Triterpenes isolated from Cleome amblyocarpa: evaluation of antioxidant potential

Abstract

Investigation of the chemical constituents of Cleome amblyocarpa growing wild in Jordan resulted in the isolation and structural elucidation of two new dammarane triterpenes along with 9 other known compounds. The new compounds were identified as 17-hydroxyambylone (1) and 15β-acetoxy-17α-hydroxycabralealactone (2). The known compounds included calycopterine (3), 17α-hydroxycabraleahydroxylactone (4), cleocarpanol (5), ambylone (6), β-sitosterol (7), β-sitosteryl glucoside (8), isorhamnetin-3-O-rhamnoside (9), kaempferol-3,7-O-dirhamnose (10) and 3′-O-methylquercetin-3,7-di-O-rhamnopyranoside (11). Structural elucidation of all isolated compounds was based on thorough investigation of their spectroscopic data including NMR (1D and 2D), HRESIMS, IR, and UV-Vis spectroscopy. LC-MS/MS analysis versus a selected set of authentic samples led to the detection of 21 constituents, including 9 of the isolated compounds. Antioxidant activities of isolated pure compounds were assessed individually and compared to ascorbic acid and α-tocopherol using DPPH^˙ and ABTS^˙+ assay methods. Compounds 9–11 showed strong antioxidant activities whereas compounds 4–6 exhibited low activity. New compounds 1 and 2 demonstrated moderate DPPH^˙ radical scavenging power (IC₅₀ = 14.70 ± 2.52 and 77.90 ± 3.77 μg mL⁻¹, respectively) and a moderate ABTS^˙+ scavenging effect (IC₅₀ = 22.6 ± 0.04 and 78.30 ± 1.13 μg mL⁻¹).