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Flavonoids from Digitalis thapsi Leaves J. de Pascual Teresa, F. Díaz, F. J. Sánchez, J. M. Hernández and M. Grande Department of Organic Chemistry, Facultad de Ciencias, Salamanca, Spain

Key Word Index: Digitalis thapsi; Scrophulariaceae; Flavonoids.

From the leaves of D. thapsi seven flavonoids have been isolated: 3,7,3'-trimethylquercetin, I, polycladin, 11, 3'-methoxicalycopterin, III, jaranol, IV, calycopterin, V, penduletin, VI and cirsimaritin, VII. Calycopterin was the only flavonol previously described in this species. Digitalis thapsi L. (Scrophulariaceae) is an endemism of the west of the Iberian Peninsula. There are some works on this plant [1—4] but recent phytochemical studies are not available. With regard to flavonoid contents, calycopterin (= thapsin), V, was the only flavonol isolated by W. KARRER from "a Spanish drug of Digitalis leaves" which was assumed to be D. thapsi [5]. As we have isolated this flavonol from classified plant material, the assumption of W. KARRER has been confirmed. The benzene extract from D. thapsi leaves (4.5 0 /o based on dry leaf wt.), was separated into neutral (35 0 /o), phenolic (59 0 /o) and acidic (6 °/o) fractions. Seven flavonoids were isolated from the phenolic fraction by chromatography and crystallization and their structures were established by spectral data. All isolated compounds show typical flavonoid bands in the IR (3400–3200, 1080–990, 1660–1635 and 1610–1490 cm- 1 ) and UV spectra. The bathochromic shift induced in the UV-spectra by AIC1 3 , NaOAc and NeOMe led us to eonclude that in all cases there are only two free hydroxyls attached at C-5 and C-4'. The PMR spectra of I, II and III show an ABX system characteristic of a 1,2,4-

trisubstituted aromatic ring (B ring), but IV, V, VI and VII show an A_B, pattern of 1,4-disubstituted aromatic ring. The main fragments in MS are those corresponding to M + , A* and deriv. (RDA) and B + . A parallelism between ions from I and IV, III and V and II, VI and Vil, can be observed in agreement with a similar substitution in ring A. The substitution pattern in ring B is clearly shown by ion B + ( m/e 151 or 121). The above data led us to identify the isolated flavonoids as: 3,7,3'-trimethylquercetin, I [6], polycladin, II [7], 3'-methoxycalycopterin, III [8], jaranol, IV [9], calycopterin, V [10], penduletin, VI [11] and cirsimaritin, VII [12]. Mp ' s and spectral data are consistent with those reported. elsewhere. Flavonols VI and V are more abundant than II and III. The remaining flavonoids are present in small amounts.

R 8 A:.

Meo

R6

II

OH 0 I II III IV -,' VI VII

R3

Rs

R8

R3 ,

OMe OMe OMe OMe OMe OMe H

H OMe OMe H OMe OMe OMe

H H OMe H OMe H H

OMe OMe OMe H H H H

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Table I MS-data of flavonoids MS (m/e, °/o) I [ M]` [M-1]" [ M-15]` [M-43][A- H]* [A-15]' [A-43]* [B]' Other ions

344 343 329 301 167

II (100) (63) (63) (74) (70)

109 (17) 151 (49) 217 (39)

III

IV 314 313 299 271 167 —

374 373 359 331

(100) (30) (78) (21)

404 (14) — 389 (24) —

181 153 151 167

(40) (7C) (98) (55)

211 (27) 183 (46) 151 (100) —

Because of their structure, these flavonfrom D. thapsi may be effective as inhibitors of blood cell agregation [13]. Mp's were measured in a Kofler and are uncorrected. PMR were measured in DMSO-de at 60 MHz with TMS as an internal standard. MS were measured at 180° and 70 eV. Extraction and purification. — The plant was collected near Mesegar de Corneja, Avila (Spain) and a voucher specimen (nr. 4208) deposited at the Herbarium of the Department of Botany, Salamanca University. The air dried leaves (700 g) were powdered and ethanol. The benzene extract in ether was treated with 5°/o NaOH. After evaporation, and extracted with benzene (r. t., 24 h, 3 times) the ethereal phase gave a neutral fraction (9.68 g, 35 °/o). The alkaline solution was neutralized with CO, and extracted with ether to yield a phenolic fraction (16.26 g, 59°/o). By acidulation of the aqueous phase, an acidic fraction (1.63 g, 6°/s) was isolated. The phenolic fraction was chromatographed on a dry silicagel column with benzene/EtOAc 7/3 (system A). Each fraction of this chromatography was purified by further crystallization andlor preparative CC or TLC with the lower phase of CHCI 3/MeOH/H 2 O 95/4/1 (system B) to give pure flavonoids I—VII.

oids

Acknowledgement We thank Prof. B. CASASECA, Dept. of Botany, Salamanca University, for the classification of the plant.

(100) (88) (8) (68) (42)

121 (78) 187 (43)

V

VI

374 (10)

344 343 329 301 197 181 153 121 —

359 (13)

211 183 121 161

(21) (41) (100) (44)

VII (100) (48) (57) (43) (7) (7) (12) (19)

314 313 299 271 — 181 153 121 119

(73) (18) (77) (44) (35) (100) (19) (37)

References 1. Costa Novella, E. and V. Sanchez Lozano: An. Quím., 48B, 893 (1952); Ibid., 50B, 315, 679 (1954). 2. Lorenz Gil, A., A. Casas and E. Primo Yufera: An. Quím., 54B, 761 (1958). 3. Arroyo, J., L. Carreras and C. Gonzalez: Farmacognosia (Madrid), 22, 125 (1962). 4. Zambalamberi, B., L. San Roman and M. Gomez Serranillos: Galenica Acta (Madrid), 23, 97 (1970). 5. Karrer, W.: Helv. Chico. Acta, 17, 1560 (1934). 6. Valesi, A. G., E. Rodriguez, G. Vander Velde and T. J. Mabry: Phytochemistry, 11, 2821 (1972). 7. Shen, M. C., E. Rodriguez, K. Kerr and T. J. Mabry: Phytochemistry, 15, 1045 (1976). 8. Rama, A. V. and M. Varadan: Indian J. Chem. 11, 403 (1973). 9. Pascual Teresa, J. de, C. P. Marcos and I. S. Bellido: An. Quím., 64B, 623 (1966). 10. Rodriguez, E., G. Vander Velde, T. J. Mabry, S. Sankara Subramanian and A. G. R. Nair: Phytochemistry, 11, 2311 (1972). 11. Rodriguez, E., N. J. Carman and G. Vander Velde: Phytochemistry, 11, 3509 (1972). 12. Brieskorn, C. H. and W. Biechele: Tetrahedron Letters, 2603, 1969. 13. McClure, J. W. in J. B. Harborne, T. J. Mabry and H. Mabry (eds.): The Flavonoids, p. 970. London, 1975, Chapman and Hall. Address: Prof. Dr. J. de Pascual Teresa, Departamento de Química Orgánica, Facultad de Ciencias, Universidad de Salamanca, Spain