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Molecules (Basel, Switzerland) Jan 2019The utility of an electron-deficient, air stable, and commercially available Lewis acid tris(pentafluorophenyl)borane has recently been comprehensively explored. While... (Review)
Review
The utility of an electron-deficient, air stable, and commercially available Lewis acid tris(pentafluorophenyl)borane has recently been comprehensively explored. While being as reactive as its distant cousin boron trichloride, it has been shown to be much more stable and capable of catalyzing a variety of powerful transformations, even in the presence of water. The focus of this review will be to highlight those catalytic reactions that utilize a silane as a stoichiometric reductant in conjunction with tris(pentafluorophenyl) borane in the reduction of alcohols, carbonyls, or carbonyl-like derivatives.
Topics: Alcohols; Boranes; Catalysis; Chemical Phenomena; Esters; Hydrocarbons, Fluorinated; Lewis Acids; Oxidation-Reduction; Silanes
PubMed: 30691072
DOI: 10.3390/molecules24030432 -
Angewandte Chemie (International Ed. in... Apr 2018Tailor-made: Discussed herein is the ability to adapt biology's mechanisms for innovation and optimization to solving problems in chemistry and engineering. The... (Review)
Review
Tailor-made: Discussed herein is the ability to adapt biology's mechanisms for innovation and optimization to solving problems in chemistry and engineering. The evolution of nature's enzymes can lead to the discovery of new reactivity, transformations not known in biology, and reactivity inaccessible by small-molecule catalysts.
Topics: Biocatalysis; Boranes; Cytochromes c; Directed Molecular Evolution; High-Throughput Screening Assays; Protein Engineering; Rhodothermus; Silanes
PubMed: 29064156
DOI: 10.1002/anie.201708408 -
Future Medicinal Chemistry Apr 2013The compound class of 3-carboranyl thymidine analogues (3CTAs) are boron delivery agents for boron neutron capture therapy (BNCT), a binary treatment modality for... (Review)
Review
The compound class of 3-carboranyl thymidine analogues (3CTAs) are boron delivery agents for boron neutron capture therapy (BNCT), a binary treatment modality for cancer. Presumably, these compounds accumulate selectively in tumor cells via intracellular trapping, which is mediated by hTK1. Favorable in vivo biodistribution profiles of 3CTAs led to promising results in preclinical BNCT of rats with intracerebral brain tumors. This review presents an overview on the design, synthesis, and biological evaluation of first- and second-generation 3CTAs. Boronated nucleosides developed prior to 3CTAs for BNCT and non-boronated N3-substituted thymidine conjugates for other areas of cancer therapy and imaging are also described. In addition, basic features of carborane clusters, which are used as boron moieties in the design and synthesis of 3CTAs, and the biological and structural features of TK1-like enzymes, which are the molecular targets of 3CTAs, are discussed.
Topics: Animals; Boranes; Boron Neutron Capture Therapy; Humans; Molecular Docking Simulation; Neoplasms; Nitrogen; Prodrugs; Thymidine; Thymidine Kinase
PubMed: 23617430
DOI: 10.4155/fmc.13.31 -
The Journal of General Physiology Feb 1975Retinochrome is a photosensitive pigment located primarily in the inner portions of the visual cells of cephalopods. Its absorption spectrum resembles that of rhodopsin,...
Retinochrome is a photosensitive pigment located primarily in the inner portions of the visual cells of cephalopods. Its absorption spectrum resembles that of rhodopsin, but its chromophore is all-trans retinal, which light isomerizes to 11-cis, the reverse of the situation in rhodopsin. The 11-cis photoproduct of retinochrome slowly reverts to retinochrome in the dark. The chromophoric site of retinochrome is more reactive than that of most visual pigments: (a) Hydroxylamine converts retinochrome in the dark to all-trans retinal oxime + retinochrome opsin. (by Sodium borohydride reduces it to N-retinyl opsin. (c) Lambda max of retinochrome shifts from 500 to 515 nm as the pH is raised from 6 to 10, with a loss of absorption above pH 8; meanwhile above this PH a second band appears at shorter wavelengths with lambda max 375 nm. These changes are reversible. (d) If retinochrome is incubated with all-trans 3-dehydroretinal (retinal2) in the dark, some 3-dehydroretinochrome (retinochrome2, lambda max about 515 nm) is formed. Conversely, when retinochrome2, made by adding all-trans retinal2 to bleached retinochrome or retinochrome opsin, is incubated in the dark with all-trans retinal some of it is converted to retinochrome. Retinal and 3-dehydroretinal therefore can replace each other as chromophores in the dark.
Topics: Borohydrides; Chemical Phenomena; Chemistry; Color; Cysteine; Decapodiformes; Hydrogen-Ion Concentration; Hydroxylamines; Isomerism; Light; Preservation, Biological; Retinal Pigments; Spectrum Analysis
PubMed: 235007
DOI: 10.1085/jgp.65.2.235 -
Angewandte Chemie (International Ed. in... Sep 2020The first trans-selective cyanoboration reaction of an alkyne, specifically a 1,3-enyne, is described. The reported palladium-catalyzed cyanoboration of 1,3-enynes is...
