Search

Cells receive growth and survival stimuli through their attachment to an extracellular matrix (ECM) (1). Overcoming the addiction to ECM-induced signals is required for anchorage-independent growth, a property of most [...]

A new approach fro the synthesis of 1,4-benzodiazepine derivatives based on the interaction of methyl 1-arylaziridine-2-carboxylates with N-[2-bromomethyl(phenyl)trifluoroacetamides is described. The one-pot reaction proceeds via the N-benzylation and highly regioselective ring-opening reaction of aziridine by bromide anion followed by the [Et.sub.3]N-mediated intramolecular cyclocondensation between amide nitrogen and alkyl bromide moieties.

Single-molecule magnets with larger spins are generated when the carboxylate ligation is altered by the oxime moiety. The oxime moiety is twisted, due to which there is structural distortion to the core of the molecule that enhances the magnetism of the molecule.

Chemical rescue of activity was used in combination with evolutionary comparison and mutagenesis to identify the carboxylase active site base. Results of the combined studies provide compelling and specific evidence that Lys218 acts as a general base in the mechanism of the carboxylase.

The visual pigment rhodopsin is a seven-transmembrane (7-TM) G protein-coupled receptor (GPCR). Activation of rhodopsin involves two pH-dependent steps that include proton uptake at a conserved cytoplasmic motif between TM helices 3 and 6, and disruption of a salt bridge between a protonated Schiff base (PSB) and its carboxylate counterion in the transmembrane core of the receptor.

Detailed mechanistic studies on the palladium-catalyzed direct arylation of pyridine N-oxides were performed to gain insight into the order of each reaction component and general mechanistic of reaction. The successful reaction process in presence of carboxylate base indicated that Pd[(OAc).sub.2] plays a pivotal role in the reaction mechanism not only as a precatalyst, but also as a source of acetate base required for the C-H bond cleavage step.

Gold-catalyzed hydroacyloxylation of alkynes with carboxylic acids is described. The catalyst P[Ph.sub.3]AuCl/AgP[F.sub.6] affords the Markonikov addition products, while P[Ph.sub.3]AuCl/AgOTf catalyst gives the more stable isomerized products via the Markonikov products.

The Lewis acid-mediated direct carboxylation of aromatic compounds with C[O.sub.2] efficiently promoted by the addition of silyl chlorides bearing three alkyl and/or aryl substituents in total on the silicon atom is described. Based on the finding for the mass balance related to silicon which showed the silyl chlorides to be recycled during the reaction sequence, a feasible mechanism is proposed for the present carboxylation.

An efficient and general synthetic strategy is described for preparing high-molecular-weight hydrophilic polymers bearing both carboxylic acid and hydroxyl pendant groups. Poly(5,6-dihydroxyoxanorbornane carboxylic acid) is prepared by ring-opening metathesis polymerization of methyl 5-oxanorbornene-2-carboxylate in the presence of Grubbs catalyst II and is modified to tune the hydrophobic/hydrophilic properties by introducing either hydroxyl or carboxylic acid functionalities.

Soluble mouse CLK-1 (MCLK1) was expressed in Escherichia coli as a heterologous host to characterize the aging-associated enzyme CLK-1, which is proposed to be a member of the carboxylate-bridged diiron family of proteins. Biochemical analyses of the in vitro activity of MCLK1 with quinone substrates revealed that NADH could serve directly as a reductant for catalytic activation of dioxygen and substrate oxidation by the enzyme, in absence of an additional reductase protein component.

A detailed study was conducted to obtain a novel bifunctional chelate alternatives to the aminocarboxylate macrocycles NOTA ([N.sub.3][O.sub.3]) or DOTA [N.sub.4][O.sub.4]) for application of radioisotopes of Ga to diagnostic nuclear medicine. The results from the complete syntheses, characterizations, labeling studies, and biodistribution profiles of the linear [N.sub.4][O.sub.2] chelate [H.sub.2]dedpa which coordinates [super 67]Ga quantitatively to form [[super 67]Ga(dedpa)](+) after 10 min at RT represents the new platform chelates with higher stability than that of DOTA.

