J. Serb. Chem. Soc. 70 (2) 171–175 (2005) UDC " alpina": 547.473:661.183.7 JSCS – 3260 Note

NOTE On the occurrence of sonchuside A in and its chemosystematic significance

CHRISTIAN ZIDORN1*,RITAE.SCHWAHA1, ERNST P. ELLMERER2 and HERMANN STUPPNER1

1Institut für Pharmazie, Abteilung für Pharmakognosie, Universität Innsbruck, Josef-Moeller-Haus, Innrain 52, A-6020 Innsbruck (e-mail: [email protected]) and 2Institut für Organische Chemie, Universität Innsbruck, Innrain 52a, A-6020 Innsbruck, Austria

(Received 3 February, revised 10 June 2004)

Abstract: The subaerial parts of Cicerbita alpina yielded the guaianolide 8-ace- tyl-15b-D-glucopyranosyllactucin (1) and the germacranolide Sonchuside A (2). The sonchuside A is reported for the first time from the Cicerbita. 1H-NMR and 13C NMR data of compounds 1 and 2 measured in deuterodimethyl sulfoxide and deuteromethanol, respectively, are given and the chemosystematic implications of the occurrence of sonchuside A in C. alpina are discussed briefly.

Keywords: Cicerbita alpina (L.) Wallr., Lactuceae, , sonchuside A, ses- quiterpene lactones, chemosystematics.

INTRODUCTION The Lactuceae tribe of the Asteraceae family is a rich source of sesquiterpene lactones. Cicerbita alpina (L.) Wallr., a member of the subtribe Lactucinae1 has so far yielded 11b,13-dihydrolactucin,2 8-acetyl-15b-D-glucopyranosyllactucin,2 8-ace- tyllactucin,3 8-acetyl-11b,13-dihydrolactucin,3 and lactucin.3 In the present com- munication, the isolation of sonchuside A (Scheme 1), the first non-guaiane type sesquiterpene lactone isolated from the genus Cicerbita, is reported.

RESULTS AND DISCUSSION

8-Acetyl-15b-D-glucopyranosyllactucin (1) and sonchuside A (2) were isolated from the methanolic extract of air-dried and ground subaerial parts of Cicerbita alpina employing silica gel column chromatography (CC) and Sephadex LH-20 CC.

* Author to whom correspondence should be addressed. Tel.: +43-512-507-5302; fax: +43-512 -507-2939.

171 172 ZIDORN et al.

Scheme 1. Structures of 8-acetyl-15b-D-glucopyranosyllactucin (1) and sonchuside A (2). The structures were elucidated by comparing the obtained ESI MS, 1D NMR, and 2D NMR data with those given in the literature.2,4,5 As the published NMR data for both compounds were obtained using pyridine-d5 as the solvent, the NMR data measured in DMSO-d6 and methanol-d4 for compounds 1 and 2 respectively, are given in Table I.

TABLE I. NMR data of 8-acetyl-15b-D-glucopyranosyllactucin (1)a and sonchuside A (2).b 12 Position 1H-NMR 13C-NMR 1H-NMR 13C-NMR Sesquiterpene moiety 1 132.7 4.89 1H, m* 125.9 2 194.1 2.39 2H, m* 33.9 36.601H,br s 133.4 4.49 1H, t (8.0) 84.4 4 169.5 141.4 53.971H,m* 47.6c 4.89 1H, m* 128.2 63.971H,m* 80.2 4.81 1H, m* 82.6 73.531H,m 52.8c 1.70 1H, m* 55.5 84.871H,m 68.8 1.85 1H, m 29.3 1.71 1H, m* SONCHUSIDE A 173

TABLE I. Continued

12 Position 1H-NMR 13C-NMR 1H-NMR 13C-NMR 92.851H,dd (13.0, 12.0) 43.5 2.35 1H, m* 42.2 2.34 1H, dd (13.0, 2.0) 2.03 1H, m 10 145.0 138.9 11 136.5 2.37 1H, m* 43.2 12 168.1 181.3 1.21 3H, d 13 6.04 1H, d (3.0) 120.9 13.3 (7.0) 5.67 1H, d (3.0) 14 2.13 3H, br s 20.8 1.51 3H, s 16.6 1.76 3H, d 15 4.66 2H, dd (10.0, 1.5) 67.8 12.2 (1.0) Glucose moiety 4.22 1H, d 1’ 4.26 1H, d (7.5) 102.8 102.5 (7.5) 2’ 3.04 1H, m* 73.5 3.25 1H, m* 75.1 3’ 3.15 1H, m* 76.8 3.34 1H, m* 77.9 4’ 3.12 1H, m* 69.9 3.27 1H, m* 71.6 5’ 3.15 1H, m* 76.4 3.27 1H, m* 77.9 3.88 1H, dd 6’ 3.69 1H, dd (12.0, 3.5) 60.9 62.6 (12.0, 2.0) 3.67 1H, dd 3.46 1H, dd (12.0, 5.5) (12.0, 5.5) Acetyl moiety 1” 169.6 2” 2.34 3H, s 20.7 a 1 Measured in DMSO-d6 and referenced to solvent residual and solvent signals at 2.50 ppm ( H) and 13 b 39.5 ppm ( C), respectively. Measured in methanol-d4 and referenced to solvent residual and sol- vent signals at 3.31 ppm (1H) and 49.0 ppm (13C), respectively. All signal assignments are based on HSQC and HMBC experiments. cSignal assignments for carbons 5 and 7 were obviously exchanged in the original publicaiton.2*Overlapping signals. This is the first report of the isolation of sonchuside A from C. alpina.Asall sesquiterpene lactones isolated previously from the genus Cicerbita belong to the guaiane type, the germacrane derivative sonchuside A is also the first non-guaiane type sesquiterpene lactone derivative reported for this genus. 174 ZIDORN et al.

