COMPLETA ASIGNACIÓN DE LOS ESPECTROS DE 'H Y '3C RMN DE DOS GUAYANOLIDAS CONOCIDAS AISLADAS DE Centaurea niusimomum

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1 REVISTA COLOMBIANA DE QUÍMICA, VOLUMEN 32, No. DE 2003 COMPLETA ASIGNACIÓN DE LOS ESPECTROS DE 'H Y '3C RMN DE DOS GUAYANOLIDAS CONOCIDAS AISLADAS DE Centaurea niusimomum COMPLETE ASSIGNMENT OF THE '^C AND 'H NMR SPECTRA OF TWO KNOWN GUAIANOLIDES ISOLATED FROM Centaurea niusimomum K. Medjroubi', F. Benayachel', F. León"" J. Bermejo" Recibido: 02/05/03 - Aceptado: 30/06/03 RESUMEN Se complementan los datos espectroscópicos de dos guayanolidas conocidas aisladas de C. musimomum por 'H, "C y 2D RMN (HSQC, HMBC, 'H-'H COSY). Palabras clave: Centaurea musimomum, guayanolidas, 'H RMN, 'X RMN, 2DRMN. ABSTRACT Complementary 'H, '^C and 2D NMR (HSQC, HMBC, 'H-'H COSY) spectroscopic data are provided for two known guaianolides. Key words: Centaurea musimomum, guaianolides, 'HRMN, "CRMN, 2DRMN. INTRODUCTION Sesquiterpene lactones are part of a biologically active group of substances found in several plant families, most notably the Compositae which have yielded over 3000 structures. Their biological activity is increasingly appreciated - a recent detailed studies (,2) have singled out several lactones with useful anthelmintic, antibiotic, allergenic and, above all, cytotoxic properties. One particular series of lactones with marked inhibitory action on the cell growth of many types of tumour (3) has been identified from among the antineoplastic agents obtained from plants (4). Sesquiterpene lactones irrítate the nose, eyes and gastrointestinal tract. Sheep and goats are the main livestock Department de Chimie, Faculté des Sciences, Universilé de Constantine. Route de Aín El Bey Constantine Algérie. Instituto Universitario de Bio-Orgánica "Antonio González''-Instituto de Producios Naturales y Agrobiología C.S.l.C, Iji Laguna, Tenerife. España. Instituto Canario de Investigación del Cáncer. La Laguna, Tenerife, España. 7

2 REVISTA COLOMBIANA DE QUÍMICA, VOLUMEN 32, No. DE 2003 species affected (5), primarily because the plants are unpalatable and therefore rarely consumed in toxic quantities by cattíe and horses. The toxicity of sesquiterpene lactones is due to the binding of the exocyclic methylene group with tissue constituents, such as sulphydril groups and other nucleophilic components (6). One and two-dimensional NMR data are given for two known guaianolides from Centaurea musimomum (7,8) to supplement the Information already available for these two compounds. EXPERIMENTAL General Experimental Procedures 'H and '^c NMR spectra were taken on a Bruker AMX-500 spectrometer with standard pulse sequences, operating at 500 MHZ for 'H and 25 MHZ for '^c. CDCLS Figure. Correlations for compound, a) 'H-'H COSY; b) HMBC (arrows '^C-'H). 8

3 REVISTA COLOMBIANA DE QUÍMICA, VOLUMEN 32, No. DE 2003 was used as solvent and TMS as internal standard. Plant Material Centaurea musimomum was collected in the Souk-Ahras área in the East of Algería in June 992. It was identified by Dr Nadra Khalfallah and deposited in the herbarium of Research Unit of Chemistry, University of Constantine. Extraction and Isolation Air-dried powdered aerial parts (50 g) were soaked in MeOH (2 L). The MeOH extract was evaporated and the residue dissolved in H2O (00 ml). The solvent was treated with Pb(oAc). After 3 min centrifugation, the mixture was filtered and the yellow-coloured fíltrate extracted with CHCI3 (3 X 50 mi). The extract was concentred in vacuo at room temp, the residue weighing 6 g. A part of this residue (3 g) was separated by CC (silica gel mesh) using solvent mixtures (CHCI3- Me2C0) with increasing polarities. The fraction was divided into nine crude ones. Fractions 3 (20 mg) and 8 (80 mg) were studied. Fraction 3 on rechromatography on sílica gel using solvent mixtures (hexane- Et20-Me2CO) with increasing polarities gave 2 (70.2 mg) and fraction 8 on rechromatography on a sílica gel column with CHCls-hexane Et OAc, :: gave (6. mg). Spectral data for compounds I and 2: 4^, 5-Dihydro-3-dehydrosolstitialin A (). Crystals, mp (54-56 ); \aw^ 4-45 (CHCL3, c 0.04); IR v ax 3400, 770, 730,and 640 cm'; EI-MS: 280 [M]+ (Ci5 H20 05) 'H and '^c NMR data, see Table. 4^,5-Dihydro-3-dehydrosolstitialin A monoacetate (2)". Crystals, mp (43-44 ); [ajo" +25 (CHCL3, c 0.); IR Vrnax 340, 770, 720, and 640 cm'; EI-MS: 322 [M]+ (C,7H2206) 'H and '^C NMR data, see Table. RESULTS AND DISCUSSION The '^c NMR, DEPT and mass spectra of and 2 showed 5 and 7 carbón signáis, respectively, indicating molecular formula C5H20O5 and C7H22O6. Complete 'H and '^c connectivity was established by extensive use and interpretation of 2D ('H-'H) COSY, HSQC (one bond '^C-'H correlation) and HMBC (long-range '^C-'H correlations) NMR spectra (Table ) The arrangement of the functional groups and the full structures of and 2 were attributed from the 'H-'H COSY spectrum of in which the following 8H/H (ppm) correlations were observed (Figure ): H-la (3.09) with H-2P (2.52), H-2a (2.56) and H-5a (2.28); H-4(3 (2.32) with CH3-5a (.26) and H-5a; H-5a with H-la and H-6P (4.5); H-6p with H-5a, H-7a (2.63); H-7a with H-8a (.56); H-3a (3.77) with H-3b (3.83). The functional groups in were confirmed by HMBC data (Figure ), the important correlations being between c-3 ( ) and H-la, H-5a, H2-2; between c-5 (5 5.40) and H-la, H-4p, H-7a, 9

