol, Methanol:Propan-2-ol, Propan-1-ol:Water and Propan-2-ol:Water were acquired. The type and quantitative estimation of solute-solvent interactions at play were determined by fitting spectral patterns to solvent parameters using multilinear regression.Results: Preferential solvation was detected by the non-ideality of the plots of E12 as against the mole fractions of co-solvent in all binary mixtures. In pure solvents, the spectral shifts of AZ-01, 03 and 04, which exist predominantly in the hydrazone form, were affected by polarity of solvent milieu while solvent basicity and acidity, in that order, were the significant parameters for AZ-02. In aqueous alcoholic mixtures, solvent polarity was contributory, although to different degrees, to the observed spectral data of the four dyes. However, solvent acidity and basicity were the primary determinants of spectral shifts observed with AZ-04 and AZ-03 respectively. Spectra-structure relationships identified the formation of the charged hydrazone tautomer which requires stabilisation by polar solvent milieu as responsible for the observed trend. In addition, interactions between new aggregated solvent-solvent species and the propionic acid substituent present in AZ-03 contributed to its spectral shifts.Conclusion: The solvatochromic properties of the phenylazonaphthalene series in binary mixtures have been successfully studied.

Dinuclear heme and non-heme metal complexes as bioinspired catalysts for oxidation reactions

Inspired by catalytic sites of cytochrome c oxidase (CcO) and nitric oxide reductase (NOR), a new series of dinuclear heme–non-heme complexes is described. The complexes are derived from the association between an iron(III)–protoporphyrin IX containing a covalently attached Gly-L-His-OMe residue to one propionic acid substituent (HMGH) and a metal complex with a tridentate amino-bis(benzimidazole) (BBH) ligand, mimicking the tris-histidine coordination of FeB and CuB in NOR and CcO, respectively. Besides the coordination of FeIII and CuII with the BBH ligand, we also explored the role of “non-biomimetic” metals, such as CoII, MnII, or ZnII, in order to establish the priority among the ancillary metal ions in cooperating with the ferric heme and promoting its catalytic activity in oxidation reactions. pH-spectrophotometric titrations show that the presence of the non-heme metal decreases the pKa of water-bound to hemin (pKa = 8.4 ± 0.1), with a larger effect with iron(III), copper(II) and zinc(II) complexes (pKa of 6.4 ± 0.1, 6.0 ± 0.1 and 6.5 ± 0.1, respectively), which suggests that an interaction with the non-heme metal center takes place also at a micromolar range. NMR spectra indicate that the interaction between hemin and the non-heme center is not strong enough to convert the high spin configuration of FeIII–heme to low spin as observed for CcO and NOR enzymes. The dinuclear complex enhances the peroxidase-like activity of heme in kinetic studies performed at pH 5.5, 7.0 (using 3-(4-hydroxyphenyl)-propanoic acid as the substrate) and 9.0 (using o-phenylenediamine). In particular, the stronger effects are observed with FeIII, CuII, and CoII complexes, which increase the turnover rates of hemin throughout the pH range analyzed. At neutral and basic pH the KM value decreases up to one fourth indicating a positive cooperation between HMGH and [M(BBH)]n+ in binding the substrates. Moreover, the presence of the non-heme center facilitates the binding of H2O2 and formation of high valent ˙PFeIVO species. These data show that interaction between the two metal centers occurs with heme in several oxidation states.

Porphomethene inhibitor of uroporphyrinogen decarboxylase: analysis by high‐performance liquid chromatography/electrospray ionization tandem mass spectrometry

An uroporphomethene inhibitor of uroporphyrinogen decarboxylase, characterized by high-performance liquid chromatography/electrospray ionization tandem mass spectrometry, was reported recently (Phillips et al., Proceedings of the National Academy of Sciences of the United States of America 2007; 104: 5079-5084). Close examination of the tandem mass spectrometric fragmentation pattern of the compound showed that it is not a tetrapyrrole or an uroporphyrinogen or uroporphyrin related molecule. The product ion spectrum showed a fragmentation pattern typical of a poly(ethylene glycol) structure. Characteristic fragmentations of the side-chain acetic acid and propionic acid substituents of a uroporphyrin or uroporphyrinogen derivative were absent.

