Anti-inflammatory sesquiterpene dimers and diterpenes from the aerial part of Inula japonica

Characterization of Sesquiterpene Dimers from the Flowers of Inula japonica and the Structural Revisions of Related Compounds

Sesquiterpene dimers are mainly found in the Asteraceae family. However, conflicting reports on the structures of these compounds can be found in the literature. Herein, we describe ten sesquiterpene dimers isolated from the flowers of Inula japonica, including configurational revisions of japonicone H (1-1), japonicone D (2-1), inulanolide A (4-1), japonicone X (5-1), and inulanolide F (5-2) to compounds 1, 2, 4, and 5, respectively. Five new related metabolites (3 and 6-9) are also described. Application of GIAO NMR/DP4+ analyses and ECD/OR calculations enabled us to revise the absolute configurations of an additional 13 sesquiterpene dimers isolated from plants of the genus Inula. Compounds 1, 2, 4, and 6 exhibited inhibition of nitric oxide production in lipopolysaccharide activated RAW264.7 macrophages with IC50 values of 4.07-10.00 μM.

Inubritantrimers A-D: Trimerized Sesquiterpenoid [4 + 2] Adducts Featuring a Distinctive Spiro-Polycyclic Scaffold from Inula britannica

Inubritantrimer A (1), a trace trimerized sesquiterpenoid [4 + 2] adduct featuring an unusual exo-exo type spiro-polycyclic scaffold, together with three new endo-exo [4 + 2] adducts, inubritantrimers B-D (2-4), were discovered from the flowers of Inula britannica. Their structures were elucidated using 1D/2D NMR, X-ray diffraction, and ECD approaches. 1 is characterized as a novel exo-exo trimer, synthesized biogenetically from three sesquiterpenoid monomers, featuring a unique linkage of C-11/C-1', C-13/C-3' and C-13'/C-3″, C-11'/C-1″ through a two-step exo [4 + 2] cycloaddition process. Compounds 1-4 exhibited modest cytotoxicity against breast cancer cells with IC50 values in the range of 5.84-12.01 μM.

Dimerized sesquiterpenoid [4 + 2] adducts with ferroptosis-promoting activity from Inula britannica Linn

Inubritanolides C and D (1 and 2), two exo sesquiterpenoid [4 + 2] adducts with unprecedented interconverting conformations of twist-chair and chair, together with two previously undescribed endo [4 + 2] dimers (3 and 4) were discovered from Inula britannica flowers. Dimers 1 and 2 have an undescribed carbon skeleton comprising of eudesmanolide and guaianolide units with the linkage mode of C-11/C-1' and C-13/C-3' via a Diels-Alder cycloaddition reaction. Their structures were elucidated using 1D/2D NMR, X-ray diffraction, ECD, and variable-temperature NMR experiments. Dimer 2 displayed a strong inhibitory effect on breast cancer cells by promoting lipid ROS production, showing its potential as ferroptosis inducer.

Japonicone A and related dimeric sesquiterpene lactones: molecular targets and mechanisms of anticancer activity

OBJECTIVE AND DESIGN

Japonicone A (Jap-A) is a sesquiterpene lactone (SL) dimer isolated from the plant Inula japonica Thunb. and the leading compound in the japonicone series of SL dimers which comprises 25 members (Jap-A to Jap-Y). We have analyzed the anticancer properties of Jap-A and the associated molecular targets.

METHODS

All literature data on japonicones and related SL dimers, including inulanolide A (Inu-A) and lineariifolianoid A (Lin-A) have been analyzed. Molecular models of the compound/target interactions were constructed to support our analysis.

RESULTS

Inulae Flos (Xuan Fu Hua) is used in traditional medicine in China and Korea to treat inflammatory diseases. The plant contains diverse japonicones and structurally related SL dimers. The interactions of Jap-A with the two main proteins, the pro-inflammatory cytokine TNF-α and the ubiquitin ligase MDM2, are at the origin of the anti-inflammatory and anticancer effects. Molecular docking analyses suggest that Inu-A is better adapted than Lin-A and Jap-A to form stable complexes with both TNF-α and MDM2. Jap-A exhibits marked capacities to inhibit cancer cell proliferation and dissemination and to trigger apoptosis, both in vitro and in vivo in several tumor models in mice. Its analogue Inu-A is more potent, functioning as a dual inhibitor of the MDM2-NFAT1 pathway.

CONCLUSION

This review shed some new light on the molecular targets and potential therapeutic benefits of these SL dimers and should help the design of novel anticancer agents derived from these compounds.