Antimicrobial, antioxidant and butyrylcholinesterase inhibition activities of extracts and isolated compounds from Scadoxus pseudocaulus and semi-synthetic farrerol derivatives

A.L. Ngankeu Pagning, Jean-de-Dieu Tamokou, M. Lateef Khan, M. Imran Ali, Abdul Hameed, David Ngnokam, L. Azefack Tapondjou, Jules-Roger Kuiate, M. Shaiq Ali

Laboratory of Environmental and Applied Chemistry, Department of Chemistry, Faculty of Science, University of Dschang, PO Box 067, Dschang, Cameroon.

Abstract

Six known compounds: sideroxylin (1), 5-hydroxylmethyl-2-furancarboxaldehyde (2), C-6,O-7-dimethyldenaromadendrin (3), 4-(hydroxymethyl)-5-hydroxy-2H-pyran-2-one (4), 7-deoxy-trans-dihydronarciclasine or trans-dihydrolycoricidine (5) and farrerol (6) were isolated from Scadoxus pseudocaulus (Björnstad & Friis) Friis & Nordal (Amaryllidaceae), famous for the treatment of liver cancer, cardiovascular disease, microbial diseases and mental disorders in Western region of Cameroon. The flavanone named farrerol (6) was partially modified by esterification reactions to give six novel semi-synthetic flavanone derivatives named 4′,7-diparamethylbenzoylfarrerol (7), 4′,7-dibutyrylfarrerol (8), 4′-butyrylfarrerol (9), 4′-dodecanoylfarrerol (10), 7-octanoylfarrerol (11) and 4′-octanoylfarrerol (12). Structures of isolated constituents and derivatives were elucidated with the aid of their NMR and MS spectral data as well as with the reported data. The antimicrobial, antioxidant and butyrylcholinesterase inhibition activities of the extracts and their isolated compounds as well as the six novel semi-synthetic flavanone derivatives were evaluated. Ethyl acetate fraction (MIC = 64–512 μg/mL) and compounds 6, 7 and 10 (MIC = 2–16 μg/mL) displayed good antibacterial and antifungal activities that varied among the microbial species. Compound 11 is the most potent antioxidant with IC₅₀ 49.7 μM which is comparable to standard butylated hydroxyanisole having IC₅₀ value of 44.2 μM. Compounds 12, 4 and 6 also have significant antioxidant activity with IC₅₀ value 56.5, 59.5 and 58.2 μM, respectively. Compound 7 showed excellent butyrylcholinesterase inhibition activity (IC₅₀ = 12.6 μM) when compared with standard eserine (IC₅₀ = 7.8 μM). The overall results of this study indicate that most active samples could be used as complementary medicine after due host toxicity testing.

Keywords: Scadoxus pseudocaulus; Amaryllidaceae; Farrerol; Derivatization; Antimicrobial activity; Antioxidant activity; Butyrylcholinesterase inhibition.