David S. Larsen

A family of 13 tetranuclear zinc(II)-lanthanide(III) complexes of a [3 + 3] Schiff-base macrocycle derived from 1,4-diformyl-2,3-dihydroxybenzene

A family of thirteen tetranuclear heterometallic zinc(II)-lanthanide(III) complexes of the hexa-imine macrocycle (L(Pr))(6-), with general formula Zn(II)(3)Ln(III)(L(Pr))(NO(3))(3)·xsolvents (Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm or Yb), were prepared in a one-pot synthesis using a 3:1:3:3 reaction of zinc(II) acetate, the appropriate lanthanide(III) nitrate, the dialdehyde 1,4-diformyl-2,3-dihydroxybenzene (H(2)L(1)) and 1,3-diaminopropane. A hexanuclear homometallic zinc(II) macrocyclic complex [Zn(6)(L(Pr))(OAc)(5)(OH)(H(2)O)]·3H(2)O was obtained using a 2:0:1:1 ratio of the same reagents. A control experiment using a 1:0:1:1 ratio failed to generate the lanthanide-free [Zn(3)(L(Pr))] macrocyclic complex. The reaction of H(2)L(1) and zinc(II) acetate in a 1:1 ratio yielded the pentanuclear homometallic complex of the dialdehyde H(2)L(1), [Zn(5)(L(1))(5)(H(2)O)(6)]·3H(2)O. An X-ray crystal structure determination revealed [Zn(3)(II)Pr(III)(L(Pr))(NO(3))(2)(DMF)(3)](NO(3))·0.9DMF has the large ten-coordinate lanthanide(III) ion bound in the central O(6) site with two bidentate nitrate anions completing the O(10) coordination sphere. The three square pyramidal zinc(II) ions are in the outer N(2)O(2) sites with a fifth donor from DMF. Measurement of the magnetic properties of [Zn(II)(3)Dy(III)(L(Pr))(NO(3))(3)(MeOH)(3)]·4H(2)O with a weak external dc field showed that it has a frequency-dependent out-of-phase component of ac susceptibility, indicative of slow relaxation of the magnetization (SMM behaviour). Likewise, the Er and Yb analogues are field-induced SMMs; the latter is only the second example of a Yb-based SMM. The neodymium, ytterbium and erbium complexes are luminescent in the solid phase, but only the ytterbium and neodymium complexes show strong lanthanide-centred luminescence in DMF solution.

Role of phosphatidylinositol mannosides in the interaction between mycobacteria and DC-SIGN.

ABSTRACT The C-type lectin dendritic cell (DC)-specific intercellular adhesion molecule 3-grabbing nonintegrin (DC-SIGN) is the major receptor on DCs for mycobacteria of the Mycobacterium tuberculosis complex. Recently, we have shown that although the mannose caps of the mycobacterial surface glycolipid lipoarabinomannan (ManLAM) are essential for the binding to DC-SIGN, genetic removal of these caps did not diminish the interaction of whole mycobacteria with DC-SIGN and DCs. Here we investigated the role of the structurally related glycolipids phosphatidylinositol mannosides (PIMs) as possible ligands for DC-SIGN. In a binding assay with both synthetic and natural PIMs, DC-SIGN exhibited a high affinity for hexamannosylated PIM6, which contains terminal α(1→2)-linked mannosyl residues identical to the mannose cap on ManLAM, but not for di- and tetramannosylated PIM2 and PIM4, respectively. To determine the role of PIM6 in the binding of whole mycobacteria to DC-SIGN, a mutant strain of M. bovis bacillus Calmette-Guérin deficient in the production of PIM6 (ΔpimE) was created, as well as a double knockout deficient in the production of both PIM6 and the mannose caps on LAM (ΔpimE ΔcapA). Compared to the wild-type strain, both mutant strains bound similarly well to DC-SIGN and DCs. Furthermore, the wild-type and mutant strains induced comparable levels of interleukin-10 and interleukin-12p40 when used to stimulate DCs. Hence, we conclude that, like ManLAM, PIM6 represents a bona fide DC-SIGN ligand but that other, as-yet-unknown, ligands dominate in the interaction between mycobacteria and DCs.