The catalytic enantioselective [S.sub.N]2' displacement of (Z)-allylic trichloroacetimidates catalyzed by the palladium(II) complex [[COP-OAc].sub.2] is used for the asymmetric synthesis of chiral branched allylic esters and the nature of the catalytic mechanism and its rate- and enantiodetermining steps are analyzed. The results are consistent with a novel mechanism in which chelation of the imidate nitrogen to form a cationic palladium(II) intermediate has activated the alkene by external carboxylate in the enantiodetermining step.

A facile synthesis of 2-carbamoyl-2-cyanocyclopropanecarboxylates through a tandem iodosobenzene/tetrabutylammonium iodide-induced oxidative cyclization and a subsequent neighboring group-assisted decarboxylation of the Michael adducts of 2-cyanoacetamides with [alpha],[beta]-unsaturated malonates is described. The method is observed to proceed smoothly under mild conditions and with good functional group tolerance and could be used to obtain highly functionalized cyclopropanes in moderate to good yields and with excellent diastereoselectivities.

Five non-interpenetrated microporous coordination polymers (MCPs) are derived by vertex desymmetrization by using linkers with symmetry inequivalent coordinating groups and these MCPs have included properties like rare metal clusters, new network topologies and supramolecular isomerism. The structural features present in MCPs derived from the reduced symmetry linkers have included the presence of more than one type of Cu-paddlewheel in a structure derived from a terphenyl tricarboxylate and a three-bladed zinc paddlewheel metal cluster in an MCP derived from a pentacarboxylated triphenylbenzene linker.

A tripodal receptor is developed that is capable of extracting uranyl ion from aqueous solutions. The crystal structure of the complex has shown that the carboxylates have coordinated to uranyl ion while the amides hydrogen bond to one of the uranyl oxo-oxygen atoms.

The application of the lissamine rhodamine B sulfonyl azide as an effective reagent for the detection of different protein thiocarboxylates in the bacterial proteome is discussed.

The crystal structure of the aminotransferase WbpE from Pseudomonas aeruginosa PAO1 complex with the cofactor pyridoxal 5' phosphate (PLP) and product UDP-GlcNAc(3N[H.sub.2])A as the external aldimine is described. The studies have represented the structural analysis of a nucleotide sugar aminotransferase with a bound product modified at the C2' C3' and C6' positions and have also provided insights into a novel target for treatment of P. aeruginosa infection.

The article explains the synthesis, as well as properties of the various supramolecular polyhedral columns and vesicles, which are formed from the self-assembly of hybrid dendrons. The polyhedral shape exhibited by these supramolecular dendrimers is also analyzed.

The effect of the three-His motif in Dke1 on the geometric and electronic structure of the [Fe.sup.II] centers is analyzed by a combination of absorption, CD, MCD and VTVH MCD spectroscopies and DFT calculations. The studies have helped in understanding the effects of perturbation of the facial triad ligation of the non-heme ferrous enzymes on their geometric and electronic structure and also their contributions to reactivity.

Several crystal structures of N-acetyl-L-ornithine transcarbamylase (AOTCase) from Xanthomonas campestris (xc) are determined and [super 13]C NMR spectroscopy has shown that Lys302 is post-translationally carboxylated. Activity assays with the wild-type enzyme and many mutants have shown that the post-translational modification of lysine 302 has a key role in catalysis.

A rotational-echo adiabatic-passage double-resonance [super 13]C{[super 17]O} solid-state NMR experiment is used for proving that the glycine produced in the oxygenase reaction of ribulose bisphosphate carboxylase-oxygenase is incorporated into protein of intact, water-stressed soybean leaves exposed to [super 13]C[O.sub.2] and [super 17][O.sub.2]. The direct incorporation of glycine into protein has shown that water stress has suppressed photorespiration in soybean leaves.

Various spectroscopic methods were utilized to understand the important roles of both resting and substrate-bound forms of cysteine dioxygenase (CDO), a mononuclear non-heme Fe-dependent dioxygenase in the Fe(II) and Fe(III) states in the catalytic mechanism of the enzyme. The results provide a more complete description of several catalytically relevant species and provide support for a reaction mechanism similar to that established for many structurally related 2-His-1-carboxylate Fe(II)-dependent dioxygenases.

