Direct Catalytic Decarboxylative Amination of Aryl Acetic Acids

The decarboxylative coupling of a carboxylic acid with an amine nucleophile provides an alternative to the substitution of traditional organohalide coupling partners. Benzoic and alkynyl acids may be directly aminated by oxidative catalysis. In contrast, methods for intermolecular alkyl carboxylic acid to amine conversion, including amidate rearrangements and photoredox‐promoted approaches, require stoichiometric activation of the acid unit to generate isocyanate or radical intermediates. Reported here is a process for the direct chemoselective decarboxylative amination of electron‐poor arylacetates by oxidative Cu catalysis. The reaction proceeds at (or near) room temperature, uses native carboxylic acid starting materials, and is compatible with protic, electrophilic, and other potentially complicating functionality. Mechanistic studies support a pathway in which ionic decarboxylation of the acid generates a benzylic nucleophile which is aminated in a Chan–Evans–Lam‐type process.     

Construction and characterization of a small-bore electrospray ionization source

A simple, economical, and efficient electrospray ionization (ESI) source has been constructed in the configuration of a probe that makes use of a standard 13 mm vacuum lock. The principal components have been placed inside a glass tube making use of the electrical insulating properties of the glass while allowing for visual adjustments to be readily made. The ESI source, a variation of an atmospheric pressure ionization interface, is a modified version of designs published by Chait et al. (Rapid Comm. Mass Spectrom. 1990, 4, 81–87) and Knapp et al. (Anal. Chem. 1991, 63, 1658–1660) wherein a heated metal capillary is used for desolvation. The ESI probe has been tested on three different Extrel quadrupole mass spectrometers, with removable ion volumes, using polypeptides and small proteins. No modifications to the standard electron ionization/chemical ionization lens assembly were required to obtain excellent results other than removal of the ion volume. The spectra acquired were in excellent agreement with those previously published.     

Confronting the challenges of natural product-based antifungal discovery

Starting with the discovery of penicillin, the pharmaceutical industry has relied extensively on natural products (NPs) as an unparalleled source of bioactive small molecules suitable for antibiotic development. However, the discovery of structurally novel and chemically tractable NPs with suitable pharmacological properties as antibiotic leads has waned in recent decades. Today, the repetitive "rediscovery" of previously known NP classes with limited antibiotic lead potential dominates most industrial efforts. This limited productivity, exacerbated by the significant financial and resource requirements of such activities, has led to a broad de-emphasis of NP research by most pharmaceutical companies, including most recently Merck. Here we review our strategies--both technological and philosophical--in addressing current antifungal discovery bottlenecks in target identification and validation and how such efforts may improve NP-based antimicrobial discoveries when aligned with NP screening and dereplication.     

Comparison of the transient stress–strain response of rubber to its linear dynamic behavior

Master curves of the small strain and dynamic shear modulus are compared with the transient mechanical response of rubbers stretched at ambient temperature over a seven‐decade range of strain rates (10^?4 to 10³ s^?1). The experiments were carried out on 1,4‐ and 1,2‐polybutadienes and a styrene–butadiene copolymer. These rubbers have respective glass transition temperatures, T_g, equal to ?93.0, 0.5, and 4.1 °C, so that the room temperature measurements probed the rubbery plateau, the glass transition zone, and the onset of the glassy state. For the 1,4‐polybutadiene, in accord with previous results, strain and strain rate effects were decoupled (additive). For the other two materials, encroachment of the segmental dynamics precluded separation of the effects of strain and rate. These results show that for rubbery polymers near T_g the use of linear dynamic data to predict stresses, strain energies, and other mechanical properties at higher strain rates entails large error. For example, the strain rate associated with an upturn in the modulus due to onset of the glass transition was three orders of magnitude higher for large tensile strains than for linear oscillatory shear strains. © 2011 Wiley Periodicals, Inc.* J Polym Sci Part B: Polym Phys, 2011     

Synthesis of 2-acetamido-1,2-dideoxy-d-galacto-nojirimycin [DGJNAc] from d-glucuronolactone: the first sub-micromolar inhibitor of α-N-acetylgalactosaminidases

2-Acetamido-1,2-dideoxy-d-galacto-nojirimycin [DGJNAc], prepared in 20% overall yield from d-glucuronolactone, is the first potent competitive sub-micromolar inhibitor of α-N-acetyl-galactosaminidases (K_i 0.081 μM from chicken liver, K_i 0.136 μM from Charonia lampas). DGJNAc is a good competitive—whereas the enantiomer l-DGJNAc is a very weak but non-competitive—inhibitor of β-hexosaminidases.     

