Rebecca Braslau

Synthesis and applications of optically active nitroxides

Abstract This article reviews the synthesis of optically active nitroxides and their applications in enantioselective oxidations, in stereoselective carbon-oxygen bond-forming reactions, as anticancer compounds, and as spin labels.

A convenient chemoselective semihydrogenation of acetylenes using homogeneous catalysis

Abstract Acetylenes and some dienes are rapidly reduced to olefins by a combination of acetic acid and a silicon hydride in the presence of a Pd(0) catalyst.

Acyl hydrazines as precursors to acyl radicals

Abstract The use of acyl hydrazines (hydrazides) as precursors for the stoichiometric generation of acyl radicals is explored. Two classes of substrates are examined: unsubstituted acyl hydrazines and acyl hydrazines substituted with a leaving group (2-nitrobenzenesulfonyl or ‘nosyl’). Both types are successfully converted to acyl radicals, and are then trapped by nitroxide radicals to give acyloxyamine products. Cyclization reactions are demonstrated for both classes of substrates. A low temperature modification of the McFayden–Stevens reaction is also developed.

A Synthesis of β-necrodol via a palladium catalyzed reductive enyne cyclization

Abstract The Pd catalyzed reductive enyne cyclization provides an approach to control 1,3- diastereoselectivity and thereby provides a five step synthesis of β-necrodol, a key substituent of the defensive secretion of the red-lined carrion beetle.

Palladium-Catalyzed Coupling of Stannyl Allenes With Aryl Iodides

Abstract Substituted allenes are prepared by coupling stannyl allenes with aryl iodides under palladium(O) catalysis. A concise and versatile sequence starting from propargyl alcohols provides a route for the preparation of substituted allenes under extremely mild conditions.

SYNTHESIS OF SEVERAL NOVEL OPTICALLY ACTIVE NITROXYL RADICALS

Abstract Optically active nitroxyl radicals are prepared from enantiomerically pure bicyclic terpenoids. (−)-Camphoxyl radical (−)-4 derived from commercially available oxazolidinone ( (−)-1 ) and (+)-camphoxyl radical (+)-4 derived from (−)-camphene are readily prepared, conformationally rigid, enantiomeric nitroxyl radicals. (−)-Camphorsulphonic acid is used to prepare two additional optically active nitroxyl radicals 9 and 12 .

Synthesis of fluorinated alkoxyamines and alkoxyamine-initiated nitroxide-mediated precipitation polymerizations of styrene in supercritical carbon dioxide†

TIPNO (2,2,5-trimethyl-4-phenyl-3-azahexane-3-nitroxide)-alkoxyamine was found to give reasonably controlled/living nitroxide-mediated (NMP) precipitation polymerizations of styrene in supercritical carbon dioxide (scCO2). In contrast under the same conditions, the analogous SG1 (N-tert-butyl-N-(1-diethylphosphono-2,2-dimethylpropyl)nitroxide)-alkoxyamine gave higher rates of polymerization and inferior controlled/living character. The circumvention of the requirement for excess free [nitroxide]0 allowed the study of nitroxide partitioning effects in scCO2 for three newly synthesized fluorinated alkoxyamines. Two alkoxyamines dissociated into scCO2-philic fluorinated TIPNO-nitroxide derivatives, while another contains a similar sized fluorinated “foot”. Despite the increased steric bulk about the N–O bond for the novel fluorinated alkoxyamines, all polymerizations proceeded at a similar rate and level of control to the TIPNO system in solution (toluene). PREDICI simulations for the styrene/TIPNO system are used to support extensive partitioning effects observed in scCO2 for the fluorinated alkoxyamines.

Abstraction of deuterium from dideuteroglycine by aryl radical: A model for 1, 4-benzene diradical reactions with proteins

Abstract Aryl radicals are generated by oxidation of aryl hydrazine with PbO 2 or via photolysis of aryl iodide. Abstraction of deuterium from dideuteroglycine derivatives is demonstrated as a model for the possible reaction of 1, 4-aryl diradicals with amino acid residues in proteins.

Urushiol Detection using a Profluorescent Nitroxide

A method to visually detect minute amounts of urushiol, the toxic catechol from poison oak, poison ivy, and poison sumac, has been developed utilizing the reaction of a profluorescent nitroxide with the B-n-butylcatecholboronate ester formed in situ from urushiol and B-n-butylboronic acid. The resulting N-alkoxyamine is strongly fluorescent upon illumination with a fluorescent lamp, allowing the location of the toxic urushiol contamination to be visualized. This methodology constitutes the groundwork for the future development of a spray to detect urushiol to avoid contact dermatitis, as well as to detect catecholamines for biomedical applications.

Use of a Nanoscale Pore to Read Short Segments within Single Polynucleotide Molecules

Single-stranded polynucleotide molecules impede ionic current when they are driven through a nanoscale pore formed by the α-hemolysin heptameric channel (see J. Kasianowicz, D. Deamer, D. Branton, this volume). The duration and frequency of these blockades correlate with the length and concentration of the polymer examined. This suggests that translocation of RNA and DNA strands through the nanopore might also be used to derive a direct, high-speed readout of each molecule’s linear composition. We have recently shown that this is possible. Homopolymers of polycytidylic acid (poly C), polyadenylic acid (poly A), and polyuridylic acid (poly U) cause blockades of current through the α-hemolysin pore that are distinguishable from one-another based on amplitude and duration. These differences are due to the predominant secondary structure adopted by each homopolymer at room temperature in neutral buffer. We have also demonstrated that the nanopore instrument has sufficient sensitivity and resolution to detect short, discrete blocks within single polynucleotide molecules during translocation. For example, within an individual RNA strand, the transition from a 30-nucleotide poly A segment to a 70-nucleotide poly C segment can be read as an abrupt, 10 pA current change. A larger current change can also be observed at the transition between nucleotides and an abasic deoxyribose-phosphate segment inserted into a synthetic DNA strand. These polymers may be used to encode targeting molecules such as antibodies, gene specific oligonucleotides, and peptide agonists.