Effects of hydrolysable tannins from Terminalia citrina on type III secretion system (T3SS) and their intestinal metabolite urolithin B represses Salmonella T3SS through Hha-H-NS-HilD-HilC-RtsA-HilA regulatory pathway.

Gamma-proteobacteria is a class of gram-negative opportunistic pathogens existing in the intestinal flora, often leading to diarrhea and intestinal infectious diseases, and plays an important role in maintaining intestinal homeostasis. Type III secretion system (T3SS), an important virulence system, is closely related to the adhesion and invasion and pathogenicity to host cells. Therefore, anti-virulence agents targeting T3SS are important strategies for controlling pathogenic infections. In this study, the anti-Salmonella T3SS active compounds neochebulagic acid (1), ellagic acid (2) and urolithin M5 (3) were isolated from seed extract of Terminalia citrina by activity-guided isolation method. Based on the fact that urolithins are the main and stable intestinal microbiota metabolites of hydrolysable tannins, we found that the metabolite urolithin B repressed translation and secretion of SipC through the Hha-H-NS-HilD-HilC-RtsA-HilA regulatory pathway. The results provide evidence for Terminalia seeds and ellagitannin-rich berries and nuts in regulating intestinal homeostasis and treating bacterial infection.

Structural optimizations and bioevaluation of N-substituted acridone derivatives as strong topoisomerase II inhibitors.

Previously, an array of N-substituted acridone derivatives have been reported as potent topoisomerase II (topo II) inhibitors, and preliminary structure-activity relationship (SAR) outcomes revealed that the linker between 1-NH and N-methyl piperazine motif of the tricyclic acridone scaffold significantly affected their anti-proliferative potencies. To further explore the SARs of acridone-derived topo II inhibitors, a wider range of novel acridone derivatives were herein synthesized via two rounds of structural optimizations on two validated hits, E17 and E24. Initially, the linker length was optimized, and then influences of N-methyl piperazinyl moiety and disposition of three N atoms on the bioactivity were investigated. As a result, a newly developed topo II inhibitor 6 h was found to be more potent than E17 and E24, thereby serving as a tool compound for the follow-up mechanistic study. Compound 6 h functioned as a strong topo IIα/ß inhibitor, caused obvious DNA damage, and induced apoptosis by triggering the loss of mitochondrial membrane potential (Δψm). Further molecular docking and MD study illustrated the favorable interactions of 6 h with both topo IIα and topo IIß subtypes.

Specialised metabolites as chemotaxonomic markers of Coptosapelta diffusa, supporting its delimitation as sisterhood phylogenetic relationships with Rubioideae.

From the aerial extracts of Coptosapelta diffusa (Champ. ex Benth.) Steenis, twenty-one compounds were isolated and identified by means of column chromatography and NMR and MS techniques, respectively. Amongst, ten ones were determined to be undescribed compounds including six seco-iridoid glucosides (1-6), 2-(hydroxymethyl)-1,2,3,4-tetrahydroanthracene-9,10-dione (7) and three guaiane-type sesquiterpenes (15-17). Compounds 7, 8 and 9 exhibited inhibitory activities against Staphylococcus aureus ATCC25923 with MIC of 8, 4 and 8 µg/mL. The use of 1-6 (iridoids), 7-14 (anthraquinones) and 15-17 (sesquiterpenes) as chemotaxonomic markers for this species was evidenced. Structurally, 7-14 are similar to those anthraquinones isolated from other species of the family Rubiaceae, confirming their close phylogenetic relationship. Whereas, these iridoids and sesquiterpenes with unique structures provided chemotaxonomic evidence to support the genus Coptosapelta (the tribe Coptosapelteae) as a sister of the subfamily Rubioideae. These results contrast with the general producing tendency of indole alkaloids by the species of the subfamily Cinchonoideae, and merit chemotaxonomic significance for the delimitation of Coptosapelta.