Applications of differential scanning calorimetry to enzyme kinetics

Differential scanning calorimetry has been investigated for its application to the experimental study of the temperature dependence of the kinetics of enzyme—substrate reactions. A reaction cell was developed which allows mixing of enzyme and substrate solutions directly in the calorimeter. The device was used to study the zero-order reaction of acetylcholinesterase with acetylcholine and the first-order reaction of α-chymotrypsin with N-acetyl-l-alanine methyl ester. The reaction cell is found to be satisfactory in the isothermal mode for both first- and zero-order reactions and in the scanning mode for the zero-order reactions but not for the first-order reaction. Limitations of the design are described for general enzyme kinetic studies.     

On the mechanism and origin of the stereoselectivity in iodo-deboronation and chloro-deboronation of hindered alkenyl boronate esters using either ICl-NaOMe or ICl-pyridine

Conversion of hindered alkenyl boronate esters into the corresponding iodoalkene, or alkenyl chloride can be carried out stereoselectively using ICl. In the presence of NaOMe, direct reaction of ICl is favoured yielding the E-iodoalkene, however, the reaction with ICl followed by NaOMe can be used to give different major alkenyl iodide and chloride products, depending upon reaction temperature, ICl source and alkenyl boronate stereoelectronics.     

Synthesis of an azabicyclic framework towards (±)-actinophyllic acid

Lewis acid mediated intramolecular Mannich reaction between an azocinone and a 3-formylindole was investigated as part of a study towards the synthesis of actinophyllic acid. The intramolecular Mannich reaction resulted in a single diastereomer of the 1-azabicyclo[4.2.1]nonan-5-one core framework, although single crystal X-ray structure analysis revealed that this had the undesired stereochemistry in comparison with the natural product.     

A Bifunctional B,N-Based Asymmetric Catalytic Nitrostyrene-Michael Addition Acting through a 10-Membered Ring Cyclic Transition State

The B,N-bifunctional catalyst homoboroproline has been applied to a catalytic asymmetric nitroalkene-Michael addition to β-nitrostyrene analogues, showing broad substrate tolerance, high conversions and moderate to good asymmetric induction. The ability of homoboroproline to act as an efficient catalyst based on enamine-formation of the secondary amine, coupled with intramolecular Lewis-acid chelation of the nitro function, in a non-FLP manner, to effect efficient and enantioselective catalysis via a proposed large 10-membered ring transition state is remarkable and reinforced by theoretical calculations.     

Synthetic Diphenylacetylene-Based Retinoids Induce DNA Damage in Chinese Hamster Ovary Cells without Altering Viability

All-trans-retinoic acid (ATRA), the active metabolite of vitamin A, plays a pivotal role in cell differentiation, proliferation and embryonic development. It is an effective therapy for dermatological disorders and malignancies. ATRA is prone to isomerization and oxidation, which can affect its activity and selectivity. Novel diphenylacetylene-based ATRA analogues with increased stability can help to overcome these problems and may offer significant potential as therapeutics for a variety of cancers and neurodegenerative diseases, including amyotrophic lateral sclerosis. Here, we investigated the effects of these retinoids on cell viability and genotoxicity in the widely used model system of the rapidly proliferating Chinese hamster ovary cell line. DC360 is a fluorescent ATRA analogue and DC324 is a non-active derivative of DC360. EC23, DC525, DC540, DC645, and DC712 are promising analogues with increased bioactivity. The cytotoxic activity of the compounds was evaluated by ATP assay and DNA damage was tested by comet assay. No cytotoxicity was observed in the 10⁻⁶–10⁻⁵ M concentration range. All compounds induced DNA migration similar to ATRA, but DC324, DC360 and EC23 did so to a greater extent, particularly at higher concentrations. We believe that retinoid receptor-independent genotoxicity is a general characteristic of these compounds; however, further studies are needed to identify the molecular mechanisms and understand their complex biological functions.     

A novel scandium ortho-methoxynitrosobenzene-dimer complex: mechanistic implications for the nitroso-Diels-Alder reaction

Arylnitroso dienophiles exist in equilibrium with their dimeric counterparts, which in turn form stable bidentate complexes with scandium(III) triflate and react with cyclohexadiene to give the corresponding Diels-Alder adduct at the same rate as the normal thermal process.     

The interconversion of primary alkyl halides

Using tetra-alkylammonium halides dissolved in alkyl halides as reagents a variety of halogen exchange reactions can be carried out conveniently in high yield. In particular, it becomes practicable to use -CH₂Cl as a protected equivalent of -CH₂Br.