A highly efficient [(NHC)Au']-based (NHC = N-heterocyclic carbene) catalytic system was developed for the carboxylation of aromatic and heteroaromatic C-H bonds. The significant base strength of the Au-OH species which is at the origin of the activation process permits the facile functionalization of C-H bonds without the use of other organometallic reagents.

The synthesis of analogues of the two reverse phosphonohydroxamic acids is described, in which the length of the carbon spacer is modified, the N-methyl group of the acid is replaced by an ethyl group and the phosphate group is replaced by isosteric moieties like sulfonate or carboxylate functionalities. The potential of the analogues to inhibit the Escherichia coli 1-deoxy-D-xylulose 5-phosphate reducto-isomerase (DXR) is analyzed.

Several molecular dynamics simulations are conducted to explain the various effects of binding of [Mg.sup.2+] cofactor to ribonuclease H. The various protein medium effects on the interactions are also analyzed.

Controlled in vivo bioconjugation of a targeted intracellular protein to semiconductor quantum dots (QDs) is demonstrated. The proof-of-concept, highlighting targeted intracellular bioconjugation to QDs, has suggested that many cytoplasmic proteins expressing the ubiquitous hexahistidine affinity handle can be specifically attached to QDs in vivo.

Prokaryotic ubiquitin-like protein (Pup) is coupled to substrate proteins via an isopeptide bond in order to target them for degradation by the proteasome. A combination of NMR and biochemical experiments with free lysine and a physiological protein substrate (PanB) is used for showing that the coupling has occurred through the side-chain carboxylate of the glutamate in the GGE motif rather than the carboxy terminus but that the glutamate is located at the C-terminal position to be coupled.

The article explains the various molecular mechanisms that are associated with the enantioselectivity of the (R)- and (S)-hydroxypropylthioethanesulfonate dehydrogenases. The application of these compounds for the aliphatic epoxide carboxylation is also determined.

Fluorescence studies are conducted to demonstrate the strong emission bands at 471 and 529 nm exhibited by fluorescent metal-organic framework, [[In.sub.2][(OH).sub.2](TBAPy)]*(guests) and the carboxylate ligand 1,3,6,8-tetrakis(p-benzoic acid)pyrene (TBAPy). The strongly enhanced lifetime and the emission intensity by spatial separation of the optically active ligand molecules within the MOF structure are found to be dependent on the amount and chemical nature of the guest species in the pores.

A family of molecular heptacadmium carboxylate clusters templated inside [3+3] Schiff base macrocycles is isolated and analyzed by variable temperature solution and solid-state NMR spectroscopy, single-crystal X-ray diffraction (SCXRD), and density functional theory (DFT) calculations. The studies have helped in understanding the host-guest and dynamics properties of a new family of metallocavitands and have helped in designing new supramolecular catalysts and materials.

The treatment of oxazolidinone carboxylic acid with potassium carbonate has produced olefin by a double decarboxylation reaction. 15,16-Normaltrexone derivative prepared from double decarboxylation product has displayed strong affinity for the [mu] opioid receptor, showing it to be a new opioid lead compound.

The addition of [H.sup.+] to a synthetic ([mu]-1,2-peroxo)diiron(III) model complex has resulted in protonation of a carboxylate instead of the peroxo ligand. The results have shown a similar role for protons in the dioxygen activation reactions in soluble methane monooxygenase and related carboxylate-bridged diiron enzymes.

An asymmetric allylic substitution with sodium carboxylate is developed by using a planar-chiral cyclopentadienyl ruthenium complex. Optically active allylic esters are prepared with high regio- and enantioselectivities.

A Pd(II)-catalyzed reaction protocol was developed for the carboxylation of ortho-C-H bonds in anilides to form N-acyl anthranilic acids. The newly developed reaction procedure provides an efficient pathway for the rapid assembly of biologically and pharmaceutically significant molecules, such as benzoxazinones and quinazolinones, from simple anilides without installing and removing an external directing group.