8-Acetyl-15b-D-glucopyranosyllactucin (1) has been reported exclusively from Cicerbita alpina.2,3 In contrast, sonchuside A(2) has been reported from nine different sources: endivia L.6 Cichorium intybus L.,6–8 Crepidiastrum lanceolatum Nakai,9 Hypochaeris radicata L.,10 tatarica C.A. Mey.,11 Notoseris triflora (Hemsl.) C. Shih,12 Sonchus oleraceus L.,4 Taraxacum bicorne Dahlst.,13 and Tara- xacum obovatum DC.14 Notably, all the listed species belong to the Lactuceae tribe of the Asteraceae family.1 However, sonchuside A does not seem to be a suitable chemosystematic marker for one of the eleven subtribes of the Lactuceae erected by Bremer,1 because the compound occurs a) in Cichorium, which is not assigned to a subtribe, b) the Lactucinae genera Lactuca and Notoseris, c) the Crepidinae genera Crepidiastrum and Taraxacum, d) the genus Hypochaeris (subtribe Hypochaeridinae), and e) the genus Sonchus (subtribe Sonchinae). On the other hand, sonchuside A (2) might be an interesting compound to identify infraspecific taxa within C. alpina. Djordjevi} et al.3 isolated five lactucin derivatives in a recent investigation of C. alpina from Montenegro, but were not able to detect sonchuside A. In contrast, sonchuside A was one of the main compounds in the plant material from the Tyrolean Alps. To corroborate the assumption that C. alpina occurs in different chemotypes within its area of distribution, further comparative investigations of extracts from dif- ferent geographic origins have to be performed.

EXPERIMENTAL Plant material C. alpina was collected in August 2002 at the Zillertaler Höhenfahrweg S the Talbach brook/Schwaz/Tyrol/Austria at an altitude of 1900 m a.m.s.l. [coordinates (WGS84): N 47°14’12”; E 11°49’41”]. A voucher specimen (code: CZ-20020822C-1) is deposited in the herbarium of the Institut für Pharmazie, Abt. Pharmakognosie. Extraction and isolation Air-dried subaerial parts (690 g) of C. alpina were ground and extracted exhaustively with MeOH. The extract was dried in vacuo (134 g), re-dissolved in a mixture of MeOH/H2O (1/1, v/v) and successively partitioned with petroleum ether and EtOAc. The EtOAc layer was dried in vacuo, yielding 9.71 g of dry matter. This was fractionated by silica gel CC using a gradient of petroleum ether/CH2Cl2 and MeOH with increasing polarities, resulting in fifteen fractions. Fraction IX (1.82 g) was partially dissolved in 5 ml of MeOH and further fractionated by Sephadex LH-20 CC using MeOH as an eluant. The un-dissolved residue was washed three times with 5 ml of cold MeOH, yielding 476 mg of compound 1. Sephadex LH-20 CC fractions containing compound 2 were finally purified by silica gel CC using a gradient of CH2Cl2, yielding 98.2 mg of compound 2.20mg aliquots of the pure compounds were dissolved in DMSO-d6 (1) and MeOH-d4 (2), respectively, and their NMR spectra were measured on a Bruker Advance 300 spectrometer at 300 MHz (1H) and 75 MHz (13C). ESI mass spectra of 1 and 2 were measured in the positive mode on a Finnigan SSQ 7000 (quadrupole MS) mass spectrometer employing a CID value of 0, a corona amperage of 5 mA, a sheath gas pressure of 65 psi, and a vaporizer temperature of 400 °C. Acknowledgements: The authors wish to thank M. Dobner, M. Ganzera, and R. Spitaler (Innsbruck, Austria) for helping collect the plant material, M. Ganzera (Innsbruck, Austria) for the MS measurements and the Austrian Science Fund (FWF, project P15594) for financial support. SONCHUSIDE A 175

IZVOD

O POJAVI SONHUZIDA A U Cicerbita alpina I WENOM HEMOSISTEMATI^KOM ZNA^EWU

1 1 2 1 CHRISTIAN ZIDORN ,RITAE.SCHWAHA , ERNST P. ELLMERER i HERMANN STUPPNER 1 Institut für Pharmazie, Abteilung für Pharmakognosie, Universität Innsbruck, Josef-Moeller-Haus, Innrain 52, A-6020 Innsbruck (e-mail: [email protected]) and 2Institut für Organische Chemie, Universität Innsbruck, Innrain 52a, A-6020 Innsbruck, Austria

U nadzemnim delovima biqke Cicerbita alpina na|en je gvajanolid 8-acetil-15b-D-glu- kopiranozillaktucin (1) i germakranolid sonhuzid A (2). Sonhuzid A je prvi put na|en u rodu Cicerbita. Dati su 1H-NMR i 13C-NMR podaci za jediwewa 1 i 2 dobijeni u deutero-dimetil-sulfoksidu, odnosno deutero-metanolu i ukratko diskutovane hemo- sistemati~ke implikacije pojave sonhuzida u C. alpina. (Primqeno 3. februara, revidirano 10. juna 2004)

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