Dicopper(II) complexes of a new pyrazolate-containing Schiff-base macrocycle and related acyclic ligand

Dicopper(II) complexes of two new 3,5-disubstituted-pyrazole-based ligands, bis(quadridentate) macrocyclic ligand (L1)(2-) and bis(terdentate) acyclic ligand (L2)(-), were synthesised by Schiff base condensation of 3,5-diformylpyrazole and either one equivalent of 1,3-diaminopropane or two equivalents of 2-(2-aminoethyl)pyridine in the presence of one or two equivalents of copper(II) ions, respectively. Copper(II) acetate monohydrate was employed in the synthesis of [Cu(2)(L1)(OAc)(2)], [Cu(2)(L2)(H(2)O)(2)(OAc)(3)] and [Cu(II)(2)(L1)(NCS)(2)]; in the last of these one equivalent of NaNCS per copper(II) ion was also added. The fourth complex, [Cu(2)(L2)(NCS)(2)(DMF)]BF(4), was prepared using copper(II) tetrafluoroborate hexahydrate, along with two equivalents of NaOH and six of NaSCN. All four of these dimetallic complexes have been characterised by single crystal X-ray diffraction: the two macrocyclic complexes are the first such Schiff base complexes to be so characterised. A feature common to all four of the structures is bridging of the two copper(II) centres by the pyrazolate moiety/moieties. The structure determinations show that the coordination mode of the acetate groups in both [Cu(2)(L1)(OAc)(2)].2MeOH.H(2)O and [Cu(2)(L2)(H(2)O)(2)(OAc)(3)] is unidentate as had been tentatively predicted by analysis of the infrared spectra (DeltaOCO of 199 and 208 cm(-1), respectively). The magnetochemical studies of the macrocyclic complexes, over the temperature range 4-300 K, revealed strong antiferromagnetic coupling with J = -169 and -213 cm(-1) for [Cu(2)(L1)(OAc)(2)].2H(2)O and [Cu(II)(2)(L1)(NCS)(2)].DMF respectively. The J values have been discussed in relation to a published correlation involving the CuN(pyrazolate)N(pyrazolate) angles.

Using exomarkers to assess mitochondrial reactive species in vivo

BACKGROUND The ability to measure the concentrations of small damaging and signalling molecules such as reactive oxygen species (ROS) in vivo is essential to understanding their biological roles. While a range of methods can be applied to in vitro systems, measuring the levels and relative changes in reactive species in vivo is challenging. SCOPE OF REVIEW One approach towards achieving this goal is the use of exomarkers. In this, exogenous probe compounds are administered to the intact organism and are then transformed by the reactive molecules in vivo to produce a diagnostic exomarker. The exomarker and the precursor probe can be analysed ex vivo to infer the identity and amounts of the reactive species present in vivo. This is akin to the measurement of biomarkers produced by the interaction of reactive species with endogenous biomolecules. MAJOR CONCLUSIONS AND GENERAL SIGNIFICANCE Our laboratories have developed mitochondria-targeted probes that generate exomarkers that can be analysed ex vivo by mass spectrometry to assess levels of reactive species within mitochondria in vivo. We have used one of these compounds, MitoB, to infer the levels of mitochondrial hydrogen peroxide within flies and mice. Here we describe the development of MitoB and expand on this example to discuss how better probes and exomarkers can be developed. This article is part of a Special Issue entitled Current methods to study reactive oxygen species - pros and cons and biophysics of membrane proteins. Guest Editor: Christine Winterbourn.

A self-adjuvanting vaccine induces cytotoxic T lymphocytes that suppress allergy

Epitope-based peptide vaccines encompass minimal immunogenic regions of protein antigens to allow stimulation of precisely targeted adaptive immune responses. However, because efficacy is largely determined by the functional status of antigen-presenting cells (APCs) that acquire and present peptides to cells of the adaptive immune system, adjuvant compounds are needed to enhance immunogenicity. We present here a vaccine consisting of an allergen-derived peptide conjugated to a prodrug of the natural killer-like T (NKT) cell agonist α-galactosylceramide, which is highly effective in reducing inflammation in a mouse model of allergic airway inflammation. Unlike other peptide-adjuvant conjugates that directly activate APCs through pattern recognition pathways, this vaccine encourages third-party interactions with NKT cells to enhance APC function. Therapeutic efficacy was correlated with marked increases in the number and functional activity of allergen-specific cytotoxic T lymphocytes (CTLs), leading to suppression of immune infiltration into the lungs after allergen challenge in sensitized hosts.

