Journal of Natural Medicines

, Volume 62, Issue 3, pp 325–327

A new homoisoflavan from Caesalpinia sappan

Authors

  • Huanxin Zhao
    • Institute of Materia MedicaShandong Academy of Medical Sciences
    • Institute of Materia MedicaShandong Academy of Medical Sciences
  • Yuanshu Wang
    • Institute of Materia MedicaShandong Academy of Medical Sciences
  • Wei Li
    • Faculty of Pharmaceutical SciencesToho University
  • Kazuo Koike
    • Faculty of Pharmaceutical SciencesToho University
Note

DOI: 10.1007/s11418-008-0231-6

Cite this article as:
Zhao, H., Bai, H., Wang, Y. et al. J Nat Med (2008) 62: 325. doi:10.1007/s11418-008-0231-6

Abstract

A new homoisoflavan, 7,3′,4′-trihydroxy-3-benzyl-2H-chromene (1), was isolated from the dried heartwood of Caesalpinia sappan L., together with seven known phenolic compounds. The structure of the new compound (1) was determined on the basis of spectroscopic analysis.

Keywords

Caesalpinia sappanHomoisoflavanLeguminosae

Introduction

Sappan Lignum, the dried heartwood of Caesalpinia sappan L. (Leguminosae), has long been used in traditional medicine as an emmenagogue, hemostatic, and anti-inflammatory agent in China [1] and has been reported to be rich in homoisoflavonoids and brazilins [2]. Pharmacological studies on this plant have demonstrated antioxidant [3] and anticomplementary [4] activities. The potential medicinal importance prompted us to investigate its chemical constituents, which resulted in the isolation of a new homoisoflavan, 7,3′,4′-trihydroxy-3-benzyl-2H-chromene (1), along with seven known phenolic compounds. To our knowledge, homoisoflavans possessing a double bond located at C-3 and C-4 have not been reported as a natural product. This paper deals with the structural characterization of the new compound 1 by spectroscopic analysis.

Results and discussion

The ethanolic extract of the heartwood of C.sappan was suspended in H2O and EtOAc. A portion of the EtOAc-soluble fraction was separated by chromatographic procedures to give a new homoisoflavan, 7,3′,4′-trihydroxy-3-benzyl-2H-chromene (1) (Fig. 1), along with seven known phenolic compounds, 4-O-methylsappanol (2) [5], 4-O-methylepisappanol [5], 3′-deoxy-4-O-methylsappanol [6], intricatinol [7], caesalpin J [8], protosappanin A [9], and brazilin [10]. The structures of the known compounds were determined by comparison of their spectroscopic data with those reported in the literature.
https://static-content.springer.com/image/art%3A10.1007%2Fs11418-008-0231-6/MediaObjects/11418_2008_231_Fig1_HTML.gif
Fig. 1

Structures of 1 and 2

Compound 1 was obtained as a brown powder. The molecular formula was determined as C16H14O4 by HRESIMS (m/z 271.09566 [M + H]+, calcd. 271.09703). The UV spectrum displayed absorptions bands at 286.0 and 216.5 nm, suggesting the presence of an oxygenated phenylic ring [11]. The 13C NMR spectrum revealed 16 carbon resonances; seven were assigned as methines, two as methylenes, and seven as quaternary carbons, including four oxygenated olefinic carbons, by analysis of the DEPT spectra. All protonated carbons were assigned by analysis of the HMQC spectrum. The 1H NMR spectrum of 1 showed two sets of ABX-type aromatic resonances at δ 6.79 (1H, d, J = 8.1 Hz), 6.33 (1H, dd, J = 8.1, 2.6 Hz), and 6.22 (1H, d, J = 2.6 Hz), and δ 6.75 (1H, d, J = 8.0 Hz), 6.57 (1H, dd, J = 8.0, 2.1 Hz), and 6.72 (1H, d, J = 2.1 Hz). It also showed an isolated olefinic resonance at δ 6.14 (1H, br s) and two resonances attributable to an oxymethyl and a benzylic methylene at δ 4.54 (2H, s) and δ 3.27 (2H, s), respectively. Comparison of the 13C NMR spectra of 1 and 2 showed that their C ring carbon resonances were different. Namely, two sp3 carbons (δ 69.7 and 78.4) in 2 were substituted by two olefinic carbons (δ 131.1 and 119.4) in 1. Also a methoxyl group at C-4 was absent in 1. The proton and carbon signals were further assigned as shown in Table 1 by analysis of the HMBC spectrum (Fig. 2). Thus, the structure of 1 was established as 7,3′,4′-trihydroxy-3-benzyl-2H-chromene.
Table 1

1H (500 MHz) and 13C (125 MHz) data of 1 in acetone-d6

Position

δH, mult., J in Hz

δC

Position

δH, mult., J in Hz

δC

2

4.54, s

67.7

8a

 

154.3

3

 

131.1

9

3.27, s

38.7

4

6.14, br s

119.4

1′

 

129.8

4a

 

