Sixteen chemically varied metabolites were isolated from
the bulbs
of Hippeastrum vittatum (L’Her.)
Herb., including eight flavonoids [3′-methyl isoliquiritigenin (2), 7-hydroxyflavan (8), 7-hydroxyflavanone (9), 7-hydroxyflavan-3-ol (10), 7-methoxy-3′,4′-methylenedioxyflavan-3-ol (11), 7-hydroxy-3′,4′-methylenedioxy flavan (12), 2′,4′-dihydroxy-3′-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)], one
phenol derivative [p-nitrophenol (5)], and one steroid [β-sitosterol 3-O-β-glucopyranoside (16)]. Their structures were elucidated by combining one-
and two-dimensional NMR and ESI-MS techniques and by comparison with
the reported literature data and some authentic samples. Except for
lycorine (1), the isolated metabolites were obtained
herein for the first time from Hippeastrum plants,
among which compound 13 was identified as a new chalcone
derivative. Additionally, the total phenolic and flavonoid contents
of the total ethanol extract and different fractions of the bulbs
were determined by the Folin–Ciocalteu and aluminum chloride
colorimetric methods, respectively, whereas their antioxidant potential
was compared using the phosphomolybdenum and 2,2′-diphenyl-1-picrylhydrazyl
(DPPH) free radical scavenging assays. Finally, the binding affinities
of compounds 1–16 to some key target proteins
of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2),
namely, main protease (Mpro), papain-like protease (PLpro),
and RNA-dependent RNA polymerase (RdRp), were screened and compared
using molecular docking analysis. The possible chemotaxonomic significance
of the identified metabolites was also discussed.