Phytochemical investigation of Amphilophium paniculatum; an underexplored Bignoniaceae species as a source of SARS-CoV-2 Mpro inhibitory metabolites: Isolation, identification, and molecular docking study
Mamdouh Nabil Samy, Eman Zekry Attia, Mai E. Shoman, Hany Ezzat Khalil, Sachiko Sugimoto, Katsuyoshi Matsunami, John Refaat Fahim
Abstract
Bignoniaceae plants are multipurpose herbal remedies with privileged chemical and biological profiles; nevertheless, some members in this family, e.g. Amphilophium species, have been scarcely investigated. Therefore, this work explores the chemical complexity of the underexplored species, Amphilophium paniculatum (L.) Kunth as a potential source of inhibitory phytochemicals against the recently emerging coronavirus disease (COVID-19). Overall, 13 structurally varied metabolites were isolated from the ethyl acetate and n-butanol fractions of A. paniculatum leaves for the first time in the genus and identified by different spectral techniques, including 1H and 13C NMR, DEPT, and HR–ESI–MS analyses. The characterized compounds (1–13), along with those previously obtained by our group from the same species (14–22) revealed varying binding affinities to the active site of SARS-CoV-2 Mpro, among which, eight molecules exhibited lower binding energies (–9.54 to –7.45 kcal/mol) than the ligand N3 (–7.44 kcal/mol); with polyphenolic metabolites, namely flavonoids, phenylethanoids, and lignans had the most stable interactions, respectively. These results highlighted the noteworthy diversity of A. paniculatum metabolites and their marked homogeneity with those produced by other Bignoniaceae plants, which would help expand our phytochemical and chemotaxonomic knowledge on this species. Coupling such phytochemical data with molecular docking studies could also allow a time- and cost-effective search for potential anti-COVID-19 agents.