4 REVISTA COLOMBIANA DE QUÍMICA, VOLUMEN 32, No DE 2003 Table. 'H and 'C NMR chemical shifts for and 2 including 'C-'H Long-Range correlations"'' I Position ñc ÓH (mult.) HMBC (C^H) 2 5c SH (mult.) HMBC (C^H) lo ddd ( ) H2-2. H-5, H> ddd (8.3, ) H2-2. H-5. H2-I4 2a dd (9. 7.8) H-l. H dd (9. 7.8) H-l, H-4. H-5 2P 2.52 dd (9. 3.6) 2.49 dd (9, 3.4) H2-2, H-4. H-5, Me H-l. H2-2. H-4. H-5. Me-5 4( m H2-2, H-6, Me m H-6. H2-8, Me-5 5a t. br (8.5) H-l. H-4. H-7. Me brt (8.3) H-l, H-4. H-7. Me dd( ) H-7. H dd (0. 8.3) H-5. H-7. H2-8 7a m H-6, H2-8. H2-I m H-6. H2-8. H2-I3 8ax dq (2.7,5.) H-6, H2-9, H> m H-6. H2-9, H2-I4 8eq 2.22 m 2.9 m 9ax m H-l, H-7, H2-8, H2-I m H-l. H-7. H2-8, H2-4 9eq 2.65 m 2.57 m H-l. H-5. H2-8, H:-9. H2-I H-l, H2-8, H2-9, H2-I H-7, H2-I H-7, H2-I H2-I a 3b d (.2) 3.83 d (.2) H d (.5) 4. d(.5) H-7 4a 4b s 4.99 s H-l.H: d (3.7) 4.62 d (3.7) H-l. H2-9 5 c=o d (7.) H-4. H d (6.8) H-4, H-5 H2-I3. Me-7. Actyl-Me s Assignments canfirmed by decoupling. 'H-'H COSY. HSQC and HMBC spectra. J value.s are given in Hz. 20

5 REVISTA COLOMBIANA DE QUÍMICA, VOLUMEN 32, No DE 2003 H3-5; between c- ( ) and H2-I3, H-7a; between c-2 and H2-3; and between c-3 (63.2) and H-7a. We definitively determined the structure of by X-ray analysis (7). These signáis show certain similarities to those of the monoacetyl derivative 2 (Table ), the structure of which was obtained on the basis of its 2D NMR spectrum. Compound 2 was previously described by Herz et al. (8,9) on the basis of 'H and "c NMR spectra and x ray analysis. We observed that the assignments of c- and c-4 given by those authors were interchanged with respect to those found by US for compound 2. HMBC spectrum (Figure 2) shown important correlations between c- (5 39,52) and H2-4, between c-4 (8 47,06) and H3-I5. (Figure 2). ACKNOWLEDGMENT This research was supported by FEDER grant No. FD (J.B.B and F.L) REFERENCES. Danierwiski W., Kocoz M. and Zoltowska B. (995). Structure oflactarorufín B and Activity. Bull. Acad. Pol. Sci., Schmidt T. J. (999), Toxic activities of sesquiterpene lactones: Structural and biochemical aspects. Current Organic Chemistry, 3(6), Kupchan S. M.; Hemingway J. C, Cassady T. M. and Knox J. R. (967), Isolation and structural elu- *...*. -. * a VÍ"".«-! «0 0 0 T I. ; : i i ' - M n 09., «-rr -^ I i 0 f ; Figure 2. HMBC (long-range '^C-'H correlations) spectrum of compound 2. 2

6 REVISTA COLOMBIANA DE QUÍMICA, VOLUMEN 32, No DE 2003 cidetion ofeuparotin acétate, a novel guaianolide tumor inhibitor from Eupatoriam rotundifolium. J. Am. Chem. Soc, 89 (465). 4. Mitchell J. C; Friting B.; Singh B. and Towers G. H. N. (970). Allergic contad dermatitis from Frullania and Compositae. The role of sesquiterpene lactones. / investig. Dermatol Elissalde M. H.; Ivie, G. W.; Rowe L. D. and Elissalde G. S. (983) Considerations of the structure of sesquiterpene lactones on biological activity: influence of the amethyle - ne-y-lactone moiety on mast cell degranulation. Am. J. Vet. Res., 44 (894). 6. Lee K. H.; May I. H.; Mar E. C; StamesC. O.; Elgebaly S. A.; Waddell T. G.; Hadgraft R. L; Ruffner C. G. and Weider I. (977) Sesquiterpene antitumor agents: inhibitors of cellular metabolism Science, 96, (533). 7. González-Platas J.; Ruiz-Pérez C; González A. G.; Bermejo J. and Medjroubi K. (999) Acta Cryst., 4p,5-dihydro-3-dehydrosolstitialin A, 055(837). 8. Óksüz S.; Clark R. J. and Herz W. (993) A guaianolide dial monoacetate from Centaurea beben and C solstitialis ssp, Schouwii. Phytochemistry, 33(5), Bruno M.; Diaz J. G.; Herz W. (99). Guaianolides and lignans from Centaurea solstitialis subsp schouwii. Phytochemistry, 30 (2):