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A New Flavone Glucoside, Apigenin 7-O-glucoside 4'-acetate and a New Fern Constituent, Quercetin 3-O-rhamnoside-7-O-glucoside from Dryopteris villarii.

A New Flavone Glucoside, Apigenin 7-O-glucoside 4'-acetate and a New Fern Constituent, Quercetin 3-O-rhamnoside-7-O-glucoside from Dryopteris villarii.--Ten flavonol O-glycosides (based on kaempferol and quercetin), two flavanone O-glycosides (based on naringenin and eriodictyol) and three Cglycosylflavones (vitexin, vitexin 7-O-glucoside and orientin) have previously been identified by Hiraoka (Biochem. Syst. Ecol. 6:171-175. 1978) in eighteen Dryopteris species whereas 3-desoxyanthocyanins have been found in red sori of Dryopteris erythrosora (Eat.) Kuntze by Harborne (Phytochemistry 5: 589-600. 1966). In addition kaempferol 7-O-(6"-succinyl-glucoside) was found in four Dryopteris species and an unusual flavan was isolated from Dryopteris filix-mas (L.) Schott as shown in a review by Markham (pp. 427-468, in J.B. Harborne ed., The Flavonoids, Advances in Research since 1980, Chapman and Hall, London and New York. 1988). Twenty-one flavonoids (15 flavonol glycosides, three flavone glycosides and three aglycones) have been found recently in Dryopteris villarii by Imperato (Amer. Fern J. 96: 93-96. 2006; Amer. Fern J. 97(2): 124-126. 2007; Nat. Prod. Commun. 2: 909-912. 2007).

This paper deals with identification of three flavonoids (I-III) from aerial parts of Dryopteris villarii (Bellardi) Schinz & Thell collected in the Botanic Garden of the University of Naples (Italy). The fern was identified by Dr. R. Nazzaro (Universita "Federico II", Naples); a voucher specimen (NAPEA 3496) has been deposited in Herbarium of Dipartimento di Biologia, Universita "Federico II", Naples, Italy (NAP).

Flavonoids (I-III) were isolated from an ethanolic extract of aerial parts of Dryopteris villarii by preparative paper chromatography in BAW (n-butanolacetic acid-water, 4:1:5, upper phase), 15% AcOH (acetic acid) and BEW (n-butanol-ethanol-water, 4:1:2.2). Further purification was carried out by Sephadex LH-20 column chromatography eluting with methanol.

Color reactions (brown to yellow in UV+N[H.sub.3]), [R.sub.f] values on Whatman N.1 paper (0.73 in BAW;0.60 in 15% AcOH; 0.28 in [H.sub.2]O) and UV spectral analysis with the customary shift reagents ([[lambda].sub.max] (nm) (MeOH) 267, 323;+NaOMe 286, 356 (sh); +Al[Cl.sub.3] 275, 299, 344, 382; +Al[Cl.sub.3]/HCl 276, 297, 341, 380) suggested that flavonoid (I) may be a flavonoid glycoside with a free hydroxyl group at postion 5. Total acid hydrolysis (2N HCl; 2 hr at 100[degrees]C) gave apigenin and D-glucose whereas alkaline hydrolysis (2N NaOH; 2 hr at room temperature in a sealed tube) gave apigenin 7-O-glucoside identified by [R.sub.f] values and enzymatic hydrolysis with [beta]-glucosidase (from almonds) which gave apigenin and D-glucose. Electrospray mass spectrum (positive mode) showed a quasimolecular ion [[M+H].sup.+] at m/z 475 and fragment ions at m/z 313 (acetylapigenin+H), m/z 294 (apigenin +H+Na) and m/z 135 (acetyl B-ring). These results suggest that flavonoid (I) is apigenin 7-O-glucoside 4'-acetate (Fig. 1), a new natural product. Only two flavone glycosides having an acetyl group at position 4' have previously been reported from plants; these compounds are apigenin 7-O-glucoside 4'-p-coumarate identified by Petrenko (Khim. Prirodn. Soedin Akod. Nauk. Uz. SSR 6: 414-419.1965) in Leonorus quinquelobatus (Labiatae) and apigenin 7-O-glucoside 4'-p-caffeate identified by Gella et al. (Farmatsevtychnyi. Zhurnal 22: 80-85. 1967) in Mentha piperita L. (Labiatae).


