Chemical profile of the polar extract of Paepalanthus microphyllus (Guill.) Kunth (Eriocaulaceae)

Perfil químico do extrato polar de Paepalanthus microphyllus(Guill.) Kunth (Eriocaulaceae)

ORIGINAL PAPERS

Chemical profile of the polar extract of Paepalanthus microphyllus (Guill.) Kunth (Eriocaulaceae)

Perfil químico do extrato polar de Paepalanthus microphyllus(Guill.) Kunth (Eriocaulaceae)

Lourdes Campaner dos SantosI, ^*; Miriam Sannomiya^I; Sonia Piacente^II; Cosimo Pìzza^II; Paulo Takeo Sano^III; Wagner Vilegas^I

^IInstituto de Química, Universidade Estadual Paulista "Júlio de Mesquita Filho"

^IIDipartimento di Scienze Farmaceutiche, Università degli Studi di Salerno

^IIIInstituto de Biociências, Universidade de São Paulo

ABSTRACT

From the ethanolic extract of the capitulae of Paepalanthus microphyllus, one caffeic acid derivative (1) was isolated. The structure of the compound was characterized by spectroscopic methods, mainly 1D and 2D NMR experiments, as well as ESMS spectrometry. In addition, three flavonoids of taxonomic relevance were isolated and identified by comparison to literature data.

Uniterms: Caffeic acid derivative. Eriocaulaceae. Paepalanthus

RESUMO

Do extrato etanólico dos capítulos de Paepalanthus microphyllus, isolou-se um derivado do ácido cafeico (1). Sua estrutura foi caracterizada por métodos espectroscópicos (RMN mono e bi-dimensionais) e por espetrometria de massas Electrospray. Foram, também, isolados outros três flavonóides (2-4) de interesse taxonômico, os quais foram identificados por métodos espectroscópicos e comparados com dados da literatura.

Unitermos: Derivado do ácido cafeico. Eriocaulaceae. Paepalanthus

INTRODUCTION

The Eriocaulaceae family encompasses around 1200 species, many of which are ornamental and endemic of Brazil (Giulietti et al., 2000). However, few of these plants have been chemically studied. Among the investigated species, those belonging to Paepalanthus genus are known for the production naphthopyranone and flavonoid glycosides (Vilegas et al., 1998; Vilegas et al., 1999a,b; Santos et al., 2001a,b; Piacente et al., 2001). The isolated compounds have shown a number of biological activities, like mutageniticity (Tavares et al., 1999; Coelho et al., 2000; Moreira et al., 2000).

This work deals with the chemical investigation of P. microphyllus Giull. Kunth., that belongs to subgenus Paepalocephalus section Eriocaulopsis, that grows wild at Serra do Cipó, Espinhaço Chain, Minas Gerais State, Brazil.

MATERIALS AND METHODS

Plant material

Capitula of P. microphyllus (Guill.) Kunth. (Eriocaulaceae) were collected in February 1997, at Serra do Cipó, in Espinhaço Chain, Minas Gerais State, Brazil. The specimen were determined by Prof. Paulo Takeo Sano from Instituto de Biociências, USP, São Paulo. A voucher specimen (CFCR 5610) has been deposited at the Herbarium SPF (Departamento de Botânica, Instituto de Biociências, Universidade de São Paulo, Brazil).

General experimental procedures

Capitulae of Paepalanthus microphyllus (300 g) were powdered and extracted successively with n-hexane, methylene choride an EtOH (1 week each). Solvents were evaporated under vacuum. The EtOH-extract (2.0 g) was chromatographed on a Sephadex LH-20 collumn (100x5cm), with MeOH as eluent. Fractions (8 mL) were collected and checked by TLC [Si gel plates, BAW (n-BuOH/AcOH/H₂O 12:3:5, v/v/v)]. Fractions were further purified by HPLC on a Waters 590 system equipped with a Waters R401 refractive index detector and with a Waters (m-Bondapak RP-18) column (30 cm x 7.6 mm i.d) using MeOH-H₂O (1:1, v/v) as eluent equiped with a Photo Diode-Array Detector set at 254 nm. We obtained the pure compounds 1,3-di-E-caffeoylglycerol 1, and the flavonoids 3',4',5,6,7,8-hexahydroxyflavone 2, 3',4',5,6,7-pentahydroxyflavone 3 and 3',4',5,6-tetra-hydroxy-7-O-β-D-glucopyranosilflavone, 4 (Figure 1). NMR spectra in CD₃OD were obtained using a Bruker DRX-600 spectrometer, operating at 599.19 MHz for ¹H and 150.86 MHz for ¹³C. 2D experiments: ¹H-¹H-COSY (Chemical shift correlation spectroscopy), inverse-detected ¹H-¹³C HSQC (heteronuclear single quantum coherence), HMBC (heteronuclear multiple bond connectivity). ESMS were performed in a Fisons Platform spectrometer in the positive mode (70 V). The sample were dissolved in MeOH and injected directly.

