Structural characterization and SARS-CoV-2 inhibitory effects of alkaloids from the roots of Asarum heterotropoides var. mandshuricum (Aristolochiaceae)

Asarum heterotropoides var. mandshuricum F. Maekawa (Aristolochiaceae), well-known as "Marchurian Wildginger", shows many bioactivities that contribute to its therapeutic effects against a wide range of diseases. In this study, phytochemical investigation of A. hetertotropoides var. mandshuricum root extract led to the isolation of one previously undescribed amide (asamide A) with a rare five-membered-ring acetonide group in natural sources and one new amide mixture (asamide B/C) together with fifteen known alkaloids and one known amide mixture. Structural elucidation of the new alkaloids was carried out based on conventional NMR spectroscopy, HRESI-MS, and ECD calculation. To the best of our knowledge, this is the first report on the isolation of asaroidoxazine B from A. heterotropoides var. mandshuricum and compounds N-feruloyl tyramine, trans-N-feruloyl octopamine, and N-trans-p-coumaroyltopamin from the genus Asarum. The isolated alkaloids were examined for their inhibitory effects on PDB6LU7 protein of SARS-CoV-2 by molecular docking. Accordingly, the isolated aristolactams, especially aristolactam glycosides were found to be promising agents for the research and development of the new anti-SARS-CoV-2 drugs.