Measurements of the absolute absorption cross sections of the Ã←X transition in organic peroxy radicals by dual-wavelength cavity ring-down spectroscopy

We demonstrate an experimental method for the accurate measurement of the absorption cross section of transient species, such as organic peroxy radicals in which the concentration of the radicals is determined via the absorption of a stable coproduct that is produced stochiometrically. The requirements for the experimental apparatus, a dual-wavelength cavity ring-down spectrometer, and the chemical protocol for transient species generation are discussed. The capability of this approach is demonstrated by measuring the peak absorption cross section of the ethyl peroxy radical, C?2H?O?, whose value for the ?←X electronic transition at 7596 cm?1 (λ = 1316.5 nm) is found to be σ(p)(EP) = 5.29(20) × 10?21 cm2. These present results are compared to those obtained from other methods of measurement of σ(p)(EP). Possible random and systematic errors are discussed.     

Improved silicon nitride surfaces for next-generation microarrays

This work reports how the use of a standard integrated circuit (IC) fabrication process can improve the potential of silicon nitride layers as substrates for microarray technology. It has been shown that chemical mechanical polishing (CMP) substantially improves the fluorescent intensity of positive control gene and test gene microarray spots on both low-pressure chemical vapor deposition (LPCVD) and plasma-enhanced chemical vapor deposition (PECVD) silicon nitride films, while maintaining a low fluorescent background. This results in the improved discrimination of low expressing genes. The results for the PECVD silicon nitride, which has been previously reported as unsuitable for microarray spotting, are particularly significant for future devices that hope to incorporate microelectronic control and analysis circuitry, due to the film's use as a final passivating layer.     

Coupling of NMR to ACOMP for Terpolymerization Monitoring and Control

Monitoring and control of free radical copolymerization using automatic continuous online monitoring of polymerization reactions (ACOMP) with UV detection has been recently achieved. It is difficult, however, to achieve spectral separation of similar monomers with UV alone. Here, nuclear magnetic resonance (NMR) is coupled to ACOMP for the first time and terpolymerization reactions involving acrylamide (Am), sodium acrylate (Ac), and styrene sulfonate (SS) are monitored, and a first attempt at active composition control is made. The NMR resolves the concentrations of Am and Ac, while the UV resolves SS and the sum of Am and Ac. NMR analysis is performed in water, using signal suppression, to eliminate the need for deuterated solvents. From this, instantaneous fractions of each comonomer in the terpolymer are continuously known, along with weight average molecular weight and intrinsic viscosity, IV. Am and Ac have similar reactivities, whereas the reactivity ratio of SS is much larger. Hence, there is high composition drift in batch polymerization and SS is rapidly consumed, leaving a final copolymer of Am and SS to form. Maintaining constant terpolymer composition is taken as a first step toward active control.     

Automated mass spectrometry imaging with a matrix-assisted laser desorption ionization time-of-flight instrument

The automated use of a matrix-assisted laser desorption ionization (MALDI) mass spectrometer (MS) is described for image analysis of samples through implementation of new software for instrument control, data acquisition, and data analysis. The software permits automated acquisition of MS MALDI spectra to form an ordered data array and contains display features to provide images at one or more mass-to-charge ratio values. The technique can be used to scan tissue samples, blotted samples, gels, or other sample surfaces where the image analysis of that sample is required. The program achieves a time of typically 1 s per image point, permitting an analysis made up of large numbers of points with high spatial resolution up to 850 dpi. The features of the software are demonstrated in this paper with samples of printed images, where visible images can be compared to those obtained by mass spectrometry. Quantitative aspects are introduced by analyzing a series of sample spots containing different amounts of several proteins.     

Oxidative Coupling of Aryl Boron Reagents with sp3‐Carbon Nucleophiles: The Enolate Chan–Evans–Lam Reaction

Reported is a versatile new oxidative method for the arylation of activated methylene species. Under mild reaction conditions (RT to 40 °C), Cu(OTf)₂ mediates the selective coupling of functionalized aryl boron species with a variety of stabilized sp³‐nucleophiles. Tertiary malonates and amido esters can be employed as substrates to generate quaternary centers. Complementing either traditional cross‐coupling or S_NAr protocols, the transformation is chemoselective in the presence of halogen electrophiles, including aryl bromides and iodides. Substrates bearing amide, sulfonyl, and phosphonyl groups, which are not amenable to coupling under mild Hurtley‐type conditions, are suitable reaction partners.