Dual Antiviral Mechanism of the Hexane Extract of Psoralea drupacea Bunge Fruits Against SARS-CoV-2: 3CLpro Inhibition and RBD-ACE2 Blockade

The hexane extract of Psoralea drupacea Bunge fruits was initially evaluated for antivi-ral activity against SARS-CoV-2 based on GC-MS data indicating high bakuchiol con-tent (87.74%). Unexpectedly, the extract showed no antiviral effect in Vero E6 cells due to cytotoxicity (CC₅₀ = 7.5 μg/mL), while purified bakuchiol demonstrated moderate antiviral activity (IC₅₀ = 6.2 ± 0.8 μg/mL; SI = 2.9). Quantitative NMR revealed that the actual bakuchiol content in the extract was 44.3% — approximately half the GC-MS value — explaining the lack of efficacy at non-cytotoxic concentrations. Both the ex-tract and purified bakuchiol effectively blocked the RBD-ACE2 interaction in a com-petitive ELISA (71.3% inhibition at 50 μM for bakuchiol; IC₅₀ = 18.5 μM). Notably, the extract also inhibited the viral main protease 3CLpro (IC₅₀ = 32.0 ± 3.5 μg/mL), while purified bakuchiol showed no such activity. These findings reveal a dual mechanism: bakuchiol inhibits viral entry via RBD-ACE2 blockade, while other extract components (e.g., angelicin, psoralen) suppress viral replication via 3CLpro inhibition.