Separation of Two Main Triterpene Glycosides from Sea Cucumber Pearsonothuria Graeffei by High-Speed Countercurrent Chromatography

Acta Chromatographica 20(2008)2, 269–276 DOI: 10.1556/AChrom.20.2008.2.11

Separation of Two Main Triterpene Glycosides from Sea Cucumber Pearsonothuria graeffei by High-Speed Countercurrent Chromatography

PING DONG1, CHANG-HU XUE1,*, AND QI-ZHEN DU2

1College of Food Science and Technology, Ocean University of China, No. 5, Yu Shan Road, Qingdao, Shandong Province, 266003, P.R. China 2Institute of Food and Biological Engineering, Zhejiang Gongshang University, Hangzhou, 310035, P.R. China E-mail: [email protected]

Summary. Holostane series glycosides have been isolated by a new and effective method. Two main triterpene glycosides from sea cucumber Pearsonothuria graeffei extract were successfully purified by one-step high-speed countercurrent chromatography (HSCCC) using a two-phase solvent systems comprising ethyl acetate–n-butanol– methanol–water 2.4:2.6:0.2:4.8 (v/v) to yield holothurin A and echinoside A with purities 93.5 and 95.5%, respectively. The chemical structures were elucidated by ESIMS and NMR analysis.

Introduction

Sea cucumber has been a traditional healthy food for thousands of years. Triterpene glycosides are the most important secondary metabolites of sea cucumbers because of their biological activities, including antifungal, cyto- toxic, hemolytic, cytostatic, and immunomodulatory effects [1–4]. More than 100 of these compounds have been isolated from sea cucumbers. Most of the known sea-cucumber glycosides have lanostane aglycones with an 18(20)-lactone and a sugar chain composed of up to six monosaccharide units. Every type of sea cucumber contains several saponins with quite similar chemical structures [5–7]. Pearsonothuria graeffei (Holothuriidae) is a sea cucumber widely distributed around Taiwan, the Nansha Islands, Madagascar, the Maldives, the Philippines, Guam, and Fiji. The triterpene glycosides in Pearsonothuria graeffei were effective against several human tumor cells in our earlier study.

Unauthenticated | Downloaded 10/02/21 05:32 PM UTC 270 Ping Dong et al.

Traditional methods for purification for these compounds, including several steps of repeated silica gel chromatography, reversed-phase silica gel chromatography, and preparative HPLC, result in losses of the compounds, are time-consuming, or are of low efficiency. High-speed countercurrent chromatography (HSCCC) is an all-liquid partition chromatographic system based on rapid partitioning of analytes between two immiscible liquid phases which works without a solid support [8], on which compounds with sugar groups can be irreversibly adsorbed [9–11]. This paper describes the separation of two triterpene glycosides from sea cucumber Pearsonothuria graeffei by high-speed countercurrent chromatography.

Experimental

Reagents

Organic solvents, including ethyl acetate, methanol, and n-butanol, were of analytical grade. Water was purified by use of a Millipore (USA) water- purification system.

Extraction of Triterpene Glycosides from Pearsonothuria graeffei

Pearsonothuria graeffei (100 g, dry weight) collected from the Philippines were crushed and extracted three times, at 70°C, with 1 L 60% ethanol. The ethanol extract was evaporated, and the residue was partitioned between n- butanol and water. The n-butanol extract was evaporated and dried to yield 12.83 g crude glycosides, of which 0.5 g was used directly for HSCCC separation.

HSCCC Separation

The HSCCC separation was conducted in a multi-layer coil planetary centri- fuge chromatograph fabricated by the Institute of Food and Biological En- gineering, Zhejiang Gongshang University, Hangzhou, China. It was equipped with a 480-mL capacity coil column made of 1.6 mm i.d. polytetrafluoroethylene (PTFE) tubing. The HSCCC separation system comprised the HSCCC instrument, a JL-5B pump (Beijing, China), an injec- tion loop, and a BS-100 fraction collector (Shanghai, China).

