Amaryllidaceae Alkaloids Screen Unveils Potent Anticoronaviral Compounds and Associated Structural Determinants

Betacoronaviruses encompass a spectrum of respiratory diseases, from common cold caused by the human coronavirus (HCoV)-OC43 to life-threatening severe acute respiratory syndrome (SARS)-CoV-2. Addressing the constant need for novel antiviral compounds, we turned to the exploration of 40 plant-specialized metabolites produced by the medicinal plant family Amaryllidaceae, known to produce lycorine, a strong antiviral alkaloid. The present screen included 35 alkaloids with representatives of 8 ring-type structures. Pancracine, crinamine, hemanthamine, and hemanthidine exhibited potency comparable to lycorine in blocking HCoV–OC43 replication, while amarbellisine demonstrated superior efficacy (SI = 60, EC₅₀ = 0.2 μM). Their anticoronaviral activity was confirmed using a SARS-CoV-2 replicon system. Time-of-drug-addition experiments established that a postentry step consistent with ribonucleic acid (RNA) replication or translation was targeted. Most antiviral Amaryllidaceae alkaloids selectively induced the expression of transcripts associated with the integrated stress response. Structure–activity relationship analyses elucidated key functional groups contributing to antiviral properties in the crinine- and lycorine-type. This study reveals that Amaryllidaceae produce a diverse repertoire of promising antiviral compounds in addition to lycorine, offering insights for developing new antiviral agents.