Lithium Binaphtholate-Catalyzed Michael Reaction of Malonates with Maleates and Its Application to the Enantioselective Synthesis of Tricarboxylic Acid Derivatives.

The Michael reaction of malonates with maleates afforded the corresponding adducts in high yields with high enantioselectivities (up to 98% enantiomeric excess (ee)) by using dilithium 3,3'-dichlorobinaphtholate as a catalyst. The obtained Michael adducts could be converted to optically active tricarboxylic acid (TCA) derivatives via the Krapcho reaction.

Versatile C(3)-symmetric scaffolds and their use for covalent stabilization of the foldon trimer.

C3-Symmetric trimesic acid scaffolds, functionalized with bromoacetyl, aminooxyacetyl and azidoacetyl moieties, respectively, were synthesized and compared regarding their utility for the trivalent presentation of peptides using three different chemoselective ligation reactions, i.e. thioether and oxime formation, as well as the "click" reaction. The latter ligation method was then used to covalently stabilize the trimer of foldon, a 27 amino acid trimerization domain of bacteriophage T4 fibritin, by linking the three foldon monomers to the triazido-functionalized trimesic acid scaffold. This reaction dramatically enhanced the thermal stability of the trimer, while maintaining the correct fold, as demonstrated by CD spectroscopy and X-ray crystal structure analysis, respectively, of the foldon-scaffold conjugates.

Molecular self-assembly at nanometer scale modulated surfaces: trimesic acid on Ag(111), Cu(111) and Ag/Cu(111).

The balance between molecule-molecule and molecule-surface interactions is a determining factor in the creation of well-ordered organic networks formed by self-assembly on crystalline metal surfaces. We have used a scanning tunneling microscope under ultrahigh vacuum conditions to study the molecular self-assembly of trimesic acid on a surface that is modulated on a comparable nanometer scale as the size of the molecules. This is made of one layer of silver grown on a Cu(111) surface where it forms a periodic reconstruction. It is shown that the self-assembly of trimesic acid at room temperature, where intermolecular interactions are taking place via hydrogen bonds, is strongly disturbed due to the modulated substrate and the spatially varying potential imposed on the molecules. Annealing to 350 K partly deprotonates the molecules and changes the intermolecular interactions to stronger ionic hydrogen bonds. This reduces the influence of the modulated substrate and allows the molecules to self-assemble into long-range ordered networks on the surface. Comparisons are made to self-assembly on the flat surfaces of Ag(111) and Cu(111), where we always find well-ordered molecular networks.

Antifungal activity of homoaconitate and homoisocitrate analogs.

Thirteen structural analogs of two initial intermediates of the L-α-aminoadipate pathway of L-lysine biosynthesis in fungi have been designed and synthesized, including fluoro- and epoxy-derivatives of homoaconitate and homoisocitrate. Some of the obtained compounds exhibited at milimolar range moderate enzyme inhibitory properties against homoaconitase and/or homoisocitrate dehydrogenase of Candida albicans. The structural basis for homoisocitrate dehydrogenase inhibition was revealed by molecular modeling of the enzyme-inhibitor complex. On the other hand, the trimethyl ester forms of some of the novel compounds exhibited antifungal effects. The highest antifungal activity was found for trimethyl trans-homoaconitate, which inhibited growth of some human pathogenic yeasts with minimal inhibitory concentration (MIC) values of 16-32 mg/mL.

Synthesis, characterization and experimental investigation of Cu-BTC as CO2 adsorbent from flue gas.

Porous Cu-BTC material was synthesized by the solvothermal method. Powder X-ray diffraction (PXRD) was used to test the phase purity of the synthesized material and investigate its structural stability under the influence of flue gas components. The thermal stability of the material was determined through thermal gravimetric (TG) analysis. Scanning electron microscopy (SEM) was employed to study the microstructure of the material. Cu-BTC was demonstrated not only to have high CO2 adsorption capacity but also good selectivity of CO2 over N2 by means of packed bed tests. The adsorption capacity of Cu-BTC for CO2 was about 69 mL/g at 22 degrees C. The influence of the main flue gas components on the CO2 capacity of the material were discussed as well.

Synthetic and computational studies on the tricarboxylate core of 6,7-dideoxysqualestatin H5 involving a carbonyl ylide cycloaddition-rearrangement.

