SECONDARY METABOLITES FROM PEPEROMIA SUI

J. Chil. Chem. Soc., 53, Nº 2 (2008) SECONDARY METABOLITES FROM PEPEROMIA SUI MING-JEN CHENG1,2*, AND IH-SHENG CHEN1* 1 School of Pharmacy, College of Pharmacy, Kaohsiung Medical University, Kaohsiung, Taiwan 807, R.O.C. Correspondence: Professor I. S. Chen Ph. D. School of Pharmacy, College of Pharmacy, Kaohsiung Medical University, Kaohsiung, Taiwan 807, R.O.C. 2 Bioresource Collection and Research Center, Food Industry Research and Development Institute, Hsinchu, Taiwan, R.O.C. (Received: 23 July 2007 - Accepted: 2 April 2008) ABSTRACT One chromone, peperosuione (1), together with eighteen known compounds were identified from the whole plant of Peperomia sui (Piperaceae). Peperovulcanone A (2) isolated firstly from the P. vulcanica also obtained from this study, its structure was revised on the basis of spectroscopic evidences. All of the isolates constituents were determined by means of spectral analyses. Keywords: Peperomia sui; Piperaceae; Chromone; Peperosuione; Peperovulcanone A. INTRODUCTION The Peperomia is the second largest genus in Piperaceae. About 1000 species widely distributed in tropical and subtropical regions; five species are native to Taiwan, namely P. japonica, P. nakaharai, P. reflexa, P. rubrivenosa, and P. sui, mostly growing on trees or moss-covered rocks. P. sui Lin & Lu, an endemic species in Taiwan, is a succulent herb and distributed in forests from low to medium altitudes1. Less than 11 species of Peperomia has been undergone phytochemical studies in previously researches. Its common constituents are phenylpropanoid, benzopyran, chromone, prenylated quinone, secolignan, and acylcyclohexane-1,3-dione2–7. The methanolic extracts of the whole plant of this species showed significant cytotoxicity on high-throughput screening against HONE-1 and NUGC-3 cancer cell lines in vitro. In the previous study from the whole plant of this plant, thirty-four compounds including three new polyketides, one new acylresorcinol and thirty known compounds were reported5. Carefully examination on this plant has resulted in the isolation of nineteen compounds as additional constituents, including one new compound. We herein reported the isolation, structural elucidation of a new chromone name peperosuione (1) and the structural revision of peperovulcanone A (2), a previously reported new constituent obtained from P. vulcanica. EXPERIMENTAL General experimental procedures Melting points were determined with a YANACO micro-melting point apparatus and were uncorrected. IR spectra were taken on a Hitachi 26030 spectrophotometer. UV spectra were obtained on a JASCO UV-240 spectrophotometer. EIMS spectra were recorded on a VG Biotech Quattro 5022 spectrometer. HREIMS were recorded on a JEOL JMX-HX 110 mass spectrometer. 1H NMR and 13C NMR spectra were measured on a Varian Gemini 200, and Varian Unity Plus 400 spectrometers, and are given in parts per million (δ) downfield from internal TMS. Si gel 60 (Merck 70-230 mesh, 230-400 mesh) was used for column chromatography, and Si gel 60 F254 (Merck) for TLC. Plant material Whole plants of P. sui were collected from Wutai, Pingtung County, Taiwan, in May 2001. A voucher specimen (Chen 6100) was deposited in the Herbarium of the School of Pharmacy, Kaohsiung Medical University, Taiwan, Republic of China. Extraction and separation of compounds Dried whole plants (8.9 kg) were extracted with MeOH at room temperature, and concentrated in vacuo to leave a brownish viscous residue. The