Identification and structure-activity relationships for a series of N, N-disubstituted 2-aminobenzothiazoles as potent inhibitors of S. aureus

An internal collection of commercial and synthetically derived small molecule compounds was screened against several drug-resistant bacterial pathogens. Compound 1, a known N, N-disubstituted 2-aminobenzothiazole, was found to be a potent inhibitor of Staphylococcus aureus and several associated clinically relevant strains of methicillin-resistant S. aureus suggesting a possible novel mechanism of inhibition. It failed to show activity in any of the Gram-negative pathogens it was tested in. Evaluation in Escherichia coli BW25113 and Pseudomonas aeruginosa PAO1, as well as in their respective hyperporinated and efflux pump-deletion mutants revealed that activity in Gram-negative bacteria is diminished because this benzothiazole scaffold is a substrate for bacterial efflux pumps. Several analogs of 1 were synthesized to generate basic structure-activity relationships for the scaffold which highlighted that the N-propyl imidazole moiety was critical for the observed antibacterial activity.

Synthesis and Evaluation of Troponoids as a New Class of Antibiotics

Novel antibiotics are urgently needed. The troponoids [tropones, tropolones, and α-hydroxytropolones (α-HT)] can have anti-bacterial activity. We synthesized or purchased 92 troponoids and evaluated their antibacterial activities against Staphylococcus aureus, Escherichia coli, Acinetobacter baumannii, and Pseudomonas aeruginosa. Preliminary hits were assessed for minimum inhibitory concentrations (MIC₈₀) and cytotoxicity (CC₅₀) against human hepatoma cells. Sixteen troponoids inhibited S. aureus/E. coli/A. baumannii growth by ≥80% growth at <30 μM with CC₅₀ values >50 μM. Two selected tropolones (63 and 285) inhibited 18 methicillin-resistant S. aureus (MRSA) strains with similar MIC₈₀ values as against a reference strain. Two selected thiotropolones (284 and 363) inhibited multidrug-resistant (MDR) E. coli with MIC₈₀ ≤30 μM. One α-HT (261) inhibited MDR-A. baumannii with MIC₈₀ ≤30 μM. This study opens new avenues for development of novel troponoid antibiotics to address the critical need to combat MDR bacterial infections.

Assembly of high-areal-density deuterium-tritium fuel from indirectly driven cryogenic implosions

The National Ignition Facility has been used to compress deuterium-tritium to an average areal density of ~1.0±0.1 g cm(-2), which is 67% of the ignition requirement. These conditions were obtained using 192 laser beams with total energy of 1-1.6 MJ and peak power up to 420 TW to create a hohlraum drive with a shaped power profile, peaking at a soft x-ray radiation temperature of 275-300 eV. This pulse delivered a series of shocks that compressed a capsule containing cryogenic deuterium-tritium to a radius of 25-35 μm. Neutron images of the implosion were used to estimate a fuel density of 500-800 g cm(-3).

[With the scalpel against the immune system: HIV infection complicated by an unclear colitis]

A 35-year-old Kenian lady with advanced immunodeficiency due to HIV infection started on an antiretroviral therapy. Five months later, a severe colitis was diagnosed, however, no causal pathogen could be found. In order to avoid imminent perforation, a hemicolectomy became necessary, and immediately the symptoms and inflammation markers normalized rapidly. M. tuberculosis could be proven in culture in a draining abdominal lymph node. We assume that the severe inflammation was caused by an immune restoration inflammatory syndrome (IRIS). Essentials in diagnosis, pathogenesis and therapy of IRIS are discussed.

Maxillary sinus grafting with a nano-structured biomaterial: preliminary clinical and histological results

BACKGROUND

In this study the potential of a new and entirely synthetic, nano-structured hydroxyapatite-based biomaterial for sinus floor augmentation is evaluated.

METHODS

20 sinus floor elevations were carried out in a total of 20 patients. After a healing period of 6 months, in 10 cases cylinder-shaped bone biopsies were taken from the augmented maxillary region using trephine burs.

RESULTS

The healing period progressed without any complications. General and specific histological analysis of the bone biopsies showed a high osteoclast activity at the margin of the biomaterial which was well integrated into the newly formed bone.

CONCLUSION

This study demonstrates that new trabecular bone is formed after grafting with the nanocrystalline bone substitute after 6 months. Ongoing histomorphological studies are necessary to quantify the biomaterial-bone ratio and the exact amount of newly built bone in the augmented cavity after 6 months.

Bovine hemoglobin as a basis for artificial oxygen carriers

Under physiological conditions of pH and [Cl-] ions the oxygen affinity of bovine hemoglobin is lower than that of human hemoglobin. The difference tends to disappear at low ionic strength, while it increases at high ionic strength. In the presence of Cl- ions bovine hemoglobin is not sensitive to 2,3-DPG, while in the absence of Cl- ions human and bovine hemoglobin respond to 2,3-DPG in a similar way. This is due to a high preferential binding of halogens by the deoxy-conformation in the bovine system. Reaction of deoxy-bovine hemoglobin with 2,3-dibromo-salycyl-fumarate results in a decreased oxygen affinity. Compounds can be purified by anion exchange chromatography which have the sedimentation velocity of tetrameric hemoglobins. They fail to dissociate into dimers at acid pH because of the presence of intramolecular crosslinks. Reverse phase chromatography shows that both kind of subunits are modified by the reaction. The half time of retention in rats of these tetramers is near 5 h. Bovine red cells do not contain 2,3-DPG, therefore they can be stored in the cold in saline for at least 2 months without significant modifications of their oxygen affinity. The oxygen affinity of bovine red cells can be modulated by addition and subtraction of Cl- ions from and by changing the pH of the media.

Bovine hemoglobin as a potential source of hemoglobin-based oxygen carriers: crosslinking with bis(2,3-dibromosalycyl)fumarate

Reaction in anaerobic conditions of bovine hemoglobin with bis(2,3-dibromosalycyl)fumarate resulted in new derivatives with P50 in excess of 40 mmHg, as determined at 37 degrees C in 0.15 M Cl- at pH 7.4. Although the chromatographic preparations indicated some heterogeneity of the reacted material, the proteins obtained were homogeneous with regard to sedimentation velocity, which showed the presence of only nondissociable tetrameric species. SDS gel electrophoresis showed the presence of a new band with a mobility corresponding approximately to a molecular mass of 32 kDa, indicating the presence of covalent intramolecular crosslinks between subunit pairs. Chromatographic analyses indicated that both alpha and beta chains were chemically modified. The retention times in rats of the crosslinked hemoglobin was 10-times longer than that of untreated hemoglobin.

Solvent regulation of oxygen affinity in hemoglobin. Sensitivity of bovine hemoglobin to chloride ions

Under physiological conditions of pH (7.4) and chloride concentration (0.15 M), the oxygen affinity of bovine hemoglobin is substantially lower than that of human hemoglobin. Also, the Bohr effect is much more pronounced in bovine hemoglobin. Numerical simulations indicate that both phenomena can be explained by a larger preferential binding of chloride ions to deoxyhemoglobin in the bovine system. Also, they show that the larger preferential binding may be produced by a decreased affinity of the anions for oxyhemoglobin, thereby stressing the potential relevance of the oxy conformation in regulating the functional properties of the protein. The conformation of the amino-terminal end of the beta subunits appears to regulate the interaction of hemoglobin with solvent components. The pronounced sensitivity of the oxygen affinity of bovine hemoglobin to chloride concentration and to pH suggests that in bovine species these are the modulators of oxygen transport in vivo.