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.

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.

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.

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.

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.

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.

Assembly of 1,2,3-benzenetricarboxylic acid and sliver(I) metal center to a novel 3D supramolecular framework: syntheses, structure and properties.

The reaction of AgNO3, pyrazine (pyz) and 1,2,3-benzenetricarboxylic acid (H3btc) leads to a new 3D supramolecular architecture, namely {[Ag(H2btc)(pyz)]·(H2O)2}n (1), which has been characterized by IR spectroscopy, elemental analysis, thermogravimetry, photoluminescent and powder X-ray diffraction (PXRD). Compound 1 displays a 3D supramolecular network, which is built from cationic Ag-pyz chains and anionic [(H2btc)n·2H2O]- layers through the weak Ag⋯O interaction. Complex 1 exhibits photoluminesscence with an emission maximum at ca.391 nm upon excitation at ca. 241 nm.

Evidence of benzilic rearrangement during the electrochemical oxidation of D-glucose to D-glucaric acid.

During the course of the 2,2,6,6-tetramethyl-1-piperidinyloxy free radical-catalyzed electrochemical oxidation of D-glucose to D-glucaric acid a new side-product was observed. This compound was isolated and identified as a tricarboxylic acid of unique structure, which was named maribersonic acid. Its structure was proven by different experiments coupled with several analytical methods, and its appearance during the electrochemical oxidation of D-glucose was rationalized through a thorough study.

'2+1' tricarbonyltechnetium(I)/tricarbonylrhenium(I) mixed-ligand complexes with methyl thiosalicylate and isocyanide ligands as potential precursors of radiopharmaceuticals.

The complexes of [(99m)Tc]-tricarbonyltechnetium(I) and [(188)Re]-tricarbonylrhenium(I), of the '2+1' type, with methyl thiosalicylate as an anionic bidentate ligand and with either tert-butyl 3-isocyanopropionate or glycine-glycine-tyrosine 4-isocyanobutyrate as monodentate ligands, have been prepared on the n.c.a. scale. The complexes exhibit different lipophilicity and high stability in neutral aqueous solutions. Based on the results of the challenge experiment with histidine, cysteine and glutathione the studied complexes might be considered to be promising models for radiopharmaceutical precursors.

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.

Synthesis and fluorescence properties of ten lanthanide benzene-1,3,5-tricarboxylate complexes.

Ten new lanthanide benzene-1,3,5-tricarboxylate complexes Tb(btc).6H(2)O (1), nano-scale Tb(btc).6H(2)O (2), Tb(2)(btc)(2)(phen)(3).4H(2)O (3), TbLn(Hbtc)(2)(phen)(2) Cl(2).H(2)O [Ln=Y(4), and Gd (5), btc=benzene-1,3,5-tricarboxy-late], TbLa(btc)(2)(phen)(3).6H(2)O (6) and TbM(btc)(C(2)H(5)OH)(2)Cl(2).2H(2)O [M=Zn (7), Cd (8), Mn (9) and Ni (10)] have been synthesized and characterized. The fluorescence intensity of nano-scale complex (2) is stronger than that of the complex (1), indicating that there are new and special fluorescence properties in nano-scale complex due to the nano-scale effect and quenching by the proximity of surface defects. The fluorescence intensity of the ternary complex (3) is stronger than that of the binary complex (1). The studies of the fluorescence spectra and lifetimes of the other seven complexes show obviously different results. The luminescent intensity of the complexes (4), (5), (6), (7) and (8), which contain the metal ions Y(3+), La(3+),Gd(3+), Zn(2+) and Cd(2+), increased remarkably. Complexes (9) and (10), containing Mn(2+) and Ni(2+), respectively, exhibit fluorescence quenching, which is caused by the unsaturated d-layer electrons consuming the energy in the form of radiative transition.

Surface-modification-directed controlled adsorption of serum albumin onto magnetite nanocuboids synthesized in a gel-diffusion technique.

Magnetite nanocuboids have been synthesized via gel-diffusion technique in agarose gel. Here, the agarose gel matrix has been used as an organic template for formation and growth modification of magnetite. Gel mineralization mimics the membrane-based biomineralization, controls the diffusion process and gives the micro/nano environment for the crystal growth. We also attempt to understand the influence of different surface modifications of synthesized magnetite nanocuboids on protein interaction. For this purpose, magnetite particles were coated with trimesic acid (benzene-1,3,5-tricarboxylic acid) and stearic acid, which generates a hydrophilic and a hydrophobic modified surface, respectively. We report controlled adsorption behavior of bovine serum albumin (BSA) by surface modification of magnetite nanocuboids with different functional groups. The adsorption capacity of BSA increases on trimesic acid-coated surfaces compared to bare magnetite surfaces, while it decreases on stearic acid-coated surfaces. In situ fluorescence spectroscopy has been used to analyze the tertiary protein structure in the adsorbed state on these three surfaces. Partial unfolding in the tertiary structure of BSA was observed upon adsorption onto bare magnetite surfaces. On trimesic acid-coated surfaces, tertiary unfolding of BSA was greater than on bare magnetite surfaces, while BSA undergoes minor tertiary structural change on stearic acid-coated surfaces.

