Entandrophragma angolense : Chemical Constituents and Biological Activities

Entandrophragma angolense (Meliaceae) is an African medicinal plant used for the treatment of fever, ulcer, rheumatism, eye inflammation, and swelling. Previous studies have shown anti-ulcer, anti-neoplastic, anti-inflammatory, anti-feedant, and anti-microbial activities of the plant extracts and some of the isolated compounds. These activities can be ascribed to the limonoid and triterpenoid constituents of the plant. The stem bark of Entandrophragma angolense growing in Nigeria was collected and extracted with organic solvents. The extracts were purified to yield forty secondary metabolites, including ten new constituents: three limonoids, one glabretal- and five tirucallane-type triterpenoids, and a catechin glucoside. Of these undescribed structures, 23-O-deethylandirolide S was obtained as a racemic pair of C-23 epimers in 1:1 ratio as estimated by quantitative 1H NMR analysis combined with the global spectral deconvolution method. For all isolates, structural elucidation, including stereochemical assignment, was accomplished by interpretation of nuclear magnetic resonance (NMR), mass spectrometric (MS), and in some cases electronic circular dichroism (ECD) data. The isolation of 3,4-seco-tirucallane- and glabretal-type triterpenoids highlights the chemotaxonomic significance of these markers. Inhibitory activity of the isolated compounds was evaluated against nitric oxide production in LPS-treated RAW 264.7 cells, followed by inducible nitric oxide synthase protein measurement, and moluccensin O and (-)-catechin were found active. Analgesic activity of the extracts and methyl angolensate was evaluated using a mouse model and the results suggested the analgesic potential of E. angolense for pain management. All isolated compounds were also tested for cytotoxicity against cancer cell lines. Entangolensin F (21) displayed modest activities against MDA-MB-231 (IC50 = 1.9 µM), OVCAR3 (IC50 = 3.1 µM), MDA-MB-435 (IC50 = 3.4 µM) and HT29 (IC50 = 5.9 µM) cells. When tested in a panel of enzymes, including acetylcholinesterase, SARS-CoV 3CLpro, SARS-CoV-2 PLpro, MERS-CoV PLpro, and MMP-14, none of the compounds displayed significant activity. Results obtained from this study have expanded our knowledge about the chemical profile and biological potential of Entandrophragma angolense. Further studies are warranted with the goal of developing this medicinal plant and/or its chemical ingredients into useful medicines for the treatments of diseases such as inflammation, pain crisis, and cancer

Identification of Small Molecule Inhibitors against Staphylococcus aureus Dihydroorotase via HTS

Drug-resistant Staphylococcus aureus is an imminent threat to public health, increasing the importance of drug discovery utilizing unexplored bacterial pathways and enzyme targets. De novo pyrimidine biosynthesis is a specialized, highly conserved pathway implicated in both the survival and virulence of several clinically relevant pathogens. Class I dihydroorotase (DHOase) is a separate and distinct enzyme present in gram positive bacteria (i.e., S. aureus, B. anthracis) that converts carbamoyl-aspartate (Ca-asp) to dihydroorotate (DHO)-an integral step in the de novo pyrimidine biosynthesis pathway. This study sets forth a high-throughput screening (HTS) of 3000 fragment compounds by a colorimetry-based enzymatic assay as a primary screen, identifying small molecule inhibitors of S. aureus DHOase (SaDHOase), followed by hit validation with a direct binding analysis using surface plasmon resonance (SPR). Competition SPR studies of six hit compounds and eight additional analogs with the substrate Ca-asp determined the best compound to be a competitive inhibitor with a KD value of 11 µM, which is 10-fold tighter than Ca-asp. Preliminary structure-activity relationship (SAR) provides the foundation for further structure-based antimicrobial inhibitor design against S. aureus