Dihydropyranoflavones from Pongamia pinnata

Abstracts

From the stem bark of Pongamia pinnata, two new compounds, 3-methoxy-(3<FONT FACE=Symbol>²</FONT>,4<FONT FACE=Symbol>²</FONT>-dihydro- 3<FONT FACE=Symbol>²</FONT>-hydroxy-4<FONT FACE=Symbol>²</FONT>-acetoxy)-2<FONT FACE=Symbol>²</FONT>,2<FONT FACE=Symbol>²</FONT>-dimethylpyrano-(7,8:5 <FONT FACE=Symbol>²</FONT>,6<FONT FACE=Symbol>²</FONT>)-flavone and 3-methoxy-(3<FONT FACE=Symbol>²</FONT>,4<FONT FACE=Symbol>²</FONT>-dihydro-4<FONT FACE=Symbol>²</FONT>- hydroxy-3<FONT FACE=Symbol>²</FONT>-acetoxy)-2<FONT FACE=Symbol>²</FONT>,2<FONT FACE=Symbol>²</FONT>-dimethylpyrano-(7,8:5 <FONT FACE=Symbol>²</FONT>,6<FONT FACE=Symbol>²</FONT>)-flavone, were isolated, along with six known compounds, caryophyllene oxide, obovatachalcone, 8-hydroxy-6-methoxy-3-pentyl-1H-isochromen-1-one, 6,7,2,2-dimethylchromono-8,gamma,gamma-dimethylallylflavanon e, isolonchocarpin, ovaliflavanone A. Their structures were determined on the basis of the spectroscopic data interpretation.

Pongamia pinnata; prenylated flavonoids; flavone

Das cascas do caule de Pongamia pinnata foram isolados dois novos compostos, 3-metoxi-(3<FONT FACE=Symbol>²</FONT>,4<FONT FACE=Symbol>²</FONT>-diidro- 3<FONT FACE=Symbol>²</FONT>-hidroxi-4<FONT FACE=Symbol>²</FONT>-acetoxi)-2<FONT FACE=Symbol>²</FONT>,2<FONT FACE=Symbol>²</FONT>-dimetilpirano-(7,8:5 <FONT FACE=Symbol>²</FONT>,6<FONT FACE=Symbol>²</FONT>)-flavona e 3-metoxi-(3<FONT FACE=Symbol>²</FONT>,4<FONT FACE=Symbol>²</FONT>-diidro-4<FONT FACE=Symbol>²</FONT>- hidroxi-3<FONT FACE=Symbol>²</FONT>-acetoxi)-2<FONT FACE=Symbol>²</FONT>,2<FONT FACE=Symbol>²</FONT>-dimetilpirano-(7,8:5 <FONT FACE=Symbol>²</FONT>,6<FONT FACE=Symbol>²</FONT>)-flavona, juntamente com seis compostos conhecidos, óxido de cariofileno, obovatachalcona, 8-hidroxi-6-metoxi-3-pentil-1H- isocromeno-1-ona, 6,7,2,2-dimetilcromono-8,gama,gama-dimetilalilflavonona, isolonchocarpin, ovaliflavanona A. Suas estruturas foram determinadas a partir da interpretação de dados espectroscópicos.

SHORT REPORT

Dihydropyranoflavones from Pongamia pinnata

Hao Yin^{*, I}; Si Zhang^{*, I, II}; Jun Wu^I; Haihan Nan^I

^IGuangdong Key Laboratory of Marine Materia Medica, South China Sea Institute of Oceanology, Chinese Academy of Sciences, 164 West Xingang Road, Guangzhou, 510301, P.R. China

^IIHainan Key Lab of Tropical Marine Biotechnology, Chinese Academy of Science, Sanya, 572000, P.R. China

ABSTRACT

From the stem bark of Pongamia pinnata, two new compounds, 3-methoxy-(3²,4²-dihydro- 3²-hydroxy-4²-acetoxy)-2²,2²-dimethylpyrano-(7,8:5 ²,6²)-flavone and 3-methoxy-(3²,4²-dihydro-4²- hydroxy-3²-acetoxy)-2²,2²-dimethylpyrano-(7,8:5 ²,6²)-flavone, were isolated, along with six known compounds, caryophyllene oxide, obovatachalcone, 8-hydroxy-6-methoxy-3-pentyl-1H-isochromen-1-one, 6,7,2,2-dimethylchromono-8,g,g-dimethylallylflavanon e, isolonchocarpin, ovaliflavanone A. Their structures were determined on the basis of the spectroscopic data interpretation.

