Sesquiterpene lactones from Lactuca saligna

Phytochemistry,Vol. 34, No. 6, pp. 1644-1646, 1993

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Printed in Great Britain.

SESQUITERPENE LACTONES FROM LACTUCA W. Department of Phytochemistry,

KISIEL*

and D.

003 l-9422/93 $6.00 + 0.00 1993 Pergamon Press Ltd

SALIGNA

GROMEK

Institute of Pharmacology, Polish Academy of Sciences, 31-343 Krakbw, Poland (Received in revisedform 10 June 1993)

Key Word Index-Lmtuca

Abstract-In

saligna; Asteraceae; Lactuceae; sesquiterpene &tones; glycosides; salignoside.

addition to known compounds, salignoside (a new guaianolide glycoside) was isolated from the roots of

Luctuca saligna and its structure was determined on the basis of spectral and hydrolytic studies.

INTRODUCTION

The aerial parts of Luctucu saligna L. reportedly [l] contain lactucin (4) and lactucopicrin (5) together with 1l/$13-dihydrolactucopicrin (6), but there is no information on the root constituents. In the present paper we describe isolation from the roots of the known sesquiterpene lactones l-8 and 10,and the structure detetmination of a new sesquiterpene lactone glycoside 9, named salignoside, which is a minor component of the plant. RESULTS AND DISCUSSION

Rb

1

a

3

R’

H

H

Glc

4 H

5 H

6 H

R*

Ii

H

Ii

OH

A

A

X

CH,

~,ar~e

?i,aMe

CH2

(332

H,aMe

The ethanol extract of the roots of Lactuca saligna was repeatedly chromatographed as described in the Experi0 mental to afford a sesquiterpene lactone glycoside frac-+0H tion and five aglycones identified as 8-deoxylactucin (1) A: -o-c-c& [2], jacquinelin (2) [3], lactucin (4) [2, 4, 51, lactucopicrin (5) [2,4, 51 and 11/$13-dihydrolactucopicrin (6) [6]. With the exception of 6, they were identified by direct comparison with authentic samples. Compound 6 was characterized by comparing its spectral data (MS, ‘H NMR) with those reported in the literature [6]. The sesquiterpene lactone glycoside fraction showed two major spots on TLC and was found to consist of five compounds after HPLC separation. Separation of the less polar glycosides yielded lactuside A (10)[7] and crepidiaside B (3) [S], the former being the main compon10 9 8 7 ent of the roots. The two glycosides and their aglycones H Glc R’ Glc were identified with authentic samples. H Glc R* H Compounds 7-9 were isolated from the more polar H.aMe glycoside mixture. The very similar ‘HNMR spectra X CH2 H,aMc indicated the presence of a series of closely related Compound 8 was identified as ixerin F by comparison compounds. The molecular mass and fragmentation patwith an authentic sample [9], while the ‘HNMR spectern of each compound were established by FAB mass trum of 7 coincided with the less detailed 90 MHz spectrometry in the positive ion mode: m/z 447 [M spectrum reported for macrocliniside A [lo]. As the +Na]+ and m/z 285 [M+Na162]+ for 7; m/z 449 [M ‘HNMR data for 7 and 8 in the literature are not +Na]+ and m/z 287 [M+Na-162]+ for 8 and 9. complete, they are listed in Table 1. The mass spectra of 8 and 9 indicated the same *Author to whom correspondence should be addressed. molecular formulae, C,,H,,O, and C,,H,,O,, for the

”

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Short Reports Table 1. ‘HNMR

data of 7-9 (in pyridine-d,, TMS as int. standard, S-values)

H

7 (300 MHz)

1 2

3.66 2.19 2.43 4.88 2.96 4.25 3.41 1.59 248 4.81

2’ 3

5 6 7 8 8’ 9 11 13 13 14 14’

br q dt dt br t br t t m ddd ddd t

9 (500MHz)

br q dt

3.74 br q 2.06 dt 252-2.61 m* 4.80 br t 2.79 br t 4.10 t 2.52-2.61 m* 1.42 ddd

3.67 218 2.44 4.88 2.94 4.19 2.50 1.50 2.32 4.79 2.31

dt

br t br t t dddd ddd ddd

br t dq

5.42 d 6.25 d

1.20 d

5.15 s

5.14 9

5.56 br s 15’ 5.96 br s Glucose moiety 1 5.07 d 2 4.10 br t 3 4.27 m 4 5 3.97 m 6 4.40 dd 6’ 4.56 dd

