Pascal Hoffmann

Systematic structural studies of iron superoxide dismutases from human parasites and a statistical coupling analysis of metal binding specificity

Superoxide dismutases (SODs) are a crucial class of enzymes in the combat against intracellular free radical damage. They eliminate superoxide radicals by converting them into hydrogen peroxide and oxygen. In spite of their very different life cycles and infection strategies, the human parasites Plasmodium falciparum, Trypanosoma cruzi and Trypanosoma brucei are known to be sensitive to oxidative stress. Thus the parasite Fe‐SODs have become attractive targets for novel drug development. Here we report the crystal structures of FeSODs from the trypanosomes T. brucei at 2.0 Å and T. cruzi at 1.9 Å resolution, and that from P. falciparum at a higher resolution (2.0 Å) to that previously reported. The homodimeric enzymes are compared to the related human MnSOD with particular attention to structural aspects which are relevant for drug design. Although the structures possess a very similar overall fold, differences between the enzymes at the entrance to the channel which leads to the active site could be identified. These lead to a slightly broader and more positively charged cavity in the parasite enzymes. Furthermore, a statistical coupling analysis (SCA) for the whole Fe/MnSOD family reveals different patterns of residue coupling for Mn and Fe SODs, as well as for the dimeric and tetrameric states. In both cases, the statistically coupled residues lie adjacent to the conserved core surrounding the metal center and may be expected to be responsible for its fine tuning, leading to metal ion specificity. Proteins 2009.

Bismuth Triflate as a Safe and Readily Handled Source of Triflic Acid: Application to the Oxa–Pictet–Spengler Reaction

The oxa–Pictet–Spengler reaction with various aldehydes and β-arylethanol yields 1-substituted-isochromans in the presence of bismuth triflate as catalyst in good yields. The method was extended to O,O-acetals to afford the corresponding 1,1-disubstituted-isochromans in good yields. These studies also provide insights into the catalytic role of triflic acid generated upon hydrolysis of Bi(OTf)3 by residual water. The low toxicity and easy handling of Bi(OTf)3 by comparison with triflic acid make these procedures an attractive method to provide isochromans in good to excellent yields.

Synthesis and uptake of nitric oxide-releasing drugs by the P2 nucleoside transporter in Trypanosoma equiperdum

A series of S-nitrosothiols, structurally related to the NO*-donor S-nitroso-N-acetylpenicillamine, and of organic nitrate esters that contain amidine groups which specify a recognition via the trypanosomal purine transporter P2, were synthesized and tested for their ability to inhibit the uptake of [2-(3)H]adenosine on Trypanosoma equiperdum.

Peroxynitrite-induced nitration of tyrosine-34 does not inhibit Escherichia coli iron superoxide dismutase.

The peroxynitrite anion is a potent oxidizing agent, formed by the diffusion-limited combination of nitric oxide and superoxide, and its production under physiological conditions is associated with the pathologies of a number of inflammatory and neurodegenerative diseases. Nitration of Escherichia coli iron superoxide dismutase (Fe-SOD) by peroxynitrite was investigated, and demonstrated by spectral changes and electrospray mass spectroscopic analysis. HPLC and mass studies of the tryptic digests of the mono-nitrated Fe-SOD indicated that tyrosine-34 was the residue most susceptible to nitration by peroxynitrite. Exclusive nitration of this residue occurred when Fe-SOD was exposed to a cumulative dose of 0.4 mM peroxynitrite. Unlike with human Mn-SOD, this single modification did not inactivate E. coli Fe-SOD at pH 7.4. When Fe-SOD was exposed to higher concentrations of peroxynitrite (7 mM), eight tyrosine residues per subunit of the protein, of the nine available, were nitrated without loss of catalytic activity of the enzyme. The pK(a) of nitrated tyrosine-34 was determined to be 7.95+/-0.15, indicating that the peroxynitrite-modified enzyme appreciably maintains its protonation state under physiological conditions.

