Phytochemical Investigation and Biological Studies on Selected Searsia Species

Mkhuseli Koki; Masande Yalo; Masixole Makhaba; Ndikho Nako; Fanie Rautenbach; Jelili A Badmus; Jeanine Marnewick; Ahmed A Hussein; Wilfred T Mabusela

doi:10.3390/plants11202793

Phytochemical Investigation and Biological Studies on Selected Searsia Species

Plants (Basel). 2022 Oct 21;11(20):2793. doi: 10.3390/plants11202793.

Authors

Mkhuseli Koki¹, Masande Yalo^{1

2}, Masixole Makhaba^{1

3}, Ndikho Nako¹, Fanie Rautenbach⁴, Jelili A Badmus⁴, Jeanine Marnewick⁴, Ahmed A Hussein³, Wilfred T Mabusela¹

Affiliations

¹ Department of Chemistry, University of the Western Cape, Private Bag X17, Bellville 7538, South Africa.
² Department of Pharmacology, Faculty of Health Sciences, University of Free State, Bloemfontein 9300, South Africa.
³ Chemistry Department, Cape Peninsula University of Technology, Symphony Rd., Bellville 7535, South Africa.
⁴ Applied Microbial and Health Biotechnology Institute, Cape Peninsula University of Technology, Symphony Rd., Bellville 7535, South Africa.

Abstract

Searsia is the more recent name for the genus Rhus, which contains over 250 individual species of flowering plants in the family Anacardiaceae. Several Searsia species are used in folk medicine and have been reported to exhibit various biological activities. Although known to exhibit different terpenoids and flavonoids, the chemistry of the Searsia genus is not comprehensively studied due to the structural complexity of the compounds. In this study, the extraction, isolation, and identification of secondary metabolites from three Searsia species (Searsia glauca, S. lucida, and S. laevigata) were conducted using chromatographic and spectroscopic techniques and afforded five known terpenes, viz., moronic acid (1), 21β-hydroxylolean-12-en-3-one (2), lupeol (11), α-amyrin (9), and β-amyrin (10), in addition to six known flavonoids, myricetin-3-O-β-galactopyranoside (3), rutin (4), quercetin (5), apigenin (6), amentoflavone (7), and quercetin-3-O-β-glucoside (8). The structural elucidation of the isolated compounds was determined based on NMR (1D and 2D) and comparison with the data in the literature. Biological assays, such as antioxidant and enzyme inhibition activity assays, were conducted on the plant extracts and the isolated compounds. The antioxidant capacities of hexane, dichloromethane, ethyl acetate, methanol, and butanol main extracts were investigated using ferric ion reducing power (FRAP), oxygen radical absorbance capacity (ORAC), and Trolox equivalent antioxidant capacity (TEAC) assays. The results showed high antioxidant activities for methanol and butanol extracts of the three plants. The isolated compounds were tested against alpha-glucosidase and alpha-amylase, and the results showed the potent activity of moronic acid (C1) (IC₅₀ 10.62 ± 0.89 and 20.08 ± 0.56 µg/mL, respectively) and amentoflavone (C7) (IC₅₀ 5.57 ± 1.12 µg/mL and 19.84 ± 1.33 µg/mL, respectively). Isolated compounds of and biological assays for S. glauca, S. lucida, and S. laevigata are reported for the first time.

Keywords: Searsia genus; alpha-amylase; alpha-glucosidase; amentoflavone; anti-diabetic activity; enzyme inhibition; moronic acid; oxidative stress.

Grants and funding

This research received no external funding.