Nanomolar inhibition of the enterobactin biosynthesis enzyme, EntE: synthesis, substituent effects, and additivity

2,3-Dihydroxybenzohydroxamoyl adenylate (I) was prepared as a potential product analog inhibitor of EntE (EC# 2.7.7.58), a 2,3-dihydroxybenzoate AMP ligase from Escherichia coli that is required for the biosynthesis of enterobactin. This compound, obtained by the aqueous reaction of imidazole-activated adenosine 5'-phosphate and 2,3-dihydroxybenzohydroxamic acid, is a competitive inhibitor with a Ki value of 4.5 x 10(-9)M. Deletion of the catecholic 3-OH group of (I), in compound (II), reduced inhibitory activity by a factor of 3.5, whereas, removal of both the 3-OH and 2-OH groups, in (III), reduced inhibitory activity by a factor of approximately 2000. Acetohydroxamoyl adenylate (IV), in which the entire catechol moiety of (I) is replaced by a hydrogen atom, gave <or= 10% inhibition at 6 x 10(-4)M, indicating a reduction in affinity by more than 10(5). The binding free energy of (I) is nearly equivalent to the sum of the corresponding values for adenosine 5'-phosphate and 2,3-dihydroxybenzoate.

A Competitive Molecular Recognition Study: Syntheses and Analysis of Supramolecular Assemblies of 3,5-Dihydroxybenzoic Acid and Its Bromo Derivative with Some N-Donor Compounds

A molecular recognition study of 3,5-dihydroxybenzoic acid (1) and its bromo derivative 4-bromo-3,5-dihydroxybenzoic acid (2) with the N-donor compounds 1,2-bis(4-pyridyl)ethene (bpyee), 1,2-bis(4-pyridyl)ethane (bpyea), and 4,4'-bipyridine (bpy) is reported. Thus, the syntheses and structural analysis of molecular adducts 1 a-1 c (1 with bpyee, bpyea, and bpy, respectively) and 2 a-2 c (2 with bpyee, bpyea, and bpy, respectively) are discussed. In all these adducts, recognition between the constituents is established through either O--H...N and/or O--H...N/C--H...O pairwise hydrogen bonds. In all the adducts both OH and COOH functional groups available on 1 and 2 interact with the N-donor compounds, except in 2 a, in which only COOH (COO-) is involved in the recognition process. The COOH moieties in 1 a, 1 b, and 2 b form only single O--H...N hydrogen bonds, whereas in 1 c and 2 c, they form pairwise O--H...N/C--H...O hydrogen bonds. In addition, subtle differences in the recognition patterns resulted in the formation of cyclic networks of different dimensions. In fact, only 1 c forms a four-molecule cyclic moiety, as was already documented in the literature for this kind of assemblies. All complexes have been characterized by single-crystal X-ray diffraction. The supramolecular architectures are quite elegant and simple, with stacking of sheets in all adducts, but a rather complex network with a threefold interpenetration pattern was found in 2 c.

A Green Method for the Electroorganic Synthesis of New 1,3-Indandione Derivatives

This is an environmentally friendly method in the field of electroorganic reactions under controlled potential electrolysis, without toxic reagents at a carbon electrode in an undivided cell which involves the (EC) mechanism reaction and comprises two steps alternatively; (i) electrochemical oxidation and (ii) chemical reaction. In particular, the electrochemical oxidation of 4-tert-butylcatechol, 4-methylcatechol and 2,3-dihydroxybenzoic acid in the presence of 2-phenyl-1,3-indandione has been studied in a water-acetonitrile (90 : 10) mixture. The research includes the use of a variety of experimental techniques, such as cyclic voltammetry, controlled-potential electrolysis, and spectroscopic identification of products (FT-IR, (1)H-NMR, and MS spectrometry).

Stereoselective alkylation of tartrate derivatives. A concise route to (+)-O-methylpiscidic acid and natural analogues

The lithium enolate of (2S,3S,5S,6S)-dimethoxy-2,3-dimethyl-1,4-dioxane-5,6-dithiocarboxylate undergoes stereoselective mono- and/or dialkylations to afford two new stereogenic centers. The alkylation products obtained possessed a cis stereochemistry, which was confirmed by the synthesis of natural 4'-O-methylpiscidic acid dimethyl ester .

