Formation of organorhodium complexes via C–H bond activation of 1,3-di(phenylazo)benzene

Reaction of a potential NCN-pincer ligand, viz. 1,3-di(phenylazo)benzene (L), with [Rh(PPh3)(3)Cl] affords, via a C-H bond activation, an interesting dinuclear Rh(II) complex (1), and with RhCl3 center dot 3H(2)O affords a mononuclear Rh(III) complex (2) containing a catalytically useful Rh-OH2 fragment.

Síntese de ligantes quirais pentacíclicos 1,5 e bicíclicos 1,3 di substituídos e suas aplicações como indutores quirais na reação de adição de dietilzinco ao bensaldeído

Neste trabalho foi observado um rearranjodiotrópico do composto quiral (+)-1 o que levou na sua racemização. Verificou-se que esse processoé termicamente permitido pela simetria dos orbitais de fronteira HOMO-LUMO. Posteriormente, constatou-se que o rearranjo não era somente governado pela temperatura, mas também pelas condições reacionais, respeitada a simetria de orbitais. A partir da obtenção dos precursores quirais (−)-40 e (−)-41 através de reação de transesterificação de (±)-40 com acetato de vinila catalisada pela lípase da Cândida rugosa, realizou-se a síntese de uma série de compostos quirais bicíclicos 1,3 di-substituídos, dióis e aminoálcoois. Estes bicíclicos quirais foram testados como indutores quirais na reação de adição enantioseletiva de dietilzinco ao benzaldeído. Observou-se, no caso dos aminoálcoois, que a posição do estereocentro C-O tem uma importância fundamental no processo, determinando o grau de enantioseletividade da reação. Sintetizou-se o aminoálcool (+)-63 o qual foi utilizado na redução enantioseletiva de cetonas pró-quirais através da síntese, in situ, de sua oxazaborolidina.

Compostos fenólicos e atividade antioxidante de Leiothrix flavescens (Bong.) Ruhland (Eriocaulaceae)

This paper describes a chemical investigation (by high-speed counter-current chromatography) of an extract in methanol of the capitula (flower-heads) of the endemic Brazilian herb Leiothrix flavescens (Bong.) Ruhland (Eriocaulaceae). Fractionation of this extract by preparative chromatography and identification of the isolated compounds by spectrometric methods (IR, UV, ESI-MS, NMR) led to the identification of flavones (apigenin, luteolin and 6-methoxyluteolin) and 1,3-di-O-feruloyl glycerol. The antioxidant activity of the extract was determined by DPPH reduction and the total phenolic content by the Folin-Ciocalteau assay. It was found that the methanolic extract of L. flavescens possesses strong antioxidant activity. Additionally, the chemical profile provided useful data for a discussion of the taxonomy of the Eriocaulaceae.

Synthesis and evaluation of 2,5-di(4-aryloylaryloxymethyl)-1,3,4-oxadiazoles as anti-cancer agents

A series of 2,5-di(4-aryloylaryloxymethyl)-1,3,4-oxadiazoles 9a-j were obtained via multistep synthesis from hydroxybenzophenones 4a-e. The cytotoxicity of compounds 9a-j was evaluated against human leukemia cell lilies (K562 and CEM). The compounds exhibited moderate to good anti-cancer activity with compounds 9b and 9i having a chloro group exhibiting the best activity (IC50 = 10 mu M). Compound 9i exhibited activity against both the cell lines and 9b only exhibited activity against CEM. Further, a lactate dehydrogenase (LDH) assay and DNA fragmentation studies of the compounds 9a-j were also performed. (C) 2013 Elsevier Masson SAS. All rights reserved.

