Journal of Natural Medicines

, Volume 65, Issue 1, pp 191–193

Aromatic compounds and their antioxidant activity of Acer saccharum

Authors

    • Faculty of Pharmaceutical SciencesTokushima Bunri University
  • Yuki Kawahara
    • Faculty of Pharmaceutical SciencesTokushima Bunri University
  • Shigenobu Arihara
    • Faculty of Pharmaceutical SciencesTokushima Bunri University
  • Toshihiro Hashimoto
    • Faculty of Pharmaceutical SciencesTokushima Bunri University
Note

DOI: 10.1007/s11418-010-0450-5

Cite this article as:
Yoshikawa, K., Kawahara, Y., Arihara, S. et al. J Nat Med (2011) 65: 191. doi:10.1007/s11418-010-0450-5

Abstract

A new lignan glycoside, 5-(3″,4″-dimethoxy-phenyl)-3-hydroxy-3-(4′-hydroxy-3′-methoxybenzyl)-4-hydroxymethyl-dihydrofuran-2-one 4′-O-α-l-rhamnopyranoside (1), with seven known compounds, compound 2, koaburside, icariside E4, cleomiscosin C, cleomiscosin D, scopoletin, and 5′-demethylaquillochin, were isolated from the EtOH extract of the wood of Acer saccharum (Aceraceae). Their structures were determined by 1D and 2D nuclear magnetic resonance (NMR) and mass spectroscopy analysis. All of the isolated compounds, 18, were tested for their antioxidant activity in superoxide dismutase (SOD)-like assay.

Keywords

Acer saccharumLignan glycosidePhenylpropanoidAromatic compoundAntioxidant activitySODAceraceae

Introduction

As a part of a research program aimed at the discovery of biologically active compounds from natural sources, we reported previously the isolation, structure elucidation, and the antimicrobial activity of phenylpropanoid, flavonol, and lignan from Firmiana simplex [1]. Here, we have paid attention to the chemical study for Acer saccharum (satoukaede in Japanese, Aceraceae), which is known for fallen arbor leaves belonging to Aceraceae as the tree for which their autochthonism is North America and to obtain maple syrup [2]. The previous chemical studies on this tree led to the isolations of scopoletin [3], urusane and oleanane type triterpenes, and steroids [4].

Results and discussion

The wood of Acer saccharum was exhaustively extracted with EtOH at room temperature for 1.5 months. The extract was separated by ordinary-phase silica gel and reverse-phase silica gel to furnish a novel lignan glycoside, compound 1 (1), along with seven known compounds, compound 2 (2) [5], koaburside (3) [6], icariside E4 (4) [5], cleomiscosin C (5), cleomiscosin D (6) [7], scopoletin (7) [3], and 5′-demethylaquillochin (8) [8] (Fig. 1). This is the first report of the isolations of 26 and 8 from A. saccharum.
https://static-content.springer.com/image/art%3A10.1007%2Fs11418-010-0450-5/MediaObjects/11418_2010_450_Fig1_HTML.gif
Fig. 1

