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Israel Journal of Chemistry

Shweta Ganapati, Lyle Isaacs
This article traces the development of acyclic cucurbit[n]uril-type receptors with a focus on work from the Isaacs group. First, we describe the synthesis of methylene bridged glycoluril dimers capped with aromatic sidewalls which allowed us to probe the interconversion of the S- and C-shaped dimers which is a fundamental step in CB[n] formation. The C-shaped compounds were found to undergo discrete self-assembly (dimerization) in both water and organic solvents which lead us to investigate multicomponent self-sorting systems...
April 2018: Israel Journal of Chemistry
Scott E Denmark
This perspective represents a (highly personal) examination of the past, present and future of synthetic organic chemistry. The central thesis posits that the confluence of factors that led to the "Golden Age of Natural Product Synthesis" in the second half of the twentieth century can be traced back to the identification of the therapeutic potential of steroid hormones culminating in the introduction of oral contraceptives. The tremendous benefits of those activities to the development of organic synthesis as a vibrant discipline led to the exponential increase in strategies and methods and the ability to tackle, larger and larger molecules of greater and greater complexity...
February 2018: Israel Journal of Chemistry
Stephanie H Carpenter, Michael L Neidig
Detailed studies of iron speciation and mechanism in iron-catalyzed cross-coupling reactions are critical for providing the necessary fundamental insight to drive new reaction development. However, such insight is challenging to obtain due to the prevalence of mixtures of unstable, paramagnetic organoiron species that can form in this chemistry. A physical-inorganic research approach combining freeze-trapped inorganic spectroscopic studies, organometallic synthesis and GC/kinetic studies provides a powerful method for studying such systems...
December 2017: Israel Journal of Chemistry
Nathan T Coles, Ruth L Webster
Catalytic dehydrocoupling methodologies, whereby dihydrogen is released from a substrate (or intermolecularly from two substrates) is a mild and efficient method to construct main group element-main group element bonds, the products of which can be used in advanced materials, and also for the development of hydrogen storage materials. With growing interest in the potential of compounds such as ammonia-borane to act as hydrogen storage materials which contain a high weight% of H2 , along with the current heightened interest in base metal catalyzed processes, this review covers recent developments in amine and phosphine dehydrocoupling catalyzed by iron complexes...
December 2017: Israel Journal of Chemistry
Jennifer V Obligacion, Hongyu Zhong, Paul J Chirik
The activation of readily prepared, air-stable cobalt (II) bis(carboxylate) pre-catalysts for the functionalization of C( sp 2 )-H bonds has been systematically studied. With the pyridine bis(phosphine) chelate, iPr PNP, treatment of 1-(O2 Ct Bu)2 with either B2 Pin2 or HBPin generated cobalt boryl products. With the former, reduction to (iPr PNP)CoI BPin was observed while with the latter, oxidation to the cobalt(III) dihydride boryl, trans -(iPr PNP)Co(H)2 BPin occurred. The catalytically inactive cobalt complex, Co[PinB(O2 Ct Bu)2 ]2, accompanied formation of the cobalt-boryl products in both cases...
November 2017: Israel Journal of Chemistry
Alexander M Khenkin, Madhu Vedichi, Linda J W Shimon, Matthew A Cranswick, Johannes E M N Klein, Lawrence Que, Ronny Neumann
The iron(II) triflate complex ( 1 ) of 1,2-bis(2,2'-bipyridyl-6-yl)ethane, with two bipyridine moieties connected by an ethane bridge, was prepared. Addition of aqueous 30% H2 O2 to an acetonitrile solution of 1 yielded 2 , a green compound with λmax =710 nm. Moessbauer measurements on 2 showed a doublet with an isomer shift (δ) of 0.35 mm/s and a quadrupole splitting (Δ E Q ) of 0.86 mm/s, indicative of an antiferromagnetically coupled diferric complex. Resonance Raman spectra showed peaks at 883, 556 and 451 cm-1 that downshifted to 832, 540 and 441 cm-1 when 1 was treated with H2 18 O2 ...