RESULTS AND DISCUSSION

Compound 1 was colourless and amorphous. The IR spectra showed hydroxy groups (3400 cm^-1), an α,β-unsaturated ester (ν_C=O 1700 cm^-1), an alkene conjugated with an aromatic ring (ν_C=C 1620 cm^-1), and an aromatic ring (1590, 1505 cm^-1). The ESMS (70V, positive mode) gave the quasi-molecular ion [M + H]⁺ at m/z 417, corresponding to the molecular formula C₂₁H₂₀O_9, and fragment at m/z 180, corresponding to the formula protonated [C₉H₇O₄ + H]⁺, and m/z 238, corresponding to the fragment [C₁₂H₇O₁₃ + H]⁺. Loss of the two units of the caffeoyl moiety of 1 led to the glycerol unit observed at m/z 60.

In the ¹H NMR spectrum, the signals for the primary alcoholic functions and the secondary alcoholic function of a glycerol unit were evident at δ 4.29 (4H, m) for the two OCH₂ groups of glycerol and the signal of an OCH group at δ 4.16 (1H, m). Also evident were two doublets typical of a trans double bond at δ 6.32 (2H, d, J = 16.0 Hz) and 7.57 (2H, d, J = 16.0 Hz) and signals at d 6.56 (2H, dd, J = 1.5 and 8.0 Hz), 6.77 (2H, d, J = 8.0 Hz) and 7.07 (2H, d, J = 1.5 Hz). The above signals suggested the occurrence of two caffeoyl moieties (Birkofer et al., 1968) which should be linked to C-1 and C-3 of the glycerol unit in a symmetrical position in agreement with the ¹H NMR and ¹³C NMR signals. The HMBC spectrum showed connectivities for H-1 and H-3 of the glycerol unit (δ 4.29) and (C=O) of the caffeoyl units (δ 169.0). Thus, 1 was identified as 1,3-O-di-E-caffeoylglycerol.

The structures of the flavonoids 2-4 compounds were unambiguously determined by means of spectroscopic methods (IR, ESMS, ¹H, ¹³C and 2D NMR experiments COSY, HSQC, HMBC) and compared to those previously reported (Agrawal, 1989; Harborne, Mabry, 1982; Harborne, 1998).

Caffeic acid and other hydroxycinnamic derivatives are of major importance for the protection of plants against herbivores and pathogens (Bazzalo et al., 1985). They also have important biological activities. Braca et al. (2003) reported the antioxidant and free radical scavenging activities of caffeoyl acid derivatives from different Aconitum species. Baset et al. (1996) reported the in vitro hepatoprotective activity of four di-O-caffeoyl quinic acid derivatives from propolis. Kwon et al. (2000) reported the inhibitory activity against human immunodeficiency virus-1 presented by the caffeoyl quinic acid isolated from the aerial parts of Aster scaber Thunb. (Asteraceae).

Natural bitter phenolic glycerol derivatives have been isolated from a number of Lilium species (Liliaceae) as well as from plants of the Gramineae, Bromeliaceae and Salicaceae families (Shimomura et al, 1986; Shimomura et al., 1989).

CONCLUSION

The presence of compound 1 in P. microphyllus is the first report of a natural phenolic glyceride in Eriocaulaceae. Since it is reported the bitter taste of this kind of substance, this could explain the fact that species from this family are hardly attacked by insect in the region where they occur. Further studies are in progress to check this possibility.

ACKNOWLEDGEMENTS

We thank FUNDUNESP and FAPESP for financial aid, for FAPESP to a fellowship to M.S. and to CNPq for a grant to W.V.

Recebido para publicação em 20 de novembro de 2003

Aceito para publicação em 15 de outubro de 2004.

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Publication Dates

• Publication in this collection
  23 Mar 2010
• Date of issue
  Sept 2004

History

• Accepted
  15 Oct 2004
• Received
  20 Nov 2003