Synthesis and photocleavage of a new dimeric bis(o-nitrobenzyl) diether tether

A new photocleavable linker, 4,4'-bis(alkoxymethyl-3,3'-dinitro)biphenyl, is reported that undergoes photolysis at two positions to release two equivalents of primary, secondary, or benzylic alcohol in yields that are higher than those obtained from the analogous monomeric o-nitrobenzyl ethers.     

Benzylic modifications of meso-alkyl-substituted porphyrins via oxidation with DDQ

The reactions at the benzylic positions of meso-alkyl-substituted porphyrins have been achieved via the reaction with DDQ in the presence of alcohol or water for the first time, and ethenyl porphyrins from methoxylated porphyrins and an acetoxy porphyrin from the hydroxyl porphyrin were prepared.     

Asymmetric synthesis of all-carbon benzylic quaternary stereocenters via Cu-catalyzed conjugate addition of dialkylzinc reagents to 5-(1-arylalkylidene) Meldrum's acids

The asymmetric synthesis of all-carbon benzylic quaternary stereocenters has been successfully achieved through copper-catalyzed addition of dialkylzinc reagents to 5-(1-arylalkylidene) and 5-(dihydroindenylidene) Meldrum's acids in the presence of phosphoramidite ligand. The resulting benzyl-substituted Meldrum's acids and 1,1-disubstituted indanes were obtained in good yields and up to 99% ee. The significance of substituting the position para, meta, and ortho to the electrophilic benzylic center was highlighted. A benzyl Meldrum's acid product was further transformed to a 3,3-disubstituted 1-indanone and a beta,beta-disubstituted pentanoic acid.     

Differentiation of diiodothyronines using electrospray ionization tandem mass spectrometry

Diiodothyronines 3,5-diiodothyronine (3,5-T2), 3',5'-diiodothyronine (3',5'-T2), and 3,3'-diiodothyronine (3,3'-T2) are important metabolites of 3,5,3'-triiodothyronine (T3) and 3,3',5'-triiodothyronine (rT3; reverse T3). In this paper, a novel and rapid method for identifying and quantifying 3,5-T2, 3',5'-T2 and 3,3'-T2 has been introduced using electrospray ionization tandem mass spectrometry (ESI-MS/MS). Fragmentation patterns were proposed on the basis of our data obtained by ESI-MS/MS. MS2 spectra in either negative ionization mode or positive ionization mode can be used to differentiate 3,5-T2, 3',5'-T2 and 3,3'-T2. On the basis of the relative abundance of fragment ions in MS2 spectra under the positive ionization mode, quantification of the 3,5-T2, 3',5'-T2 and 3,3'-T2 isomers in mixtures is also achieved without prior separation.     

Cyclopentadithiophene (CPDT) dimer dication: bipolaron model for quaterthiophenes

[structure: see text] Cyclopentadithiophene (CPDT) dimers in which both 3,3' and 4' ',3' " positions were bridged with 1,3-dioxalane, carbonyl, or dicyanovinylidene were prepared. These compounds have small HOMO-LUMO gaps (1.03-2.25 eV). The electrochemical oxidation of a dicyanovinylidene-bridged CPDT dimer gave a dication that had a quinoid-like structure.     

Preparation of Anion Exchange Membrane Based on Imidazolium Functionalized Poly(arylene ether ketone)

The authors presented a novel synthetic route for the imidazolium functionalized poly(arylene ether ketone)s, derived from an engineering plastics polymer, a poly(arylene ether ketone) with 3,3',5,5'-tetramethyl-4,4'-dihydroxybiphenyl moiety(PAEK-TM). The preparation of anion exchange membranes comprised converting benzylic methyl groups to bromomethyl groups by a radical reaction, followed by the functionalization of bromomethylated PAEK with alkyl imidazoles, i.e., methyl, butyl or vinyl imidazole. The structure of imidazolium functionalized PAEK was proved by ¹H NMR spectra. A class of flexible and tough membranes was then achieved by subsequent film-forming and anion exchange processes. The water uptake and hydroxide conductivities of membranes are comparable or superior to those of quaternary ammonium(QA) anion exchange membranes. This work demonstrated a new route for non-QA anion exchange membrane design, avoiding the chloromethylation reagent and precisely controlling the degree and location of imidazolium groups.     