Synthesis and evaluation of 2,5-di(4-aryloylaryloxymethyl)-1,3,4-oxadiazoles as anti-cancer agents

A series of 2,5-di(4-aryloylaryloxymethyl)-1,3,4-oxadiazoles 9a-j were obtained via multistep synthesis from hydroxybenzophenones 4a-e. The cytotoxicity of compounds 9a-j was evaluated against human leukemia cell lilies (K562 and CEM). The compounds exhibited moderate to good anti-cancer activity with compounds 9b and 9i having a chloro group exhibiting the best activity (IC50 = 10 mu M). Compound 9i exhibited activity against both the cell lines and 9b only exhibited activity against CEM. Further, a lactate dehydrogenase (LDH) assay and DNA fragmentation studies of the compounds 9a-j were also performed. (C) 2013 Elsevier Masson SAS. All rights reserved.

Synthesis and structural characterisation of [Cu2[(PDC)2(bpa)(H2O)2]•nH2O•mDMF (n=3 and m=1 for 1, n=7 and m=0 for 2, PDC=2,5-pyrindinedicarboxylate and bpa= 1,2-di(4-pyridil)ethane))

[EN] Combination of polycarboxylate anions and dipyridyl ligands is an effective strategy to produce solid coordination frameworks (SCF) which are crystalline materials based on connections between metal ions through organic ligands. In this sense, combination of polycarboxylate anions and dipyridyl ligands is an effective strategy to produce extended structures. In this context, this work is focused on two novel CuII-based SCFs exhibiting PDC (2,5-pyridinedicarboxylate) and bpa (1,2-di(4-pyridyl)ethane), being the first structures reported in literature containing both ligands. Chemical formula are [Cu2[(PDC)2(bpa)(H2O)2]•3H2O•DMF (1), and [Cu2(PDC)2(bpa)(H2O)2]•7H2O (2), where DMF is dimethylformamide. Compounds 1 and 2 have been characterized by means of XRD, IR, TG/DTG, and DTA analysis.

Effect of the nucleating agent 1,3 : 2,4-di(3,4-dimethylbenzylidene) sorbitol on the gamma phase content of propylene/ethylene copolymer

The influence of the concentration of a nucleating agent (NA), namely 1,3:2,4-di(3,4-dimethylbenzylidene) sorbitol (DMDBS), on the gamma phase content in a propylene/ethylene copolymer was investigated by means of Differential Scanning Calorimetry (DSC), Wide-Angle X-ray Diffraction (WAXD), Small- Angle X-ray Scatter (SAXS) and Polarized Optical Microscopy (POM).

Poly[di-mu(3)-chloro-mu(2)-trans-1,2-di-4-pyridylethylene-dicopper(I)]: a two-dimensional organic-inorganic hybrid constructed from linear CuCl clusters and bridging ligands

The structure of the title compound, [Cu2Cl2(C12H10N2)](n), contains infinite CuCl staircase-like chains, which lie about inversion centres. The trans-1,2-di-4-pyrid-ylethyl-ene mol-ecules also lie about inversion centres and connect the CuCl chains through Cu-N coordination bonds into a two-dimensional organic-inorganic hybrid network. The planar sheets are stacked along the c axis and associated through weak C-H center dot center dot center dot Cl inter-actions. The results show a reliable structural motif with controllable separation of the CuCl chains by variation of the length of the ligand.

The antioxidant activity of 2-(4(or 2)-hydroxyl-5-chloride-1,3-benzene-di-sulfanimide)-chitosan

