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Eleven new acylphloroglucinols, including six new formylated phloroglucinol-monoterpene meroterpenoids, eucalyprobusals A–F (1–6), one monomeric acylphloroglucinol, eucalyprobusone B (7), and four dimeric acylphloroglucinols, eucalyprobusones C–F (8–11) were purified from the fruits of Eucalyptus robusta. The establishment of the structures of 1–11 was achieved by a combination of NMR and HRESIMS data analyses, electron circular dichroism (ECD), and single-crystal X-ray diffraction. Compounds 6, 8, and an inseparable mixture of 10 and 11 were found to be potent AChE inhibitors with IC50 values of 3.22 ± 0.36, 3.82 ± 0.22, and 2.55 ± 0.28 μΜ, respectively. Possible interaction sites of 6, 8, 10, and 11 with AChE were investigated by means of molecular docking studies, and the results revealed that AChE residues Asn87, Ser125, Thr83, Tyr133, Tyr124, Tyr337, and Tyr341 played crucial roles in the observed activity of the aforementioned compounds.

Eucalyptus is a large genus of the Myrtaceae family with high value in various fields of industry. Recently, attention has been focused on the functional properties of Eucalyptus extracts. These extracts have been traditionally used to combat various infectious diseases, and volatile oils are usually considered to play a major role. But the positive effects of non-volatile acylphloroglucinols, a class of specialized metabolites with relatively high content in Eucalyptus, should not be neglected. Herein, non-volatile acylphloroglucinols from leaves of Eucalyptus robusta were evaluated for their abilities to inhibit Zika virus (ZIKV) which is associated with severe neurological damage and complications. The results showed eucalyprobusone G, a new symmetrical acylphloroglucinol dimer, possessed the significant ability to inhibit ZIKV without inducing cytotoxicity. The EC50 values of eucalyprobusone G against the African lineage (MR766) and Asian lineage (SZ-WIV01) of ZIKV were 0.43 ± 0.08 and 10.10 ± 3.84 μM which were 110 times and 5.8 times better than those of the reference compound ribavirin, respectively. Further action mode research showed that eucalyprobusone G impairs the viral binding and RdRp activity of NS5. The results broaden the functional properties of Eucalyptus robusta and indicate acylphloroglucinol dimers could be developed as anti-ZIKV agents.