The Crystal Structure of Biphenyltetracarboxylic Dianhydride Isomers

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PHOTODEGRADATION OF HEXACHLOROPHENE AND RELATED POLYCHLORINATED PHENOLS

Abstract— –Irradiation of hexachlorophene in absolute ethanol yields a series of dechlorinated bisphenols resulting from loss of chlorine at the ortho and para positions relative to the hydroxy groups. The two primary photoproducts. 2.2'-dihydroxy-3,3', 5,6,6'-pentachlorodiphenylmethane and 2,2'-dihydroxy-3,5,5', 6,6'-pentachlorodiphenylmethane were identified by independent syntheses.     

Direct assignment of the absolute configuration of a distinct class of deoxyribonucleoside cyclic N-acylphosphoramidites at phosphorus by M-GOESY nuclear magnetic resonance spectroscopy

The determination of the absolute configuration of deoxyribonucleoside cyclic N-acylphosphoramidites at phosphorus toward the synthesis of P-stereodifined phosphorothioated oligodeoxyribonucleotides is easily accomplished with computer-assisted molecular modeling and M-GOESY NMR spectroscopy. Specifically, computer-modeling diasteromeric phosphoramidite 3 has identifed a proximal (2.55 A) through-space interaction between benzylic H-5 and sugar H-2' ', which can predictably be detected by M-GOESY NMR in SP-3 but not in RP-3 because of being too distant (5.85 A). Consistent with computer-assisted modeling predictions, M-GOESY NMR spectra of SP-3 and RP-3 revealed NOE signals generated from nuclei near the selectively excited H-2' ' that are common to both SP-3 and RP-3, namely those of H-2', H-4', H-3', and H-1'. In addition, a diagnostic NOE signal at 5.5 ppm (benzylic H-5) is, as predicted, only detected in SP-3 and thus provides an unequivocal assessment of the configuration of the diastereomer at phosphorus. M-GOESY NMR data also confirm that the condensation of deoxyribonucleoside cyclic N-acylphosphoramidites with base-activated nucleosidic or nucleotidic 5'-hydroxyls proceeds via a single nucleophilic event.     

Direct oxidative installation of nitrooxy group at benzylic positions and its transformation into various functionalities

C-H Nitrooxylation at benzylic positions has been achieved by employing the N-hydroxyphthalimide (NHPI) catalyst/cerium(IV) ammonium nitrate (CAN) reagent system. The nitrooxy groups were demonstrated to function as tentative hydroxy protecting groups, as well as excellent leaving groups for N- and C-substitution reactions. Hence, the present method offers a unique way to synthesize diverse O-, N-, or C-functionalized benzylic compounds from simple alkyl aromatics.     

Synthesis and chiral HPLC analysis of the dibenzyltetrahydrofuran lignans,larreatricins, 8'-epi-larreatricins, 3,3'-didemethoxyverrucosins and meso-3,3'-didemethoxynectandrin B in the creosote bush (Larrea tridentata): evidence for regiospecific control of coupling

The creosote bush (Larrea tridentata) lignans are linked via 8-8' bonds, with the simplest apparently being E-p-anol derived. Of the latter, four of the six theoretically possible diastereoisomers were isolated, namely (-)-larreatricin, (-)-8'-epi-larreatricin, meso-3,3'-didemethoxynectandrin B and the new compounds, (+)- and (-)-3,3'-didemethoxyverrucosins. Following synthesis of each in either racemic or meso form, and chiral HPLC separation of the antipodes of the racemates, it was established that naturally occurring (-)-larreatricin and (-)-8'-epi-larreatricin were present in 92 and 98% enantiomeric excess, respectively, whereas 3,3'-didemethoxyverrucosin was essentially racemic and 3,3'-didemethoxynectandrin B was in the meso-form. The evidence suggests that formation of these lignans occurs under regiospecific, rather than stereoselective, coupling control. This contrasts with laccase-catalyzed "random" coupling of E-p-anol in vitro which generates the corresponding racemic 8-8', 8-3' and 8-O-4' linked dimeric moieties.     

