Flavones and Steroids from Leaves and Barks of Aquilaria subintegra
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FLAVONES AND STEROIDS FROM LEAVES AND BARKS OF Aquilaria subintegra
Mastura Ibrahim,1 Saripah Salbiah Syed Abdul Azziz,1* Chee Fah Wong,2 Fauziah Abdullah,3 and Yuhanis Mhd Bakri1
The genus Aquilaria is a precious tree due to its high value of resin-impregnated heartwood. It belongs to the family of before Thymelaeaceae. Twenty-one species have been reported from Aquilaria globally, of which Aquilaria subintegra is one of them [1]. Previous phytochemical studies on Aquilaria species revealed the isolation of sesquiterpene and chromone derivatives [2–8], and limited information on chemical constituents of the leaves [9–12]. In addition, there are a limited number of phytochemical study on A. subintegra. Pharmacological studies of A. subintegra revealed a few properties such as anti-lipase [13, 14], anticancer [15], antidiabetic [16], and anti-Alzheimer disease [17]. The CH 2 Cl2 extract of leaves and barks afforded eight phytochemicals, including five flavones, namely, 5-hydroxy-7,4′-dimethoxyflavone (1) [18], luteolin-7,3′,4′-trimethyl ether (2) [18], 5,3′-dihydroxy-7,4′-dimethoxyflavone (3) [18], 7,3′-dimethoxyluteolin (4) [19], 5,7-dihydroxy-4′-methoxyflavone (5) [20], and three steroids, viz. β-sitosterol (6), stigmasterol (7) [21], and β-sitostenone (8) [22]. All compounds were obtained for the first time from this species. The fresh sample was collected from Kajang, Selangor, Malaysia in July 2014. The voucher specimen was deposited at the Herbarium of Universiti Pendidikan Sultan Idris (Voucher No. AMWNI-M6002/1). The total amount of barks (1800 g) and leaves (3300 g) of A. subintegra was air dried and extracted with CH2Cl2, three times (72 h each time) at room temperature. Then the extracts were concentrated using a rotary evaporator to give 17.0 and 43.3 g of bark and leaf crude extracts, individually. The bark extract was subjected to the first separation using column chromatography (CC) on silica gel and afforded 12 fractions (Frs. C1-1–C1-12). Fraction C1-5 was rechromatographed over a silica gel column, eluted with CH2Cl2–MeOH, and enriched gradually with MeOH to furnish 113 fractions (Frs. C2-1–C2-113). Fraction C2-6 was subjected to column chromatography (CC) on SiO2 and eluted with CH2Cl2–EtOAc mixtures to obtain 5-hydroxy-7,4′dimethoxyflavone (1) (13.0 mg). Fraction C4-12 (39.6 mg) from C1-5 was further purified using CC with the eluting solvent system CH2Cl2–EtOAc to afford another flavone, namely luteolin-7,3′,4′-trimethyl ether (2) (10.0 mg). The combined Frs. C2-11 and C2-12 (230 mg) were subjected to multiple CC, eluting with mixtures of CH2 Cl2 and MeOH, to yield 5,3′-dihydroxy-7,4′-dimethoxyflavone (3) (5.0 mg) and 7,3′-dimethoxyluteolin (4) (5.0 mg). A steroid compound, β-sitosterol (6) was purified from Fr. C1-5 using the eluting system CH2Cl2–MeOH. The leaf crude extract (43.3 g) was subjected to CC over SiO2 with a gradient solvent system of n-hexane– CH2Cl2–MeOH to afford 22 fractions (Frs. L1-1–L1-22). Fraction L1-14 was rechromatographed using multiple CC to yield 5-hydroxy-7,4′-dime
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