Synthesis of gamma,delta-unsaturated and delta,epsilon-unsaturated alpha-amino acids from fragmentation of gamma- and delta-lactones

A noncoded amino acid of cyclomarin A (1) was synthesized in a racemic fashion. The method employs a six-membered ring template to control the relative stereochemistry and introduction of the functional groups. Ultimately, Pd-catalyzed fragmentation of the lactone provided gamma,delta-unsaturated and delta,epsilon-unsaturated alpha-amino acids. A Pd-catalyzed ring opening of a gamma-lactone is also reported.     

Detonation waves in trinitrotoluene

Fabry-Perot, ORVIS, and VISAR laser interferometry are used to obtain nanosecond time resolved particle velocity histories of the free surfaces of copper and tantalum discs accelerated by detonating trinitrotoluene (TNT) charges and of the interfaces between TNT detonation products and lithium fluoride crystals. TNT detonation reaction zone profiles are measured for self-sustaining detonation and piston supported overdriven (supracompressed) waves. The experimental records are compared to particle velocity histories calculated using very finely zoned meshes of the exact dimensions with the DYNA2D hydrodynamic code. The Ignition and Growth reactive flow model, which is based on the Zeldovich-von Neumann-D?ring (ZND) theory of detonation, yields excellent agreement with the experimental records for TNT using an unreacted von Neumann spike pressure of 25 GPa, a reaction rate law which releases 90% of the chemical energy within 80 ns and the remaining 10% over an additional 200 ns, and a reaction product equation of state fit to cylinder test data assuming a Chapman-Jouguet pressure of 19 GPa. The late time energy release is attributed to diffusion controlled solid carbon particle formation. Received 26 July 1997 / Accepted 29 December 1997     

Total syntheses of conformationally constrained didemnin B analogues. replacements of N,O-dimethyltyrosine with L-1,2,3,4-tetrahydroisoquinoline and L-1,2,3,4-tetrahydro-7-methoxyisoquinoline.

The design and synthesis of two conformationally constrained analogues of didemnin B are described. The [N,O-Me(2)Tyr(5)]residue of didemnin B was replaced with L-1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid (Tic) and L-1,2,3,4-tetrahydro-7-methoxyisoquinoline-3-carboxylic acid (MeO-Tic), which mimic the N,O-dimethylated tyrosine while constraining the conformation of the molecule. Preliminary results indicate that the conformation of the [N,O-Me(2)Tyr(5)]residue closely matches the conformation imposed by the Tic replacement.     

Homogenization for¶Stochastic Hamilton-Jacobi Equations

Homogenization asks whether average behavior can be discerned from partial differential equations that are subject to high-frequency fluctuations when those fluctuations result from a dependence on two widely separated spatial scales. We prove homogenization for certain stochastic Hamilton-Jacobi partial differential equations; the idea is to use the subadditive ergodic theorem to establish the existence of an average in the infinite scale-separation limit. In some cases, we also establish a central limit theorem. Accepted: (April 23, 1999)     

Hetero-Diels-Alder and pyroglutamate approaches to (2S,4R)-2-methylamino-5-hydroxy-4-methylpentanoic acid

The stereoselective syntheses of fully protected (2S,4R)-2-methylamino-5-hydroxy-4-methylpentanoic acid, a non-coded amino acid of cyclomarin A, and its diastereomer are reported. A pyroglutamate template was employed in the key diastereoselective alkylation used for introducing the 4-methyl stereochemistry. In addition, the first diastereoselective intramolecular hetero-Diels-Alder of a 2-cyano-1-azadiene with an electron deficient dienophile is described.     