The chemical structures of compounds 18

Compound 1 was obtained as a colorless oil, and showed a [M+H]+ peak at m/z 549.2006 in the high-resolution (HR)-FAB-MS, which corresponded to the molecular formula C27H34O12, including eleven unsaturations. The IR spectrum of 1 showed absorptions at 3400, 1760, and 1050 cm−1. The 13C-nuclear magnetic resonance (NMR) distortionless enhancement by polarization transfer (DEPT) and the 1H-NMR spectra were similar to those of olivil [9], except for the presence of one carbonyl carbon (δ 178.8), one methoxy carbon (δ 55.6), and 6-deoxy-hexose moiety. On acid hydrolysis with 2.5% H2SO4, 1 liberated l-rhamnose identified by HPLC analysis using an optical rotation detector (see the following section) [10]. The gross structure of 1 was determined by analysis of the 2D NMR data, including heteronuclear multiple quantum coherence (HMQC), heteronuclear multiple bond correlation (HMBC), and rotation-frame Overhauser enhancement spectroscopy (ROESY) experiments. Two 1,3,4-trisubstituted aromatic rings, one α-rhamnopyranosyl group, and CH–CH–CH2 partial structure were deduced from COSY correlations (Fig. 2). In the HMBC data, the connectivity from H2-6 (δ 3.88, 3.71) to C-2 (δ 178.8), C-3 (δ 81.8), C-4 (δ 52.0), C-1′ (δ 131.8), C-2′ (δ 116.1), C-6′ (δ 124.0), from H-5 (δ 5.61) to C-1″ (δ 131.9), C-2″ (δ 110.1), C-6″ (δ 120.0), from H-6′ (δ 7.30) to C-4′ (δ 145.7), and from H-1′″ (δ 5.99) to C-4′ revealed the presence of γ-butyrolactone, that is, 3-hydroxy-4-hydroxymethyl-dihydrofuran-2-one, 4′-hydroxy-3′-methoxybenzyl, and 3″,4″-dimethoxy-phenyl, and then they were connected between C-3 and C-6, C-5 and C-1″, α-rhamnopyranosyl group, and C-4′ positions (Fig. 2, Table 1). The relative configurations of three successive chiral centers at C-3, C-4, and C-5 in 1 were indicated by the following NOE analysis as shown in Fig. 3. The NOEs between H-5 (δ 5.61)/H2-7 (δ 4.63, 4.14), H-4 (δ 3.06)/H-2′ (δ 7.40), /H-6′ (δ 7.30), /H-2″ (δ 6.80), and /H-6″ (δ 6.90) indicated the β-orientations of HO-3 and H-5, and the α-orientation of H-4. Three methoxy groups at two 1,3,4-trisubstituted aromatic rings could also be confirmed at the C-3′, C-3″, and C-4″ positions from the NOEs between H-2′/OMe (δ 3.65), H-2″/OMe (δ 3.69), and H-5″ (δ 6.82)/OMe (δ 3.62) (Fig. 3). Thus, from the above findings, the structure of 1 was formulated as shown for 1.
https://static-content.springer.com/image/art%3A10.1007%2Fs11418-010-0450-5/MediaObjects/11418_2010_450_Fig2_HTML.gif
Fig. 2

COSY (thick lines) and HMBC (arrows) correlations for compound 1

https://static-content.springer.com/image/art%3A10.1007%2Fs11418-010-0450-5/MediaObjects/11418_2010_450_Fig3_HTML.gif
Fig. 3

ROESY correlations for compound 1

Table 1

NMR spectral data for compound 1 (in pyridine-d5, 150 and 600 MHz)

Position

δC

δH (J, Hz)

Position

δC

δH (J, Hz)

2

178.8

 

1′″

101.8

5.99 (d, 1.3)

3

81.8

 

2′″

72.1

4.81 (dd, 3.3, 1.3)

4

52.0

3.06 (m)

3′″

72.6

4.72 (dd, 9.3, 3.3)

5

78.8

5.61 (d, 9.3)

4′″

73.8

4.36 (t, 9.3)

6

42.6

3.88 (d, 13.1)

5′″

71.1

4.47 (m)

  

3.71 (d, 13.1)

6′″

18.6

1.60 (d, 6.3)

7

57.9

4.63 (dd, 11.0, 7.4)

   
  

4.14 (dd, 11.0, 4.4)

   

1′

131.8

    

2′

116.1

7.40 (d, 1.6)

   

3′

151.0

    

4′

145.7

    

5′

119.0

7.38 (d, 8.2)

   

6′

124.0

7.30 (d, 8.2, 1.6)

   

1″

131.9

    

2″

110.1

6.80 (d, 1.9)

   

3″

150.2

    

4″

150.2

    

5″

111.9

6.82 (d, 8.2)

   

6″

120.0

6.90 (d, 8.2, 1.9)

   

3′-OMe

55.8

3.65s

   

3″-OMe

55.8

3.69s

   

4″-OMe

55.6

3.62s

   

The antioxidant activity of 17 has been studied with superoxide dismutase (SOD) assay kit. Vitamin C was used as a positive control (IC50 66.2 μM). Among these, compounds 2, 5, and 6 exhibited significant SOD-like activity, IC50 3.6, 46.0, and 21.2 μM, respectively.