A mitochondria-targeted mass spectrometry probe to detect glyoxals: implications for diabetes

The glycation of protein and nucleic acids that occurs as a consequence of hyperglycemia disrupts cell function and contributes to many pathologies, including those associated with diabetes and aging. Intracellular glycation occurs after the generation of the reactive 1,2-dicarbonyls methylglyoxal and glyoxal, and disruption of mitochondrial function is associated with hyperglycemia. However, the contribution of these reactive dicarbonyls to mitochondrial damage in pathology is unclear owing to uncertainties about their levels within mitochondria in cells and in vivo. To address this we have developed a mitochondria-targeted reagent (MitoG) designed to assess the levels of mitochondrial dicarbonyls within cells. MitoG comprises a lipophilic triphenylphosphonium cationic function, which directs the molecules to mitochondria within cells, and an o-phenylenediamine moiety that reacts with dicarbonyls to give distinctive and stable products. The extent of accumulation of these diagnostic heterocyclic products can be readily and sensitively quantified by liquid chromatography–tandem mass spectrometry, enabling changes to be determined. Using the MitoG-based analysis we assessed the formation of methylglyoxal and glyoxal in response to hyperglycemia in cells in culture and in the Akita mouse model of diabetes in vivo. These findings indicated that the levels of methylglyoxal and glyoxal within mitochondria increase during hyperglycemia both in cells and in vivo, suggesting that they can contribute to the pathological mitochondrial dysfunction that occurs in diabetes and aging.

Synthetic approaches to the angucycline antibiotics: Synthesis of the C-glycosidic CD ring system

The syntheses of the protected C-glycosyl substituted CD ring system of the angucycline antibiotics and analogues thereof are reported. The key step in their preparation was the C-glycosylation reaction of 5-hydroxy-1,4-dimethoxynaphthalene and a series of 1-O-acyl-2-deoxy and 1-O-acyl-2, 6-dideoxy sugar electrophiles promoted by boron trifluoride etherate. The use of the participating solvent, acetonitrile, was essential for the success of the reaction.

Asymmetric Diels–Alder reactions. Part 3. Influence of butadiene structure upon the diastereofacial reactivity of (E)-1-(2′,3′,4′,6′-tetra-O-acetyl-β-D-glucopyranosyloxy)buta-1,3-dienes

(E)-1-(2′,3′,4′,6′-Tetra-O-acetyl-β-D-glucopyranosyloxy)buta-1,3-diene (1c), its 3-methyl derivative (1d), its 2,3-dimethyl derivative (1e), its (3Z)-4-acetoxy-3-(t-butyldimethylsilyloxy) derivative (1f), its 3-(t-butyldimethylsilyloxy) derivative (1g), and its (3Z)-3-(t-butyldimethylsilyloxy)-2,4-dimethyl derivative (1h) have been prepared and their diastereofacial reactivities towards N-phenylmaleimide and tetracyanoethylene assessed. With the former dienophile in benzene at ambient temperature, the dienes (1c, d, f, g) gave ca. 87 : 13 mixtures of the cycloadduct pairs (2c) and (3c), (2d) and (3d), (2f) and (3f), and (2g) and (3g); however, the dienes (1e, h) afforded only the cycloadducts (2e, h). With tetracyanoethylene in benzene at ambient temperature, the aforecited dienes reacted to give mixtures of cycloadducts, ranging from a 69 : 31 mixture of the cycloadducts (6c) and (7c) in the case of the diene (1c) to an 89 : 11 mixture of the cycloadducts (6h) and (7h) in the case of the diene (1h).

A stereoselective approach to the angucyclinone antibiotics: A total synthesis of the C-1 epimer of (±)-rubiginone B1

Abstract A stereoselective Lewis acid-promoted cycloaddition reaction of 5-hydroxy-1,4-naphthoquinone and dienol (12) gave a key intermediate (14) which was transformed into the title compound (18) in 35% overall yield.

Synthetic approaches to the angucycline antibiotics: the total syntheses of (±)-rubiginone B1 and B2, (±)-emycin A, and related analogues

The syntheses of the angucyclinone antibiotics; (±)-rubiginone B13 and B24, (±)-ochromycinone 7, and (±)-emycin A 12 are reported. The key step for the construction of the benzo[a]anthracene nucleus in each of the syntheses was a highly stereoselective, tetra-O-acetyl diborate-promoted Diels–Alder cycloaddition of 5-hydroxy-1,4-naphthoquinone 8 and the diene, E-(1R*,5R*)-l-acetoxy-3-(2′-methoxyvinyl)-5-methylcyclohex-2-ene 21. Base-induced aromatisation of the cycloadduct 30 gave the benzo[a]anthraquinone, (1R*,3R*)-1-acetoxy-8-hydroxy-1,2,3,4-tetrahydrobenzo[a]anthracene-7,12-dione 28 which served as an intermediate for the syntheses of the above natural products. The syntheses of (±)-13-norrubiginone B134 and B235, and (±)-1-epi-rubiginone B111 using modifications of the synthetic strategy are also described.