November 2017: Israel Journal of Chemistry
Joshua R Hummel, Jonathan A Ellman
α -Branched amines are ubiquitous in drugs and natural products, and consequently, synthetic methods that provide convergent and efficient entry to these structures are of considerable value. Transition-metal-catalyzed C-H bond additions to imines have the potential to be highly practical and atom-economic approaches for the synthesis of a diverse and complex array of α -branched amine products. These strategies typically employ readily available starting inputs, display high functional group compatibility, and often avoid the production of stoichiometric waste byproducts...
November 2017: Israel Journal of Chemistry
Su-Tang Lo, André F Martins, Veronica Clavijo Jordan, A Dean Sherry
Zinc has long been the focus of many biological investigations because of its essential role in biology including a catalytic role in many enzymes, a structural role in the many zinc finger proteins, and a physiological role in many secretory cell processes. Divalent zinc is known to be highly abundant in healthy prostate tissues and lower in prostate cancer (PCa). Given the need for newer diagnostic methods for detection of prostate cancer, zinc-responsive probes of various types have been considered as imaging tools for detecting tissue levels of zinc...
September 2017: Israel Journal of Chemistry
Rehana Akter, Andisheh Abedini, Zachary Ridgway, Xiaoxue Zhang, Joel Kleinberg, Ann Marie Schmidt, Daniel P Raleigh
Much of our knowledge of diabetes is derived from studies of rodent models. An alternative approach explores evolutionary solutions to physiological stress by studying organisms that face challenging metabolic environments. Polar bears eat an enormously lipid-rich diet without deleterious metabolic consequences. In contrast, transgenic rodents expressing the human neuropancreatic polypeptide hormone amylin develop hyperglycemia and extensive pancreatic islet amyloid when fed a high fat diet. The process of islet amyloid formation by human amylin contributes to β-cell dysfunction and loss of β-cell mass in type-2 diabetes...
July 2017: Israel Journal of Chemistry
Kayla M Pate, Regina M Murphy
Amyloid disorders, such as Alzheimer's, are almost invariably late-onset diseases. One defining diagnostic feature of Alzheimer's disease is the deposition of beta-amyloid as extracellular plaques, primarily in the hippocampus. This raises the question: are there natural protective agents that prevent beta-amyloid from depositing, and is it loss of this protection that leads to onset of disease? Proteins in cerebrospinal fluid (CSF) have been suggested to act as just such natural protective agents. Here, we describe some of the early evidence that led to this suggestion, and we discuss, in greater detail, two CSF proteins that have garnered the bulk of the attention...
July 2017: Israel Journal of Chemistry
Ryan P McGlinchey, Jennifer C Lee
Amyloids are traditionally observed in the context of disease. However, there is growing momentum that these structures can serve a beneficial role where the amyloid carries out a specific function. These so called 'functional amyloids' have all the structural hallmarks of disease-associated amyloids, raising the question as to what differentiates a well-behaved benign amyloid from a lethally destructive one. Here, we review our work on the repeat domain (RPT) from Pmel17, an important functional amyloid involved in melanin biosynthesis...
July 2017: Israel Journal of Chemistry
Lingyun Zhang, Jeremy D Schmit
We present a theoretical model for the nucleation of amyloid fibrils. In our model we use helix-coil theory to describe the equilibrium between a soluble native state and an aggregation-prone unfolded state. We then extend the theory to include oligomers with β -sheet cores and calculate the free energy of these states using estimates for the energies of H-bonds, steric zipper interactions, and the conformational entropy cost of forming secondary structure. We find that states with fewer than ~10 β -strands are unstable relative to the dissociated state and three β -strands is the highest free energy state...
July 2017: Israel Journal of Chemistry
Pravin Kumar, Nathalie Schilderink, Vinod Subramaniam, Martina Huber
Human α-synuclein, a protein relevant in the brain with so-far unknown function, plays an important role in Parkinson's disease. The phosphorylation state of αS was related to the disease, prompting interest in this process. The presumed physiological function and the disease action of αS involves membrane interaction. Here, we study the effect of phosphorylation at positions 87 and 129, mimicked by the mutations S87A, S129A (nonphosphorylated) and S87D, S129D (phosphorylated) on membrane binding. Local binding is detected by spin-label continuous-wave electron paramagnetic resonance...
