Biomimetic total synthesis of malbrancheamide and malbrancheamide B

The biomimetic total syntheses of both malbrancheamide and malbrancheamide B are reported. The synthesis of the two monochloro species enabled the structure of malbrancheamide B to be unambiguously assigned. The syntheses each feature an intramolecular Diels-Alder reaction of a 5-hydroxypyrazin-2(1H)-one to construct the bicyclo[2.2.2]diazaoctane core, which has also been proposed as the biosynthetic route to these compounds.     

Salts of methylated 5-aminotetrazoles with energetic anions

1-methyl-5-aminotetrazole (4, MAT) can easily be protonated by strong acids, yielding known but largely uninvestigated 1-methyl-5-aminotetrazolium nitrate (4a) and perchlorate (4b). Methylation, rather than protonation, of 4 with iodomethane followed by the exchange of the iodide (5a) for nitrate (5b), perchlorate (5c), azide (5d), and dinitramide (5e) yields a new family of energetic methylated aminotetrazole salts. In all cases, stable salts were obtained and fully characterized by vibrational (IR, Raman) spectroscopy, multinuclear NMR spectroscopy, mass spectrometry, elemental analysis, and X-ray structure determination. Compounds 4a, 4b, and 5c crystallize in the monoclinic space group P2(1)/n, whereas compounds 5b and 5e crystallize in the orthorhombic space group P2(1)2(1)2(1) and 5d in the orthorhombic Fddd. Initial safety testing (impact, friction, and electrostatic sensitivity) and thermal stability measurements (DSC) were also carried out. The MAT salts all exhibit good thermal stabilities (decomposition above 150 degrees C). The constant volume energies of combustion (DeltacU) of 4a, 5b, 5d, and 5e were determined to be -2510(10) cal/g, -3190(30) cal/g, -4500(100) cal/g, and -2570(70) cal/g, respectively, experimentally using oxygen bomb calorimetry. From the experimentally determined density, chemical composition and energies of formation (back calculated from the heats of combustion), the detonation pressures and velocities of 4a (8100 m/s, 25.6 GPa), 5b (7500 m/s, 20.2 GPa), 5d (8200 m/s, 21.7 GPa), and 5e (7500 m/s, 21.2 GPa) were predicted using the EXPLO5 code.     

Carborane Substituents Promote Direct Electrophilic Insertion over Reduction–Metalation Reactions

Two‐electron reduction of 1,1′‐bis(o‐carborane) followed by reaction with [Ru(η‐mes)Cl₂]₂ affords [8‐(1′‐1′,2′‐closo‐C₂B₁₀H₁₁)‐4‐(η‐mes)‐4,1,8‐closo‐RuC₂B₁₀H₁₁]. Subsequent two‐electron reduction of this species and treatment with [Ru(η‐arene)Cl₂]₂ results in the 14‐vertex/12‐vertex species [1‐(η‐mes)‐9‐(1′‐1′,2′‐closo‐C₂B₁₀H₁₁)‐13‐(η‐arene)‐1,13,2,9‐closo‐Ru₂C₂B₁₀H₁₁] by direct electrophilic insertion, promoted by the carborane substituent in the 13‐vertex/12‐vertex precursor. When arene=mesitylene (mes), the diruthenium species is fluxional in solution at room temperature in a process that makes the metal–ligand fragments equivalent. A unique mechanism for this fluxionality is proposed and is shown to be fully consistent with the observed fluxionality or nonfluxionality of a series of previously reported 14‐vertex dicobaltacarboranes.     

Isomerization dynamics and control of the eta2/N equilibrium for pyridine complexes

A series of pyridine complexes are prepared of the general form TpW(NO)(PMe3)(pyr) where pyr is either pyridine or a substituted pyridine. Depending on substitution pattern, the pyridine can be either N- or eta2-coordinated, and the role of the pyridine substituents and metal oxidation state in determining this equilibrium is explored. For eta2-pyridine complexes, the substituent pattern and solubility characteristics also determine the ratio of coordination diastereomers. Rates of both intra- and interfacial linkage isomerizations are explored along with the pyridine rotational barrier. This study is supported by DFT calculations and X-ray data and includes characterization of both eta2-pyridine and eta2-pyridinium complexes.     

Standard reference materials for foods and dietary supplements

Well-characterized certified reference materials are needed by laboratories in the food testing, dietary supplement, and nutrition communities to facilitate compliance with labeling laws and improve the accuracy of information provided on product labels, so that consumers can make good choices. As a result of the enactment of the Nutrition Labeling and Education Act of 1990 and the Infant Formula Act of 1980, the National Institute of Standards and Technology (NIST) worked to develop a series of food-matrix standard reference materials (SRMs) characterized for nutrient concentrations. These include SRM 1544 Fatty Acids and Cholesterol in a Frozen Diet Composite, SRM 1546 Meat Homogenate, SRM 1548a Typical Diet, SRM 1566b Oyster Tissue, SRM 1846 Infant Formula, SRM 1946 Lake Superior Fish Tissue, SRM 1947 Lake Michigan Fish Tissue, SRM 2383 Baby Food Composite, SRM 2384 Baking Chocolate, SRM 2385 Slurried Spinach, and SRM 2387 Peanut Butter. With the enactment of the Dietary Supplement Health and Education Act of 1994, NIST has been working to develop suites of dietary supplement SRMs characterized for active and marker compounds and for toxic elements and pesticides, where appropriate. An updated SRM 1588b Organics in Cod Liver Oil, a suite of ephedra-containing materials (SRMs 3240–3245), a carrot extract in oil (SRM 3276), and a suite of ginkgo-containing materials (SRMs 3246–3248) are available. Several other materials are currently in preparation. Dietary supplements are sometimes provided in forms that are food-like; for these, values may also be assigned for nutrients, for example SRM 3244 Ephedra-Containing Protein Powder. Both the food-matrix and dietary supplement reference materials are intended primarily for validation of analytical methods. They may also be used as “primary control materials” in assignment of values to in-house (secondary) control materials to confirm accuracy and to establish measurement traceability to NIST.