The use of boron in small-molecule pharmaceuticals is increasing. Boron's ubiquitous occurrence in nature and the recent success of a boronic acid drug (Velcade®) in the clinic have alleviated many concerns over its use in pharmaceuticals. In addition, the unique physicochemical properties of boronic acids make them an attractive addition to the medicinal chemists toolbox. This tutorial review will discuss these properties and potential benefits for anyone interested in finding novel enzyme inhibitors. An exceptional class of boronic acids, the oxaboroles, will be highlighted and their properties and uses will be discussed in detail. Finally, the current paradigm for the reaction of boronic acids with enzyme nucleophiles will be summarized.

In this work, we present an investigation into the physical properties of a unique class of aromatic boronic acids, the benzoxaboroles. Using spectrophotometric methods, the ionization constants of a family of substituted benzoxaboroles are determined. Heterocyclic ring modifications are examined to determine their effects on the ionization of the boronic acid moiety. It is also shown that the substituent effects about the aromatic ring follow a Hammett relationship with the compounds' measured pK a values. Finally, these substituent effects are also shown to extend to the sugar binding properties of these compounds under physiologically relevant conditions. Combined, these data will inform medicinal chemists wishing to tailor the ionization and/or ability of this class of compound to bind diol-containing biomolecules.

Evidence has been presented for a metabolic multienzyme complex, the purinosome, that participates in de novo purine biosynthesis to form clusters in the cytoplasm of living cells under purine-depleted conditions. Here we identified, using fluorescent live cell imaging, that a microtubule network appears to physically control the spatial distribution of purinosomes in the cytoplasm. Application of a cellbased assay measuring the rate of de novo purine biosynthesis confirmed that the metabolic activity of purinosomes was significantly suppressed in the absence of microtubules. Collectively, we propose a microtubule-assisted mechanism for functional purinosome formation in HeLa cells.metabolism | protein complex | purine biosynthesis

Vacuum matrix-assisted ionization (vMAI) uses select matrix compounds which when exposed to the vacuum of a mass spectrometer produce gas-phase ions from associated volatile or nonvolatile analyte without external energy input. Here, a vMAI source was constructed to replace the commercial inlet of a Thermo Orbitrap mass spectrometer. This allowed for rapid introduction of the matrix/analyte sample by a probe, contrary to vacuum matrix-assisted laser desorption/ionization (MALDI) sources. The matrix/analyte sample is inserted into a region of the "S-lens" entrance, where the spontaneously formed ions can be effectively transferred to the mass analyzer. This specifically designed ion source requires no laser, high voltage, heat, or nebulizing gases. A low voltage is used to transmit the ions through the commercial "S-lens" assembly and airflow can be used to modulate the ionization event. A few picograms of the drug erythromycin, assisted by the 3-nitrobenzonitrile vMAI matrix, is sufficient to produce mass spectra for over 1 min with the MH ion as the base peak in each mass spectrum. There is minimal carryover when loading high concentration samples and complex mixtures, contrary to direct infusion electrospray ionization, providing the probe is thoroughly cleaned between each new sample acquisition. Analyses of biological fluids, bacterial extracts, tissue, and high concentration samples have so far shown no indication of inlet or instrument contamination with these samples. The typical ultrahigh resolution and mass accuracy of the mass spectrometer are achieved, and a path forward to potential high throughput acquisitions demonstrated. It is expected that robustness can be introduced to any mass spectrometer through implementation of such a simple source.

In this work, the reaction between phenylboronic acid and the diol-containing, fluorescent dye Alizarin Red S (ARS) was probed. Fluorescence titrations, (11)B NMR measurements, and both pre- and steady-state kinetic experiments were used for the characterization of this reaction over a large pH range (4-10.5). It was shown that ARS preferentially reacted with the boronic (neutral, trigonal) form of phenylboronic acid; however, the boronate (anionic, tetrahedral) form was also reactive. All in all, four reactant species were implicated in the formation of four different adduct species. The rate of a given adduct formation depended on the combination of the solution pH and the pK(a)'s of both ARS and the arylboronic acid. The reaction was found to proceed in two distinct kinetic steps with the products and starting materials in facile exchange. In addition, the elucidation of the mechanism indicated the presence of two fluorescent products with the structure of the major contributor differing from what had been cited in the literature.