Four New Flavonoids Isolated from the Aerial Parts of Cadaba rotundifolia Forssk. (Qadab).

Abstract

Cadaba rotundifolia (Forssk.) (family: Capparaceae; common name: Qadab) is one of four species that grow in the Red Sea costal region in the Kingdom of Saudi Arabia. The roots and leaves of C. rotundifolia is traditionally used to treat tumors and abscesses in Sudan. A previous phytochemical study of the roots yielded a quaternary alkaloid, but no report on chemical constituents of the aerial parts of the C. rotundifolia growing in Saudi Arabia has been issued so far. Oxidative stress and advanced glycation end products (AGEs) are thought as causal factors in many degenerative diseases, such as Alzheimer’s disease, diabetes, atherosclerosis and aging. In this study, a total of twenty compounds, including four previously undescribed acylated kaempferol glucosides, were isolated from the aerial parts of C. rotundifolia collected in Saudi Arabia. These new compounds were identified as kaempferol 3-O-[2-O-(trans-feruloyl)-3-O-β-d-glucopyranosyl]-β-d-glucopyranoside (1), kaempferol 3-O-β-neohesperidoside-7-O-[2-O-(cis-p-coumaroyl)-3-O-β-d-glucopyranosyl]-β-d-glucopyranoside (2), kaempferol 3-O-[2,6-di-O-α-l-rhamnopyranosyl]-β-d-glucopyranoside-7-O-[6-O-(trans-feruloyl)]-β-d-glucopyranoside (3) and kaempferol 3-O-[2,6-di-O-α-l-rhamnopyranosyl]-β-d-glucopyranoside-7-O-[6-O-(trans-p-coumaroyl)]-β-d-glucopyranoside (4). Their structures were established based on UV-visible, 1D, 2D NMR, and HR-ESI-MS analyses. Of the assayed compounds, 17 and 18 showed potent radical scavenging activity with IC50 values of 14.5 and 11.7 µM, respectively, and inhibitory activity toward AGEs together with compound 7 with IC50 values 96.5, 34.9 and 85.5 µM, respectively.