A new dinuclear heme-copper complex derived from functionalized protoporphyrin IX

A new biomimetic model for the heterodinuclear heme/copper center of respiratory oxidases is described. It is derived from iron(III) protoporphyrin IX by covalent attachment of a Gly-L-His-OMe residue to one propionic acid substituent and an amino-bis(benzimidazole) residue to the other propionic acid substituent of the porphyrin ring, yielding the Fe(III) complex 1, and subsequent addition of a copper(II) or copper(I) ion, according to needs. The fully oxidized Fe(III)/Cu(II) complex, 2, binds azide more strongly than 1, and likely contains azide bound as a bridging ligand between Fe(III) and Cu(II). The two metal centers also cooperate in the reaction with hydrogen peroxide, as the peroxide adducts obtained at low temperature for 1 and 2 display different optical features. Support to this interpretation comes from the investigation of the peroxidase activity of the complexes, where the activation of hydrogen peroxide has been studied through the phenol coupling reaction of p-cresol. Here the presence of Cu(II) improves the catalytic performance of complex 2 with respect to 1 at acidic pH, where the positive charge of the Cu(II) ion is useful to promote O-O bond cleavage of the iron-bound hydroperoxide, but it depresses the activity at basic pH because it can stabilize an intramolecular hydroxo bridge between Fe(III) and Cu(II). The reactivity to dioxygen of the reduced complexes has been studied at low temperature starting from the carbonyl adducts of the Fe(II) complex, 3, and Fe(II)/Cu(I) complex, 4. Also in this case the adducts derived from the Fe(II) and Fe(II)/Cu(I) complexes, that we formulate as Fe(III)-superoxo and Fe(III)/Cu(II)-peroxo exhibit slightly different spectral properties, showing that the copper center participates in a weak interaction with the dioxygen moiety.

Rational design, synthesis, and structure-activity relationships of novel factor Xa inhibitors: (2-substituted-4-amidinophenyl)pyruvic and -propionic acids.

An inhibitor of factor Xa (fXa), the m-substituted benzamidine AXC1578 (1a), was structurally modified with the aim of increasing its potency. In particular, pyruvic acid and propionic acid substituents were incorporated into the P1 benzamidine moiety to introduce a favorable interaction with the oxy-anion hole in the catalytic triad region of fXa. This strategy was based on computational docking studies using the extracted active site of fXa. The validity of the computational model was supported by the acquisition of X-ray crystal structures of the 1a-trypsin and 3b-trypsin complexes (the homology around the active sites of fXa and trypsin is high). The above modifications significantly increased the inhibitory activity toward fXa, whereas the high selectivity for fXa versus thrombin was maintained or enhanced. Compounds 3b, 3c, 3e, and 4b are considered to be potential lead compounds for the development of orally active anticoagulant drugs because they demonstrated potent activity when administered orally to cynomolgus monkeys.

Structural requirements for recognition of essential porphyrin byPorphyromonas gingivalis

Porphyromonas gingivalis is an anaerobic Gram negative bacterium implicated in destructive infection of the tissues that support the teeth. This organism is unusual in that it cannot synthesize the porphyrin macrocycle and is therefore dependent on exogenous porphyrin for growth. Accordingly, in addition to physiologically relevant sources of heme, growth is stimulated by a number of iron-free porphyrins. Without exception, the capacity of porphyrins to support normal growth of P. gingivalis was associated with recognition by a sub-domain protein HA2 which is located within three outer-membrane proteins and which recognizes the porphyrin macrocycle in an iron-independent manner. Previous analysis in our laboratories indicated that recognition of the propanoate face of porphyrin was a distinguishing feature of the HA2 receptor. More detailed analysis indicated that derivatization of the two propionic acid substituents as their methyl esters or taurine derived N-(ethyl-2-sulfonic acid)amides abolished recognition by HA2 whereas the ethylenediamine derived N-(2-aminoethyl)amides did not affect binding by HA2 . The importance of the 2- and 4-vinyl groups of protoporphyrin IX for transport and growth was evaluated by testing compounds with hydrogen, sulfonic acid and glycol substituents at the 2- and 4-positions. While these derivatives bound HA2 with high affinity, study of protoporphyrin isomers indicated that the distribution of vinyl group substitution was important in regulating recognition by HA2 . In this report, the behaviour of mesoporphyrin IX in which the vinyl groups are replaced by ethyl groups and of chlorin E4 which contains only one propionic acid sidechain, were investigated to further define the structural requirements for recognition by HA2 . Both porphyrins were recognized by low affinity interactions. Based on these findings, a model for binding is proposed. The apparently unique mode of recognition of porphyrins by the receptor presents opportunities for specific targeting of this pathogenic organism.