Phenolic acid derivatives with potential anticancer properties--a structure-activity relationship study. Part 1: methyl, propyl and octyl esters of caffeic and gallic acids

The antiproliferative and cytotoxic properties of polyphenolic acid derivatives, structurally related with the natural models caffeic and gallic acids, have been tested in human cervix adenocarcinoma cells (HeLa). Simultaneous structural information was obtained for these compounds through theoretical ab initio methods. This study was conducted for the following esters: methyl caffeate (MC, 1), propyl caffeate (PC, 2), octyl caffeate (OC, 3), methyl gallate (MG, 4), propyl gallate (PG, 5) and octyl gallate (OG, 6). A significant growth-inhibition effect was assessed for some of these compounds, clearly dependent on their structural characteristics. Marked structure-activity relationships (SARs)--namely the number of hydroxyl ring substituents--were found to rule the biological effect of such systems.

Synthesis of Analogues of Congo Red and Evaluation of Their Anti-Prion Activity

No cure as of yet exists for any of the transmissible spongiform encephalopathies. In this paper, we describe the synthesis of analogues of Congo red and evaluation against a cellular model of infection, the SMB (scrapie mouse brain) persistently infected cell line, for their ability to inhibit the infectivity of the abnormal form of prion protein (PrP-res). The compounds have also been tested for their ability to inhibit the polymerization of PrPC by PrP-res. A number of analogues showed inhibition of PrP-res infectivity at nanomolar concentrations. Several analogues show promise; the most active compound, 2a, inhibits the formation of PrP-res in SMB cells with an EC50 of 25-50 nM.

Synthesis and inverse electron demand Diels-Alder reactions of 3,6-bis(3,4-dimethoxybenzoyl)-1,2,4,5-tetrazine

The synthesis of 3,6-bis(3,4-dimethoxybenzoyl)-1,2,4,5-tetrazine (2) and the scope of its reactivity in inverse electron demand Diels-Alder reactions are disclosed representing the first systematic study of the [4 + 2] cycloaddition reactions of 3,6-diacyl-1,2,4,5-tetrazines.

Synthesis and protein kinase inhibitory activity of balanol analogues with modified benzophenone subunits

A series of analogues of the protein kinase C (PKC) inhibitory natural product balanol which bear modified benzophenone subunits are described. The analogues were designed with the goal of uncovering structure-activity features that could be used in the development of PKC inhibitors with a reduced polar character compared to balanol itself. The results of these studies suggest that most of the benzophenone features found in the natural product are important for obtaining potent PKC inhibitory compounds. However, several modifications were found to lead to selective inhibitors of the related enzyme protein kinase A (PKA), and several specific modifications to the polar structural elements of the benzophenone were found to provide potent PKC inhibitors. In particular, it was found that replacement of the benzophenone carboxylate with bioisosteric equivalents could lead to potent analogues. Further, a tolerance for lipophilic substituents on the terminal benzophenone ring was uncovered. These results are discussed in light of recently available structural information for PKA.

Potential tuberculostatic agents. Topliss application on benzoic acid [(5-nitro-thiophen-2-yl)-methylene]-hydrazide series

Nitroaromatic compounds such as nifuroxazide are used in many human enteropathogenic bacteria infections without causing an increase in the plasmidial antibiotic resistance of the aerobic Gram-negative intestinal Enterobacteriaceae. For these reasons, these compounds have been synthesized using the rational approach of Topliss' decision tree. Generally, this approach allows us to obtain the most active derivative from the series in a few steps. These compounds were tested against Mycobacterium tuberculosis in vitro and the most active of the series identified. A new lead for potential tuberculostatic activity has been predicted and will be used in further QSAR studies.

Synthesis and conformational property of tannin-like p-tert-butylcalix[4]arene 1,3-diesters stabilized by intramolecular hydrogen bonds

Tannin-like p-tert-butylcalix[4]arene 1,3-digallate was synthesized, and its conformational property was investigated by dynamic (1)H NMR and X-ray crystallography. It was found that the 3-OH (or 5-OH) group of the galloyl group in p-tert-butylcalix[4]arene 1,3-digallate is placed at the position where an unusual nonbonded close contact is observed between the OH group and the aromatic ring of the galloyl group facing each other. The calixarene 1,3-diesters of various hydroxybenzoic acids were also prepared, and the conformational properties of those calixarenes were compared with that of p-tert-butylcalix[4]arene 1,3-digallate. A significant contribution of the 3- and 5-OH groups in pendant groups toward the close contact was found. It was suggested that the conformation of p-tert-butylcalix[4]arene 1,3-digallate was stabilized by intramolecular hydrogen bonds including OH.O and OH-pi interactions.

