Xanthone from the Fruits of Terminalia Arjuna

2,7-dimethoxyxanthone (1) along with a well known compound β-sitosterol-3-O-β-Dglucopyranoside (2) were isolated from the methonalic extract of the fruits of Terminalia arjuna. Their structures were elucidated by spectroscopic (NMR and mass) analysis.


Plant material
The fruits of Terminalia arjuna W. & A. were collected from the campus of University of Rajshahi, Bangladesh, during September 2007 and was authenticated by Bangladesh National Herbarium, Dhaka, Bangladesh.A voucher specimen has been deposited (Acc.No. 32612, DACB) in the Bangladesh National Herbarium, Dhaka, Bangladesh.

Extraction and isolation
Air dried fruits of T. arjuna was powdered (18 kg) and extracted with methanol (MeOH) (60 Lx3) at room temperature for 3 days.MeOH was evaporated under vacuum to give a solid product (850 g), which was dissolved again in MeOH and partitioned with n-hexane to remove sticky and gummy materials.MeOH was evaporated under vacuum to give a residue (590 g).200 g from this residue was suspended in H 2 O and partitioned with dichloromethane (5 Lx3), ethyl acetate (5 Lx3) and n-butanol (5 Lx3) successively.The Ethyl acetate fraction (E, 14.5 g) was subjected to column chromatography over silica gel (30x7 cm) eluted with ethyl acetate : n-hexane and the fractions were collected at 20% ethyl acetate (E-1), 50% ethyl acetate (E-2), 75% ethyl acetate (E-3), 100% ethyl acetate (E-4) and 100% methanol (E-5).Fraction E-1 (0.6 g) was subjected to column chromatography with silica gel (25x2.5 cm) and eluted with 20% ethyl acetate : n-hexane to give a mixture which on further purification by preparative TLC over silica gel with 40% acetone : n-hexane as eluent gave a compound 2,7-dimethoxyxanthone [27][28][29] was obtained from fraction E-3 by reversed-phase C18 silica gel and Sephadex LH 20 column chromatography.

Results and Discussion
Compound 1 [Fig. 1  Compound 1 showed two aromatic protons at  H 7.41 as a doublet (J=2.4Hz, H-1 and H-8), other two aromatic protons at  H 7.39 as a doublet of doublet (J=2.4,9.0 Hz, H-3 and H-6, and another two aromatic protons at  H 6.79 as a doublet (J=9.0Hz, H-4 and H-5).A signal appeared as singlet at  H 3.82 integrated for six protons were assigned for two methoxy groups.Thus, the structure of compound 1 was established as 2,7dimthoxyxanthone which was synthesized by en ndez and ahfouz and their co-worker [25,26].Compound 1 was isolated first time from any natural source.

Conclusion
Synthesized compound 1 was isolated from the methanolic extract of the fruits of Terminalia arjuna and the structure was identified as 2,7-dimthoxyxanthone which was isolated first time from any natural source, confirmed by SciFinder ® .Compound 2 showed the physical and spectral data similar to the reported.
] was isolated as a brown amorphous solid with [α] D 25 : -9.6º (c 2.5, CH 3 OH).The molecular formula C 15 H 12 O 4 with ten degrees of unsaturation was determined by EI MS at m/z 256 [M [31] FAB MS (positive ion mode) at m/z 257, FAB MS (negative ion mode) at m/z 255 and13C NMR (BB), DEPT 90º and DEPT 135º experiment data.IR spectrum has displayed bands for carbonyl group (1660 cm -1 ) with aromatic ring (1588, 1455, 900-650 cm -1 ) functionalities[30]. UV spectrum (MeOH) exhibited absorptions at 216, 249 and 302 nm characteristic of a furanocoumarin moiety[31].13CNMR(BB),DEPT 135º and DEPT 90º experiments showed eight signals for 15 carbon atoms, which includes two methyl, six methylene and seven quaternary carbons.One quaternary carbon has showed resonance at δ C 168.8 (C-9) for a carbonyl group.Due to plane of symmetry, all others carbons and protons in compound 1 appeared as one signal for every two symmetric carbons and protons in 1 H and13C NMR spectra, respectively.