Electron Transfer Processes in the Reactivity of Nonsteroidal Anti‐inflammatory Drugs in the Ground and Excited States

The nonsteroidal anti-inflammatory drugs (NSAID), naproxen, sulindac and indomethacin, were shown to donate electrons to nitro blue tetrazolium (NBT) when irradiated with UV light in deoxygenated aqueous buffer solution (pH 7.4, 30 degrees C). The reaction was monitored spectrophotometrically by the appearance of the diformazan reduction product from NBT. The electron transfer process facilitates the decomposition of the drugs. Naproxen in the presence of NBT is photodegraded principally to the alcohol (2-[1-hydroxyethyl]-6-methoxynaphthalene) at a rate approximately 20-fold faster than when irradiated alone in deoxygenated conditions. The photoproduct from naproxen also participates in the electron transfer to NBT but at a much slower rate than naproxen. Irradiation of sulindac or indomethacin in the presence of NBT caused the slow photoreduction of NBT to diformazan. In the absence of NBT, indomethacin and sulindac are essentially unreactive when irradiated in aqueous solution. The ability of a number of NSAID to act as electron donors in their ground state was studied by observing their oxidation by potassium peroxodisulfate in pH 7.0 phosphate buffer at 50 degrees C. The HPLC analysis of the drug remaining showed that the 2-arylpropionic acid NSAID (naproxen, ibuprofen, ketoprofen and suprofen) reacted at a rate equivalent to the thermal decomposition of peroxodisulfate. The major products were the same as detected in the photooxidation of these drugs, resulting from decarboxylation and oxygen addition but also included a dimeric compound. On the other hand, the NSAID that do not contain the propionic acid substituent all reacted more slowly with peroxodisulfate, enabling specific reaction rate constants to be evaluated.

Electron Transfer Processes in the Reactivity of Nonsteroidal Anti-inflammatory Drugs in the Ground and Excited States

The nonsteroidal anti-inflammatory drugs (NSAID), naproxen, sulindac and indomethacin, were shown to donate electrons to nitro blue tetrazolium (NBT) when irradiated with UV light in deoxygenated aqueous buffer solution (pH 7.4, 30°C). The reaction was monitored spec-trophotometrically by the appearance of the diformazan reduction product from NBT. The electron transfer process facilitates the decomposition of the drugs. Naproxen in the presence of NBT is photodegraded principally to the alcohol (2-[1-hydroxyethyl]-6-methoxynaphthalene) at a rate approximately 20-fold faster than when irradiated alone in deoxygenated conditions. The photoproduct from naproxen also participates in the electron transfer to NBT but at a much slower rate than naproxen. Irradiation of sulindac or indomethacin in the presence of NBT caused the slow photoreduction of NBT to diformazan. In the absence of NBT, indomethacin and sulindac are essentially unreactive when irradiated in aqueous solution. The ability of a number of NSAID to act as electron donors in their ground state was studied by observing their oxidation by potassium peroxodisulfate in pH 7.0 phosphate buffer at 50°C. The HPLC analysis of the drug remaining showed that the 2-arylpropionic acid NSAID (naproxen, ibuprofen, ketoprofen and suprofen) reacted at a rate equivalent to the thermal decomposition of peroxodisulfate. The major products were the same as detected in the photooxidation of these drugs, resulting from decarboxylation and oxygen addition but also included a dimeric compound. On the other hand, the NSAID that do not contain the propionic acid substituent all reacted more slowly with peroxodisulfate, enabling specific reaction rate constants to be evaluated.

Synthesis, biological evaluation, and structure-activity relationships of 3-acylindole-2-carboxylic acids as inhibitors of the cytosolic phospholipase A2.