Flavonoid (II) was identified as quercetin 3-O-rhamnoside-7-O-glucoside by UV spectral analysis with the customary shift reagents, total acid hydrolysis which gave quercetin, D-glucose and L-rhamnose and electrospray mass spectrum (positive mode) which showed a quasimolecular ion [[M+H].sup.+] at m/z 611 and fragment ions at m/z 465 (quercetin glucoside+H), at m/z 449 (quercetin rhamnoside +H) and at m/z 303 (quercetin +H). Since the intensity of the ion at m/z 465 was much higher than that at m/z 449, D-glucose is linked at position 7 and L-rhamnose is linked at position 3 of the aglycone (Cabrera, pp. 1-22, in F. Imperato ed., Phytochemistry: Advances in Research, Research Signpost, Trivandrum, 2006). Flavonoid (II) is a new fern constituent.

Flavonoid (III) was identified as apigenin 7-O-(sulphatoglucoside) by UV spectral analysis with the customary shift reagents, total acid hydrolysis (which gave apigenin, D-glucose and sulphate), alkaline hydrolysis which gave apigenin 7-O-glucoside and sulphate) and electrospray mass spectrum (negative mode) which showed a quasimolecular ion [[M-H].sup.-] at m/z 511 and fragment ions at m/z 431 (apigenin glucoside -H) and m/z 269 (apigenin-H). Since a large number of flavonoid sulphates have been found in plants that have association with aquatic habitat, it has been suggested that these sulphates represent an ecological adaption to the habitat; however Flamini et al. (Phytochemistry 57: 559-564. 2001); Phytochemistry 58: 1229-1233. 2001) have isolated a number of flavonoid sulphates from roots and aerial parts of Centaurea bracteata Scop. (Asteraceae). Flavonoid sulphates have previously been reported by Imperato from the fern species Asplenium filix-foemina Bernh (Chem. Ind.: 525-526. 1979), A. fontanum Bernh (Chem. Ind.: 540-541.1980), A. septentrionale (L.) Hoffm. (Chem. Ind.: 390-391. 1983), Adiantum capillus-veneris L. (Chem. Ind.: 957-958. 1982; Phytochemistry 21: 2158-2159. 1982) and Cystopteris fragilis (L.) Bernh (Chem. Ind.: 204-205. 1983).

Two flavonoids (IV and V) present in trace amounts have been partially characterized as apigenin Copentoside (IV) and methoxyapigenin C-pentoside (V) by electrospray mass spectra (positive mode) which showed a quasimolecular ion [[M+H].sup.+] at m/z 403 and a quasimolecular ion [[M+H].sup.+] at m/z 433 respectively and fragment ions typical of flavone Copentosides (Cabrera, 2006); in addition flavonoid (V) was different from vitexin and isovitexin in paper chromatography. UV spectral analysis with the customary shift reagents and [R.sub.f] values in paper chromatography were in agreement with the above partial structures.

The author thanks Universita della Basilicata for financial support, Dr. F. Lelario for several mass spectra and Mr. A. Lo Vecchio for technical assistance.--FILIPPO IMPERATO, Universita della Basilicata, Dipartimento di Chimica, 85100 Potenza, Italy.
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Title Annotation:Shorter Notes
Author:Imperato, Filippo
Publication:American Fern Journal
Article Type:Report
Geographic Code:1USA
Date:Oct 1, 2008
Previous Article:Eleven new species in the grammitid fern genus Melpomene (Polypodiaceae).
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