115.3

2′

6.72, d, 2.1

115.9

5

6.79, d, 8.1

126.9

3′

 

145.1

6

6.33, dd, 8.1, 2.6

108.1

4′

 

143.7

7

 

157.9

5′

6.75, d, 8.0

115.3

8

6.22, d, 2.6

102.6

6′

6.57, dd, 8.0, 2.1

120.3

https://static-content.springer.com/image/art%3A10.1007%2Fs11418-008-0231-6/MediaObjects/11418_2008_231_Fig2_HTML.gif
Fig. 2

Key HMBC correlations of 1

Experimental

General

UV spectra were obtained with a Shimadzu Biospec-Mini spectrophotometer, IR spectra were measured with a Thermo Nicolet 670 FTIR spectrometer (by the KBr disk method), and HRESIMS were acquired with a Jeol JMS-T100CS spectrometer. 1H and 13C NMR spectra were measured with a Jeol ECP-500 spectrometer with TMS as the internal reference, and chemical shifts are expressed in δ (ppm). Silica gel (200–300 mesh; Qingdao Ocean Chemical Factory, China) and Sephadex LH-20 (GE Healthcare Bio-Sciences AB, Sweden) were used for column chromatography (CC).

Plant material

The dried heartwood of C. sappan was collected on August, 2006, from Yunnan province of the People’s Republic of China and identified by one of the authors, H.B.

Extraction and isolation

The dried heartwood of C. sappan (5 kg) was extracted with 95% EtOH three times. Evaporation of the solvent under reduced pressure gave the EtOH extract (380.6 g). The extract was partitioned between EtOAc and H2O. Removal of the solvent from the EtOAc phase yielded EtOAc-soluble extract (310.2 g). A portion of the EtOAc extract (160.4 g) was subjected to silica gel CC (100 mm i.d. × 600 mm) with a CHCl3–MeOH gradient to give 14 fractions (A-N). Fraction F (1.1 g) (CHCl3–MeOH (95:5) eluate) was loaded on a column of silica gel (20 mm i.d. × 200 mm) and eluted with CHCl3–acetone (95:5, 92:8, and 88:12) to give seven fractions (F-1 to F-7). Fraction F-2 (29 mg) (CHCl3–acetone (95:5) eluate) was separated by Sephadex LH-20 CC (25 mm i.d. × 150 mm) with 70% MeOH to give intricatinol (8 mg). Fraction F-6 (186 mg) (CHCl3–acetone (88:12) eluate) was further purified by Sephadex LH-20 CC (25 mm i.d. × 150 cm) with 70% MeOH to give 1 (105 mg). Fraction G (20.8 g) (CHCl3–MeOH (95:5 and 92:8) eluate) was fractionated by silica gel CC (55 mm i.d. × 500 mm, CHCl3–acetone (9:1, 85:15, 8:2, and 7:3)) to give six fractions (G-1 to G-6). Fraction G-2 (353 mg) (CHCl3–acetone (85:15) eluate) was chromatographed on silica gel (15 mm i.d. × 300 mm) with CH2Cl2–acetone (92:8, 9:1, and 85:15) to give brazilin (16 mg). Fraction G-5 (1.4 g) (CHCl3–acetone (8:2) eluate) was further separated by Sephadex LH-20 CC (25 mm i.d. × 150 mm) with 60% MeOH to afford caesalpin J (52 mg) and protosappanin A (84 mg). Fraction H (5.6 g) (CHCl3–MeOH (92:8) eluate) was subjected to silica gel CC (30 mm i.d. × 450 mm) with CHCl3–acetone (9:1, 85:15, 8:2, and 7:3) to give four fractions (H-1 to H-4). Fraction H-2 (102.9 mg) (CHCl3–acetone (85:15) eluate) was purified by Sephadex LH-20 CC (25 mm i.d. × 150 mm) with 70% MeOH to give 3′-deoxy-4-O-methylsappanol (81 mg). Further separation of the fraction I (54.5 g) (CHCl3–MeOH (9:1) eluate) was achieved by silica gel CC (75 mm i.d. × 500 mm) with CHCl3–MeOH (95:5, 92:8, 9:1, 85:15, and 8:2) to give five fractions (I-1 to I-5). Fraction I-2 (2.0 g) (CHCl3–MeOH (95:5) eluate) was further separated by Sephadex LH-20 CC (25 mm i.d. × 150 mm) with 70% MeOH to give 2 (85 mg) and 4-O-methylepisappanol (49 mg).

7,3′,4′-Trihydroxy-3-benzyl-2H-chromene (1). Brown powder. IR (KBr) cm−1: 3,333, 1,617, 1,591 and 1,506. UV λmax(MeOH) nm (log ε): 286.0 (0.40), 216.5 (1.02). HRESIMS m/z: 271.09566 (calcd. for C16H15O4 [M + H]+: 271.09703). 1H NMR (500 MHz, acetone-d6) and 13C NMR (125 MHz, acetone-d6): see Table 1.

Copyright information

© The Japanese Society of Pharmacognosy and Springer 2008