Keywords:Pongamia pinnata, prenylated flavonoids, flavone

RESUMO

Das cascas do caule de Pongamia pinnata foram isolados dois novos compostos, 3-metoxi-(3²,4²-diidro- 3²-hidroxi-4²-acetoxi)-2²,2²-dimetilpirano-(7,8:5 ²,6²)-flavona e 3-metoxi-(3²,4²-diidro-4²- hidroxi-3²-acetoxi)-2²,2²-dimetilpirano-(7,8:5 ²,6²)-flavona, juntamente com seis compostos conhecidos, óxido de cariofileno, obovatachalcona, 8-hidroxi-6-metoxi-3-pentil-1H- isocromeno-1-ona, 6,7,2,2-dimetilcromono-8,g,g-dimetilalilflavonona, isolonchocarpin, ovaliflavanona A. Suas estruturas foram determinadas a partir da interpretação de dados espectroscópicos.

Introduction

Pongamia pinnata (Linn) Pierre (Leguminosae, Papilionaceac; synonym, Pongamia glabra Vent), the only one species of genus Pongamia, is a medium sized glabrous tree, grows in the littoral regions of South Eastern Asia and Australia. All parts of the plant have been used as crude drug for the treatment of tumors, piles, skin diseases, wounds and ulcers.¹ Extracts of the plant possess significant anti-diarrhoeal, anti-fungal, anti-plasmodial, anti-ulcerogenic, anti-inflammatory, and analgesic activities.² Previous phytochemical investigation of this plant indicated the presence of abounding prenylated flavonoids such as furanoflavones, furanoflavonols, chromenoflavones, furanochalcones, and pyranochalcones.³ In this paper, we reported the isolation and identification of two new flavones (1, 2) from the stem bark of Pongamia pinnata.

Results and Discussion

The EtOH extract of Pongmia pinnata stem bark was submitted to successive chromatography, affording two new prenylated flavones 1 and 2 (Figure 1) along with six known compounds 3-8.

Compound 1, a white powder, gave a molecular ion [M⁺] at m/z 410.13657 in the HREIMS, indicating a molecular formula C₂₃H₂₂O₇ (calc. 410.13655). Together with HMQC spectra, the 1D NMR (¹³C, ¹H and DEPT, Table 1) spectra of compound 1 displayed resonances for one conjugated ketone (d_C 173.4, C-4), a pair of ortho-coupling aromatic protons (d_H 7.98, 1H, d, J 8.9 Hz, H-5; d_H 6.96, 1H, d, J 8.9 Hz, H-6), a monosubstituted aromatic ring (d_H 7.95, 2H, m, H-2¢, 6¢; d_H 7.55, 3H, m, H-3¢, 4¢, 5¢), two oxygenated methines (d_H 3.93, 1H, d, J 4.8 Hz, H-3²; d_C 69.3, C-3²; d_H 6.46, 1H, d, J 4.8 Hz, H-4²; d_C 63.2, C-4²), a acetoxy group (d_H 1.90, 3H, s, d_C 170.0, d_C 21.0, OAc-4²), two methyls (d_H 1.41, 3H, s, d_C 26.4, Me₁-2²; d_H 1.38, 3H, s, d_C 21.3, Me₂-2²), a methoxy group (d_H 3.81, 3H, s, d_C 60.1, OCH₃-3), and an oxygenated quaternary carbon (d_C 79.5, C-2²). With great similarity to those of 5-methoxy-(3²,4²-dihydro-3²,4²-diacetoxy)-2 ²,2²-dimethylpyrano-(7,8:5²,6²)-flavone,⁴ these 1D NMR data suggested that compound 1 was a flavone with a acetylated dihydropyrano unit. In HMBC spectra, the correlation between H-5 (d_H 7.98, 1H, d, J 8.9 Hz) and C-4 (d_C 173.4) indicated that the ring A was unsubstituted at the C-5 and C-6 position. The observed HMBC correlations from H-3²(d_H 3.93, 1H, d, J 4.8 Hz, H-3²) to C-8 (²_C 108.2), from H-4²(d_H 6.46, 1H, d, J 4.8Hz) to C-8 (d_C 108.2), C-7(d_C 158.3), and C-9 (d_C 155.0) suggested that the dihydropyran ring is attached to A ring at C-7(oxygenated) and C-8 postion. The location of the acetoxy group at C-4²were established by HMBC correlations from protons of Me₁-2², Me₂-2²to C-3², and from H-4²to the carbonyl of OAc-4². The location of the methoxyl group (d_H 3.81) at C-3 was revealed by the HMBC correlation from the protons of methoxy group to C-3 (d_C 141.1). The substitution of a hydroxyl group at C-3²(d_C 72.9) was enclosed by chemical shift of C-3²in ¹³C NMR spectra and the HREIMS data. The molecular structure of 1 contained two chiral carbon atoms, and the relative configuration of C-3² and C-4² was determined as cis on the basis of coupling constant J₃²_{, 4}² (4.8 Hz) and the difference (0.03 ppm) in the methyl proton signals at d_H 1.41 and d_H 1.38 of the 2²-gem dimethyl group.⁵ Accordingly, compound 1 was characterized as 3-methoxy-(3²,4²-dihydro-3²-hydroxy-4 ²-acetoxy)-2²,2²-dimethylpyrano-(7,8:5 ²,6²)-flavone.