Method for the quantitation of iodothyronines in body tissues and fluids using high-performance liquid chromatography.

The separation and quantitation of iodotyrosines and iodothyronines [3-monoiodo-L-tyrosine, 3,5-diiodo-L-tyrosine, 3,5-, 3,3' and 3',5'-diiodo-L-tyronines, 3,5,3'-triiodo-L-thyronine (T3), reverse 3,3',5'-triiodo-L-thyronine and 3,3',5,5'-tetraiodo-L-thyronine (T4)] from animal tissues (brain, liver and serum) by a new high-performance liquid chromatographic (HPLC) method is described. Rats were infused with iso-osmotic sodium chloride containing 100 microM phloretin to block deiodination. The tissues were extracted using differential pH values to separate other amines from the amine containing iodothyroid hormones. Aliquots of tissue extracts (25-100 microliters) were reacted overnight with 5-dimethylaminonaphthalene-1-sulfonyl chloride and their iodotyrosine and iodothyronine content determined by HPLC utilizing fluorimetric detection. Resolution of the individual compound peaks was achieved by gradient elution with a 3.0 mM H3PO4 buffer. Greater sensitivity has been achieved (less than 1.0 pmol/g) utilizing fluorescence rather than ultraviolet absorbance for the quantitation of these iodinated compounds. The method is superior also to other methods in that recoveries, based on those of 125I-labelled T4 and T3, were 89-97%.     

New atropisomeric N-N ligands for CO/vinyl arene copolymerization reaction

New atropisomeric bidentate bipyridine-based ligands (3,3'-(ethylenedioxy)-2,2'-bipyridine 4; 3,3'-(propylenedioxy)-2,2'-bipyridine 4; 3,3'-(butylenedioxy)-2,2'-bipyridine 5) containing a bridge between the 3,3' positions of the aromatic rings have been prepared. Together with the previously reported analogous ligands ((R)-3,3'-(1-methylethylenedioxy)-2,2'-bipyridine) 1and ((S,S)-3,3'-(1,2-dimethylethylenedioxy)-2,2'-bipyridine) 2, they were used to synthesize the corresponding bis-chelated dicationic complexes [Pd(N-N)2][PF6]2. Crystal structures and comparison of the data obtained by X-ray analysis on four of these complexes is reported. These palladium compounds were used as precatalysts in the CO/styrene and CO/4-Me-styrene copolymerization reactions, where they showed that small variations in the ligand backbone remarkably affects the productivity of the catalytic system.     

Method for the determination of three toxic non-ortho chlorine substituted coplanar PCBs in environmental samples at part-per-trillion levels

A method has been devised combining alkali digestion, carbon chromatography and high-resolution gas chromatography for the determination of 3,3',4,4'-tetra, 3,3',4,4',5-penta, and 3,3',4,4',5,5'-hexachlorobiphenyl, the biologically active congeners of PCBs and approximate isostereomers of 2,3,7,8-TCDD. This method permits determinations of parts-per-trillion levels of these toxic residues in biological samples. Interference both from biogenic and from xenobiotic substances was reduced to extremely low levels. Using this method, 13.5 ng of 3,3'4,4'-tetrachlorobiphenyl/g, 0.89 ng of 3,3'4,4',5-pentachlorobiphenyl/g and 0.64 ng of 3,3',4,4'5,5'-hexachlorobiphenyl/g were detected on wet weight basis in the blubber of a finless porpoise. To our knowledge this is the first report on the three toxic non-ortho chlorine substituted PCB residues detected in a higher mammal in the wilderness.     

Synthesis of nitrogen-bridged terthiophenes by tandem Buchwald-Hartwig coupling and their properties

The first synthesis of nitrogen-bridged terthiophenes (NBTTs) has been achieved by a tandem Buchwald-Hartwig coupling of 3,3',3",4'-tetrabromo-2,2':5',2"-terthiophene. Several NBTT derivatives bearing aryl or alkyl moieties on the N-atoms could be synthesized. Their fundamental electrochemical characteristics and HOMO-LUMO levels were found to be influenced by the substituents on the N-atoms.     

