Homo- and hetero-dimeric sesquiterpenoids with unprecedented skeletons and their co-occurring monomers from Vernonia solanifolia with anti-liver steatotic potential

Background Sesquiterpenoids show potential as therapeutics against metabolic dysfunction-associated steatotic liver disease (MASLD). Vernonia solanifolia Benth. has been traditionally used to treat abdominal pain and enteritis. However, the anti-steatotic effect of V. solanifolia and its chemical principles have not been illustrated. Methods The structures of new compounds were determined through extensive spectroscopic analysis including 1D/2D nuclear magnetic resonance (NMR), high-resolution electrospray ionization mass spectrometry, ultraviolet and infrared. Especially, the structure of compound 6 was further verified by single crystal X-ray diffraction, and the relative and absolute configurations of compounds 1 – 5 and 7 – 9 were resolved with the help from density-functional theory-NMR and time-dependent density-functional theory-electronic circular dichroism calculation. The lipid-lowering activity was evaluated on palmitic acid/oleic acid (P/O)-treated AML12 hepatocytes. The biological evaluation was performed using Nile Red staining, flow cytometry, commercial kits, and Western blotting. Results Nine new sesquiterpenoid dimers and their co-occurring monomers ( 1 – 9 ) were identified from the leaves of V. solanifolia . A unique 10/5/6/5/7 pentacyclic ring system is exemplified in compounds 1 and 2 . These compounds were constructed from a germacranolide and a 4,5- seco -guaianolide monomer through an unprecedented spiro cyclohexene ring. The first examples of germacrane-guaiane and guaiane-xanthane heterogeneous dimers are shown in compounds 3 and 4 , respectively, which also possess a spiro cyclohexene ring linkage. A guaianolide dimer featuring a rare C-13/C-13ʹ linkage is exhibited in compound 5 . The plausible biosynthetic pathways for compounds 1 and 5 were proposed. The isolates were tested for their lipid-lowering effect on P/O-treated AML12 hepatocytes, and the results showed that compound 3 significantly reduced lipid content in hepatocytes by triggering the AMP-activated protein kinase/acetyl-CoA carboxylase/peroxisome proliferator-activated receptor γ coactivator-1 α signaling pathway. Conclusion Five homo- and hetero-dimeric sesquiterpenoids with unprecedented skeletons were characterized from V. solanifolia , together with four new co-occurring monomers. It’s the first time to report the lipid-lowering activity of sesquiterpenoids from this genus, which might be developed as lead compounds against MASLD.