Ethacrynic acid as a lead structure for the development of potent urease inhibitors

Ethacrynic acid and a series of its analogues were synthesized and subsequently evaluated for their inhibitory effect on jack bean urease. Ethacrynic acid showed, even at low concentrations, very potent inhibitory activity against the enzyme. For ethacrynic acid, the inhibition potential increased with increasing preincubation time of ethacrynic acid and enzyme, whereas for some other compounds a higher preincubation time lead to a significant reduction of their activity. We could demonstrate that the α,β-unsaturated carbonyl unit of our compounds is mandatory to inhibit the enzyme, possibly due to its ability to bind to cysteine residues in the active site of the jack bean urease.     

Hydrothermal Raman microscopy studies of manganese carbonyls

We present here the application of Raman microscopy in providing simultaneous visual and spectroscopic characterisation of the physical and chemical changes occurring in organometallic materials while undergoing hydrothermal treatment. The effect of water at elevated pressures and temperatures on three prototype manganese carbonyls, Mn₂(CO)₁₀, (η⁵-C₅H₅)Mn(CO)₃ and Mn(CO)₅Br, was investigated. A Bassett-type hydrothermal diamond-anvil cell (HDAC) was used to subject each compound to conditions of at least 22.1 MPa and 374 °C (i.e., beyond the critical point of water), while Raman microscopy was used to monitor the structural changes occurring during the heating and cooling cycles of the cell. The hydrothermal studies showed that Mn₂(CO)₁₀, (η⁵-C₅H₅)Mn(CO)₃ and Mn(CO)₅Br dissolved in subcritical water at 150, 125 and 225 °C, respectively. Moreover, Mn(CO)₅Br is also believed to have dimerized to Mn₂(CO)₈Br₂ when the cell temperature was increased to 425 °C.     

Design and synthesis of potential mechanism-based inhibitors of the aminotransferase BioA involved in biotin biosynthesis

BioA, a pyridoxal 5'-phosphate (PLP) dependent aminotransferase, catalyzes the second step of biotin biosynthesis, converting 7-keto-8-aminopelargonic acid (KAPA) into 7,8-diaminopelargonic acid (DAPA). Amiclenomycin (ACM) isolated from cultures of different Streptomyces strains is a potent mechanism-based inhibitor of BioA that operates via an aromatization mechanism, irreversibly labeling the PLP cofactor. However, ACM is plagued by inherent chemical stability. Herein we describe the synthesis of four inhibitors, inspired by ACM but containing an allylic amine as the chemical warhead, designed to both improve stability and operate via a complementary Michael addition-pathway upon enzymatic oxidation of the allylic amine substrate to an enimine. Acyclic analogue M-1 contains a terminal olefin as the pro-Michael acceptor. The synthesis of M-1 features an alkyne-zipper reaction and the Overman rearrangement as key synthetic operations. The cyclic analogues M-2/3/4 contain either an endocyclic or exocyclic olefin as the pro-Michael acceptor. These were all prepared using a common strategy employing DIBAL reduction of a precursor bicyclic lactam, followed by in situ Horner-Wadsworth-Emmons (HWE) olefination as the key synthetic steps.     

A review of recent advances in electrochemically modulated extraction methods

The use of electrochemistry and electrical behavior as a control and manipulation factor in analyte extractions is reviewed. Electromodulated extractions of ionic and neutral analytes are possible using this general approach. Extractions based on solid–liquid, liquid–liquid and membrane behaviors have been demonstrated and reported together with analyte extractions from real matrices and interfacing with instrumental detection methods. The electromodulation strategy offers great opportunities for selectivity in sample preparation.     

Acoustic radiation force analysis using finite difference time domain method

Acoustic radiation force exerted by standing waves on particles is analyzed using a finite difference time domain Lagrangian method. This method allows the acoustic radiation force to be obtained directly from the solution of nonlinear fluid equations, without any assumptions on size or geometry of the particles, boundary conditions, or acoustic field amplitude. The model converges to analytical results in the limit of small particle radii and low field amplitudes, where assumptions within the analytical models apply. Good agreement with analytical and numerical models based on solutions of linear scattering problems is observed for compressible particles, whereas some disagreement is detected when the compressibility of the particles decreases.     

Identification of the adduct between a 4-aza-3-ene-1,6-diyne and DNA using electrospray ionization mass spectrometry

The interactions between a novel enediyne [1-methyl-2-(phenylethynyl)-3-(3-phenylprop-2-ynyl)-3H-benzimidazolium] (1) and various cytosine-containing oligonucleotides were studied using electrospray ionization mass spectrometry (ESI-MS) in a flow injection analysis mode useful for small volumes. This enediyne ligand, developed as a potential alternative to the highly cytotoxic natural enediynes, some of which have been successfully used as anti-tumor agents, has previously been shown to interact with DNA through frank strand scission as well as via the formation of adducts that lead to 2'-deoxycytidine-specific cleavage. Through ESI-MS, the structures of these adducts were examined and a sequence dependence of the 2'-deoxycytidine-specific cleavage was noted. Collisionally activated dissociation of the observed adducts confirmed the strength of the interactions between the enediyne and DNA and supports a direct linkage between the enediyne and the cytosine nucleobase, likely the result of a nucleophilic attack of the phenylethynyl group by the cytosine amine.     

Origins of Large Rate Enhancements in the Nazarov Cyclization Catalyzed by Supramolecular Encapsulation

The self‐assembled supramolecular host [Ga₄L₆]^12? ( 1 ; L=N,N‐bis(2,3‐dihydroxybenzoyl)‐1,5‐diaminonaphthalene) catalyzes the Nazarov cyclization of 1,3‐pentadienols with extremely high levels of efficiency. The catalyzed reaction proceeds at a rate over a million times faster than that of the background reaction, an increase comparable to those observed in some enzymatic systems. A detailed study was conducted to elucidate the reaction mechanism of both the catalyzed and uncatalyzed Nazarov cyclization of pentadienols. Kinetic analysis and ¹⁸O‐exchange experiments implicate a mechanism, in which encapsulation, protonation, and water loss from substrate are reversible, followed by irreversible electrocyclization. Although electrocyclization is rate determining in the uncatalyzed reaction, the barrier for water loss and for electrocyclization are nearly equal in the assembly‐catalyzed reaction. Analysis of the energetics of the catalyzed and uncatalyzed reaction revealed that transition‐state stabilization contributes significantly to the dramatically enhanced rate of the catalyzed reaction.     

Affinity monolith chromatography: a review of principles and recent analytical applications

Affinity monolith chromatography (AMC) is a type of liquid chromatography that uses a monolithic support and a biologically related binding agent as a stationary phase. AMC is a powerful method for the selective separation, analysis, or study of specific target compounds in a sample. This review discusses the basic principles of AMC and recent developments and applications of this method, with particular emphasis being given to work that has appeared in the last 5 years. Various materials that have been used to prepare columns for AMC are examined, including organic monoliths, silica monoliths, agarose monoliths, and cryogels. These supports have been used in AMC for formats that have ranged from traditional columns to disks, microcolumns, and capillaries. Many binding agents have also been employed in AMC, such as antibodies, enzymes, proteins, lectins, immobilized metal ions, and dyes. Some applications that have been reported with these binding agents in AMC are bioaffinity chromatography, immunoaffinity chromatography or immunoextraction, immobilized-metal-ion affinity chromatography, dye–ligand affinity chromatography, chiral separations, and biointeraction studies. Examples are presented from fields that include analytical chemistry, pharmaceutical analysis, clinical testing, and biotechnology. Current trends and possible directions in AMC are also discussed.