Sixth International Electronic Conference on Synthetic Organic Chemistry (ECSOC-6), http://www.mdpi.org/ecsoc-6, 1-30 September 2002

[C002]

Flavonoids from the roots of Isoetes longissimum

J. A. Seijas*^a, M. P. Vázquez-Tato*^a, J. Crecente-Campo^a

Pablo  Ramil-Rego^b, M. Inmaculada Romero^b, Pedro Fernández^b

Isoetes longissimum Bory (see figure) is a rare aquatic pteridophyte whose only known European location is Galicia (northwest Spain), this specie has otherwise been recorded only from Algeria¹. Due to this highly restricted distribution and known the particular sensitivity of oligotrophic fresh waters habitats, I. longissimum was classified by Salvo as endangered at European level in his listing of rare pteridophytes of the Iberian Peninsula.

In view of this, it was necessary to carry out a phytochemical study of this taxon, since it had never been studied before. This communication deals with the preliminary study of this specie, which afforded the isolation and characterization of 4 flavonoids. 

  So, the dried and ground roots (346 g) were extracted, successively, in a Soxhlet apparatus with n-hexane, chloroform, CHCl₃-MeOH (9:1) and MeOH (2 L x 12h). After removal of solvents, in vacuum at up to 40ºC, the following residues were obtained: 20.250 g, 4.982 g, 4.983 g and 3.689 g, respectively. Each residue was purified by repeated SiO₂ flash chromatography(EtOAc:hexane (2:8)®EtOAc®MeOH), preparative TLC and repurification by HPLC (ZORBAX RX-SIL, 9.4 mm x 25 cm), leading to the isolation of the same compounds, although in different ratios.

The flavonoids isolated were identified by exhaustive analysis of 1H and 13C NMR spectroscopy, COSY, NOESY and HETCOR experiments, and by comparison of their spectroscopic properties with literature reports. These were: 5-hydroxy-7,4’-dimethoxyflavone² (genkwanin, the major component), 7,3’,4’-trimethoxyluteolin,³ 7,4’-dimethoxyluteolin,⁴ and 5-hydroxy-7,3’,4’,5’-tetramethoxyflavone^3b,5 (corymbosin).

5-hydroxy-7,4’-dimethoxyflavone                    7,3’,4’-trimethoxyluteolin, 7,4’-dimethoxyluteolin

1H RMN, 13C NMR, COSY, NOESY, HETCOR             1H RMN, 13C NMR, COSY, NOESY, HETCOR

7,4’-dimethoxyluteolin                                       5-hydroxy-7,3’,4’,5’-tetramethoxyflavone

1H RMN, NOESY                                               1H RMN, 13C NMR, COSY, NOESY, HETCOR

Plant material

The roots were collected in Jly 201 at Parga river, Lugo (Spain). A voucher specimen documenting the collection is on deposit at Lugo Herbarium (nº 820).

Acknowledgments

Xunta de Galicia ( infraestructura PR405A 98/59-0 and project PGIDT01PXI26203PR) for financial support.

References

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2.- Zembower, D. E.; Zhang, H., J. Org. Chem. 1998, 63, 9300-9305.

3.- a)Ahond, A.; Guilhem, J.; Hamon, J. ; Hurtado, J.; Ponpat, C.; Pusset, M.; Séveret, T.; Poiter, P. J. Nat. Prod. 1990, 53, 875-881. b) Zahir, A.; Jossang, A. J. Nat. Prod. 1996, 59, 701-703.

4.- Ampofo, S. A.; Roussis, V.; Wiemer, D. F. 1987, 26, 2367-2370.

5.- Joshi, B. S.; Rane, D. F. Tetrahedron Lett. 1967,  46, 4579-4581.