The first trans-selective cyanoboration reaction of an alkyne, specifically a 1,3-enyne, is described. The reported palladium-catalyzed cyanoboration of 1,3-enynes is site-, regio-, and diastereoselective, and is uniquely enabled by the 1,4-azaborine-based Senphos ligand structure. Tetra-substituted alkenyl nitriles are obtained providing useful boron-dienenitrile building blocks that can be further functionalized. The utility of our method has been demonstrated with the synthesis of Satigrel, an anti-platelet aggregating agent.
Topics: Boranes; Catalysis; Cyanides; Density Functional Theory; Fatty Acids, Monounsaturated; Hydrocarbons; Palladium; Platelet Aggregation Inhibitors; Stereoisomerism
PubMed: 32511855
DOI: 10.1002/anie.202005882 -
Molecules (Basel, Switzerland) Oct 2020Understanding the hydrogen atom abstraction (HAA) reactions of -heterocyclic carbene (NHC)-boranes is essential for extending the practical applications of boron...
Understanding the hydrogen atom abstraction (HAA) reactions of -heterocyclic carbene (NHC)-boranes is essential for extending the practical applications of boron chemistry. In this study, density functional theory (DFT) computations were performed for the HAA reactions of a series of NHC-boranes attacked by CHCN, Me and Et radicals. Using the computed data, we investigated the correlations of the activation and free energy barriers with their components, including the intrinsic barrier, the thermal contribution of the thermodynamic reaction energy to the kinetic barriers, the activation Gibbs free energy correction and the activation zero-point vibrational energy correction. Furthermore, to describe the dependence of the activation and free energy barriers on the thermodynamic reaction energy or reaction Gibbs free energy, we used a three-variable linear model, which was demonstrated to be more precise than the two-variable Evans-Polanyi linear free energy model and more succinct than the three-variable Marcus-theory-based nonlinear HAA model. The present work provides not only a more thorough understanding of the compositions of the barriers to the HAA reactions of NHC-boranes and the HAA reactivities of the substrates but also fresh insights into the suitability of various models for describing the relationships between the kinetic and thermodynamic physical quantities.
Topics: Boranes; Density Functional Theory; Heterocyclic Compounds; Hydrogen; Kinetics; Methane; Models, Molecular; Temperature
PubMed: 33019654
DOI: 10.3390/molecules25194509 -
Chimia 2012N-Hetereocyclic carbene (NHC) complexes of boranes are stable compounds that can be used as co-initiators for the type II photopolymerization of acrylates. The present... (Review)
Review
N-Hetereocyclic carbene (NHC) complexes of boranes are stable compounds that can be used as co-initiators for the type II photopolymerization of acrylates. The present account summarizes this new development for polymerization and boron chemistry. In particular, NHC-boranes are air- and water-tolerant, which enhances the practicality of the photopolymerizations.
Topics: Acrylates; Air; Boranes; Free Radicals; Heterocyclic Compounds; Methane; Molecular Structure; Photochemical Processes; Polymerization; Water
PubMed: 22871279
DOI: 10.2533/chimia.2012.382 -
Molecules (Basel, Switzerland) Dec 2022A number of (hetero)boranes are known in which a main group atom 'bridges' a B-B connectivity in the open face, and in such species has previously been described as...
A number of (hetero)boranes are known in which a main group atom 'bridges' a B-B connectivity in the open face, and in such species has previously been described as simply a bridge or, alternatively, as a vertex in a larger cluster. In this study we describe an approach to distinguish between these options based on identifying the best fit of the experimental {B} cluster fragment with alternate exemplar {B} fragments derived from DFT-optimized [BH] models. In most of the examples studied atom is found to be better regarded as a vertex, having 'a 'verticity' of ca. 60-65%. Consideration of our results leads to the suggestion that the radial electron contribution from to the overall skeletal electron count is more significant than the tangential contribution.
Topics: Electrons; Boranes
PubMed: 36615384
DOI: 10.3390/molecules28010190 -
Journal of the American Chemical Society Jul 2008Metal-free homoallylic oxygen-directed intramolecular hydroboration is reported. Regioselectivities from 20:1 to 82:1 favoring the 1,3-dioxy-substituted products have...
Metal-free homoallylic oxygen-directed intramolecular hydroboration is reported. Regioselectivities from 20:1 to 82:1 favoring the 1,3-dioxy-substituted products have been achieved using Me2S.BH3/TfOH followed by standard oxidative workup. Branching at the C5 position improves regioselectivity.
Topics: Alcohols; Alkenes; Boranes; Iodine; Oxidation-Reduction; Propanols
PubMed: 18572941
DOI: 10.1021/ja800402g -
Biochimica Et Biophysica Acta May 1999The nitric oxide (NO) synthase family of enzymes generate NO from L-arginine, which acts as a biologic effector molecule in a broad number of settings. This report... (Review)
Review
The nitric oxide (NO) synthase family of enzymes generate NO from L-arginine, which acts as a biologic effector molecule in a broad number of settings. This report summarizes some of the current information regarding NO synthase structure-function, reaction mechanism, control of catalysis, and protein interactions.
Topics: Animals; Arginine; Boranes; Calmodulin; Catalysis; Cattle; Mammals; Mice; Nitric Oxide; Nitric Oxide Synthase; Nitric Oxide Synthase Type I; Nitric Oxide Synthase Type II; Nitric Oxide Synthase Type III; Rats; Signal Transduction; Structure-Activity Relationship
PubMed: 10320659
DOI: 10.1016/s0005-2728(99)00016-x