Boletín de la Sociedad Chilena de Química
versión impresa ISSN 0366-1644
Bol. Soc. Chil. Quím. v.46 n.1 Concepción mar. 2001
BENZODIHYDROFURANS IN THE RESINOUS EXUDATE
FROM DIPLOSTEPHIUM CINEREUM
1Laboratory of Chemical Ecology,, Faculty of Chemistry and Biology, University of Santiago
of Chile, Casilla 40, Correo 33, Santiago, Chile;
2Centro Chimica dei Riccetori C.N.R., Universita Cattolica del Sacro Cuore, Largo
Francesco Vito 1, Rome, Italy.
3Departament of Chemistry, Faculty of Sciences, Autonomous University of Barcelona,
Bellaterra, Barcelona, Spain.
(Received: September 1, 2000 - Accepted: November 15, 2000)
Two new benzodihydrofurans have been isolated from the resinous exudate of Diplostephium cinereum. Their structures were elucidated by high-resolution spectroscopic methods as 13-(2-methylpropanoyloxy)toxol (2) and 13-[(R)-3-hydroxy-3-phenylpropanoyloxy]toxol (3).
KEY WORDS: Diplostephium cinereum, Asteraceae, resinous exudate, benzodihydrofurans, 13-(2-methylpropanoyloxy)toxol, 13-[(R)-3-hydroxy-3-phenylpropanoyloxy]toxol.
Del exudado resinoso de Diplostephium cinereum, se han aislado dos benzodihidrofuranos. Sus estructuras fueron determinadas por espectroscopía de alta resolución como: 13-(2-metilpropanoiloxi)toxol (2) y 13[(R)-3-hidroxi-3-fenilpropanoiloxi]toxol (3).
PALABRAS CALVES: Diplostephium cinereum, Asteraceae, exudado resinoso, benzodihidrofuranos, 13-(2-metilpropanoiloxi)toxol, 13[(R)-3-hidroxi-fenilpropanoiloxi]toxol.
The large genus Diplostephium (Asteraceae, Asterae, Asterinae) is well represented in the Andean region of South America from Venezuela to northern Chile with around 90 species. 1) From D. meyenii, D. floribundum and D. ericoides (defatted, air dry and milled plants) clerodane diterpenoids and geranyl geraniol derivatives were isolated, and some chemotaxonomic conclusions were postulated.2,3) D. cinereum Cuatr. Vernacular names "Coba" and "Kova" (Chile), "Coha" (Perú) and "Quilicoha" (Bolivia), is a resinous shrub used as a magic plant in religious ceremonies by Andean Highland communities. The intensive use of this plant has led it to become an endangered species.4) In a previous communication, known flavonoids were informed as minor compounds in the resinous exudate of D. cinereum.5) We now describe the isolation and characterization of two new derivatives of toxol (1).
Specimens of D. cinereum were collected during the flowering season, April 1997, in the Vilayuyumani creek, Parinacota (1º Región, Chile, 18º 15´S, 69º 20´W). A Voucher specimen (Nº 88661-97) was deposited in the herbarium of the ethnobotanic laboratory, MASMA, Arica, Chile.
Extraction and isolation
The resinous exudate of D. cinereum Cuatr. was extracted by inmersion of the fresh plant material (85 g) in CH2Cl2 for 15-20 s at room temperature. The CH2Cl2 extract was concentrated to a sticky residue (10.8 g, 12,7% fresh wt.). Part of the extract (5g) was purified by CC (silica gel) using a hexane-EtOAc step gradient. Fractions 25 to 30 were purified by CC (silica gel) using hexane-EtOAc (4:1) to afford 13-(2-methylpropanoyloxy)toxol (2) (740 mg). Fractions 41-42 were purified by CC (silica gel) using CHCl3-MeOH (98:2) to afford 13-[(R)-3-hydroxy-3-phenylpropanoyloxy]toxol (3) (160 mg).
Oil, [a]D22º + 39.0 (MeOH; c 0.3); UV lmax (EtOH) nm (log e) 272 (4.0); FTIR nmax (KBr) cm-1 3416, 1738, 1675; HRMS m/z 304.13100 [M+], calculated for C17H20O5 304.13110; EIMS m/z (rel. Int.): 304 [M]+ (20), 216 (100), 201 (70), 174 (28); 1H-NMR (400 MHz, CDCl3) Table 1; 13C-NMR (100.6 MHz CDCl3) Table 1.