Aromatic inhibitors of dehydroquinate synthase: synthesis, evaluation and implications for gallic acid biosynthesis

The role of the active site metal in determining binding to 3-dehydroquinate synthase has been examined. Protocatechuic acid, catechol, and derivatives of these aromatics were synthesized that shared the common element of an ortho dihydroxylated benzene ring. Inhibition constants were determined for each aromatic as well as the variation of this inhibition as a function of whether Co(+2) or Zn(+2) was the active site metal ion.

seco-Cyclothialidines: new concise synthesis, inhibitory activity toward bacterial and human DNA topoisomerases, and antibacterial properties

seco-Cyclothialidines are a promising class of bacterial DNA gyrase B subunit inhibitors. A new seco-cyclothialidine derivative containing a dioxazine moiety, BAY 50-7952, was synthesized through a new concise pathway. One key step of the synthesis is the straightforward formation of the 2-aminothiazole derivative of S-tritylcysteine. In biological tests, BAY 50-7952 and other known seco-cyclothialidines exhibited high and selective activity toward bacterial DNA gyrase and toward Gram-positive bacteria. The dioxazine moiety and other similar groups were found to be important for the ability of the seco-cyclothialidines to penetrate bacterial membranes. The opposite enantiomer ((S)-form) of BAY 50-7952 was also synthesized, and neither significant target activity nor in vitro antibacterial activity were found, suggesting a highly selective fit of the (R)-form. Despite promising in vitro activity, only poor activity was found in the murine infection model.

A new tannase substrate for spectrophotometric assay

A new tannase substrate, protocatechuic acid p-nitrophenyl ester, 5, was synthesized using modern synthetic methods. The synthesis was designed to be performed by non-specialized chemists. It only involves four steps, three of which are protection-deprotection, and uses standard methods of separation and purification, such as recrystallization and column chromatography over silica. Under tannase action, protocatechuic acid p-nitrophenyl ester, 5, releases p-nitrophenol, which is easily measured spectrophotometrically either at 350 nm for pH values<6 or at 400 nm for pH values of 6-7 (yellow). The pH-response and the catalytic parameters of a crude Penicillium sp. tannase preparation were determined using 5 as substrate, thus showing the usefulness of this substrate in determining tannase activity.

Comparative effects of melatonin, L-deprenyl, Trolox and ascorbate in the suppression of hydroxyl radical formation during dopamine autoxidation in vitro

Degeneration of nigrostriatal dopaminergic neurons is the major pathogenic substrate of Parkinson's disease (PD). Inhibitors of monoamine oxidase B (MAO-B) have been used in the treatment of PD and at least one of them, i.e., deprenyl, also displays antioxidant activity. Dopamine (DA) autoxidation produces reactive oxygen species implicated in the loss of dopaminergic neurons in the nigrostriatal pathway. In this study we compared the effects of melatonin with those of deprenyl and vitamins E and C in preventing the hydroxyl radical (8OH) generation during DA oxidation. The rate of production of 2,3-dihydroxybenzoate (2,3-DHBA) in the presence of salicylate, an *OH scavenger, was used to detect the in vitro generation of *OH during iron-catalyzed oxidation of DA. The results showed a dose-dependent effect of melatonin, deprenyl and vitamin E in counteracting DA autoxidation, whereas vitamin C had no effect. Comparative analyses between the effect of these antioxidants showed that the protective effect of melatonin against DA autoxidation was significantly higher than that of the other compounds tested. Also, when melatonin plus deprenyl were added to the incubation medium, a potentiation of the antioxidant effect was found. These findings suggest that antioxidants may be useful in brain protection against toxicity of reactive oxygen species produced during DA oxidation, and melatonin, alone or in combination with deprenyl, may be an important component of the brain's antioxidant defenses to protect it from dopaminergic neurodegeneration.

An asymmetric aminohydroxylation approach to the azepine core of (-)-balanol

[reaction: see text]An efficient formal synthesis of the potent protein kinase C inhibitor (-)-balanol that relies on a modified asymmetric aminohydroxylation of the alpha,beta-unsaturated aryl ester (1) is reported. The aryl ester functionality and the dihydroquinyl alkaloid ligand system (DHQ)2-AQN are used to control the regio- and enantioselectivity of the process.