Compound 2, a white powder, gave a molecular ion [M⁺] at m/z 410.13665 in the HREIMS, corresponding to the molecular formula C₂₃H₂₂O₇ (calc. 410.13655). The NMR spectral data of 2 (Table 1) were closely comparable to those of compound 1, with the only difference being due to the position of the acetoxy group (d_H 2.13, 3H, s, d_C 170.5, d_C 21.3, OAc-3²) and hydroxyl group on the pyran ring. In HMBC spectra, the observed correlations from protons of Me₁-2²(d_H 1.41, 3H, s), Me₂-2²(d_H 1.35, 3H, s) to C-3²(d_C 72.9), and from H-3²(d_H 5.06, 1H, d, J 4.8 Hz) to the carbonyl of acetoxyl group suggested the acetoxy group to be located on C-3² position. Further analysis of the NMR and MS spectra of compound 2 indicated the presence of the hydroxyl group at C-4² position. The coupling constant J₃²_{, 4}² was 4.8 Hz and the chemical shift difference of gem-dimethyl signals was 0.06 ppm in ¹H NMR spectrum. This evidence suggested that the relative configuration of compound 2 was cis-form. Thus compound 2 was characterized as 3-methoxy-(3²,4²-dihydro-4²-hydroxy-3 ²-acetoxy)-2²,2²-dimethylpyrano-(7,8:5 ²,6²)-flavone.

Additionally 6 known compounds, caryophyllene oxide (3),⁶ obovatachalcone (4),⁷ 8-hydroxy-6-methoxy-3-pentyl-1H-isochromen-1-one (5),⁸ 6,7,2,2-dimethylchromono-8,g,g -dimethylallylflavanone(6),⁹ isolonchocarpin (7),¹⁰ ovaliflavanone A (8),¹¹ were isolated from this plant and their structures elucidated by comparing their spectroscopic data with those reported in the literature. Compounds 3, 5, 6 and 8 were isolated for the first time from this plant.

Experimental

General

Optical rotation were measured with a Jasco 1020 polarimeter. NMR spectra were obtained on a Bruker AVANCE 500 spectrometer (500 MHz for ¹H NMR, 125 MHz for ¹³C NMR). EIMS and HREIMS spectra were recorded on a Finnigan MAT TSQ 700 mass spectrometer. UV spectra were obtained in a Beckman DU-640 UV spectrophotometer. A Waters Nova-pack HR C18 column (19×300mm) was used for semipreparative HPLC, along with Waters 600E Multisolvent Delivery System and a Waters 996 Photodiode Array Detector.

