ABSTRACT
Four known flavones, 5-hydroxyauranetin, araneosol, calycopterin and sarothrin, were isolated from the aerial parts of Herissantia tiubae. (K. Schum) Brizicky (Malvaceae). Their structures were identified by the use of spectroscopic methods such as IR, UV, and mainly nuclear magnetic resonance, which included two-dimensional techniques (1H-1H COSY, NOESY, HETCOR, and HMBC). This is the first reported isolation of these compounds from the genus Herissantia..
Introduction
Herissantia tiubae. (K. Schum) Brizicky (Malvaceae), commonly known as mela bode., consists of a bush that belongs to the family Malvaceae. It is found in the Brazilian northeast, mainly between the states of Bahia and Pernambuco (Corrêa, Citation1978). Several species of this family are used therapeutically, in rheumatism treatment, as emollient, febrifuge, diuretic, anti-inflammatory, antiemetic, antihelminthic, among others uses (Ahmed et al., Citation1990). Previous publications on Malvaceae species describe the occurrence of flavonoids (Subramanian & Nair, Citation1972), fatty acids (Vickery, Citation1980), sesquiterpenelactones (Sharma & Ahmad, Citation1989), triterpenes (Ahmed et al., Citation1990), steroids (Ahmed et al., Citation1991), and alkaloids (Ghosal et al., Citation1975). In this paper, the isolation and structural identification of 5-hydroxyauranetin, araneosol, calycopterin, and sarothrin are discussed. This the first time that these flavones are reported in the genus Herissantia..
Materials and Methods
General analysis
Melting points were obtained with a Shimadzu DSC-50 and are uncorrected. IR spectra were recorded as KBr disks. UV spectra were taken with MeOH and MeOH with addition of NaOAc. The 1H (200 MHz) and 13C (50 MHz) NMR experiments were performed in CD3OD and CDCl3 with the solvent as reference, using a Brucker AC-200 spectrometer. COSY, NOESY, HETCOR, and HMBC were also carried out with this spectrometer. Column chromatography was performed on silica gel 60 (ASTM, 230–400 mesh, Merck) and thin-layer chromatography (TLC) on silica gel F254 (Merck). The spots were detected by inspection under UV light (254 and 366 nm) and by exposure to the I2 vapor.
Plant material
The aerial parts were collected in January 1994 near the city of Juazeirinho in the state of Paraíba, Brazil. It was identified by Prof. Maria de Fátima Agra of the Universidade Federal da Paraíba. A voucher specimen (no. 2434) is deposited at the Herbarium Lauro Pires Xavier-JPB at the above university.
Extraction and isolation
The dried aerial parts of H. tiubae. were pulverized (5 kg) and subjected to exhaustive extraction with 95% aqueous ethanol at room temperature, and the ethanol extract was concentrated under reduced pressure to afford 300 g of crude extract. This material was partitioned with hexane, CHCl3, EtOAc, and n.-buthanol. The hexane phase was subjected to a vacuum liquid chromatography, using an elution gradient from hexane to EtOAc and then from EtOAc to MeOH. In total, 7 fractions were collected. Fraction 7 was chromatographed on silica gel column, eluting with hexane/EtOAc/MeOH, with increasing polarity to yield 177 fractions. Fractions 54 to 57 were gotten together and further separated by TLC on silica gel using hexane-EtOAc 9:1, which led to isolation of the flavone 1 (Fig.). The CHCl3 phase was chromatographed over silica gel, eluting with hexane/CHCl3/MeOH, yielding 113 fractions. Fractions 49–53 were subjected to repeated chromatographic purification on silica gel eluted with hexane-CHCl3 and CHCl3-MeOH of increasing polarity to give the flavones 2, 3, and 4 (Fig.).
Figure 1 Flavonoids isolated from Herissantia tiubae..
Results and Discussion
Four flavones, reported for the first time in the genus Herissantia., were isolated from the hexane (1) and chloroform (2–4) extracts using vacuum liquid chromatography, column chromatography, and TLC. Identification of these metabolites was made on the basis of IR, UV, and NMR spectrometry. Thus, compound 1 is 5-hydroxy-3,4′,6,7,8-pentamethoxyflavone (5-hydroxyauranetin), identified by comparison of its spectral values with those of the corresponding compound reported in the literature (Rashid et al., Citation1992). This flavone has previously been found in several species (Sarin & Seshadri, Citation1960). Compound 2 was identified as 5,7-dihydroxy-3,4′,6,8-tetramethoxyflavone (araneosol), which has previously been isolated from Anaphalis araneosa. (Ali et al., Citation1979) and other plants. The spectroscopic data are in agreement with those published in the literature (Rashid et al., Citation1992). On the basis of spectroscopic analysis and comparison with reported values (Liu & Mabry, Citation1982), compound 3 was identified as 4′,5-dihydroxy-3,6,7,8-tetramethoxyflavone (calycopterin), previously isolated from Calycopteris floribunda. (Rodriguez et al., Citation1972) and other sources (Harborne, Citation1994). Compound 4 was identified as 4′,5,7-trihydroxy-3,6,8-trimethoxyflavone (sarothrin), and its spectral data are in agreement with those of a corresponding sample (Roitman & James, Citation1985). It has been isolated from other plant source (Herz, Citation1975). All the assignments of 1H and 13C chemical shifts of the flavones 1–4 were supported by the COSY, NOESY, HETCOR, and HMBC experiments. The NMR data for flavonoids 1–4 are shown in Tables and .
Table 1.. 13C NMR spectroscopic data of compounds 1Footnotea., 2Footnotea., 3Footnotea. and 4Footnoteb.
Table 2.. 1H NMR spectroscopic data of compounds 1Footnotea., 2Footnotea., 3Footnotea., and 4Footnoteb.
Although these flavones have been isolated from other source plants, this is the first work that describes these compounds in a member of the genus Herissantia.. Therefore, they can be used as chemotaxonomic markers. On the other hand, highly oxygenated flavonoids are of great interest, having a broad spectrum of biological activity (Chen et al., Citation1997). In this way, the isolated compounds can be the object of further pharmacological studies.
Acknowledgments
We are grateful to CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico-Brazil) for financial support. Appreciation is extended to Maria de Fátima Agra for identification of the plant material.
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