Conformational Landscape of α-Halopropiophenones Determined by nJC-H NMR Reveals Unexpected Patterns and Geometric Constraints.

The conformational features of α-halopropiophenones were investigated to understand the influence of α-halogens on conformation through hyperconjugative interactions, electrostatics, and steric factors. Using NMR, C-H scalar coupling constants were measured in different solvents, revealing a pattern in the conformational equilibria, which we validated by computational means. This behavior arises largely from hyperconjugative effects with the exception of the fluoro-derivatives, which are also influenced by steric and electrostatic interactions. In all cases, the contribution to hyperconjugation of the α-halo ketones is driven by the oxygen lone pair (rather than the C-X bond), which donates electron density to the adjacent C-C bonds. Additionally, C-Cα bond rotation generates distortions in the side chain, responsible for destabilization, thus affecting system conjugation. These structural features identified for the α-halo ketones are also reflected in their reactivity, which is distinct from that expected for nucleophilic addition.

Heterologous overexpression and characterization of homoserine dehydrogenase from Paracoccidioides brasiliensis.

The enzyme Homoserine dehydrogenase from Paracoccidioides brasiliensis (PbHSD), an interesting enzyme in the search for new antifungal drugs against paracoccidioidomycosis, was expressed by E. coli. Thirty milligrams of PbHSD with 94% of purity were obtained per liter of culture medium. The analysis by CD spectroscopy indicates a composition of 45.5 ± 7.3% of α-helices and 10.5 ± 7.0% ß-strands. Gel filtration chromatography indicates a homodimer as biological unity. Fluorescence emission spectroscopy has shown stability of PbHSD in the presence of urea until Cm of 4.13 ± 0.21 M, and a broad pH range in which there is no conformational change. The protein analysis by differential scanning calorimetry indicates high stability at room temperature, but low stability at high temperatures, suffering irreversible denaturation, with Tm = 58.65 ± 0.87 °C. Kinetic studies of PbHSD by molecular absorption spectroscopy in UV/Vis have shown an optimum pH between 9.35 and 9.50, with Michaelian behavior, presenting KM of 224 ± 15 µM and specific activity at optimum pH of 2.10 ± 0.07 µmol/min/mg for homoserine. Therefore, protein expression and purification were efficient, and the structural characterization has shown that PbHSD presents native conformation with enzymatic activity in kinetic assays.

Proteomic Response of Paracoccidioides brasiliensis Exposed to the Antifungal 4-Methoxynaphthalene-N-acylhydrazone Reveals Alteration in Metabolism.

Background: Paracoccidioidomycosis is a neglected mycosis with a high socioeconomic impact that requires long-term treatment with antifungals that have limitations in their use. The development of antifungals targeting essential proteins that are present exclusively in the fungus points to a potentially promising treatment. Methods: The inhibitor of the enzyme homoserine dehydrogenase drove the synthesis of N'-(2-hydroxybenzylidene)-4-methoxy-1-naphthohydrazide (AOS). This compound was evaluated for its antifungal activity in different species of Paracoccidioides and the consequent alteration in the proteomic profile of Paracoccidioides brasiliensis. Results: The compound showed a minimal inhibitory concentration ranging from 0.75 to 6.9 µM with a fungicidal effect on Paracoccidioides spp. and high selectivity index. AOS differentially regulated proteins related to glycolysis, TCA, the glyoxylate cycle, the urea cycle and amino acid metabolism, including homoserine dehydrogenase. In addition, P. brasiliensis inhibited protein synthesis and stimulated reactive oxygen species in the presence of AOS. Conclusions: AOS is a promising antifungal agent for the treatment of PCM, targeting important metabolic processes of the fungus.

Anticholinesterase activity of ß-carboline-1, 3, 5-triazine hybrids

Abstract The ß-carboline-1,3,5-triazine hydrochlorides 8-13 were evaluated in vitro against acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE). The analysed compounds were selective to BuChE, with IC50 values in the range from 1.0-18.8 µM being obtained. The N-{2-[(4,6-dihydrazinyl-1,3,5-triazin-2-yl)amino]ethyl}-1-phenyl-ß-carboline-3-carboxamide (12) was the most potent compound and kinetic studies indicate that it acts as a competitive inhibitor of BuChE. Molecular docking studies show that 12 strongly interacts with the residues of His438 (residue of the catalytic triad) and Trp82 (residue of catalytic anionic site), confirming that this compound competes with the same binding site of the butyrylthiocholine

Conformational Isomerism of 3-Chalcogenomethyl-N-Methyl-2-Pyrrolidinones: Insights from NMR Spectroscopy and Molecular Modeling.

A conformational analysis of N-methyl-2-pyrrolidinone 3-substituted by methoxyl, thiomethoxyl, and selenomethoxyl is reported by means of 1H nuclear magnetic resonance spectroscopy and electronic structure calculations. The five-membered ring has an envelope conformation with the α-carbonyl substituent being able to assume two positions: pseudo-axial and pseudo-equatorial. In vacuum, the calculations pointed to the pseudo-axial conformer as the most stable one, and this preference increases with the size of the substituent and a decrease in its electronegativity. Natural bond orbital analysis evidenced the importance of electron delocalization on the stability, and a principal component of analysis (PCA) plot of the hyperconjugative interactions revealed the main ones. Steric and electrostatic effects were also investigated by energy decomposition analysis.

Molecular docking and panicolytic effect of 8-prenylnaringenin in the elevated T-maze.

The purpose of this study was to investigate the effects of the chronic administration of a racemic mixture of 8-prenylnaringenin (8-PN) on rats submitted to the elevated T-maze (ETM) model of generalized anxiety and panic disorders. The selective serotonin (SERT) reuptake inhibitor fluoxetine was used as a positive control. Rat locomotion was assessed in a circular arena following each drug treatment. The administration of racemic 8-PN for 21 d in rats increased one-way escape latencies from the ETM open arm, indicating a panicolytic effect. To evaluate the interactions of 8-PN with monoamine transporters, a docking study was performed for both the R and S configurations of 8-PN towards SERT, norepinephrine (NET) and dopamine transporters (DAT). The application of the docking protocol showed that (R)-8-PN provides greater affinity to all transporters than does the S enantiomer. This result suggests that enantiomer (R)-8-PN is the active form in the in vivo test of the racemic mixture.