Bis-6-amidino-benzothiazole Derivative that Cures Experimental Stage 1 African Trypanosomiasis with a Single Dose

We designed and synthesized a series of symmetric bis-6-amidino-benzothiazole derivatives with aliphatic central units and evaluated their efficacy against bloodstream forms of the African trypanosome Trypanosoma brucei. Of these, a dicationic benzothiazole compound (9a) exhibited sub-nanomolar in vitro potency with remarkable selectivity over mammalian cells (>26,000-fold). Unsubstituted 5-amidine groups and a cyclohexyl spacer were the crucial determinants of trypanocidal activity. In all cases, mice treated with a single dose of 20 mg kg-1 were cured of stage 1 trypanosomiasis. The compound displayed a favorable in vitro ADME profile, with the exception of low membrane permeability. However, we found evidence that uptake by T. brucei is mediated by endocytosis, a process that results in lysosomal sequestration. The compound was also active in low nanomolar concentrations against cultured asexual forms of the malaria parasite Plasmodium falciparum. Therefore, 9a has exquisite cross-species efficacy and represents a lead compound with considerable therapeutic potential.

Systematic approach to understanding macrolide-ribosome interactions: NMR and modeling studies of oleandomycin and its derivatives

The three-dimensional structures of oleandomycin (1) and its derivatives oleandomycin-9-oxime (2) and 10,11-anhydrooleandomycin (3) were determined in different solvents by the combined use of NMR and molecular modeling methods. The experimental NMR data were compared with the results of molecular modeling and known crystal structures of the related molecules. It was shown that the dominant conformation of the lactone ring is the folded-out conformation with some amounts of the folded-in one depending on the solvent and temperature, while desosamine and cladinose sugars adopt the usual chair conformations. Modeling calculations provided evidence for conformational changes in the upper lactone region as well. Saturation transfer difference (STD) NMR experiments have provided information on the binding epitopes of 1-3 in complexes with E. coli ribosomes. The obtained molecular surfaces in close contact with ribosomes were compared with recently available 3D structures of the related macrolide-ribosome complexes, and the observed differences were discussed. The knowledge gained from this study can serve as a platform for the design of novel macrolides with an improved biological profile.

Homology modeling of human Fyn kinase structure: discovery of rosmarinic acid as a new Fyn kinase inhibitor and in silico study of its possible binding modes

Tyrosine phosphorylation represents a unique signaling process that controls metabolic pathways, cell activation, growth and differentiation, membrane transport, apoptosis, neural, and other functions. We present here the three-dimensional structure of Fyn tyrosine kinase, a Src-family enzyme involved in T-cell receptor signal transduction. The structure of Fyn was modeled for homology using the Sybyl-Composer suite of programs for modeling. Procheck and Prosa II programs showed the high quality of the obtained three-dimensional model. Rosmarinic acid, a secondary metabolite of herbal plants, was discovered as a new Fyn kinase inhibitor using immunochemical and in silico methods. Two possible binding modes of rosmarinic acid were evaluated here, i.e., near to or in the ATP-binding site of kinase domain of Fyn. Enzyme kinetic experiments revealed that Fyn is inhibited by a linear-mixed noncompetitive mechanism of inhibition by rosmarinic acid. This indicates that rosmarinic acid binds to the second "non-ATP" binding site of the Fyn tyrosine kinase.

Is the Enthalpy of Fusion of Tris(acetylacetonato)metal(III) Complexes Affected by Their Potential Energy in the Crystal State?

In this Article we present enthalpies of fusion and melting points obtained from new thermochemical measurements of tris(acetylacetonato)metal(III), M(acac)(3), complexes (M = Fe, Al, Cr, Mn, Co) using differential scanning calorimetry (DSC) and evaluate them in relation to their different values found in the literature. An enthalpy of fusion of 27.67 kJ mol(-)(1) was derived for Mn(acac)(3) from a symmetrical DSC thermogram captured for the first time. The enthalpy value was indirectly confirmed with the solubility measurements of Mn(acac)(3) in acetylacetone. A hypothesis has been stated that the enthalpy of fusion and the potential energy of M(acac)(3) in the crystal state may be related. To calculate molecular in-crystal potential energy, in this Article we proposed a molecular mechanics model for the M(acac)(3) class of compounds. Nine X-ray crystal structures of M(acac)(3) complexes (M = Fe, Al, V, Mn, Co, Cr, Sc) were included in the modeling. The conformational potential energy was minimized for a molecule surrounded by other molecules in the crystal lattice. The partial charges from two schemes, the electrostatic potential (ESP) fit and the natural population analysis (NPA), were used to construct two types of force fields to examine which force field type would yield a better fit with the experimental thermal properties. The final force fields were named FF-ESP and FF-NPA. Both force field sets reproduced well the experimental crystal data of nine M(acac)(3) complexes as well as of tris(3-methyl-2,4-pentanedionato-O,O')cobalt(III). Only in-crystal potential energies derived by FF-NPA yielded a significant correlation (correlation coefficient R = -0.71) with the measured enthalpies of fusion. The enthalpy of fusion for Co(acac)(3) could not be determined experimentally because of simultaneous decomposition and fusion, and it is predicted to be 33.2 kJ mol(-)(1) from the correlation regression line.

Synthesis, biological activity and molecular modeling studies of novel COX-1 inhibitors

Synthesis of new potential COX-1 and/or COX-2 inhibitors, derivatives of 1,1-di-(3-carboxyphenyl)ethane, their biological activity, docking results on COX-1 enzyme and absorption, distribution, metabolism, excretion (ADME) properties are presented. In addition to known interactions between ketoprofen and ibuprofen, leading NSAID agents and COX-1 active site, the possibility of formation of additional interactions is explored. Interactions with Ala527, and with one of the water molecules situated within the active site are identified. Molecular mechanics and DFT calculations for studied compounds have revealed free rotation around two central bonds (C1-C3' and C1-C3"), making them flexible, thus easier to enter and adjust to the active site. Further modifications of core structure have been undertaken to optimize biological activity and ADME properties. As a result, two of the compounds are indicated as novel COX-1 inhibitors.