Chitosan (CS) with two different molecular weights was modified by reacting with 4-hydroxyl-5-chloride-1,3-benzene-disulfo-chloride or 2-hydroxyl-5-chloride-1,3-benzene-disulfo-chloride to give new 2-(4(or 2)-hydroxyl-5-chloride-1,3-benzene-di-sulfanimide)-chitosan (2-HCBSAHCS, 2-HCBSALCS, 4-HCBSAHCS, 4-HCBSALCS). The structure of the derivatives was characterized by FT-IR and C-13 NMR spectroscopy. The antioxidant activities of the derivatives were investigated employing various established systems, such as hydroxyl radical ((OH)-O-center dot)/superoxide anion (O-2(radical anion)) scavenging/reducing power and chelating activity. All the derivatives showed stronger scavenging activity on hydroxyl radical than chitosan and ascorbic acid (Vc), and IC50 of 4-HCBSAHCS, 4-HCBSALCS, 2-HCBSAHCS and 2-HCBSALCS was 0.334, 0.302, 0.442, 0.346 mg/mL, respectively. The inhibitory activities of the derivatives toward superoxide radical by the PMS-NADH system were strong. The results showed that the superoxide radical scavenging effect of 2-(4(or 2)-hydroxyl-5-chloride-1,3-benzene-disulfanimide)-chitosan was higher than chitosan. The derivatives had obviously reducing power and slight chelating activity. The data obtained in in vitro models clearly establish the antioxidant potency of 2-(4(or 2)-hydroxyl-5-chloride-1,3-benzene-disulfanimide)-chitosan. (C) 2007 Elsevier Masson SAS. All rights reserved.

Formation of Novel Di-Nuclear Lanthanide Luminescent Sm(III), Eu(III) and Tb(III) Triple Stranded Helicates from a C2 Symmetrically 2,6-Dicarboxylic Amide based 1,3-Xylene Ligand in CH3CN

The synthesis of the C2-symmetrical ligand 1 consisting of two naphthalene units connected to two pyridine-2,6-dicarboxamide moieties linked by a xylene spacer and the formation of LnIII-based (Ln1/4 Sm, Eu, Tb, and Lu) dimetallic helicates [Ln2 · 13] in MeCN by means of a metal-directed synthesis is described. By analyzing the metal-induced changes in the absorption and the fluorescence of 1, the formation of the helicates, and the presence of a second species [Ln2 · 12] was confirmed by nonlinear- regression analysis. While significant changes were observed in the photophysical properties of 1, the most dramatic changes were observed in the metal-centred lanthanide emissions, upon excitation of the naphthalene antennae. From the changes in the lanthanide emission, we were able to demonstrate that these helicates were formed in high yields (ca. 90% after the addition of 0.6 equiv. of LnIII), with high binding constants, which matched well with that determined from the changes in the absorption spectra. The formation of the LuIII helicate, [ Lu2 · 13 ] , was also investigated for comparison purposes, as we were unable to obtain accurate binding constants from the changes in the fluorescence emission upon formation of [Sm2 · 13], [Eu2 · 13], and [Tb2 · 13].

On the halogenation of N(1),N(2)-di-t-Boc-5-hydroxy-piperazic acid esters and the conformational preferences of their 5-halo-piperazic acid products. The importance of A1,3 rotameric-strain in determining N(2)-acyl piperazic acid ring conformation

In this Letter, an unambiguous synthetic strategy is reported for the preparation of enantiomerically purecis-5-halo-piperazic acid derivatives in single diastereoisomer form. Contrary to the recent report by Shin and co-workers (Chem. Lett. 2001, 1172), in which it is claimed that the Ph₃P and N-chlorosuccinimide (NCS)-mediated chlorination of (3R,5S)-trans-N(1),N(2)-di-t-Boc-5-hydroxy-piperazic acid derivative 1proceeds with retention of configuration at C(5) to give 2, we now show that this and related Ph₃P-mediated halogenations all occur with S_N2 inversion at the alcohol center, as is customary for such reactions. Specifically, we demonstrate that the (3R,5S)-trans-5-Cl-piperazic acid derivative 2 claimed by Shin and co-workers (Chem. Lett. 2001, 1172) is in actual fact the chlorinated (3S,5R)-enantiomer 6, which must have been prepared from the cis-(3S,5S)-alcohol 3, a molecule whose synthesis is not formally described in the Shin paper. We further show here that the cis-(3R,5R)-5-Cl-Piz 13 claimed by Shin and co-workers inChem. Lett. 2001, 1172, is also (3S,5R)-trans-5-Cl-Piz 6. Authentic 13 has now been synthesized by us, for the very first time, here. Since Lindsley and Kennedy have recently utilized the now invalid Shin and co-workers’ retentive Ph₃P/NCS chlorination procedure on 1 in their synthetic approach to piperazimycin A (Tetrahedron Lett. 2010, 51, 2493), it follows that their claimed 5-Cl-Piz-containing dipeptide 25 probably has the alternate structure 26, where the 5-Cl-Piz residue has a 3,5-cis-configuration. The aforementioned stereochemical misassignments appear to have come from a mix-up of starting materials by Shin and co-workers (Chem. Lett. 2001, 1172), and an under-appreciation of the various steric and conformational effects that operate in N(2)-acylated piperazic acid systems, most especially rotameric A^1,3-strain. The latter has now been unambiguously delineated and defined here under the banner of the A^1,3-rotamer effect.