3-Acylindole-2-carboxylic acid derivatives were prepared and evaluated for their ability to inhibit the cytosolic phospholipase A2 of intact bovine platelets. To define the structural requirements for enzyme inhibition, the carboxylic acid group, the acyl residue, and the moiety in position 1 were systematically modified. Furthermore, different substituents were introduced into the phenyl part of the indole. Replacement of the carboxylic acid group in position 2 of the indole with an acetic or propionic acid substituent led to a decrease of inhibitory potency. Enzyme inhibition was optimal when the acyl residue in position 3 had a length of 12 or more carbons. Conformational restriction of the acyl residue did not influence activity. Introduction of alkyl chains at position 1 of the indole with 8 or more carbons resulted in a loss of activity. However, replacing the omega-methyl group of such compounds with a carboxylic acid moiety was found to increase inhibitory potency significantly. Among the tested indole derivatives, 1-[2-(4-carboxyphenoxy)ethyl]-3-dodecanoylindole-2-carboxyli c acid (29b) had the highest potency. With an IC50 of 0.5 microM it was about 20-fold more active than the standard cPLA2 inhibitor arachidonyl trifluoromethyl ketone (IC50: 11 microM).

Synthese und Antitumoraktivität neuer Porphyrin‐Platin(II)‐Komplexe mit an den Porphyrin‐Seitenketten gebundenem cytostatischen Platin‐Rest

Synthesis and Antitumor Activity of New Porphyrin‐Platinum(II) Complexes with the Cytostatic Platinum Fragment Attached to the Porphyrin Side ChainsFifteen ligands of the porphyrin type, all derived from natural porphyrins, and their platinum(II) complexes, in which the Pt fragment is attached to the porphyrin side chains, were synthesized and characterized. Two different kinds of ligands were prepared: eight compounds with propionic acid substituents in the positions 6 and 7 of the porphyrin skeleton and seven ligands with 3‐aminopropyl side chains in the same positions. The ligands were transformed into eight diammine(dicarboxylato)platinum(II) complexes and into seven diaminedichloroplatinum(II) complexes. One of the water‐insoluble dichloroplatinum(II) compounds was converted into a water‐soluble complex by replacement of the chloride ligands by the lactate anion. The antitumor activity of the complexes was tested in vitro towards the MDA‐MB 231 mammary carcinoma cell line, and in vivo towards the P 388 leukemia of the mouse, the hormone‐independent MXT mammary carcinoma of the mouse and the Sarcoma 180 of the mouse. The best results in antitumor activity were obtained with diammine(dicarboxylato)platinum(II) complexes.

Reactivity of pyrrole pigments: Part 16. Mesobiliverdin IXα and mesobilirubin IXα bridged between the propionic acid substituents

Mesobiliverdin IXα diesters of α,ω-dialkanols were obtained by reaction of mesobiliverdin IXα dicesium salt with diiodomethane, 1,3-dibromopropane and 1,4-dibromobutane. Mesobiliverdin IXα methylene diester was tested and compared to mesobiliverdin IXα dimethyl ester, for their photoisomerization behaviour, addition of nucleophiles at C10, protonation, and deprotonation. The constriction imposed by the internal cycle to the flexibility around the two central rings has no appreciable effect on these reactions. In fact, the small pK a differences in the protonation indicate that previous results, on the protonation of biliverdins bridged between the end rings, can be explained through a stretched structure of the protonated bile pigment implying a change in the configuration or conformation of one end ring.

Involvement of a labile axial histidine in coupling electron and proton transfer in Methylophilus methylotrophus cytochrome c''.

Methylophilus methylotrophus cytochrome c'' is an unusual monohaem protein (15 kDa) undergoing a redox-linked spin-state transition [Santos, H. & Turner, D. L. (1988) Biochim. Biophys. Acta 954, 277-286]. The midpoint redox potential of cytochrome c" was measured over the pH range 4-10. The pH dependence of the midpoint redox potential was interpreted in terms of a model that considers the redox-state dependence of the ionization of two distinct and non-interacting protonated groups in the protein. This analysis led to the following pKa values within the pH range studied: pKa10 = 6.4, pKa1r = 5.4 and pKa2r = 8.1. Proton-NMR spectroscopy was used to assist the characterization of the two ionizing groups responsible for the observed redox-Bohr effect: the group ionizing with a lower pKar was assigned to a haem propionic acid substituent and the other to the axial histidine ligand which becomes detached upon reduction, which has a pKa0 too low to be measured. It is shown that M. methylotrophus cytochrome c" is able to couple electron and proton transfer in the physiological pH range through a mechanism involving reversible change in the haem-iron coordination. Possible implications for the physiological role of the protein are discussed.

