The preparation of 2,6-diaminopyrazine, 2,6-diazidopyrazine and some of their derivatives

A much improved synthesis of the heretofore difficultly obtainable 2,6-diaminopyrazine (4) was afforded by the low-pressure catalytic hydrogenation (palladium on carbon) of 2,6-diazido-pyrazine (2) ; reaction of 2,6-dichloropyrazine (1) and sodium azide gave 2 in 84% yield. The outcome of the reduction was found to be solvent dependent: 1,2-dimethoxyethane containing aqueous ammonia gave 4 in 83% yield; 1,2-dimethoxyethane alone gave 5-aminotetrazolo[1,5-a]-pyrazine (3) in 26% yield. Additional alternative syntheses of 3 and 4 are described. A number of acyl and azo derivatives of 4 were prepared. Reactions of 2 with dimethyl acetylenedicarboxylate and ethyl acetate (base catalyzed) leading to vic-triazole derivatives are also described.     

ZIP8 exacerbates collagen-induced arthritis by increasing pathogenic T cell responses

Zinc is a trace element that is essential for immune responses. Therefore, changes in cellular zinc levels in specific immune cells may influence inflammatory autoimmune diseases, such as rheumatoid arthritis (RA). However, the regulation of zinc mobilization in immune cells and its role in the pathogenesis of RA are not fully understood. Thus, we investigated the roles of zinc transporters in RA pathogenesis. We demonstrated that ZIP8 was specifically upregulated in CD4⁺ T cells that infiltrated the inflamed joint and that ZIP8 deficiency in CD4⁺ T cells abrogated collagen-induced arthritis. ZIP8 deficiency dramatically affected zinc influx in effector T cells and profoundly reduced T cell receptor (TCR)-mediated signaling, including NF-κB and MAPK signaling, which are pathways that are involved in T helper (Th) 17 cell differentiation. Taken together, our findings suggest that ZIP8 depletion in CD4⁺ T cells attenuates TCR signaling due to insufficient cellular zinc, thereby reducing the function of effector CD4⁺ T cells, including Th17 cells. Our results also suggest that targeting ZIP8 may be a useful strategy to inhibit RA development and pathogenesis.Subject terms: Autoimmunity, Immunological disorders     

Fluorescence-based nitric oxide detection by ruthenium porphyrin fluorophore complexes

The ruthenium(II) porphyrin fluorophore complexes [Ru(TPP)(CO)(Ds-R)] (TPP = tetraphenylporphinato dianion; Ds = dansyl; R = imidazole (im), 1, or thiomorpholine (tm), 2) were synthesized and investigated for their ability to detect nitric oxide (NO) based on fluorescence. The X-ray crystal structures of 1 and 2 were determined. The Ds-im or Ds-tm ligand coordinates to an axial site of the ruthenium(II) center through a nitrogen or sulfur atom, respectively. Both exhibit quenched fluorescence when excited at 368 or 345 nm. Displacement of the metal-coordinated fluorophore by NO restores fluorescence within minutes. These observations demonstrate fluorescence-based NO detection using ruthenium porphyrin fluorophore conjugates.     

Squaric acid N-hydroxylamides: synthesis, structure, and properties of vinylogous hydroxamic acid analogues

The synthesis of squaric acid N-hydroxylamide esters 5 and amides 6 from dimethyl squarate 2a is described. These derivatives are analogues of the naturally occurring iron(III) chelator hydroxamic acid. On the basis of a comparative reactivity study, a concerted retro-Cope mechanism for the formation of the N-hydroxylamide esters 5 by reaction of dimethyl squarate with hydroxylamines is proposed. A preliminary iron(III) binding study of these hydroxamic acid analogues is presented, demonstrating binding of iron(III) to amides 6 in aqueous solutions, while the esters 5 did not show any sign of metal ion binding. 13C NMR spectroscopic data (chemical shift and spin-lattice relaxation time determination) of these and related derivatives delineate the resonance structures predominant in these molecules. The resonance structures of the derivatives rationalize their spectroscopic data, chemical reactivity, and iron(III) binding properties. Single-crystal X-ray structure analyses of squaric acid N-hydroxylamide ester 5b and squaric acid N-hydroxylamide amide 6c confirm their connectivity and provide structural evidence supporting the spectroscopically derived conclusions. The squaric acid N-hydroxylamides are potentially useful in the construction of chemosensors for iron(III).     

Photoactivation of pheophorbide a induces a mitochondrial-mediated apoptosis in Jurkat leukaemia cells

The mechanism of cell death by pheophorbide a (Pba) which has been established to be a potential photosensitizer was examined in experimental photodynamic therapy (PDT) on Jurkat cells, a human lymphoid tumor cell line. In 30-60 min after irradiation, Pba treated cells exhibited apoptotic features including membrane blebbing and DNA fragmentation. Pba/PDT caused a rapid release of cytochrome c from mitochondria into the cytosol. Sequentially, activation of caspase-3 and the cleavage of poly ADP-ribose polymerase (PARP) were followed. Meanwhile, no evidence of activation of caspase-8 was indicated in the cells. In experiments with caspase inhibitors, it was found that caspase-3 alone was sufficient initiator for the Pba-induced apoptosis of the cells. Pba specific emission spectra were confirmed in the mitochondrial fraction and the light irradiation caused a rapid change in its membrane potential. Thus, mitochondria were entailed as the crucial targets for Pba as well as a responsible component for the cytochrome c release to initiate apoptotic pathways. Taken together, it was concluded that the mode of Jurkat cell death by Pba/PDT is an apoptosis, which is initiated by mitochondrial cytochrome c release and caspase-3-pathways.     