Plant material

The material investigated were stem bark of Pongamia pinnata collected in October 2002 from Hainan Province, southern China. The material was identified by Professor Si Zhang, Guangdong Key Laboratory of Marine Materia Medica, South China Sea Institute of Oceanology, Chinese Academy of Sciences. A voucher specimen is deposited at the herbarium of the South China Sea Institute of Oceanology (No. GKLMMM005).

Extraction and isolation

The dryied and powdered stem bark (6 kg) of Pongamia pinnata was extracted with 95% EtOH three times. After evaporation of the solvents under reduced pressure, the residue (300 g) was then extracted successively resulting four extracts: petroleum (80 g), ethyl acetate (60 g), n-butanol (60 g), and aqueous (80 g). The petroleum extract was fractionated into 63 fractions by open CC over silica gel with gradient mixtures of petroleum-CHCl₃ (6:1) to CHCl₃-acetone (0:1) for elution. These fractions were pooled into 17 fractions (P-1~P-17) according to their similarity on TLC. The silica gel CC of Fraction P-8 using petroleum-EtOAc (3:1) afforded 7 fractions (P-8-1 to P-8-7). Fraction P-8-5 were purified by CC of Pharmacia-Sephadex LH-20 with MeOH-H₂O (95: 5) and separated by reverse phase semi-preparative HPLC (ODS column, using MeOH:H₂O (66:34) 8 mL min^-1, flow rate, UV: 254 nm) to give compounds 1 (1.9 mg, t_R=16 min) and 2 (5.2 mg, t_R=19 min). The CC of fraction P-6 using petroleum-EtOAc (35:1) afford 50 fractions (P-6-1 to P-6-50). The fractions P-6-10, P-6-13, P-6-18, P-6-28, P-6-35 and P-6-38, purified by CC on Pharmacia-Sephadex LH-20 (CHCl₃-MeOH 5:1) or recrystallization, yield compounds 3 (113 mg), 4 (25 mg), 5 (16 mg), 6 (9 mg), 7 (11 mg) and 8 (13 mg), respectively.

3-methoxy-(3²,4²-dihydro-3²-hydroxy-4 ²-acetoxy)-2²,2²-dimethylpyrano-(7,8:5 ²,6²)-flavone (1). [a]_D²⁵ +46.5 ° (c 0.1, CHCl₃); UV(MeOH) l_max/ nm: 255, 316; HREIMS m/z: 410.13657 (calc. for C₂₃H₂₂O₇ 410.13655); EIMS m/z (rel. int.,%): 410 [M⁺] (76), 409 (100), 349 (21), 335 (9), 333 (17), 297 (8), 165 (17), 163 (12); ¹H and ¹³C NMR spectra data: see Table 1.

3-methoxy-(3²,4²-dihydro-4²-hydroxy-3 ²-acetoxy)-2²,2²-dimethylpyrano-(7,8:5 ²,6²)-flavone (2). [a]_D²⁵ +15.8° (c 0.1, CHCl₃); UV(MeOH) l_max/nm: 252, 311; HREIMS m/z: 410.13667 (calc. for C₂₃H₂₂O₇, 410.13655); EIMS m/z (rel. int.,%): 410 [M⁺] (81), 409 (100), 349 (20), 335 (8), 333 (16), 321 (10), 297 (11), 296 (10), 295 (46), 279 (16), 165 (22), 163 (12); ¹H and ¹³C NMR spectra data: see Table 1.

Acknowledgments

The authors are grateful to the financial support by the Hi-tech Research and Development Program of China (2001AA62403), Guangdong Natural Science Fundation ((2003) 11), and Research Program of Croucher Fundation. We thank Jianshe Huang and Zhihui Xiao for NMR measurements.

Supplementary Information

Supplementary Information are available free of charge at http://jbcs.sbq.org.br, as PDF file.

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Received: November 20, 2005

Published on the web: August 1, 2006

Supplementary Information

Publication Dates

• Publication in this collection
  29 Jan 2007
• Date of issue
  Dec 2006

History

• Received
  20 Nov 2005
• Accepted
  01 Aug 2006