Unauthenticated | Downloaded 10/02/21 05:32 PM UTC Triterpene Glycosides from Sea Cucumber Pearsonothuria graeffei 271

The HSCCC solvent system was ethyl acetate–n-butanol–methanol– water 2.4:2.6:0.2:4.8 (v/v). The upper, organic, phase was used as the stationary phase and the lower, aqueous, phase as the mobile phase. After the multilayer coil column was entirely filled with the stationary phase the ap- paratus was started and adjusted to a rotation speed of 800 rpm. The HSCCC sample solution, prepared by dissolving 0.5 g of crude triterpene glycosides in 5 mL mobile phase, was injected into the HSCCC system through the sample loop by pumping mobile phase at a flow-rate of 2 mL min−1. The HSCCC elution solution was collected with a fraction collector, 10 mL for each fraction. The eluent was monitored by TLC and evaporated to dryness. The residue was dissolved in methanol for UV de- termination at 205 nm. An HSCCC chromatogram was obtained by plotting the UV data.

TLC Analysis

Thin-layer chromatography (TLC) was performed on silica gel F254 plates (Merck, Darmstadt, Germany) with chloroform–methanol–water 7:3:0.3 (v/v) as mobile phase. The triterpene glycosides were visualized by spray- ing with 15% sulfuric acid in ethanol, and subsequent heating to 110°C for 10 min.

HPLC Analysis

HPLC was performed with an Agilent (Palo Alto, USA) 1100 HPLC system, a variable-wavelength UV detector, and an ODS column (5 μm, 250 mm × 10 mm; YMC, Japan). The mobile phase was a linear gradient starting at 50% acetonitrile in 0.1% aqueous trifluoroacetic acid for 15 min and then increasing to 75% acetonitrile in 15 min. The flow rate was 1.5 mL min−1 and the detection wavelength was 205 nm.

GC–MS, ESI–MS, and NMR Analysis

1 13 H, C, and DEPT 90/135 NMR spectra were recorded in C5D5N with an Avance II 600 spectrometer. ESI–MS (positive and negative-ion modes) were obtained with a Micromass Quattro mass spectrometer. GC–MS was performed with Agilent 6890/5973i instrumentation equipped with an HP- 5 column (30 m × 0.25 mm × 0.25 μm).

Unauthenticated | Downloaded 10/02/21 05:32 PM UTC 272 Ping Dong et al.

Results and Discussion

Separation of Two Main Triterpene Glycosides by HSCCC

HPLC analysis of the crude triterpene glycosides from Pearsonothuria graeffei is shown in Fig. 2a. Peaks 2 and 5 were shown to be the two main glycosides. Several other glycosides were also present in quite low quantities (peaks 1, 3, and 4, among others). Crude glycosides from the sea cucumber Pearsonothuria graeffei (0.5 g) were separated by HSCCC using a two-phase solvent system comprising ethyl acetate–n-butanol–methanol–water 2.4:2.6:0.2:4.8 (v/v). The HSCCC separation chromatogram is illustrated in Fig. 1. Peak A was a mixture with a dark yellow spot at the origin in TLC. Peak B (compound 1) and peak C (compound 2) were colorless compounds giving dark purple spots at RF 0.21. HPLC analysis of peak B yielded a peak corresponding to peak 2 (Fig. 2b) in the chromatogram of the crude sample while peak C give a peak (Fig. 2c) corresponding to peak 5 in the chromatogram of the crude sample. The fractions corresponding peaks B and C were combined, then evaporated and lyophilized to yield 28.4 mg compound 1 and 101.3 mg compound 2, both of purity >93%.

Fig. 1. HSCCC separation of 0.5 g crude triterpene glycosides extracted from Pearsonothuria graeffei. Retention of the stationary phase was 54.6%

Unauthenticated | Downloaded 10/02/21 05:32 PM UTC Triterpene Glycosides from Sea Cucumber Pearsonothuria graeffei 273

(a)

(b)

(c) Fig. 2. HPLC analysis of (a) crude triterpene glycosides extracted from Pearsonothuria graeffei, (b) peak B in the HSCCC chromatogram, and (c) peak C in the HSCCC chromatogram

Unauthenticated | Downloaded 10/02/21 05:32 PM UTC 274 Ping Dong et al.

