Cytotoxic, α-glucosidase, and antioxidant activities of flavonoid glycosides isolated from flowers of Lotus lanuginosus Vent. (Fabaceae)

Abstract

Background: Lotus taxa (Fabaceae) were well known as an important source of polyphenols and flavonoids. Lotus lanuginosus Vent. is a widespread plant in the northern region of Saudi Arabia. Phytochemical and biological activities screening focusing of the species are rare. Objective: The objectives of this study were to isolate secondary metabolites from the flowers of L. lanuginosus Vent., elucidate their structures, and evaluate their biological activities. Materials and Methods: Chromatography methods of the n-butanolic extract of fresh flowers of L. lanuginosus led five products (1–5). Their structures were characterized based on spectroscopic evidence (ultraviolet, infrared, high-resolution mass spectrometry, and nuclear magnetic resonance) and compared to the spectral data signaled in the literature. Cytotoxic activities of the isolated compounds were evaluated against HCT-116 and MCF-7 cancer cell lines. α-glucosidase and antioxidant activities were also performed. Results: Five compounds were isolated and characterized for the first time in L. lanuginosus Vent.: Lotaustralin (1), kaempferol-7-O-α-L-rhamnopyranoside (2), kaempferol-3-O-apiofuranosyl-7-O-rhamnopyranosyl (3), isorhamnetin-3-O-rutinoside (4), and kaempferol-3-O-(2''-β-D-xylopyranosyl)-α-L-rhamnopyranoside-7-O-α-L-rhamnopyranoside (5). The results of cytotoxic activities against HCT-116 and MCF-7 cancer cell lines of the isolated compounds were presented. Among them, compounds 2 and 3 showed a moderate activity on HCT-116 cancer cells with half maximal inhibitory concentration values ranging between 8 and 31.5 μM. Moreover, compounds (2–5) displayed significant antioxidant and moderate α-glucosidase activities. Discussion and Conclusions: All the isolated products (1–5) are signaled for the first time in L. lanuginosus Vent. Among flavonoids glycosides, compound 2 showed the best cytotoxic activity. By the end of the present study, L. lanuginosus have been characterized as a highly cyanogenic plant and as an important source of polyphenols and flavonoids.