Synthesis, electrochemical, and spectroscopic studies of novel S-nitrosothiols

Abstract A series of S-nitrosothiol compounds, structurally related to the NO-donor S-nitroso-N-acetyl- d , l -penicillamine (SNAP) that contain amidin groups were synthesised by S-nitrosation of the corresponding thiols and characterised. The kinetics of decomposition were investigated and showed that the two adenine-based thionitrites exhibited an unusual stability in aqueous solution compared to SNAP, suggesting that these compounds may complex the traces of free copper ions present in solution, which is known to catalyze the decomposition of thionitrites. The electrochemical behaviour of these compounds and their nitric oxide-releasing potential were studied by means of cyclic voltammetry techniques on mercury and glassy carbon electrodes.

A free-base dipyrrin capable of forming extended architectures comparable to those of its metal(II) complex counterparts

We demonstrate the involvement of an unprecedented hydrogen-bonded dipyrrin dimer in the generation of a 3-D hydrogen-bonded network which is structurally identical to the 3-D coordination networks formed with bis(dipyrrinato)metal(II) complexes.

New potent bisubstrate inhibitors of histone acetyltransferase p300: design, synthesis and biological evaluation.

Bisubstrate‐type compound Lys‐CoA has been shown to inhibit the p300 histone acetyl transferase activity efficiently and may constitute a lead compound for a novel class of anticancer therapeutics. Based on this strategy, we synthesized a series of CoA derivatives and evaluated these molecules for their activity as p300 histone acetyltransferases inhibitor. The best activity was obtained with compound 3 bearing a C‐5 spacing linker that connects the CoA moiety to a tert‐butyloxycarbonyl (Boc) group. Based on docking simulations, this inhibitor exhibits favorable interactions with two binding areas, namely pockets P1 and P2, within the active site.

SYNTHESIS AND CHARACTERIZATION OF NEW AROMATIC THIONITRITES

Abstract Thionitrites (S-nitrosothiols) play an essential biological role as nitric oxide (NO.) carriers. Here, we present the synthesis. the characterization and the stability studies in solution of new aromatic thionitrites 1b-4b as potent nitric oxide donors. The four thionitrites were characterized by 1H NMR, UV-visible and IR spectroscopies. Their decomposition occurs within a few minutes in dichloromethane, and yields quantitatively the corresponding disulfide. NO. and the thiyl radicals coming from their decomposition were trapped by distinct spin traps to give characteristic EPR signals. 4b possesses the di-tert-butylphenol moiety responsible for the antioxidant properties of BHT and of the structurally-related drug probucol.

Superoxide-induced bleaching of streptocyanine dyes: Application to assay the enzymatic activity of superoxide dismutases

With the aim of developing a novel superoxide dismutase (SOD) activity assay, a series of polymethinium salts (streptocyanines) were prepared and studied for their ability to be reduced by superoxide radical anion generated either from the pyrogallol autoxidation or by the xanthine oxidase-catalyzed oxidation of xanthine. The nonacarbon chain streptocyanine 9Cl(NEt(2))(2) was found to be relatively stable in neutral buffered aqueous solutions, to be reduced at a significant rate by superoxide, and addition of iron-dependent superoxide dismutase (Fe-SOD) prevented its bleaching, thus constituting a good candidate as a possible superoxide indicator in a spectrophotometric SOD assay. The values found to be optimal for a SOD assay were defined as pH 7.4, wavelength 728nm, xanthine and xanthine oxidase as superoxide source, and a reaction time of 5min. Based on the color change caused by the superoxide-induced bleaching of the streptocyanine, a qualitative colorimetric method for the SOD activity detection is proposed, enabling visual detection within a short time without any instrument.

Versatile cyclization of aminoanilino lactones : Access to benzotriazoles and condensed benzodiazepin-2-thiones

Abstract Furanone 3 and pyranone 4 were obtained by the reaction of o‐phenylene derivatives with tetronic acid 1 or pyrone 2, respectively. Under diazotization reaction, these two enaminone derivatives 3 and 4 cyclized rapidly with good yields to generate benzotriazoles 5. On the other hand, when enaminones 3 and 4 were allowed to react with carbondisulfide as electrophile, cyclization led to benzodiazepin‐2‐thiones 6 fused to dihydropyrone or tetronic acid moieties.