Oxygenated Cyclohexene Derivatives from the Stem and Root Barks of Uvaria pandensis

Five new cyclohexene derivatives, dipandensin A and B (1 and 2) and pandensenols A-C (3-5), and 16 known secondary metabolites (6-21) were isolated from the methanol-soluble extracts of the stem and root barks of Uvaria pandensis. The structures were characterized by NMR spectroscopic and mass spectrometric analyses, and that of 6-methoxyzeylenol (6) was further confirmed by single-crystal X-ray crystallography, which also established its absolute configuration. The isolated metabolites were evaluated for antibacterial activity against the Gram-positive bacteria Bacillus subtilis and Staphylococcus epidermidis and the Gram-negative bacteria Enterococcus raffinosus, Escherichia coli, Paraburkholderia caledonica, Pectobacterium carotovorum, and Pseudomonas putida, as well as for cytotoxicity against the MCF-7 human breast cancer cell line. A mixture of uvaretin (20) and isouvaretin (21) exhibited significant antibacterial activity against B. subtilis (EC50 8.7 μM) and S. epidermidis (IC50 7.9 μM). (8'α,9'β-Dihydroxy)-3-farnesylindole (12) showed strong inhibitory activity (EC50 9.8 μM) against B. subtilis, comparable to the clinical reference ampicillin (EC50 17.9 μM). None of the compounds showed relevant cytotoxicity against the MCF-7 human breast cancer cell line.

Serum proteases prevent bacterial biofilm formation: role of kallikrein and plasmin

Biofilm formation is a general strategy for bacterial pathogens to withstand host defense mechanisms. In this study, we found that serum proteases inhibit biofilm formation by Neisseria meningitidis, Neisseria gonorrhoeae, Haemophilus influenzae, and Bordetella pertussis. Confocal laser-scanning microscopy analysis revealed that these proteins reduce the biomass and alter the architecture of meningococcal biofilms. To understand the underlying mechanism, the serum was fractionated through size-exclusion chromatography and anion-exchange chromatography, and the composition of the fractions that retained anti-biofilm activity against N. meningitidis was analyzed by intensity-based absolute quantification mass spectrometry. Among the identified serum proteins, plasma kallikrein (PKLK), FXIIa, and plasmin were found to cleave neisserial heparin-binding antigen and the α-peptide of IgA protease on the meningococcal cell surface, resulting in the release of positively charged polypeptides implicated in biofilm formation by binding extracellular DNA. Further experiments also revealed that plasmin and PKLK inhibited biofilm formation of B. pertussis by cleaving filamentous hemagglutinin. We conclude that the proteolytic activity of serum proteases toward bacterial adhesins involved in biofilm formation could constitute a defense mechanism for the clearance of pathogens.

Oxygenated Cyclohexene Derivatives and Other Constituents from the Roots of Monanthotaxis trichocarpa

Three new oxygenated cyclohexene derivatives, trichocarpeols A (1), B (2), and C (3), along with nine known secondary metabolites, were isolated from the methanolic root extract of Monanthotaxis trichocarpa. They were identified by NMR spectroscopic and mass spectrometric analyses, and the structure of trichocarpeol A (1) was confirmed by single-crystal X-ray diffraction. Out of the 12 isolated natural products, uvaretin (4) showed activity against the Gram-positive bacterium Bacillus subtilis with a MIC value of 18 μM. None of the isolated metabolites was active against the Gram-negative Escherichia coli at a ∼5 mM (2000 μg/mL) concentration. Whereas 4 showed cytotoxicity at EC50 10.2 μM against the MCF-7 human breast cancer cell line, the other compounds were inactive or not tested.