Experimental

General

Optical rotation was taken on a JASCO DIP-1000 polarimeter. IR spectra were measured on a JASCO FT/IR-5300 instrument. NMR spectra were recorded on a Varian UNITY 600 spectrometer. The chemical shifts are given in δ (ppm) in C5D5N solution, using tetramethylsilane (TMS) as an internal standard. NMR experiments included COSY, HMQC, HMBC, and ROESY. Coupling constants (J values) are given in Hz. HR-FAB-MS were measured on a JEOL JMS-700 MS station.

Material

A. saccharum was collected at St. Roberts, Quebec, Canada, in May 2003. A voucher specimen (TB 5429) is deposited at the Herbarium of the Department of Pharmacognosy, Tokushima Bunri University, Tokushima, Japan.

Extraction and isolation

The wood of Acer saccharum (3.7 kg) was exhaustively extracted with EtOH at room temperature for 1.5 months. The EtOH extract was partitioned between EtOAc and H2O. The EtOAc soluble-portion (54.0 g) was subjected to silica gel column chromatography with hexane–isopropyl ether–MeOH (10:1:0 → 0:1:10). Fraction 6 (3.14 g) and 7 (2.64 g) were purified by silica gel column chromatography with isopropyl ether–MeOH (20:1) to yield scopoletin (7, 157.8 mg) from fraction 6, and compound 2 (14.6 mg) from fraction 7, respectively. Fraction 9 (2.25 g) was subjected to silica gel column chromatography with isopropyl ether–MeOH–H2O (25:3:0.1) and purified by HPLC (ODS, 40–50% MeOH) to afford cleomiscosin C (5, 85 mg) and 5′-demethylaquillochin (8, 4.3 mg). Fraction 10 (4.99 g) was also subjected to silica gel column chromatography with isopropyl ether–MeOH–AcOEt–H2O (6:2:4:1) and purified by HPLC (ODS, 30–60% MeOH) to afford compound 1 (22 mg), koaburside (3, 38.7 mg), icariside E4 (4, 138.6 mg), cleomiscosin C (5, 37.3 mg), and cleomiscosin D (6, 13.4 mg).

Compound 1

Amorphous solid. [α]D −40.1° (c 1.7, MeOH). FT-IR (dry film) cm−1: 3400 (OH), 1760 (C=O), 1050 (OH). HR-FAB-MS m/z: 549.2006 (calculated for C27H34O12: 549.1973).

Acid hydrolysis of compound 1

A solution of 1 in 5% H2SO4–dioxane (1:1) was heated at 100°C for 2 h. The reaction mixture was diluted with H2O and then neutralized with Amberlite IRA-35 and evaporated in vacuo to dryness. The identification and the d or l configuration of rhamnose was determined by using RI detection (Shimadzu RID-10A) and chiral detection (Shodex OR-1) by HPLC (Shodex RSpak NH2P-50 4D, CH3CN–H2O–H3PO4, 95:5:1, 1 mL/min, 47°C), by comparison with an authentic sugar (10 mmol of l-rham). The sugar portion gave the following peak of l-(+)-Rham at 4.60 min.

Superoxide dismutase-like activity

SOD-like activity was determined according to the method of Ukeda et al. [11] using an SOD Assay Kit-WST (Dojindo Lab., Kumamoto). A test sample was dissolved in DMSO to obtain a final DMSO concentration of 0.8% (v/v).

Acknowledgments

The authors are grateful to Ms. Y. Watanabe, MIC Co. Ltd., Mr. L. Bergeron, L.B. Maple Treat Inc., and Dr. T. Ishiguro, BioPharm Toyono, for supplying the material of A. saccharum.

Copyright information

© The Japanese Society of Pharmacognosy and Springer 2010