Formal total synthesis of (-)-balanol: concise approach to the hexahydroazepine segment based on RCM

A concise synthesis of the hexahydroazepine moiety 13 of (-)-balanol 1 is described that comprises only eight steps and is distinctly shorter than all previous reported approaches to this particular compound. Sharpless epoxidation of divinylcarbinol 4 and ring closing alkene metathesis (RCM) reaction for the formation of the heterocyclic scaffold 9 constitute the key transformations of this sequence. The latter reaction is best achieved with catalytic amounts of the ruthenium indenylidene complex 18 recently reported. Furthermore, it is demonstrated that RCM can be successfully carried out even in the presence of an azido function provided that Schrock's molybdenum alkylidene complex Mo(=NAr)(=CHCMe2Ph)[OC(Me)(CF3)2]2 (Ar = 2,6-diisopropylphenyl) is used as precatalyst.

Synthesis and biological activity of nifuroxazide and analogs. II

Nifuroxazyde and six analogs were synthesized by varying the substitute from the para-position of the benzenic ring and the heteroatom of the heterocyclic ring. The MIC of seven resultant compounds was determined by serial dilutions, testing the ATCC 25923 strain of Staphylococcus aureus. A significant increase in the anti-microbial activity of thyophenic analogs, as compared with furanic and pyrrholic analogs, was observed. In addition, unlike the cyano and hydroxyl groups, the acetyl group promoted anti-microbial activity.

Asymmetric synthesis of the balanol heterocycle via a palladium-mediated epimerization and olefin metathesis

[formula: see text] The enantioselective formal synthesis of balanol, a potent protein kinase C inhibitor, was accomplished from D-serine utilizing a Pd-catalyzed equilibration of diastereomeric 5-vinyloxazolines to set the stereochemistry of the vicinal amino and hydroxyl groups. A ruthenium-catalyzed ring-closing metathesis was employed to form the seven-membered nitrogen heterocyle.

Synthesis and anti-human immunodeficiency virus type 1 integrase activity of hydroxybenzoic and hydroxycinnamic acid flavon-3-yl esters

A series of new hydroxybenzoic and hydroxycinnamic acid flavon-3-yl esters were synthesized in order to obtain compounds targeting the human immunodeficiency virus (HIV) type 1 integrase (IN). The esters were tested for anti-IN and anti-reverse transcriptase (RT) activity in enzyme assays and for anti-HIV-1, anti-proliferative and anti-topoisomerase activity in cell-based assays. In enzyme assays, the two gallic acid flavon-3-yl esters showed a notable IN inhibition (IC50 values were 8.3 and 9.1 microM, respectively), while the two caffeic acid flavon-3-yl esters exhibited a modest activity (IC50 75 and 60 microM, respectively). Replacement of hydroxyl groups resulted in loss of potency. Caffeic acid 3',4'-dichloroflavon-3-yl ester also inhibited the RT activity whereas it was not active on human topoisomerases. It therefore represents an interesting example of a compound specifically targeting more than one step of the virus replication cycle.

Anti-picornavirus activity of synthetic flavon-3-yl esters

The in vitro antiviral activity against picornaviruses (rhinovirus serotype 1B and 14, and poliovirus type 2) of new synthetic 3-hydroxyflavones, 3-acetoxyflavones, and substituted cinnamic and benzoic acid flavon-3-yl esters was evaluated. The maximum non-toxic concentration of compounds was determined in a human cell line (HeLa) suitable for the replication of the three viruses. Their antiviral potency was measured by a plaque reduction assay. Generally, rhinoviruses exhibited a higher sensitivity to the new flavonoids than poliovirus. Flavones, with sterically small substituents in position 3, showed good activity against both rhinoviruses tested. However, the introduction of bulky substituents in the same position resulted in analogues with a higher toxicity and often with a lower efficacy.

Bis[2-(4-carboxyphenoxy)carbonylethyl]phosphinic acid (BCCEP): a novel affinity reagent for the beta-cleft modification of human hemoglobin

The design, synthesis, and hemoglobin cross-linking studies of a novel organic reagent, bis[2-(4-carboxyphenoxy)carbonylethyl]phosphinic acid (BCCEP, 1) have been reported. The reagent was designed with the aid of molecular modeling, employing crystal coordinates of human hemoglobin A0. It was synthesized in three steps commencing from 4-t-butoxycarbonylphenol. The tri-sodium salt of 1 was employed to cross-link human oxyHb. While SDS-PAGE analyses of the modified hemoglobin product pointed to the molecular mass range of 32 kDa, the HPLC analyse suggested that the cross-link had formed between the beta 1-beta 2 subunits. The oxygen equilibrium measurements of the modified hemoglobin at 37 degrees C showed significantly reduced oxygen affinity (P50 = 31.3 Torr) as compared with that of cell-free hemoglobin (P50 = 6.6 Torr). The sigmoidal shape of O2 curves of the modified Hb pointed to reasonable retainment of oxygen-binding cooperativity after the cross-link formation. Molecular dynamics simulation studies on the reagent-HbA0 complex suggested that the most likely amino acid residues involved in the cross-linking are N-terminus Val-1 or Lys-82 on one of the-chains, and Lys-144 on the other. These predictions were consistent with the results of MALDI-MS analyses of the peptide fragments obtained from tryptic digestion of the cross-linked product.

