Secondary Metabolites from the Leaves of Victoria amazonica

Abstract

Victoria is a genus of water lilies, from the plant family Nymphaeaceae, which manifests as leaves that float on the water s surface. V. amazonica has a leaf that is up to 3 m in diameter, on a stalk 7–8 m in length. The genus name was given in honor of Queen Victoria of the United Kingdom. V. amazonica is native to the shallow waters of the Amazon River basin, such as oxbow lakes and bayous. It is depicted in the Guyanese coat of arms. The flowers are white the first night they are open and become pink the second night. They are up to 40 cm in diameter and are pollinated by scarab beetles. Previous studies on V. amazonica have led to the isolation of anthocyanins [1]. In the present study on the chemical components of the leaves of V. amazonica, 15 compounds were isolated. The MeOH extract of its plants were subjected to solvent partitioning and chromatographic separation to afford 15 pure substances. The chemical constituents in the plants of V. amazonica were separated with column chromatography. As a result, 15 compounds, including six steroids: -sitosterol [2], stigmasterol [2], -sitostenone [2], stigmasta-4,22-dien-3-one [2], 6 -hydroxy-sitosterone [2], and 6 -hydroxystigmasterone [2], four phenolic carboxylic acids: caffeic [3], p-hydroxybenzoic [4], protocatechuic [5], and vanillic acids [4], and five chlorophylls: pheophytin a [6], pheophorbide a methyl ester [7], methyl-132-hydroxy-(132-S)-pheophorbide b [7], 132-hydroxy-(132-S)-pheophytin a [8], and aristophyll C [9], were isolated. All of these compounds were isolated for the first time from this source. The leaves of V. amazonica were collected from Chiayi, Taiwan, May 2006. Plant material was identified by Dr. Fu-Yuan Lu (Department of Forestry and Natural Resources College of Agriculture, National Chiayi University). A voucher specimen was deposited in the School of Medical and Health Sciences, Fooyin University, Kaohsiung, Taiwan. The air-dried seeds of V. amazonica (1.3 kg) were extracted with MeOH (10 L 5) at room temperature, and the MeOH extract (102.4 g) was obtained upon concentration under reduced pressure. The MeOH extract was chromatographed over silica gel (600 g, 70–230 mesh) using n-hexane–acetone as eluent to produce five fractions. Part of fraction 1 (17.3 g) was subjected to silica gel chromatography by eluting with n-hexane–acetone (40:1), then enriched with acetone to furnish 10 fractions (1-1–1-10). Fraction 1-3 (1.9 g) was resubjected to silica gel chromatography, eluting with n-hexane–acetone (80:1) to obtain pheophytin a (13 mg) and pheophorbide a methyl ester (5 mg). Fraction 1-5 (2.2 g) was resubjected to silica gel chromatography, eluting with n-hexane–acetone (60:1) to obtain methyl-132-hydroxy-(132-S)pheophorbide b (3 mg), 132-hydroxy-(132-S)-pheophytin a (7 mg), and aristophyll C (14 mg). Part of fraction 3 (14.9 g) was subjected to silica gel chromatography by eluting with n-hexane–acetone (40:1), then enriched with acetone to furnish 10 fractions (3-1–3-10). Fraction 3-2 (1.7 g) was resubjected to silica gel chromatography, eluting with n-hexane–acetone (70:1) to obtain -sitosterol and stigmasterol (37 mg) and -sitostenone and stigmasta-4,22-dien-3-one (26 mg). Fraction 3-5 (1.1 g) was resubjected to silica gel chromatography, eluting with n-hexane–acetone (50:1) to obtain 6 -hydroxy-sitosterone and 6 -hydroxystigmasterone (5 mg). Part of fraction 8 (2.4 g) was subjected to silica gel chromatography by eluting with n-hexane–acetone, then enriched with acetone to furnish 12 fractions (8-1–8-12). Fraction 8-4 (0.4 g) was further purified by another silica gel column using n-hexane–acetone (30:1) to obtain caffeic acid (3 mg) and vanillic acid (5 mg). Fraction 8-6 (0.2 g) was further purified by another silica gel column using n-hexane–acetone (20:1) to obtain p-hydroxybenzoic acid (6 mg) and protocatechuic acid (4 mg).