Confirmation of Chemical Structures

The structures of compounds 1 and 2 were confirmed by ESI–MS and 1H, 13C, and DEPT NMR spectroscopy. ESI-MS data of compound 1 revealed pseudomolecular ion peaks at m/z 1243 [M + Na]+ in positive-ion mode and at m/z 1197 [M − Na]− in negative-ion mode, suggesting a molecular weight of 1220 Daltons. Fragment ion peaks at m/z 1123 + [M − H2O − SO3Na + Na + H] in the positive-ion mode indicated the presence of one sulfate group in the glycoside. The NMR data are shown in Ta- ble I. The presence of xylose, quinovose, glucose, and 3-O-methylglucose in the ratio 1:1:1:1 was determined by acid hydrolysis with aqueous 2 M trifluoroacetic acid followed by GC–MS analysis of the corresponding per- acetylated alditols [5]. Compared with the reference data published previ- ously [12] its structure was established as holothurin A. Compound 2 + + showed ESI–MS(pos) m/z 1229 [M + Na] , 1109 [M−H2O−SO3Na+Na + H] and ESI–MS(neg) m/z 1183 [M − Na]−. The molecular weight was determined to be 1206 Daltons. According to NMR data (Table I) and analysis of the monosaccharide by GC–MS the chemical structure was confirmed to be echinoside A [13]. The chemical structures of holothurin A and echinoside A are shown in Fig. 3.

HOO O R

O O OH NaO3SO CH O 3O OH O CH OH OH 2O 1. Holothurin A, R= O O OH 2. Echinoside A, R= OH CH2OH O OCH3 OH OH

Fig. 3. Molecular structures of holothurin A and echinoside A

Unauthenticated | Downloaded 10/02/21 05:32 PM UTC Triterpene Glycosides from Sea Cucumber Pearsonothuria graeffei 275

Table I. 1H, 13C NMR, and DEPT 135/90 spectral data for holothurin A and echinoside A in C5D5N

Holothurin A Echinoside A

1H (J in Hz) 13C DEPT 1H (J in Hz) 13C DEPT

1 1.47 m; 1.87 m 36.4 CH2 1.50 m; 1.85 m 36.2 CH2

2 1.92 m; 2.09 m 27.0 CH2 1.92 m; 2.11 m 26.9 CH2 3 3.14 d (12 Hz) 88.7 CH 3.14 d (11.4 Hz) 88.6 CH 4 – 40.0 C – 39.9 C 5 1.00 d (11.4 Hz) 52.7 CH 1.00 d (10.2 Hz) 52.5 CH

6 1.54 m 21.2 CH2 1.53 m 21.1 CH2

7 1.53 m; 1.82 m 28.3 CH2 1.55 m; 1.77 m 28.2 CH2 8 3.36 m 40.9 CH 3.37 m 40.5 CH 9 – 153.8 C – 153.9 C 10 – 39.7 C – 39.6 C 11 5.63 d (4.2 Hz) 115.6 CH 5.63 d (3.6 Hz) 115.5 CH 12 5.00 m 71.5 CH 5.02 m 71.3 CH 13 – 58.8 C – 58.5 C 14 – 45.9 C – 46.3 C

15 1.84 m; 1.41 m 36.8 CH2 1.85 m; 1.44 m 36.6 CH2

16 2.41 m; 2.99 m 35.6 CH2 2.38 m; 2.69 m 35.8 CH2 17 – 89.7 C – 89.2 C 18 – 174.5 C – 174.7 C