Enhanced Templating in the Crystallisation of Poly(E-caprolactone) Using 1,3:2,4-di(4-Chlorobenzylidene) Sorbitol

We show that small quantities of 1,3:2,4-di(4-chlorobenzylidene) sorbitol dispersed in poly(epsilon-caprolactone) provide a very effective self-assembling nanoscale framework which, with a flow field, yields extremely high levels of polymer crystal orientation. During modest shear flow of the polymer melt, the additive forms highly extended nano-particles which adopt a preferred alignment with respect to the flow field. On cooling, polymer crystallisation is directed by these particles. This chloro substituted dibenzylidene sorbitol is considerably more effective at directing the crystal growth of poly(epsilon-caprolactone) than the unsubstituted compound.

1,3-dipolar cycloaddition of CS2 to the coordinated azide in the cyclopalladated [Pd(bzan)(mu-N-3)](2). Crystal and molecular structure of di(mu-N,S-1,2,3,4-thiatriazole-5-thiolate)bis[(benzylideneaniline-C-2,N)palladium(II)]

The compound [Pd(bzan)(mu -N-3)](2) 1, bzan = benzylideneaniline, was prepared from [Pd(bzan) (mu -OOCCH3)](2) by an anion exchange reaction. The 1,3-dipolar cycloaddition of carbon disulfide to the bridged coordinated azide in the cyclometallated compound I was investigated. The species resulting from this reaction, di(mu -N,S-1,2,3,4-thiatriazol-5-thiolate)bis[(benzylideneaniline)palladium(II)] 2, was characterized by IR spectroscopy and X-ray diffraction. The compound 2 is a dimer containing two [Pd(benzylideneaniline)] moieties connected by two vicinal bridging N,S-1,2,3,4-thiatriazole-5-thiolate anions in a square-planar coordination geometry for the palladium atoms.

Determination of absolute configuration of 1,3-diols by the modified Mosher's method using their di-MTPA esters

1,3-Diols are frequently involved in biologically important compounds and, therefore, determination of the stereochemistry of these structural elements, in particular those in acyclic systems, has been one of the focuses of attention in natural products chemistry. The modified Mosher's method, commonly used for the determination of the absolute configuration of secondary alcohols, was applied to determine the absolute configuration of 1,3-diols with their di-MTPA esters. Several epimeric pairs of syn- and anti-1,3-diols with known absolute configurations were converted to the corresponding di-MTPA esters and the Delta delta values were then calculated. For the acyclic syn-1,3-diols, the Delta delta values were systematically arranged as predicted from the basic concept of the modified Mosher's method, demonstrating that the method is valid for these compounds. In contrast, the Delta delta values were irregularly arranged for the acyclic anti-1,3-diols and, accordingly, this method is not valid for these cases. These results are complementary to those of the previously reported CD exciton chirality method and, hence, the combined use of the modified Mosher's method and the CD exciton chirality method can determine the absolute configuration of the acyclic 1,3-diols. Also, this method is successfully applicable to cyclic 1,3-diols irrespective of their relative stereochemistry. (C) 2002 Wiley-lass, Inc.