Triterpenes isolated from Cleome amblyocarpa: evaluation of antioxidant potential

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).