15

8 (300 MHz)

2.52-2.61 m* 4.86 t 2.30 dq 1.24d

5.96 br d

5.09brs 5.27br s 5.48br d 5.49 br d

4.96 d 4.11 br t

4.97 d 4.09 br t

4.27 m

4.28 m

3.98 m 4.40 dd 4.58 dd

3.92m 4.39 dd 4.53 dd

5.53 br d

*Overlapped signals, intensity of 3H. J(Hz)7: 1,2=2,3=6.3; 1,2’=2’,3=8.7; 1,5=5,6=6,7=9.8;2,2’ =14; 7,8=11; 7,8’=4; 7,13=3.1; 7,13’=3.5; 8,9=8’,9=3.5; 8,8’ =ls; 8: 1,2=2,3=6.8; 1,2’=2’,3=8.4; l&5=5,6=6,7=9.6; 2,2 =13.8;7,8=11;7,8’=4;7,11=12;8,9=8’,9=3.4;8,8’=1~ 11,13 =7; 9: 1,2=2,3=6& 1,2‘=2’,3=8.7; 1,5=5,6=6,7=9.5; 52 =13.8; 7,8=11; 7,11=12; 8,9=8’,9=3.5; 8,8‘=14; X1,13=7; glucose moiety: 1,2=7.8; 5,6=5.4; 5,6‘=2~ 6,6’=12.

compounds and their aglycones, respectively. The “H NMR spectra of 8 and 9 (Table 1) suggested that the difference between the two compounds might only involve the position of attachment ofa sugar unit. This was established by enzymatic hydrolysis which in each case yielded glucose and the same aglycone, which was identified as 9a-hydroxy-11~,13-~ydro~lu~nin C by comparison with an authentic sample. The p-linkage of the glucose moiety was deduced from the coupling constant (J=7.8 Hz) of the anomeric proton signal. Thus, the structure of salignoside was determined as 9a-hydroxy11/?,13-dihydrozaluzanin C-9-O-B-D-glucopyranoside. In addition to the sesquiterpene lactone glycosides, the polar fraction contained benzyl glucoside, which showed the ‘HNMR spectrum identical to that published earlier [ll]. EXPEUIMENTAL Gene& procedure. Merck silica gel was used for CC (Art. 7754), flash CC (Art. 93851, prep. TLC (Art. 5717) and TLC (Art. 5554). Semiprep. HPLC was performed on

