Computational methods for conformational analysis of unsymmetrical 1,3-diamines: 3-aminotropanes

A comparative study has been performed to evaluate the ability of a range of computational theories to predict the relative basicity and the conformations of diamine systems. Specifically, molecular mechanics (MM3), semiempirical (AM1), and ab initio (Hartree–Fock) methods have been used in the conformational analyses of unprotonated, monoprotonated, and diprotonated 3-aminotropanes, a pair of isomeric 1,3-diamines. Use of the molecular mechanics force field, with the recently determined parameter set for protonated amines, affords results that are in agreement with experimental data, when corrected for water solvent (by setting the dielectric constant to 80). Ab initio and semiempirical calculations, in contrast, give inconsistent and incorrect results. ©1999 John Wiley & Sons, Inc. J Comput Chem 20: 1371–1378, 1999     

A Concise Synthesis of Fumagillol

A 13-step synthesis of (±)-fumagillol ( 1 ), the direct precursor of the potent angiogenesis inhibitors TNP-470 and fumagillin, from crotonaldehyde, diethylamine, and acrolein (see the scheme) has been achieved. The synthesis features a remarkable hetero-Claisen rearrangement. Small-molecule inhibitors of angiogenesis are promising chemotherapeutic agents for the treatment of cancer and inflammatory diseases.     

Generalizing the Disappearing Act: A Reply to István Aranyosi

In “The Reappearing Act” István Aranyosi postulates a new way of seeing to solve a puzzle posed in “The Disappearing Act;” an object that is exactly shaded can be seen simply by virtue of its contrast with its environment – just like a shadow. This object need not reflect, refract, absorb or block light. To undermine the motive for this heretical innovation, I generalize the puzzle to situations involving inexact shading. Aranyosi cannot extend his solution to these variations because he needs to conserve principles of camouflage. On the bright side, the solution to the puzzle that I propose in my book Seeing Dark Things does extend to these variations.     

Two-gram DTA as a thermal compatibility tool

A useful alternative to the standard techniques described by the North American Treaty Organization STANAG 4147 for determining thermal compatibilities of an energetic with other materials could be a simple 2-gram scale Differential Thermal Analysis (2gDTA). The 2gDTA system consists of samples introduced into standard size test tubes inserted into a controlled aluminum-heating block. Relatively inexpensive thermocouples are used for both temperature control and data collection. Cost of the entire system is much less than any commercial DSC. Since valuable instrumentation need not be protected, the 2gDTA allows thermal decomposition reactions to proceed to complete runaway, mimicking the true worst-case scenario.     

A Nature-Inspired Diels-Alder Reaction Facilitates Construction of the Bicyclo[2.2.2]octane Core of Andibenin B

A rapid synthesis of the bicyclo[2.2.2]octane core of andibenin B via a nature-inspired intramolecular [4+2] cycloaddition is described. This cycloaddition permits the construction of a sterically congested bicycle and simultaneously establishes three new all-carbon quaternary stereogenic centers in a highly efficient fashion.     

Droplet model for sound absorption in fluids near the critical point

The dynamic droplet model of critical fluids is applied to understanding critical fluid sound absorption. The resonance frequency of an oscillating droplet is used to explain the scaling on frequency and temperature observed in sound absorption data.