19 1.38 s 22.5 CH3 1.39 s 22.6 CH3 20 – 86.6 C – 87.1 C

21 1.76 s 18.9 CH3 1.78 s 22.9 CH3

22 4.35 t (7.2 Hz) 80.7 CH 1.85 m 38.8 CH2

23 2.07 m 28.1 CH2 1.64 m 22.2 CH2

24 1.65 m 38.5 CH2 1.17 m 39.6 CH2 25 – 81.4 CH 1.50 m 27.9 CH

26 1.19 s 27.4 CH3 0.86 s 22.5 CH3

27 1.21 s 28.6 CH3 0.87 s 22.5 CH3

30 1.24 s 28.1 CH3 1.26 s 27.9 CH3

31 1.05 s 16.7 CH3 1.07 s 16.6 CH3

32 1.67 s 20.3 CH3 1.70 s 20.0 CH3

Xyl1 4.68 d (7.2 Hz) 105.1 CH 4.69 d (7.2 Hz) 105.1 CH

Xyl4-OSO3Na 5.10 m 75.8 CH 5.16 m 75.7 CH

Qui1 5.02 d (7.8 Hz) 105.2 CH 5.07 d (7.2 Hz) 105.3 CH

Glc1 4.96 d (7.8 Hz) 104.8 CH 4.99 d (5.4 Hz) 104.8 CH

3-OMe-Glc1 5.29 d (7.8 Hz) 105.6 CH 5.36 d (7.8 Hz) 105.6 CH

Unauthenticated | Downloaded 10/02/21 05:32 PM UTC 276 Ping Dong et al.

Conclusion

The results of these experiments revealed that high-speed countercurrent chromatography (HSCCC) was an effective method for separation and purification of triterpene glycosides from crude extracts of sea cucumber Pear- sonothuria graeffei. It can be applied to the separation of holostane glycosides from other kinds of sea cucumber used as traditional healthy foods and as medical materials for thousands of years.

Acknowledgments

This work was supported by the National Natural Science Foundation of China (NO. 30471319), Program for New Century Excellent Talents in Uni- versity (NCET-04-0642) and Open Test Fund of Ocean University of China (NO. 05009).

References

[1] V.I. Kalinin, J. Theor. Biol., 206, 151–168 (2000) [2] S.Y. Zhang, Y.H. Yi, and H.F. Tang, J. Nat. Prod., 69(10), 1492–1495 (2006) [3] R. Kumar, A.K. Chaturvedi, P.K. Shukla, and V. Lakshmi, Bioorg. Med. Chem. Lett., 17(15), 4387–4391 (2007) [4] Y. Enomoto, K. Ito, Y. Kawagoe, Y. Morio, Y. Yamasaki, Br. J. Pharmacol., 88(1), 259–267 (1986) [5] Z.R. Zou, Y.H. Yi, H.M. Wu, C.C. Liaw, and K.H. Lee, J. Nat. Prod., 66, 1055–1060 (2003) [6] S.A. Avilov, A.S. Antonov, O.A. Drozdova, V.I. Kalinin, A.I. Kalinovsky, V.A. Stonik, R. Riguera, L.A. Lenis, and C. Jiménez, J. Nat. Prod., 63, 65–71 (2000) [7] S.Y. Zhang, Y.H. Yi, H.F. Tang, L. Li, P. Sun, and J. Wu, J. Asian. Nat. Prod. Res., 8, 1–8 (2006) [8] F. Oka, H. Oka, and Y. Ito, J. Chromatogr., 538, 99 (1991) [9] Q.Z. Du, Z.H. Li, and Y. Ito, J. Chromatogr. A, 923, 271 (2001) [10] Q.Z. Du, W.J. Cai, and Y. Ito, J. Liq. Chromatogr. Related Technol., 25, 2515 (2002) [11] P .Chen and Q.Z. Du, Chin. J. Chem., 21, 979 (2003) [12] I. Kitagawa, T. Nishino, M. Kobayashi, T. Matsuno, H. Akutsu, and Y. Kyogoku, Chem. Pharm. Bull., 29(7), 1951 (1981) [13] I. Kitagawa, T. Inamoto, M. Fuchida, S. Okada, M. Kobayashi, T. Nishino, and Y. Kyogoku, Chem. Pharm. Bull., 28(5), 1651 (1980)

Unauthenticated | Downloaded 10/02/21 05:32 PM UTC