Reaction of diazodiketoesters 17 and 28 with methyl glyoxylate in the presence of catalytic rhodium(II) acetate generates predominantly the 6,8-dioxabicyclo[3.2.1]octanes 29 and 30, respectively. Acid-catalysed rearrangement of the corresponding alcohol 31 favours, at equilibrium, the 2,8-dioxabicyclo[3.2.1]octane skeleton 33 of the squalestatins-zaragozic acids. Force field calculations on the position of the equilibrium gave misleading results. DFT calculations were correct in suggesting that the energy difference between 31 and 33 should be small, but did not always suggest the right major product. Calculation of the NMR spectra of the similar structures could be used to assign the isomers with a high level of confidence.

Comparing anti-HIV, antibacterial, antifungal, micellar, and cytotoxic properties of tricarboxylato dendritic amphiphiles.

Three series of homologous dendritic amphiphiles--RCONHC(CH(2)CH(2)COOH)(3), 1(n); ROCONHC(CH(2)CH(2)COOH)(3), 2(n); RNHCONHC(CH(2)CH(2)COOH)(3), 3(n), where R = n-C(n)H(2n+1) and n = 13-22 carbon atoms--were assayed for their potential to serve as antimicrobial components in a topical vaginal formulation. Comparing epithelial cytotoxicities to the ability of these homologues to inhibit HIV, Neisseria gonorrhoeae, and Candida albicans provided a measure of their prophylactic/therapeutic potential. Measurements of the ability to inhibit Lactobacillus plantarum, a beneficial bacterium in the vagina, and critical micelle concentrations (CMCs), an indicator of the potential detergency of these amphiphiles, provided additional assessments of safety. Several amphiphiles from each homologous series had modest anti-HIV activity (EC(50) = 110-130 microM). Amphiphile 2(18) had the best anti-Neisseria activity (MIC =65 microM), while 1(19) and 1(21) had MICs against C. albicans of 16 and 7.7 microM, respectively. Two measures of safety showed promise as all compounds had relatively low cytotoxic activity (EC(50) = 210-940 microM) against epithelial cells and low activity against L. plantarum, 1(n), 2(n), and 3(n) had MICs490, 1300, and 940 microM, respectively. CMCs measured in aqueous triethanolamine and in aqueous potassium hydroxide showed linear dependences on chain length. As expected, the longest chain in each series had the lowest CMC-in triethanolamine: 1(21), 1500 microM; 2(22), 320 microM; 3(22), 340 microM, and in potassium hydroxide: 1(21), 130 microM; 3(22), 40 microM. The CMC in triethanolamine adjusted to pH 7.4 was 400 microM for 1(21) and 3900 microM for 3(16). The promising antifungal activity, low activity against L. plantarum, relatively high CMCs, and modest epithelial cytotoxicity in addition to their anti-Neisseria properties warrant further design studies with dendritic amphiphiles to improve their safety indices to produce suitable candidates for antimicrobial vaginal products.

Azido derivative of tricarboxylic acid for photoaffinity labeling.

A new photoaffinity probe, 5-(1-hydroxy-4-azidophenylazo)-1,2,3-benzenetricarboxylic acid, was synthesized and characterized. This reagent can be potentially used in photoaffinity labeling of the mitochondrial tricarboxylate carrier, as well as of enzymes interacting with tricarboxylic acids. Inhibition and labeling of the mitochondrial tricarboxylate carrier is presented.

The squalestatins: synthesis and biological activity of some C3-modified analogues; replacement of a carboxylic acid or methyl ester with an isoelectronic heterocyclic functionality.

A series of squalestatins modified at the C3-position with a heterocyclic functionality was prepared and evaluated in vitro as inhibitors of squalene synthase (SQS). Structure-activity relationships for compounds with the 4,6-dimethyloctenoate at C6(S1 analogues) were different from those for analogues lacking the C6 ester (H1 analogues), with a greater dependence on the nature of the C3-substituent for the H1 series. Potent SQS inhibitory activity equivalent to that of H1 is retained by a C3-(tetrazol-5-yl) analogue, i.e., a carboxylic acid mimetic. The C3-methyl ester derivative is 10-fold less active than H1, and SQS inhibitory activity similar to that of the methyl ester was retained only in those C3-heterocycle-substituted H1 analogues for which electrostatic potential maps of the C3-substituent were closely similar to that of a methyl ester.

