Chemical Constituents of Acridocarpus orientalis and Their Chemotaxonomic Significance

Abstract

Acridocarpus orientalis (Malpighiaceae) consists of 30 species, with 11 widely distributed in Africa, six in Madagascar, and a single species in New Caledonia [1–3]. It is mainly used in Oman and UAE for the treatment of paralysis, headaches, muscle pain, tendon and joint pains, as well as to treat inflammation in cattle [4–6]. A. orientalis is a small perennial shrub with highly branched, hairy stems and yellow flowers, which grow in clusters. The air-dried plant material of A. orientalis was collected from Al-Hamra, in the Ad-Dakhiliyah region of the Sultanate of Oman in March–April 2012, and identified by a plant taxonomist at the Department of Biological Sciences and Chemistry, University of Nizwa, Nizwa, Sultanate of Oman. The voucher specimen (ACO/04/12) has been deposited in the Herbarium of the department. Previous phytochemical investigations on Acridocarpus vivy revealed the presence of five new and three known triterpenoids [1], while chromatographic separation of Acridocarpus chloropterus led to the isolation of five triterpenes and five flavonoids [7]. Previously isolated compounds 10 and 12 from A. orientalis showed significant antifungal, phytotoxic, anticancer, and anti-LPO activities [8]. The air-dried ground plant material of A. orientalis (4.1 kg) was exhaustively extracted with methanol (8 L) at room temperature. The extract was evaporated to yield a dark yellowish methanolic residue (600 g), which was partitioned in different solvents on the basis of increasing polarity to afford n-hexane (40.9 g), CH2Cl2 (84.8 g), EtOAc (30.6 g), and n-BuOH (58.3 g) fractions. The CH2Cl2 soluble fraction (84.8 g, 70–230 mesh, Merck) was loaded on a silica gel column chromatograph to afford seven main fractions (Frs. AOC-1–7). Fraction AOC-3 (15.5 g) was then further subjected to silica gel column chromatography (CC) (flash silica 230–400 mesh) to get compound 5 (3.5 mg; CH2Cl2–n-hexane, 1:9) using 10% CH2Cl2–n-hexane, 1 (28.5 mg; CH2Cl2–n-hexane, 8:2) eluted with 70% CH2Cl2–n-hexane, and 2 (16.0 mg; MeOH–CH2Cl2, 0.5:9.5) using 3% MeOH–CH2Cl2. Fraction AOC-5 was fractioned by silica gel CC and eluted with n-hexane–CH2Cl2 (up to 100%) and then with CH2Cl2–MeOH (up to 10%) to give four subfractions (Subfrs. AOCS-1–4). Compounds 3 (6.0 mg; MeOH–CH2Cl2, 0.5:9.5) and 4 (8.0 mg; MeOH–CH2Cl2, 0.5:9.5 were obtained from subfraction AOCS-2 after CC using CH2Cl2–n-hexane (70:30 to 90:10). Fraction AOC-7 was grouped into five subfractions (Subfrs. AOCS-5–9) using MeOH–CH2Cl2 (up to 10%). Subfraction AOCS-7 was subjected to CC to yield 6 (8.4 mg; CH2Cl2–n-hexane, 8:2) eluted with 70% CH2Cl2–n-hexane and 7 (6.0 mg; MeOH–CH2Cl2, 0.5:9.5) using 2% MeOH–CH2Cl2. The ethyl acetate fraction (30 g) was subjected to CC over a silica gel column (600 g, 70–230 mesh, Merck) using 10% EtOAc–n-hexane with a 5% gradient of increasing polarity up to 100% EtOAc, then by a gradient of MeOH (1%, 2%, 5%, 10%, 20%, and 40%), and finally washed with 100% MeOH; 26 fractions (Frs. AOEF-1–26) were thus collected. Five compounds were isolated using repeated column chromatography (flash silica gel 230–400 mesh), preparative TLC (silica gel 60 GF254), and using EtOAc–n-hexane mixtures of various polarities. The combined fraction (Frs. AOEF-5–15) obtained after taking TLC