On the1H NMR spectra of biliverdins with free propionic acid substituents

The1H NMR spectra of Biliverdin IXα and Mesobiliverdin XIIIα were studied in order to explain their low resolution in CDCl3/CD3OD solvent mixtures. The smallT 2 andT 1 values of these1H NMR spectra are probably due to aggregate formation promoted by the presence of the free propionic acid substituents.

A denaturation-induced proton-uptake study of horse ferricytochrome c

The observation that 6 M-urea denatures horse ferricytochrome c in the pH range 4-6, but not horse ferrocytochrome c, has been exploited to determine the denaturation-induced proton uptake of ferricytochrome c. This is related to the pKa values of ionizable groups buried within the native protein. The data indicate that one of the haem propionic acid substituents of ferricytochrome c has a pKa of less than 4.5, whereas the other has a pKa of greater than 9.

Structural basis for the variation of pH-dependent redox potentials of Pseudomonas cytochromes c-551

The redox potentials of many c-type cytochromes vary with pH over the physiological pH range. We have investigated the pH dependence of redox potential for the four homologous cytochromes c-551 from Pseudomonas aeruginosa, Pseudomonas stutzeri strain 221, Pseudomonas stutzeri strain 224, and Pseudomonas mendocina . The pH dependence is due to an ionizable group that ionizes with pKox in ferricytochrome c-551 but with a higher pK, pKred , in ferrocytochrome c-551. For P. aeruginosa cytochrome c-551 it has been shown that this ionizable group is one of the heme propionic acid substituents [Moore, G. R., Pettigrew , G. W., Pitt , R. C., & Williams, R. J. P. (1980) Biochim. Biophys. Acta 590, 261-271]but the values of pKox and pKred are significantly lower in this protein than in the other three cytochromes. NMR and chemical modification studies show that for the two P. stutzeri cytochromes c-551 and P. mendocina cytochrome c-551, this propionic acid substituent is again important for the pH dependence of the redox potential. However, a histidine occurring at position 47 in their sequences hydrogen bonds to the propionic acid and thereby raises its pK. In P. aeruginosa cytochrome c-551, His-47 is substituted by Arg-47. Hydrogen-bonding schemes involving His-47 and the propionic acid are proposed.

Beta-meso-Phenylbiliverdin IX alpha and N-phenylprotoporphyrin IX, products of the reaction of phenylhydrazine with oxyhemoproteins.

Oxyhemoglobin and oxymyoglobin were allowed to react aerobically with phenylhydrazine and p-tolylhydrazine. The chloroform extract of each reaction mixture, after treatment with H2SO4/methanol, yielded a blue pigment and a green pigment, which were identified by electronic absorption, mass, and proton NMR spectroscopy as the dimethyl esters of beta-meso-arylbiliverdin IX alpha and N-arylprotoporphyrin IX, respectively. N-Phenylprotoporphyrin IX dimethyl ester formed complexes with Zn2+, Cd2+, and Hg2+ but not with other cations. The proton NMR spectrum of the zinc complex suggested binding of the phenyl group to one of the two pyrrole rings of protoporphyrin IX with a propionic acid substituent. The effectiveness of phenylhydrazine as an inducer of Heinz body formation may be due to destabilization of the hemoglobin molecule by the replacement of heme with phenyl adducts of biliverdin and protoporphyrin.

Contact-shifted resonances in the 1H NMR spectra of cytochrome b5 Resonance identification and spin density distribution in the heme group

This paper describes the identification of some of the contact-shifted resonances in the 1H NMR spectrum of low spin ferric cytochrome b 5. In these experiments comparison with cytochrome b 5 which had been reconstituted with deuteroheme IX played an important role. NMR techniques used include double resonance experiments, line width analyses, and studies of the pH-dependence of the 1H NMR chemical shifts. The electronic heme structure derived from these resonance assignments is characterized by a highly anisotropic spin density distribution. This anisotropy is most strikingly manifested in the resonances of the vinyl and propionic acid substituents of the protoheme IX. The experiments described in this paper further revealed the coexistence in aqueous solutions of two different molecular species of cytochrome b 5, which can be simultaneously observed in the regions of the 1H NMR spectrum which contain the largely contact-shifted resonances.