July 2017: Israel Journal of Chemistry
Le Zhao, Christine E Dunne, Dane J Clausen, Justin M Roberts, Joshiawa Paulk, Haining Liu, Olaf G Wiest, James E Bradner, Robert M Williams
The synthesis of biotinylated conjugates of synthetic analogues of the potent and selective histone deacetylase (HDAC) inhibitor largazole is reported. The thiazole moiety of the parent compound's cap group was derivatized to allow the chemical conjugation to biotin. The derivatized largazole analogues were assayed across a panel of HDACs 1-9 and retained potent and selective inhibitory activity towards the class I HDAC isoforms. The biotinylated conjugate was further shown to pull down HDACs 1, 2, and 3.
April 2017: Israel Journal of Chemistry
Alyssa L Verano, Derek S Tan
Spiroketals are key structural motifs found in diverse natural products with compelling biological activities. However, stereocontrolled synthetic access to spiroketals, independent of their inherent thermodynamic preferences, is a classical challenge in organic synthesis that has limited in-depth biological exploration of this intriguing class. Herein, we review our laboratory's efforts to advance the glycal epoxide approach to the stereocontrolled synthesis of spiroketals via kinetically controlled spirocyclization reactions...
April 2017: Israel Journal of Chemistry
Masaki Morita, Shuntaro Kojima, Megumi Ohkubo, Hiroyuki Koshino, Daisuke Hashizume, Go Hirai, Keiji Maruoka, Mikiko Sodeoka
We present a full account of our synthetic studies on the racemic DEFGH-ring moiety of physalins, featuring domino ring transformation of a tricyclic key intermediate. We also report the results of a detailed mechanistic examination of the domino ring transformation, as well as a reoptimization of the 2,3-Wittig rearrangement and methylation steps. Furthermore, we have newly established a method for the preparation of an optically active synthetic intermediate by enzymatic kinetic resolution. Our work provides access to both natural and nonnatural right-side physalin structures...
April 2017: Israel Journal of Chemistry
Glenn C Micalizio, Haruki Mizoguchi
Alkoxide-directed metallacycle-mediated cross-coupling is a rapidly growing area of reaction methodology in organic chemistry. Over the last decade, developments have resulted in > thirty new and highly selective intermolecular (or "convergent") C-C bond-forming reactions that have established powerful retrosynthetic relationships in stereoselective synthesis. While early studies were focused on developing transformations that forge a single C-C bond by way of a functionalized and unsaturated metallacyclopentane intermediate, recent advances mark the ability to employ this organometallic intermediate in additional stereoselective transformations...
April 2017: Israel Journal of Chemistry
Nicholas F Polizzi, Michael J Therien, David N Beratan
Many biochemical processes, such as charge hopping or protein folding, can be described by an average timescale to reach a final state, starting from an initial state. Here, we provide a pedagogical treatment of the mean first-passage time (MFPT) of a physical process, which depends on the number of intervening states between the initial state and the target state. Our aim in this tutorial review is to provide a clear development of the mean first-passage time formalism and to show some of its practical utility...
November 2016: Israel Journal of Chemistry
Edward I Solomon, Ryan G Hadt, Benjamin E R Snyder
This review focuses on the unique spectroscopic features of the blue copper active sites. These reflect a novel electronic structure that activates the site for rapid long-range electron transfer in its biological function. The role of the protein in determining the geometric and electronic structure of this site is defined, as is its contribution to function. This has been referred to as the entatic/rack-induced state. These concepts are then extended to cytochrome c , which is also determined to be in an entatic state...
October 2016: Israel Journal of Chemistry
Harry B Gray, Jay R Winkler
Prior to 1950, the consensus was that biological transformations occurred in two-electron steps, thereby avoiding the generation of free radicals. Dramatic advances in spectroscopy, biochemistry, and molecular biology have led to the realization that protein-based radicals participate in a vast array of vital biological mechanisms. Redox processes involving high-potential intermediates formed in reactions with O2 are particularly susceptible to radical formation. Clusters of tyrosine (Tyr) and tryptophan (Trp) residues have been found in many O2 -reactive enzymes, raising the possibility that they play an antioxidant protective role...
October 2016: Israel Journal of Chemistry
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