Triketone-terpene meroterpenoids from the leaves of Rhodomyrtus tomentosa

Benzophenone Rhamnosides and Chromones from Hypericum seniawinii Maxim

Two new benzophenone glycosides, hypersens A and B, along with four known compounds, (S)-(+)-5,7-dihydroxy-2-(1-methylpropyl) chromone (3), 5,7-dihydroxy-2-isopropylchromone (4), urachromone B (5), and 3-8′′ bisapigenin (6), were isolated from Hypericum seniawinii. The structures of new compounds (1 and 2) were elucidated according to comprehensive spectroscopic data analyses. The absolute configurations of 1 and 2 were determined by electronic circular dichroism (ECD) calculations. All isolated compounds were evaluated for their neuroprotective effect using corticosterone-induced PC12 cell injury. In addition, compounds 1–6 were evaluated for their anti-inflammatory activity in lipopolysaccharide-induced RAW 264.7 cells. Compound 6 was a biflavonoid and significantly inhibited the production of nitric oxide with an IC50 value of 11.48 ± 1.23 μM.

Hyjapones A-D, trimethylated acyphloroglucinol meroterpenoids from Hypericum japonicum thunb. With anti-inflammatory activity

Four undescribed trimethylated acylphloroglucinol meroterpenoids, hyjapones A-D, along with seven known analogues, were isolated from Hypericum japonicum Thunb. Hyjapone A represents the first example of a double norflavesones-caryophyllene hybrid featuring a rare 6/6/9/4/6/6 hexacyclic frame. Hyjapone D was isolated as a natural product for the first time. Their structures and absolute configurations were established by comprehensive spectroscopic data analyses and electronic circular dichroism (ECD) calculations. The anti-inflammatory activities of all compounds were evaluated using lipopolysaccharide-induced RAW264.7 cells. Hyperjapone A showed more pronounced anti-inflammatory effect through reducing the production of nitric oxide (IC₅₀ value of 11.32 ± 2.10 μM) and proinflammatory cytokines. In addition, the mechanistic studies revealed hyperjapone A inhibited LPS-induced activation of nuclear factor-κB.

Meroterpenoids: A Comprehensive Update Insight on Structural Diversity and Biology

Meroterpenoids are secondary metabolites formed due to mixed biosynthetic pathways which are produced in part from a terpenoid co-substrate. These mixed biosynthetically hybrid compounds are widely produced by bacteria, algae, plants, and animals. Notably amazing chemical diversity is generated among meroterpenoids via a combination of terpenoid scaffolds with polyketides, alkaloids, phenols, and amino acids. This review deals with the isolation, chemical diversity, and biological effects of 452 new meroterpenoids reported from natural sources from January 2016 to December 2020. Most of the meroterpenoids possess antimicrobial, cytotoxic, antioxidant, anti-inflammatory, antiviral, enzyme inhibitory, and immunosupressive effects.