Brazilian red propolis: Chemical composition and antibacterial activity determined using bioguided fractionation.

The indiscriminate use of antibiotics is causing an increase in bacterial resistance, complicating therapeutic planning. In this context, natural products have emerged as major providers of bioactive compounds. This work performs a bioguided study of Brazilian red propolis to identify compounds with antibacterial potential and to evaluate their cytotoxicity against non-tumour cells. Using bioguided fractionation performed with the hydroalcoholic extract of red propolis from Alagoas, it was possible to obtain subfractions with remarkable bacteriostatic activity compared with the precursor fractions. The SC2 subfraction was highlighted and showed the best results with minimal inhibitory concentrations (MICs) of 56.75, 28.37, 454.00, and 227.00 µg mL-1 against Staphylococcus aureus, Bacillus subtilis, Escherichia coli, and Pseudomonas aeruginosa, respectively. However, this study also revealed a cytotoxic effect against the non-tumour Vero cell line. Furthermore, through chemical analyses using high resolution mass spectrometry, high performance liquid chromatography with UV detection, and gas chromatography coupled to mass spectrometry, we verified the presence of important marker compounds in the fractions and extracts, including formononetin (m/z 267.0663), biochanin A (m/z 283.0601), and liquiritigenin (m/z 255.0655). The results obtained in this study suggest an important antibacterial potential of red propolis subfractions. In this context, the bioguided fractionation has been a useful process, due to its ability to isolate and concentrate active compounds in a logical and rational way.

Pyridylalkylamine ligands and their palladium complexes: structure and reactivity revisited by NMR.

Pyridylmethylamines or pma are versatile platforms for different catalytic transformations. Five pma-ligands and their respective Pd complexes have been studied by liquid state NMR. By comparing (1)H, (13)C and (15)N chemical shifts for each pma/pma-Pd couple, a general trend for the metallacycle atoms concerns variations of the electronic distribution at the pendant arm, especially at the nitrogen atom of the ligand. Moreover, the increase of the chemical shift of the pendant arm nitrogen atom from primary to tertiary amine is also related to the increase of crowding within the complex. This statement is in good agreement with X-ray data collected for several complexes. Catalytic results for the Suzuki-Miyaura reaction involving the pma-Pd complexes showed within this series that a sterically crowded and electron-rich ligand in the metallacycle was essential to reach the coupling product with a good selectivity. In this context, NMR study of chemical shifts of all active nuclei especially in the metallacycle could give a trend of reactivity in the studied family of pma-Pd complexes.

Improved anomeric selectivity for the aroylation of sugars.

By manipulating the solvent and using bulky TMEDA as a base, good yields and improved anomeric selectivities were obtained for the aroylation of D-glucose over similar esterifications using pyridine. The reaction has been extended to mannose and the beta-anomer of pergalloylated mannose was predominantly obtained in one step by direct aroylation of the parent sugar.