Binding between bovine serum albumin (BSA) and a plumeran indole alkaloid (PIA) isolated from the stem bark of Aspidosperma cylindrocarpon (Apocynaceae) was studied by spectroscopic techniques (UV-Vis absorption, circular dichroism, steady state and time-resolved fluorescence), combined with molecular docking. Steady state and time resolved fluorescence data revealed that PIA can quench the BSA fluorescence via a static mechanism: energy transfer from BSA to PIA occurs with high probability. The binding is strong (Kb ca. 105-106 L mol-1), spontaneous (ΔG° ca. -35.7 kJ mol-1 at 310 K) and entropy-driven (ΔS° = 0.146 kJ mol-1 K-1). There is just one main binding site (n ca. 1) for the BSA:PIA interaction and the α-helix content of the albumin does not suffer significant perturbation upon PIA binding. Molecular docking results suggest site I as the main binding site to PIA, which is able to interact with the Trp-212, Arg-217, Val-342 and Pro-446 residues.

Four new alkaloids, Brazoides A-D, together with three known compounds squalene, β-sitosterol and lupeol, were isolated from leaves of Justicia gendarussa. These structures were established by spectrometric techniques, mainly high-resolution electrospray ionization mass spectrometry (HRESIMS) and 1D and 2D nuclear magnetic resonance (NMR), including comparative analysis with literature values. Structural determination of the compounds, Brazoides A-D, was strengthened by molecular modeling and density functional theory (DFT) calculations to predict the NMR data and compare with the experimental NMR values of these natural products. The new compounds were tested against three human cancer cell lines (glioblastoma, prostate and colon), but none exhibited activity.

UDP-N-acetylglucosamine-enolpyruvyl transferase (MurA) catalyzes the reaction between phosphoenol pyruvate and UDP-N-acetylglucosamine. We present a theoretical approach using the semiempirical PM6 method for defining protonation state of three active site residues, K22, H125, and K160. Prior comparison with neutron diffraction data showed that PM6 accurately predicted protonation states of active site residues of b-trypsin and D-xylose isomerase. Using the same methodology with MurA crystallographic data, we conclude that when reaction intermediate is located at the active site, H125 and K22 are in protonated form and K160 in neutral form.

A series of seven Schiff bases have been synthesized from 3,3-diphenylpropilamine and substituted benzaldehydes. These imines were treated with NaBH4 in ethanol affording the corresponding amines in 98-55% yields. A molecular modeling study was performed with the Schiff bases in order to compare the theoretical parameters with the experimental results. The theoretical parameters were obtained by AM1 and PM3 semi-empirical methods. The analysis of charge, electron densities and LUMO coefficients suggested that the most favorable interactions should occur with Schiff bases containing electron-donating groups, in accordance with experimental yields, showing that the higher reactivity is due to higher electrophilic character of imine carbons.

Open chain hydroxamic acid (Hx) can exist as Z and E diastereomers of two tautomers, hydroxamic acid and hydroximic acid. The conformational stability of the formohydroxamic acid isomers evaluated by PM3 compared better to ab initio results from the literature than AM1 results. Structural data of the cyclic Hx 2,4-dihydroxy-7-metoxy-2H-1,4-benzoxazin-3(4 H)-one (DIMBOA) obtained by both semiempirical methods compared well to ab initio results. pKa data from the literature for derivatives of the aldolic isomer of DIMBOA were compared to the stability of the anions resulting from the loss of protons of their phenol and hydroxamic acid groups, determined as the difference in heat of formation between anionic and neutral forms, calculated by AM1 and PM3 methods. Good correlations between theoretical and experimental data were obtained for both semiempirical methods.