1645

a Delta-Pak C 18 cartridge column (particle size 15 pm, 25 x 100 mm), coupled to a UV photodiode array detector. Sesquiterpene lactones and their glycosides isolated previously in this laboratory were used as authentic samples for comparing their physicochemical and spectral data (mmp, IR, ‘HNMR) with those of the known compounds. Plant ~[~a~. Roots of L. salignu were collected in August 1989 from plants growing in the Garden of Medicinal Plants of the Institute of Pharmacology, Polish Academy of Sciences, Krakbw, where a voucher specimen was deposited. Extraction and isolation of compounds. Fresh roots (750 g) were exhaustively extracted with EtOH at room temp. After removal of the solvent, the residue (21 g) was chromatographed on a silica gel column, packed in C,H, using C,H,-EtOAc, followed by CHCl,-MeOH gradient solvent systems, all frs having been monitored by TLC and grouped according to their homogeneity. Elution of the column with C,H,-EtOAc (8 : 2) gave a mixt. of 1 and 2 (84.5 mg), and 5 (2.2 mg) and a mixt. of 5 and 6 (8 mg), rich in 6, successively. Corn~un~ 1 and 2 were sepd as acetates by prep. TLC feluent C,H,-CH,C&Et,O, 2 : 2 : 1). Compounds 5 and 6 were purified by CC on silica gel (eluent C,H,-EtOAc, 85: 15). Elution with C,H,-EtOAc (1: 1) afforded 4 (15 mg) after purification by CC on silica gel, using C,H,-EtOAc (65: 35) as a solvent system. Elution with CHCl,-MeOH (95 : 5) yielded benzyl glucoside (2.7 mg), which was sepd by flash CC on silica gel (eluent CHCl,-MeOH, 9: 1) and was then purified by HPLC (R,=22.45 min, eluent MeOH-H,O, 35:65, flow rate: 5 ml min-‘f. Further elution with CHCl,-MeOH (95: 5 and 9: 1) resulted in sepn of 10 (186 mg) from a complex mixt. (1.48 g) of glycoside constituent. The com~und was purified by CC on silica gel (eluent CHCl,-MeOH, 97: 3). Part of the glycoside mixt. (415 mg) was rechromatographed on a silica gel column, eluted with a CHCl,-MeOH gradient solvent system, to give frs A and B containing less polar sesquiterpene lactone glycosides (10 mg) and more polar ones (43.6 mg), respectively. After HPLC sepn (MeOH-H,O, 1: 1, flow rate: 5 ml min-‘), the former yielded 3 (R, = 18.66 min, 1.1 mg) and an additional amount of 10 (R,= 13.98 min, 3.3 mg). The latter afforded 9 (R,= 17.96 min, 1.7 mg), 8 (&=27.47 min, 13.3 mg) and 7 (R,=32.99min, 7.2mg) by HPLC [MeOH-H,O, 35: 65, flow rate: 4 ml min- ’ (O-20 min), 6.5 ml min- ’ (20-40 min)]. The isolation procedure of the glycoside mixt. was repeated. Salignoside (9). Colourless solid; IR 6:: cm-‘: 3400, 1760, FAB-MS (positive ion mode, glycerol as a matrix) m/z: 449 [M+Na]+, 287 [M+Na-162]+; “HNMR is listed in Table 1. Enzymatic hydrolysis. A mixt. of glycosides 3 or 7-10 (ca. 3 mg) and the commercial /3-glucosidase (Sigma) in aq. acetate buffer soln (pH 5.0) was incubated at 37”. After the reaction was completed, the mixt. was extracted with CHCl,. Evapn of the solvent yielded an aglycone for each compound. From the H,O layer, glucose was detected by TLC.

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Acknowledgement-Financial support to this work by grant No. 4 0254 91 01 from the Committee for Scientific Research (KBN) is gratefully acknowledged. REFERENCES

1. Khalil, A. T., Abd El-fattah, H. and Mansour, E. S. (1991) Planta Med. 57, 190. 2. Pyrek, J. S. (1977) Rocz. Chem. 51, 2165. 3. Barrera, J. B., Breton-Funes, J. L. and Gonzalez, A. G. (1966) J. Chem. Sot. (C) 1298. 4. Schenk, G., Graf, H. and Schreber, W. (1939) Arch. Pharm. Deutsch 277, 137. 5. Gromek, D. (1989) Pol. J. Chem. 63, 297. 6. Beek, T. A., Maas, P., King, B. M., Leclercq, E.,

Reports Voragen, A. G. J. and Groot, A. (1990) J. Agric. Food Chem. 38, 1035. 7. Nishimura, K., Miyase, T., Ueno, A., Noro, T., Kuroyanagi, M. and Fukushima, S. (1986) Phytochemistry 25, 2375. 8. Adegawa, S., Miyase,

Kuroyanagi,

T., Ueno, A., Noro, T., M. and Fukushima, S. (1985) Chem.

Pharm. Bull. 33, 4906. 9. Asada, H., Miyase, T. and Fukushima, Chem. Pharm. Bull. 32, 3036.

S. (1984)

10. Miyase, T., Yamaki, K. and Fukushima,

S. (1984)

Chem. Pharm. Bull. 32, 3912. 11.

Miyase, T., Ueno, A., Takizawa, N., Kobayashi, H. and Karasawa, H. (1987) Chem. Pharm. Bull. 35,1109.