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.

Total syntheses of zaragozic acids A and C by a carbonyl ylide cycloaddition strategy.

A carbonyl ylide cycloaddition approach to the squalene synthase inhibitors zaragozic acids A and C is described. The carbonyl ylide precursor 8 was synthesized starting from di-tert-butyl D-tartrate (47) via an eleven-step sequence involving the regioselective reduction of the mono-MPM (MPM=4-methoxybenzyl) ether 48 with LiBH4 and the diastereoselective addition of sodium tert-butyl diazoacetate to alpha-keto ester 10. The reaction of alpha-diazo ester 8 with 3-butyn-2-one (40) in the presence of a catalytic amount of [Rh2(OAc)4] gave the desired cycloadduct 59 as a single diastereomer. The dihydroxylation of enone 59 followed by sequential transformations permitted the construction of the fully functionalized 2,8-dioxabicyclo[3.2.1]octane core 5. Alkene 79 derived from 5 serves as a common precursor to zaragozic acids A (1) and C (2), since the elongation of the C1 alkyl side chain can be attained by olefin cross-metathesis, especially under the influence of Blechert's catalyst (85).

Syntheses, spectroscopies and structures of molybdenum(VI) complexes with homocitrate.

Initial investigations into the possible role of homocitric acid in iron molybdenum cofactor (FeMo-co) of nitrogenase lead us to isolate and characterize two tetrameric molybdate(VI) species. The complexes K2(NH4)2[(MoO2)4O3(R,S-Hhomocit)2].6H2O (1) and K5[(MoO2)4O3(R,S-Hhomocit)2]Cl.5H2O (2) (homocitric acid = H4homocit, C7H10O7) are prepared from the reactions of acyclic homocitric acid and molybdates, which represent the first synthetic structural examples of molybdenum homocitrate complexes. The homocitrate ligand trapped by tetranuclear molybdate coordinates to the molybdenum(VI) atom through alpha-alkoxy and alpha-, beta-carboxy groups. The physical properties, structural parameters, and their possible biological relevances are discussed.

Synthesis of trimethyl (2S,3R)- and (2R,3R)-[2-2H1]-homocitrates and dimethyl (2S,3R)- and (2R,3R)-[2-2H1]-homocitrate lactones-an assay for the stereochemical outcome of the reaction catalysed both by homocitrate synthase and by the Nif-V protein.

Trimethyl (3R)-homocitrate 17, trimethyl (2S,3R)-[2-2H1]-homocitrate 17a and (2R,3R)-[2-2H1]-homocitrate 17b, as well as dimethyl (3R)-homocitrate lactone 18, (2S,3R)-[2-2H1]-homocitric lactone 18a and (2R,3R)-[2-2H1]-homocitric lactone 18b have been synthesised. D-quinic acid 12 was used as the source of the (3R)-centre in the unlabelled target compounds 17 and 18. (2)-Shikimic acid 19 and the (2)-[2-2H]-shikimic acid derivative 32 respectively were used in the synthesis of the labelled compounds. In the latter syntheses, Sharpless directed epoxidation of the olefin in the 5-deoxy ester diols 23 and 35 ensured a reaction from the same face as the allylic and homoallylic alcohols, and the reduction of the protected epoxides 25 and 37 ensured that the label was introduced in a stereoselective manner. The 1H NMR spectra of the labelled products present an assay for the stereochemistry of the biological reactions catalysed by homocitrate synthase and by the protein from the nifV gene.

2-Methyl-(1Z,3E)-butadiene-1,3,4-tricarboxylic acid, "isoprenetricarboxylic acid".

[reaction: see text] The synthesis of the title compound 7 from ethyl glyoxylate and dimethyl and diethyl beta-methylglutaconate is described along with its physical properties that suggest its inability to assume a cis-dienoid structure due to steric hindrance between the methyl and carboxyl groups.

Shape-complementarity in the recognition of tricarboxylic acids by a [3+3] polyazacyclophane receptor.

[structure: see text] The interaction of a macrocycle containing three trans-(1R,2R)-diaminocyclohexane units connected by p-xylene spacers with the isomers 1,3,5-benzenetricarboxylic (1,3,5-BTC), 1,2,4-benzenetricarboxylic (1,2,4-BTC), and 1,2,3-benzenetricarboxylic (1,2,3-BTC) acids and their relevant anions is studied by means of potentiometric and NMR analysis. The interaction is highest for the isomer 1,3,5-BTC, which perfectly fits within the macrocyclic cavity of the host species. The studies have been extended to the triacid 1,3,5-benzenetriacetic observing in this case the effect of a size mismatch between host and guest species.