Studies on the Nonalkaloidal Secondary Metabolites of Hippeastrum Vittatum (l'her.) Herb. Bulbs.

Sixteen chemically varied metabolites were isolated fromthe bulbsof Hippeastrum vittatum (L'Her.)Herb., including eight flavonoids [3 & PRIME;-methyl isoliquiritigenin (2), 7-hydroxyflavan (8), 7-hydroxyflavanone (9), 7-hydroxyflavan-3-ol (10), 7-methoxy-3 & PRIME;,4 & PRIME;-methylenedioxyflavan-3-ol (11), 7-hydroxy-3 & PRIME;,4 & PRIME;-methylenedioxy flavan (12), 2 & PRIME;,4 & PRIME;-dihydroxy-3 & PRIME;-methyl-3,4-methylenedioxychalcone (13), and isoliquiritigenin (14)], four acetophenones[2,6-dimethoxy-4-hydroxyacetophenone (3), 2,4-dihydroxyacetophenone (4), 2,4-dihydroxy-6-methoxy-3-methylacetophenone (6), and 2,4,6-trimethoxyacetophenone (7)], two alkaloids[lycorine (1) and narciprimine (15)], onephenol derivative [p-nitrophenol (5)], and one steroid [& beta;-sitosterol 3-O-& beta;-glucopyranoside (16)]. Their structures were elucidated by combining one-and two-dimensional NMR and ESI-MS techniques and by comparison withthe reported literature data and some authentic samples. Except forlycorine (1), the isolated metabolites were obtainedherein for the first time from Hippeastrum plants,among which compound 13 was identified as a new chalconederivative. Additionally, the total phenolic and flavonoid contentsof the total ethanol extract and different fractions of the bulbswere determined by the Folin-Ciocalteu and aluminum chloridecolorimetric methods, respectively, whereas their antioxidant potentialwas compared using the phosphomolybdenum and 2,2 & PRIME;-diphenyl-1-picrylhydrazyl(DPPH) free radical scavenging assays. Finally, the binding affinitiesof compounds 1-16 to some key target proteinsof the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2),namely, main protease (M-pro), papain-like protease (PLpro),and RNA-dependent RNA polymerase (RdRp), were screened and comparedusing molecular docking analysis. The possible chemotaxonomic significanceof the identified metabolites was also discussed.