Thermal cook-off of an HMX based explosive: Pressure gauge experiments and modeling

Safety issues related to thermal cook-off are important for handling and storing explosive devices. Violence of an event as a function of confinement is important for prediction of collateral events. There are major issues which require an understanding of the following events: (1) transit to detonation of a pressure wave from a cook-off event, (2) sensitivity of changes in HMX-based explosives with thermally induced phase transitions, and (3) the potential danger of neighboring explosive devices being affected by a cook-off reaction. Results of cook-off events of known size, confinement, and thermal history allow for development and/or calibration of computer models for calculating events that are difficult to measure experimentally. The text was submitted by the authors in English.     

Nonequilibrium Zeldovich-von Neumann-Doring theory and reactive flow modeling of detonation

This paper discusses the Nonequilibrium Zeldovich-von Neumann-Doring (NEZND) theory of self-sustaining detonation waves and the Ignition and Growth reactive flow model of shock initiation and detonation wave propagation in solid explosives. The NEZND theory identified the nonequilibrium excitation processes that precede and follow the exothermic decomposition of a large high explosive molecule into several small reaction product molecules. The thermal energy deposited by the leading shock wave must be distributed to the vibrational modes of the explosive molecule before chemical reactions can occur. The induction time for the onset of the initial endothermic reactions can be calculated using high pressure-high temperature transition state theory. Since the chemical energy is released well behind the leading shock front of a detonation wave, a physical mechanism is required for this chemical energy to reinforce the leading shock front and maintain its overall constant velocity. This mechanism is the amplification of pressure wavelets in the reaction zone by the process of de-excitation of the initially highly vibrationally excited reaction product molecules. This process leads to the development of the three-dimensional structure of detonation waves observed for all explosives. For practical predictions of shock initiation and detonation in hydrodynamic codes, phenomenological reactive flow models have been developed. The Ignition and Growth reactive flow model of shock initiation and detonation in solid explosives has been very successful in describing the overall flow measured by embedded gauges and laser interferometry. This reactive flow model uses pressure and compression dependent reaction rates, because time-resolved experimental temperature data is not yet available. Since all chemical reaction rates are ultimately controlled by temperature, the next generation of reactive flow models will use temperature dependent reaction rates. Progress on a statistical hot spot ignition and growth reactive flow model with multistep Arrhenius chemical reaction pathways is discussed. The text was submitted by the authors in English.     

Shock initiation of composition B and C-4 explosives: Experiments and modeling

Shock initiation experiments with composition B and C-4 HE were performed to obtain in situ pressure gauge data for the purpose of providing the ignition and growth reactive flow model with proper modeling parameters. A 100-mm-bore propellant-driven gas gun was utilized to initiate the explosive charges containing manganin piezoresistive pressure gauge packages embedded in the explosive sample. Experimental data provided new information on the shock velocity-particle velocity relationship for each of the investigated material in their respective pressure range. The run-to-detonation distance points in the pop plot for these experiments showed agreement with previously published data, and ignition and growth modeling calculations resulted in a good fit to the experimental data. Identical ignition and growth reaction rate parameters were used for C-4 and composition B, and the composition B model also included a third reaction rate to simulate the completion of reaction by the TNT component. This model can be applied to shock initiation scenarios that have not or cannot be tested experimentally with a high level of confidence in its predictions. This paper was presented at the International Conference “Shock Waves in Condensed Media,” St. Petersburg, September, 2006. The text was submitted by the authors in English.     

Synthesis of an N-butylpyrrolidine phase using the allyl bonded stationary phase as an intermediate

Summary The versatility of the allyl phase is exploited by using it as an intermediate in the production of a weak anion exchange material that would be difficult to synthesize directly using organochlorosilane reagents. The stability of the allyl phase under the severe reaction conditions (170° and 140 atm of CO) of aminomethylation also is demonstrated. The product N-butylpyrrolidine phase is characterized spectroscopically by ESCA and DRIFT which also indicate a high conversion (greater than 90 %) of the allyl phase. In addition, the carbon-nitrogen ratio of the product phase supports a high yield. Chromatographic characterization is done by the retention indices of the alkylarylketone homologous series and by capacity factor (k′) determinations for inorganic anions and amino acids.