Stereoselective synthesis of the 5'-hydroxy-5'-phosphonate derivatives of cytidine and cytosine arabinoside

Both the (R)- and (S)-5'-hydroxy 5'-phosphonate derivatives of cytidine and cytosine arabinoside (ara-C) have been prepared via phosphite addition or a Lewis acid mediated hydrophosphonylation of appropriately protected 5'-nucleoside aldehydes. Phosphite addition to a cytosine aldehyde protected as the 2',3'-acetonide gave predominately the 5'R isomer, while phosphite addition to the corresponding 2',3'-bis TBS derivative favored the 5'S stereochemistry. In contrast, phosphite addition to the 2',3'-bis TBS protected aldehyde derived from ara-C gave only the 5'R adduct. However, TiCl(4)-mediated hydrophosphonylation of the same ara-C aldehyde favored the 5'S stereoisomer by a 2:1 ratio. Once all four of the diastereomers were in hand, the stereochemistry of these compounds could be assigned based on their spectral data or that obtained from their O-methyl mandelate derivatives. After hydrolysis of the phosphonate esters and various protecting groups, the four alpha-hydroxy phosphonic acids were tested for their ability to serve as substrates for the enzyme nucleoside monophosphate kinase and for their toxicity to K562 cells.     

Substituent effects in ethene/styrene copolymerization: Dormant state destabilization?

Homogeneous metallocene and CGC catalyzed copolymerizations of ethene (E) and various substituted styrenes are examined. It is found that those with p‐tert‐butylstyrene (TBS) occur with dramatically higher degrees of incorporation and overall productivity than those observed under the same conditions with styrene. It is argued that that the σ‐donating effect of the tert‐butyl substituent is responsible for this performance, effecting a destabilization of an otherwise dormant benzylic species following 2,1‐insertion of the styrene. It was found possible to produce what is essentially TBS‐alt‐E (44% TBS with no sequential TBS units) using a standard constrained geometry catalyst at impressively high productivity [1.5 × 10⁶ g/(mol_Ti.bar_E.h)] and unusually low concentration of TBS (0.7 M). © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3111–3117, 2009     

Highly electron-donating 3,3'-diaryl-1,1'-bi(isobenzofuran)s synthesized by photochemical exocyclic [2 + 2 + 2] cycloaddition

Facile photochemical exocyclic [2 + 2 + 2] cycloaddition produced a series of electron-donating 1,1'-bi(isobenzofuran)s having various aryl groups at the 3,3' positions. The 1,1'-bi(isobenzofuran) skeleton with a highly coplanar structure is a useful building unit to construct the narrow bandgap pi-conjugated systems with low oxidation potentials.     

Synthesis and reactions of partially reduced biisoquinolines

An improved synthesis of the 1,1',2,2',3,3',4,4'-octahydro-1.1'-biisoquinoline ring system is described. The reactivity of this system has been investigated, including the unusually high basicity of the parent compound and its N.N'-dimethyl derivative. The resolution of the parent compound has been achieved for the first time, along with the development of a straightforward method for assaying its enantiomeric purity.     

Polycationic gramicidin s analogues with both high antibiotic activity and very low hemolytic activity

The substitution of each constituent amino acid residue of gramicidin S (GS), cyclo(-Val(1,1')-Orn(2,2')-Leu(3,3')-D-Phe(4,4')-Pro(5,5')-)(2) with Lys residue indicated that each side chain structure of the constituent amino acid residues affect largely the antibiotic activity and hemolytic activity of GS. Further, the substitution of D-Phe(4,4') and Pro(5,5') residues with basic amino acid residues as a Lys residue results the high antibiotic activity and the very low hemolytic activity. Thus, we have found novel positions on the scaffold of GS at D-Phe(4,4') and Pro(5,5') residues whose modification will significantly increase the therapeutic index.