Oleuropein aglycone aldehyde as a SARS-CoV-2 main protease inhibitor.

BACKGROUND

The evolution of SARS-CoV-2 emphasizes the urgent need for broad-spectrum antivirals targeting conserved viral enzymes such as the main protease (Mpro). Olea europaea (European olive) and Canarium album (Chinese olive) contain diverse bioactive phytochemicals with potential antiviral properties, yet their mechanistic relevance to SARS-CoV-2 remains undefined.

PURPOSE: To identify bioactive phytochemicals from European and Chinese olives and explore their mechanisms in inhibiting SARS-CoV-2 Mpro.

METHODS

Sixty-six phytochemicals were screened using a FRET-based Mpro assay. Potent candidates were further evaluated by IC50 determination, enzyme kinetics, cytotoxicity, and live-virus assays. Binding interactions were characterized using ITC and STD-NMR, while stereochemistry-dependent behavior was examined through chiral chromatographic analysis, molecular docking and molecular dynamics simulations.

RESULTS

Five compounds-Oleuropein Aglycone Aldehyde (OAA), Hydroxytyrosol (HT), Oleuropein (OL), Oleuropeinic acid (OPA), and Oleuroside (OS)-displayed significant Mpro inhibition (IC50: 4.8-15.7 μM; Ki: 3.4-18.0 μM). OAA was the most potent inhibitor through a competitive mechanism with antiviral activity against the ancestral strain (EC50 = 19.8 μM) and Omicron/Delta variants. ITC confirmed 1:1 binding (Kd = 13.5 μM), and STD-NMR showed that both 8S and 8R diastereomers interact with Mpro. Molecular modeling supported stable engagement within the catalytic pocket, where the 8S adopted an extended, multi-contact orientation, and the 8R occupied a compact subpocket.

CONCLUSION

OAA is a natural SARS-CoV-2 Mpro inhibitor exhibiting stable binding, stereochemical preference, and cross-variant antiviral activity. Its defined biochemical mechanism and stable structural engagement position OAA as a promising scaffold for antiviral development.