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925 research data, page 1 of 93

An Efficient, Stereocontrolled Synthesis of a Potent Omuralide−Salinosporin Hybrid for Selective Proteasome Inhibition

Reddy, Leleti Rajender; Fournier, Jean-François; V. Subba Reddy, B.; Corey, E. J. (2005)
Publisher: Figshare
A short and highly stereocontrolled synthesis of the potent proteasome inhibitor 3 from the (S)-threonine-derived oxazoline 4 has been developed. The synthetic sequence is summarized in Scheme . Aldol coupling of the zinc enolate of 4 with isobutyraldehyde and subsequent silylation provided the TBS ether 5 diastereoselectively (10:1). Reductive cleavage of the oxazoline ring of 5 followed by Swern oxidation of the resulting amino alcohol afforded amino ketone 6, converted further by N-acylati...

Annulation of Aromatic Imines via Directed C−H Bond Activation

Thalji, Reema K.; Ahrendt, Kateri A.; Bergman, Robert G.; Ellman, Jonathan A. (2005)
Publisher: Figshare
A directed C−H bond activation approach to the synthesis of indans, tetralins, dihydrofurans, dihydroindoles, and other polycyclic aromatic compounds is presented. Cyclization of aromatic ketimines and aldimines containing alkenyl groups tethered at the meta position relative to the imine directing group has been achieved using (PPh3)3RhCl (Wilkinson's catalyst). The cyclization of a range of aromatic ketimines and aldimines provides bi- and tricyclic ring systems with good reg...

A Convenient Preparation of Xanthene Dyes

Yang, Youjun; Escobedo, Jorge O.; Wong, Alexander; Schowalter, Corin M.; Touchy, Michael C.; Jiao, Lijuan; Crowe, William E.; Fronczek, Frank R.; Strongin, Robert M. (2005)
Publisher: Figshare
A facile synthetic route utilizing readily available reagents affords a series of regioisomerically pure xanthene dye derivatives. Advantages include relatively mild conditions and good to excellent yields. Nonpolar, highly crystalline intermediates are isolable by standard chromatographic techniques. The intermediates are in the requisite xanthene oxidation state, thus avoiding the need for relatively inefficient oxidation chemistry and/or harsh conditions. During the course of ...

Conformational Flexibility, UV−Induced Decarbonylation, and FTIR Spectra of 1-Phenyl-1,2 Propanedione in Solid Xenon and in the Low Temperature Amorphous Phase

Lopes, Susy; Gómez-Zavaglia, Andrea; Lapinski, Leszek; Fausto, Rui (2005)
Publisher: Figshare
1-Phenyl-1,2-propanedione has been isolated in low-temperature xenon matrixes and studied by FTIR spectroscopy, supported by DFT(B3LYP)/6-311++G(d,p) calculations. In good agreement with previous electron diffraction data [Shen, Q.; Hagen, K. J. Phys. Chem. 1993, 97, 985], the calculations predicted the existence of only one stable conformation for the compound, in which the OCCO dihedral angle is 135.6°. On the other hand, the experimental data clearly reveals that, in the as-...

Anion Template Effect on the Self-Assembly and Interconversion of Metallacyclophanes

Campos-Fernández, Cristian Saul; Schottel, Brandi L.; Chifotides, Helen T.; Bera, Jitendra K.; Bacsa, John; Koomen, John M.; Russell, David H.; Dunbar, Kim R. (2005)
Publisher: Figshare
Reactions of 3,6-bis(2-pyridyl)-1,2,4,5-tetrazine (bptz) with solvated first-row transition metals M(II) (M(II) = Ni, Zn, Mn, Fe, Cu) have been explored with emphasis on the factors that influence the identity of the resulting cyclic products for Ni(II) and Zn(II). The relatively small anions, namely [ClO4]- and [BF4]-, lead to the formation of molecular squares [{M4(bptz)4(CH3CN)8}⊂X][X]7, (M = Zn(II), Ni(II); X = [BF4]-, [ClO4]-), whereas the larger anion [SbF6]- favors the mole...

Nanolocalized Nonlinear Electron Photoemission under Coherent Control

Stockman, Mark I.; Hewageegana, Prabath (2005)
Publisher: Figshare
We theoretically show that two-photon coherent control yields electron photoemission from metal nanostructures that is localized in nanosize hot spots whose positions are controllable on a nanometer scale, in agreement with recent experiments. We propose to use silver V-shapes as tailored nanoantennas for which the position of the coherently controllable photoelectron emission hot spot can be deterministically predicted. We predict that the low-frequency, high-intensity (quasi-statio...

Doxazolidine, a Proposed Active Metabolite of Doxorubicin That Cross-links DNA

Post, Glen C.; Barthel, Benjamin L.; Burkhart, David J.; Hagadorn, John R.; Koch, Tad H. (2005)
Publisher: Figshare
A crystal structure establishes doxoform as a dimeric formaldehyde conjugate of the oxazolidine of doxorubicin. Doxoform is a prodrug of doxazolidine, a monomeric doxorubicin formaldehyde-oxazolidine. Both doxoform and doxazolidine inhibit the growth of cancer cells at 1−4 orders of magnitude lower concentration than doxorubicin. They also inhibit the growth of cancer cells better than doxsaliform, a prodrug for an acyclic doxorubicin−formaldehyde conjugate. Doxoform rapidly hydro...

In Situ Single-Crystal X-ray Diffraction Studies of Desorption and Sorption in a Flexible Nanoporous Molecular Framework Material

Halder, Gregory J.; Kepert, Cameron J. (2005)
Publisher: Figshare
The subtle flexibility of the framework material Co(bpy)1.5(NO3)2·(guest) (bpy = 4,4‘-bipyridine) (1·(guest)) is demonstrated quantitatively through in situ single-crystal X-ray diffraction measurements of guest desorption and sorption processes. Variable temperature unit cell determinations were employed to monitor the uptake and release of guest species, and full structural determinations have been carried out for the as-grown ethanol-loaded framework (1·(EtOH)), for the empty h...

Synthesis and Real-Time Magnetic Manipulation of a Biaxial Superparamagnetic Colloid

Kim, Jin Young; Osterloh, Frank E.; Hiramatsu, Hiroki; Dumas, R. K.; Liu, Kai (2005)
Publisher: Figshare
Superparamagnetic colloidal plates were synthesized from tetrabutylammonium stabilized Ca2Nb3O10 nanosheets and oleic acid-stabilized Fe3O4 nanoparticles. Modification with 3-aminopropyltrimethoxysilane produces amine-terminated Ca2Nb3O10 with an amine concentration of 0.43 ± 0.06 groups per Ca2Nb3O10 unit as follows from spectroscopic quantification with trinitrobenzenesulfonic acid as a dye. Treatment of the modified sheets in THF/ethanol with 5.3 nm oleic acid-stabilized magnet...

Quantitative Ranking of Crystal Packing Modes by Systematic Calculations on Potential Energies and Vibrational Amplitudes of Molecular Dimers

Gavezzotti, A. (2005)
Publisher: Figshare
Quantum chemical calculations including electron correlation and calculations with the density sums (Pixel) method have been performed on a variety of molecular dimers representing some frequently observed recognition modes in molecular condensed phases. Notwithstanding some individual fluctuations when different computational methods are used, there is a general agreement for the relative orders of magnitude. The results have been collected in a table that ranks the interactio...