The squalestatins: decarboxy and 4-deoxy analogues as potent squalene synthase inhibitors.

Squalestatins without either the hydroxy group at C-4 or the carboxylic acid at C-3 or C-4 were prepared and evaluated for their ability to inhibit rat liver microsomal squalene synthase (SQS) in vitro. These modifications were well tolerated for compounds with the 4,6-dimethyloctenoate ester at C-6 (S1 series). However in analogues without the C-6 ester (H1 series), removal of the C-4 hydroxy group gave compounds with reduced potency, whereas decarboxylation at C-3 resulted in a dramatic loss of SQS inhibitory activity. In comparison with S1 1, C-4 deoxyS1 3 and C-3 decarboxyS1 10 have shorter in vivo durations of action on the inhibition of hepatic cholesterol biosynthesis in rats. C-4 deoxyS1 3 retains good serum cholesterol-lowering ability in marmosets, while C-3 decarboxyS1 10 showed only a marginal effect even at high dose.

Synthesis and pharmacological characterization of aminocyclopentanetricarboxylic acids: new tools to discriminate between metabotropic glutamate receptor subtypes.

The four stereoisomers of 1-aminocyclopentane-1,3,4-tricarboxylic acid {ACPT-I (18) and -II (19), (3R, 4R)-III [(-)-20], and (3S,4S)-III [(+)-20]} have been synthesized and evaluated for their effects at glutamate receptors subtypes. ACPTs are ACPD analogues in which a third carboxylic group has been added at position 4 in the cyclopentane ring. None of the ACPT isomers showed a significant effect on ionotropic NMDA, KA, and AMPA receptors. On the other hand, ACPT-II (19) was found to be a general competitive antagonist for metabotropic receptors (mGluRs) and exhibited a similar affinity for mGluR1a (KB = 115 +/- 2 microM), mGluR2 (KB = 88 +/- 21 microM), and mGluR4a (KB = 77 +/- 9 microM), the representative members of group I, II and III mGluRs, respectively. Two other isomers, ACPT-I (18) and (+)-(3S,4S)-ACPT-III [(+)-20], were potent agonists at the group III receptor mGluR4a (EC50 = 7.2 +/- 2.3 and 8.8 +/- 3.2 microM) and competitive antagonists with low affinity for mGluR1a and mGluR2 (KB > 300 microM). Finally, (-)-(3R,4R)-ACPT-III [(-)-20] was a competitive antagonist with poor but significant affinity for mGluR4a (KB = 220 microM). These results demonstrate that the addition of a third carboxylic group to ACPD can change its activity (from agonist to antagonist) and either increase or decrease its selectivity and/or affinity for the various mGluR subtypes.

Rapid synthesis of the 7-deoxy zaragozic acid core.

[reaction: see text] We have developed an efficient synthesis of the 7-deoxy zaragozic acid core. The synthesis begins with a Feist-Bénary reaction that assembles all three carbons of the polycarboxylic acid portion of the core. This reaction is followed by highly diastereoselective aldol and dihydroxylation reactions that set the remaining stereocenters of the core. The synthesis finishes with lactol oxidation and lactone alcoholysis/ketal formation reactions to construct the bicyclic ring system of the core.

Scope and diastereoselectivity of the "interrupted" Feist-Bénary reaction.

[reaction: see text] The base-promoted condensation of beta-dicarbonyl compounds with alpha-haloketones, the Feist-Bénary reaction, conveniently produces highly substituted dihydrofurans. We show here that this reaction is quite general with respect to the nature of the beta-dicarbonyl compound, proceeding with beta-ketoesters, beta-oxopropionates, beta-diketones, and beta-dialdehydes. We also show that the diastereoselectivity of this reaction depends on the acidity of the nucleophile.

Template-directed C-H insertion: synthesis of the dioxabicyclo[3.2.1]octane core of the zaragozic acids.

[reaction: see text] The preparation of (+/-)-24, a model for the core of the zaragozic acids, is reported. The pivotal reaction in this endeavor is the dirhodium(II)-catalyzed intramolecular C-H bond insertion of 2-diazoacetyl-1,3-dioxane 4, a transformation which generates four of the six stereocenters present in the core structure. A novel method for the diastereoselective synthesis of pyruvic acid acetals was also developed and employed in the preparation of 4 from xylitol derivative 7.

