Tandem intramolecular Nicholas and Pauson-Khand reactions for the synthesis of tricyclic oxygen-containing heterocycles

[reaction: see text] Simple acyclic enynes can be easily converted into tricyclic ethers upon treatment with Co2(CO)8 followed by Nicholas and Pauson-Khand reactions. Tricyclic [5,8,5]- and [5,7,5]-systems can be prepared in high overall yields in only seven synthetic steps.     

Polymer Nanoparticle Hydrogels with Autonomous Affinity Switching for the Protection of Proteins from Thermal Stress

We report a new material design concept for synthetic, thermally responsive poly(N‐isopropylacrylamide)‐based copolymer nanoparticle (NP) hydrogels, which protect proteins from thermal stress. The NP hydrogels bind and protect a target enzyme from irreversible activity loss upon exposure to heat but “autonomously” release the enzyme upon subsequent cooling of the solution. Incorporation of the optimized amount of negatively charged and hydrophobic comonomers to the NP hydrogels was key to achieve these desired functions. As the NP hydrogels do not show a strong affinity for the enzyme at room temperature, they can remain in solution without adversely affecting enzymatic activity or they can be removed by filtration to leave the enzyme in solution. The results demonstrate the promise of this approach for improving the thermal tolerance of proteins.     

Convenient Synthesis of Benziodazolone: New Reagents for Direct Esterification of Alcohols and Amidation of Amines

Hypervalent iodine heterocycles represent one of the important classes of hypervalent iodine reagents with many applications in organic synthesis. This paper reports a simple and convenient synthesis of benziodazolones by the reaction of readily available iodobenzamides with m-chloroperoxybenzoic acid in acetonitrile at room temperature. The structure of one of these new iodine heterocycles was confirmed by X-ray analysis. In combination with PPh₃ and pyridine, these benziodazolones can smoothly react with alcohols or amines to produce the corresponding esters or amides of 3-chlorobenzoic acid, respectively. It was found that the novel benziodazolone reagent reacts more efficiently than the analogous benziodoxolone reagent in this esterification.     

Comparative triad of routes to an alkyne-BF2 azadipyrromethene near-infrared fluorochrome

A series of three inter-related synthetic routes to a water soluble alkyne substituted BF₂-azadipyrromethene fluorochrome is described. Each route allows for the introduction of the required reactive alkynyl group and water solubilizing propane-sulfonic acid through either more advanced pyrrole intermediates or through their earlier synthetic precursors. The advantages and disadvantages of each route lie in the number of synthetic steps required versus the formation of undesired azadipyrromethene by-products. Upon its synthesis, the alkyne-bearing fluorochrome was shown to efficiently participate in CuACC reactions with a series of azido substrates in water at room temperature and 37?°C. NIR-photophysical properties of the fluorochrome and its conjugates were similar, showing strong potential for in vitro and in vivo imaging applications.     

Preparation of Protected Allylic Primary Amines from Allylic Phenyl Selenides

The reaction of an allylic selenide with an excess of an O-alkyl-N-chloro-N-sodiocarbamate in methanol affords an alkoxycarbonyl-protected allylic primary amine with allylic transposition. The preparation of several tert-butoxycarbonyl- and benzyloxycarbonyl-protected amines is described.     

Effects of surface interactions on peptide aggregate morphology

The formation of peptide aggregates mediated by an attractive surface is investigated using replica exchange molecular dynamics simulations with a coarse-grained peptide representation. In the absence of a surface, the peptides exhibit a range of aggregate morphologies, including amorphous aggregates, β-barrels and multi-layered fibrils, depending on the chiral stiffness of the chain (a measure of its β-sheet propensity). In contrast, aggregate morphology in the presence of an attractive surface depends more on surface attraction than on peptide chain stiffness, with the surface favoring fibrillar structures. Peptide-peptide interactions couple to peptide-surface interactions cooperatively to affect the assembly process both qualitatively (in terms of aggregate morphology) and quantitatively (in terms of transition temperature and transition sharpness). The frequency of ordered fibrillar aggregates, the surface binding transition temperature, and the sharpness of the binding transition all increase with both surface attraction and chain stiffness.     

Copper(II)-catalyzed room temperature aerobic oxidation of hydroxamic acids and hydrazides to acyl-nitroso and azo intermediates, and their Diels-Alder trapping

CuCl(2), in the presence of a 2-ethyl-2-oxazoline ligand, is an effective catalyst for the room temperature, aerobic oxidation of hydroxamic acids and hydrazides, to acyl-nitroso and azo dienophiles respectively, which are efficiently trapped in situ via both inter- and intramolecular hetero-Diels-Alder reactions with dienes. Both inter- and intramolecular variants of the Diels-Alder reaction are suitable under the reaction conditions using a variety of solvents. Under the same conditions, an acyl hydrazide was also oxidized to give an acyl-azo dienophile which was trapped intramolecularly by a diene.     

The Synthesis of 5, 6, 7, 7a-Tetrahydro-1-methyl-3H-pyrrolizin-3-one by the Palladium-Catalyzed Cyclization of N-Bromoacetyl-2-vinylpyrrolidine

N-Bromoacetyl-2-vinylpyrrolidine underwent cyclization to give a pyrrolizidine derivative in the presence of a base and a catalytic amount of palladium catalyst.     

Overview of the effects of solar-terrestrial phenomena on man and his environment

Summary The effect of solar-terrestrial phenomena on our environment is a rapidly developing science. An overview of this subject is presented including known technological effects, possible effects on ozone depletion, and the much more elusive possibility that solar emissions may be linked to human health. Paper presented at the Special Session on the effects of solar-terrestrial phenomena on man and his environment of the XXIV International Cosmic-Ray Conference, Rome, August 28–September 8, 1995.