Preparation and characterization of functional group gradient surfaces

Functional group gradient surfaces where the density of functional groups changes gradually along the sample length were prepared. The functional group (? COOH, ? CONH₂, and ? OH group) gradient surfaces were produced by the treatment of low-density PE sheets using a corona with gradually increasing power, followed by the graft copolymerization of acrylic acid and subsequent substitution reaction of carboxylic acid groups to amide or hydroxyl groups. The prepared gradient surfaces were characterized by the measurement of water contact angle, FTIR-ATR, and ESCA. The gradient surfaces prepared can be used to systematically investigate the interactions of biological or other species in terms of the surface functional groups and their density of polymeric materials. © 1994 John Wiley & Sons, Inc.     

Synthesis, characterization, and stability of Fe-MCM-41 for production of carbon nanotubes by acetylene pyrolysis

Fe-substituted MCM-41 molecular sieves with ca. 1, 2, and 3 wt % Fe were synthesized hydrothermally using different sources of colloidal silica (HiSil and Cab-O-Sil) and characterized by ICP, XRD, N2 physisorption, UV-vis, EPR, TPR, and X-ray absorption. Catalysts synthesized from Cab-O-Sil showed higher structural order and stability than those from HiSil. The local environment of Fe in the mesoporous material as studied by UV-vis reveals the dominance of framework Fe in all the as-synthesized Fe-MCM-41 samples. Dislodgement of some Fe species to extraframework location occurs upon calcination, and this effect is more severe for Fe-MCM-41 (2 wt %) and Fe-MCM-41 (3 wt %), as confirmed by EPR and X-ray absorption. These materials have been used as catalytic templates for the production of carbon nanotubes (CNTs) by acetylene pyrolysis at atmospheric pressure. A relationship between the Fe loading in MCM-41 and the carbon species produced during this reaction has been established. Using our optimized conditions for this system, Fe-MCM-41 with ca. 2 wt % Fe showed the best results with particularly high selectivity for single-wall carbon nanotube (SWNT) production. This catalyst was selective for carbon nanotubes with a low amount of amorphous carbon for a narrow range of temperatures from 1073 to 1123 K. To account for the different selectivity of these catalysts for CNTs production, the local environment and chemical state of Fe in the used catalyst was further probed by X-band EPR.     

Heat shock protein 27 interacts with vimentin and prevents insolubilization of vimentin subunits induced by cadmium

Vimentin is an intermediate filament that regulates cell attachment and subcellular organization. In this study, vimentin filaments were morphologically altered, and its soluble subunits were rapidly reduced via cadmium chloride treatment. Cadmium chloride stimulated three major mitogen-activated protein kinases (MAPKs): extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and p38, and led apoptotic pathway via caspase-9 and caspase-3 activations. In order to determine whether MAPKs were involved in this cadmium-induced soluble vimentin disappearance, we applied MAPK-specific inhibitors (PD98059, SP600125, SB203580). These inhibitors did not abolish the cadmium-induced soluble vimentin disappearance. Caspase and proteosome degradation pathway were also not involved in soluble vimentin disappearance. When we observed vimentin levels in soluble and insoluble fractions, soluble vimentin subunits shifted to an insoluble fraction. As we discovered that heat-shock protein 27 (HSP27) was colocalized and physically associated with vimentin in unstressed cells, the roles of HSP27 with regard to vimentin were assessed. HSP27-overexpressing cells prevented morphological alterations of the vimentin filaments, as well as reductions of soluble vimentin, in the cadmium-treated cells. Moreover, HSP27 antisense oligonucleotide augmented these cadmium-induced changes in vimentin. These findings indicate that HSP27 prevents disruption of the vimentin intermediate filament networks and soluble vimentin disappearance, by virtue of its physical interaction with vimentin in cadmium-treated SK-N-SH cells.     

Cyclometallated Pd(II) azido complexes containing 6-phenyl-2,2'-bipyridyl or 2-phenylpyridyl derivatives: synthesis and reactivity toward organic isocyanides and isothiocyanates

Cyclometallated palladium(II) azido complexes containing C,N,N- or C,N-donor ligands, [Pd(N(3))L](HL = 6-phenyl-2,2'-bipyridine or 2-phenylpyridyl derivatives), showed different reactivities toward organic isocyanides and isothiocyanates. In particular, aryl isocyanides (CN-Ar) underwent insertion into the orthometallated Pd-C bond on the phenyl moiety of the supporting ligand (L) in [Pd(N(3))L] or [Pd(N(3))(PR(3))L] to selectively give carbodiimido [[Pd(N=C=N-Ar)L]], imidoyl [[Pd(N(3))(-C=N-Ar)(PR(3))L]], or imidoyl carbodiimido complexes [[Pd(N=C=N-Ar)(-C=N-Ar)L] or [Pd(N=C=N-Ar)(-C=N-Ar)(PR(3))L]], depending on reaction conditions. Interestingly, reactions of [Pd(N(3))(PR(3))L] with organic isothiocyanates gave unusual dinuclear complexes [(micro-SCN(4)-R)PdL](2), exhibiting the concurrent S- and N-coordinating thio-tetrazole bridge.     

Asymmetric syntheses of fused bicyclic compounds by conjugate additions of allylic organolithium species to activated olefins and subsequent cyclizations

[reaction: see text]. Addition of the configurationally stable organolithium species produced by enantioselective deprotonation of N-Boc-N-(p-methoxyphenyl) allylamines to alpha,beta-unsaturated carbonyl compounds affords 1,4-addition products in good yields with high diastereomeric and enantiomeric ratios. Further transformations of these compounds provide [3.3.0]-, [4.3.0]-, [5.3.0]-, and [5.4.0]-carbocycles and heterocycles with high stereoselectivities.