Urinary excretion of homocitric acid and methylhomocitric acid in propionic acidaemia: minor metabolic products of the citrate synthase aldol condensation reaction.

The identity of two formerly novel citric acid analogues, homocitric acid and methylhomocitric acid, in urine samples from patients with propionic acidaemia was confirmed by gas chromatography and mass spectrometry. Authentic reference substances were synthesized using a Reformatskii reaction. Homocitric acid and methylhomocitric acid were detected as minor metabolites in the urine samples from propionyl coenzyme A carboxylase deficient individuals. It was shown that these substances can be formed by the citrate synthase condensation reaction of alpha-ketoglutarate with acetyl coenzyme A and propionyl coenzyme A, respectively.

Sucrose tricarboxylate by sonocatalysed TEMPO-mediated oxidation.

Oxidation of sucrose by the NaOCl/TEMPO system provided sucrose tricarboxylate without the addition of sodium bromide as co-catalyst when high-frequency (500 kHz) ultrasound was applied, in contrast to very limited conversion without sonication. In the presence of sodium bromide, sonication also caused acceleration of the oxidation. The rate increase due to sonication of the oxidant system prior to sucrose addition suggests that ultrasound acts at the level of the formation of the nitrosonium ion, the active oxidising species in the catalytic cycle.

Synthesis, gastroprotective, antisecretory and anti-Helicobacter effect of N-[3-(3-(1-piperidinylmethyl) phenoxy)propyl]-hydroxyacetamide 2-hydroxypropane-1,2,3-tricarboxylate bismuth (3+) complex (MX1)-MX1.

MX1 (N-[3-(3-(1-piperidinylmethyl)phenoxy)propyl]-hydroxyacetamide+ ++ 2-hydroxypropane-1,2,3-tricarboxylate bismuth (3+) complex) is a novel salt of the active metabolite of H2-antagonist roxatidine with a complex of bismuth with citric acid. In a model of ethanol-induced ulcers in male Wistar rats, both roxatidine and the bismuth salt reduced the number and the total length of lesions. Comparison of roxatidine and MX1 at equimolar doses of 160 mumol kg-1 showed a more potent cytoprotective effect of MX1. The potency of anti-secretory and antiacidic effects of MX1 was more than twice that of roxatidine on histamine-stimulated secretion in female Wistar pylorus-ligated rats. Microbiological tests with the reference bismuth preparation De-Nol showed prominent anti-Helicobacter properties of MX1 in-vitro. Both test compounds had similar range of MICs to Helicobacter pylori, from 4 to 64 microgram bismuth mL-1. The cytoprotective, antisecretory, anti-acidic and anti-Helicobacter properties of the new agent MX1 warrant further more extensive pharmacological and clinical trials.

One-step preparation of 2,3,6-tricarboxy cellulose.

Water-soluble sodium 2,3,6-tricarboxylate cellulose (NaTCC) or sodium mesotartarate/monohydrated glyoxilate alternating co-polyacetal was prepared from regenerated cellulose in a yield of 82% by one-step oxidation with catalytic amounts of 2-azaadamantane N-oxyl (AZADO), NaBr, and excess NaOCl in water at room temperature under alkaline conditions. The AZADO-oxidized product was shown to have an almost homogeneous NaTCC chemical structure by its 1H and 13C NMR spectra. The weight- and number-average molecular masses of the obtained NaTCC were 10,700 and 7000. When AZADO-mediated oxidation was applied to softwood bleached kraft pulp, a water-soluble oxidized product was obtained. However, it had a more heterogeneous chemical structure showing that the complete oxidation of the C2, C3, and C6 hydroxyls to carboxyls is difficult to achieve in native cellulose.

Enantioselective synthesis of isotopically labeled homocitric acid lactone.

A concise synthesis of homocitric acid lactone was developed to accommodate systematic placement of carbon isotopes (specifically (13)C) for detailed studies of this cofactor. This new route uses a chiral allylic alcohol, available in multigram quantities from enzymatic resolution, as a starting material, which transposes asymmetry through an Ireland-Claisen rearrangement.