Oil; [a]D22 + 54.0 (MeOH, c 0.3); UV lmax (EtOH) nm (log e) 278 (3.92); FTIR nmax (KBr) cm-1 3411, 1741, 1669; HRMS m/z 382.14160 [M+], calculated for C22H22O6 382.14166; EIMS m/z (rel. Int.): 382 [M]+ (2), 364 [M-H2O]+ (4), 216 (100), 201 (50), 174 (38); 1H-NMR (400 MHz, CDCl3) d: 5.03 (1H, d, J=4.39 Hz, H-2), 5.06 (1H, d, J=4.39 Hz, H-3), 7.98 (1H, d, J=1.93, H-4), 7.86 (1H, dd, Jm=1.93 Hz and J0=8.51 Hz), 2.53 (3H, s, Me-11), 4.61 (1H, d, J=14.1 Hz, HA-13), 4.71 (1H, d, J=14.1 Hz, HB-13), 5.25 (2H, s, H-13), 2.90 (1H, dd, Jgem=6.9 Hz, J=4.6 Hz, H-2´), 2.95 (1H, dd, Jgem=6.9 Hz, J=4.6 Hz, H-2´), 4.45 (1H, d, J=4.6 Hz, H-3´), 7.20-7.31 (5H, m, H-5´, H-6´, H-7´, H-8´, H-9´), 3.28 (1H, brs, OH), 3.60 (1H, brs, OH). ; 13C-NMR (100.6 MHz CDCl3) d: 91.93 (C-2), 76.65 (C-3), 126.89 (C-4), 131.38 (C-5), 132.42 (C-6), 110.10 (C-7), 128.16 (C-8), 163.78 (C-9), 196.82 (C-10), 26.51 (C-11), 139.85 (C-12), 65.88 (C-13), 115.45 (C-14), 172.90 (C-1´), 40.65 (C-2´), 71.87 (C-3´), 127.41 (C-4´), 128.61 (C-5´), 129.50 (C-6´), 128.16 (C-7´), 129.50 (C-8´), 128.61 (C-9´).
Compound (2) (150 mg) was acid hydrolyzed and worked up in a conventional form, yielding 3-(R)-hydroxy-3-phenylpropanoic acid [aD20 + 19.3 (EtOH; c 0.0684) lit., +19.2 (EtOH).6)
RESULTS AND DISCUSSION
The methylene chloride extract of the resinous exudate of D. cinereum was subjected to column chromatography on silica gel using increasing amounts of ethyl acetate in hexane to afford 13-(2-methylpropanoyloxy)toxol (2), and 13-[(R)-3-hydroxy-3-phenylpropanoyloxy]toxol (3). Their structures were stablished through high-field bidimensional techniques (H1-H1 COSY, 13C/DEPT, HMQC, HMBC, NOEDIFF and HETCOR).
The molecular formula C17H20O5 for (2) was deduced from its exact mass [M+] at m/z 304.1310, and the UV and IR spectra were characteristic of a benzodihydrofuran structure. The 1H-NMR spectrum of (2), reinforced by the HMBC experiment, (Table 1), was very similar to that of 13-acetoxytoxol (4) 7) with a difference in the structure of the side chain of the acid ester portion. In the case of (2) a septuplet at d 2.47 (1H) and two doublets at d 1.08 and d 1.10, integrating for 3H, each one, indicated the presence of a 2-propyl radical (Table 1). The stereochemical relationship between C-2-H and C-3-H was established through a NOEDIFF experiment. Irradiation of H-2 (d 5.06, d, J=4.47 Hz), gave a NOE of 9% in the H-3 frequency (d 5.29, d, J=4.47 Hz) indicating a cis configuration between C-2-H and C-3-H.
The molecular formula C22H22O6 for (3) was deduced from its exact mass [M+] at m/z 382.14160. The analysis of the NMR spectra gave a simmilar structure to that of (2), but esterified with a different acid, which was identified through high-field bidimensional NMR techniques as 3-hydroxy-3-phenylpropanoic acid. The absolute configuration of the C-3´chiral center of (3) was obtained by acid hydrolysis and determination of the specific rotation of the resulting acid, that was found identical with the value reported for 3-(R)-hydroxy-3-phenylpropanoic acid.6)
The cis configuration between C-2-H an C-3-H was established as in (2) through a NOEDIFF experiment. Irradiation of H-2 gave a NOE of 8% in the H-3 frequency.
The chemical composition found in the resinous exudate of D. cinereum differs from the composition of the other studied species, in which only clerodane diterpenoids and geranyl geraniol derivatives had been informed.2) These results stress the need of considering both the studied plant tissue and the chemical procedure before arriving at any chemotaxonomic conclusions.
This work was supported by FONDECYT (Nº 1990209), DICYT (Universidad de Santiago de Chile); and the programs of international collaboration of Fundación Andes/CONICYT CNR (Italy) and ICI/Ministerio de Educación y Ciencia (Spain).
Corresponding Author email@example.com (A. Urzua)
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