Bis[2-(4-carboxyphenoxy)carbonylethyl]phosphinic acid (BCCEP): a new reagent for hemoglobin modification

The synthesis and hemoglobin cross-linking studies of a novel organic reagent, bis[2-(4-carboxyphenoxy)carbonylethyl]phosphinic acid (BCCEP; 2) has been reported. The reagent was synthesized in four steps from hydroxybenzoic acid. The tri-sodium salt of BCCEP was employed to cross-link oxyHb, and the product was purified by DEAE-cellulose chromatography. The purified material was analyzed by SDS-PAGE, IEF, and HPLC analyses, which clearly showed the formation of covalent, intramolecular cross-links. While SDS-PAGE analyses of individual bands pointed to the molecular weight range of 32 kDa, the HPLC analyses suggested that the cross-links had formed between beta 1-beta 2 subunits. The oxygen equilibrium measurements and the Hill plots were performed on the purified bands to assess oxygen affinity as well as cooperativity of oxygen binding of the modified hemoglobins. All bands corresponding to modified hemoglobins showed significantly reduced oxygen affinity as compared with that of cell-free hemoglobin, as desired. The modified hemoglobins, however, exhibited somewhat reduced oxygen-binding cooperativity as contrasted with human stroma-free hemoglobin. Molecular dynamics simulation studies (Insight II/Discover/Biosym) on the Reagent-HbA0 complex suggested that the most likely amino acid residues involved in the cross-linking are Lys82 or N-terminal Val1 on one of the beta chains, and Lys144 on the other.

Synthesis and biological activity of nifuroxazide and analogs

Nifuroxazide and thirteen analogs were synthesized from substituted benzoic acids and minimal inhibitory concentrations were determined using the serial dilution tests, in three sequential steps. Nifuroxazide and chloramphenicol were used as reference standards. The tests were performed in TSB against the standard bacterial strain of Staphylococcus aureus ATCC 25923.

Synthesis and protein kinase C inhibitory activities of balanol analogs with replacement of the perhydroazepine moiety

Balanol is a potent protein kinase C (PKC) inhibitor that is structurally composed of a benzophenone diacid, a 4-hydroxybenzamide, and a perhydroazepine ring. A number of balanol analogs in which the perhydroazepine moiety is replaced have been synthesized and their biological activities evaluated against both PKC and cAMP-dependent kinase (PKA). The results suggested that the activity and the isozyme/kinase selectivity of these compounds are largely related to the conformation about this nonaromatic structural element of the molecules.

Inhibition of HIV-1 in cell culture by synthetic humate analogues derived from hydroquinone: mechanism of inhibition

Humic acids are natural constituents of soil and ground water and mainly consist of mixtures of polycyclic phenolic compounds. A similar complex of compounds with a mean size of about 1000 Da, designated HS-1500, was synthesized by oxidation of hydroquinone. HS-1500 inhibited HIV-1 infection of MT-2 cells with an IC50 of 50-300 ng/ml and showed a mean cell toxicity of about 600 micrograms/ml. Inhibition of HIV-induced syncytium formation was observed at 10-50 micrograms/ml. Treatment of free and cell-attached HIV with HS-1500 irreversibly reduced its infectivity, whereas the susceptibility of target cells for the virus was not impaired by treatment prior to infection. The HIV envelope protein gp120SU bound to sepharose-coupled HS-1500 and could be eluted by high salt and detergent. HS-1500 interfered with the CD4-induced proteolytic cleavage of the V3 loop of virion gp120SU. Furthermore, binding of V3 loop-specific antibodies was irreversibly inhibited, whereas binding of soluble CD4 to gp120SU on virus and infected cells was not affected. In conclusion, our data suggest, that the synthetic humic acid analogue inhibits the infectivity of HIV particles by interference with a V3 loop-mediated step of virus entry.