MeOH extract was partitioned between n-hexane-H2O to afford a n-hexane extract (fraction A, 50 g) and H2O layer (fraction C, 350 g). The H2O layer was then partitioned with EtOAc to give EtOAc extract (fraction B, 25 g), and H2O layer (fraction C, 350 g)5. A part of fraction A (30 g) was chromatographed over Si gel, eluting with a n-hexane-EtOAc gradient, to obtain 15 fractions (A1-A15). Fraction A1 (100 mg, n-hexane-EtOAc, 50:1) was subjected to Si gel chromatography, eluting with n-hexane-EtOAc (20:1) enriched gradually with EtOAc to obtain 5 fractions (A1-1-A1-5). Fraction A1-3 (10 mg) was purified by preparative e-mail: TLC to give linoleic acid (11) (1.9 mg), 2,6-dimethoxy-p-quinone (14) (2.1 mg), peperosuione (1) (1.1 mg), and α-tocopherol (12) (3.1 mg). Fraction A3 (950 mg, n-hexane-EtOAc, 40:1) was subjected to Si gel chromatography, eluting with n-hexane-Me2CO (20:1) enriched gradually with Me2CO to obtain 7 fractions (A3-1-A3-7). Fraction A3-4 (110 mg) was purified by preparative TLC to give benzaldehyde (16) (12.1 mg), peperovulcanone A (2) (1.4 mg), a mixture of ficaprenol-10 and ficaprenol-11 (19) (12.9 mg). Fraction A5 (3.5 g, n-hexane-EtOAc, 25:1) was subjected to Si gel chromatography, eluting with n-hexane-EtOAc (10:1) enriched gradually with EtOAc to obtain 10 fractions (A5-1-A5-10). Fraction A5-8 (100 mg, n-hexane-EtOAc, 3:1) was purified by preparative TLC to give 1,2,3-trimethoxy-4,5-dioxo-6a,7-dehydroaporphine (3) (1.9 mg). Fraction A7 (2.7 g, n-hexane-EtOAc, 20:1) was subjected to Si gel chromatography, eluting with n-hexane-Me2CO (5:1) enriched gradually with Me2CO to obtain five fractions (A7-1-A-7-5). Fraction A7-3 (50 mg, nhexane-Me2CO, 5:1) was purified by preparative TLC to yield pheophytin-a (6) (3.5 mg), pheophytin-b (7) (1.7 mg), caryophyllene oxide (10) (12.1 mg). Fraction A15 (3.7 g, n-hexane-EtOAc, 2:1) was chromatographed over Si gel, eluting with a CHCl3-EtOAc gradient, to obtain 10 fractions (A15-1-A1510). Fraction A15-5 (1.1 g, n-hexane-EtOAc, 1.5:1) was resubjected to Si gel chromatography, eluting with CHCl3-MeOH (10:1) enriched gradually with MeOH to obtain methyl asterrate (18) (2.1 mg), and isofraxidin (4) (3.1 mg). Fraction B (25 g) was chromatographed over Si gel, eluting with a CHCl3MeOH gradient, to obtain 8 fractions (B1-B8). Fraction B3 (5.8 g, CHCl3MeOH, 50:1) was resubjected to Si gel, eluting with n-hexane-EtOAc (50:1) enriched gradually with EtOAc to obtain 10 fractions (B3-1-B3-10). Fraction B3-7 (500 mg, n-hexane-EtOAc, 5:1) was purified by preparative TLC to yield peperomin A (5) (2.0 mg), and pyropheophorbide (8) (2.7 mg). Fraction B8 (4.8 g, CHCl3-MeOH, 10:1), when chromatographed over silica gel with CHCl3 and CHCl3/MeOH solvent mixtures, was followed by recrystallization to give 5-(acetoxymethyl)furfural (13). Part (25 g) of fraction C (350 g) was chromatographed on Diaion HP-20 eluting with H2O, gradually decreasing the polarity with MeOH to afford 10 fractions (C-1-C-10). Fraction C-4 (273 mg) was chromatographed on Si gel, eluting with CH2Cl2-MeOH (12:1) to afford methyl-α-D-glucopyranoside (15) (13.1 mg), and succinic acid (17) (2.0 mg). Spectroscopic data Peperosuione (1): Colorless oil. [α]D25: ±0o (c 0.09, CHCl3). UV (MeOH)λmax (log ε): 239 (3.74), 275 (3.72) nm. IR (Neat) νmax: 3480 (OH), 1650 (C=O), 1615, 1580 (benzene ring) cm-1. 1H NMR (CDCl3, 400 MHz): δ 0.88 (3H, t, J = 6.8 Hz, CH3-17’), 1.25~1.33 (16H, m, H-3’~9’, 16’), 1.35 (4H, m, H-10’, 15’), 1.47 (2H, m, H-2’), 1.74 (1H, ddd (...truncated)