A new flavone glucoside from Stachys aegyptiaca

Article abstract of DOI:10.1007/s10600-007-0186-y

In addition to 5,7,3'-trihydroxy-6,4'-dimethoxyflavone, 5,7,3'-trihydroxy-6,8,4'-trimethoxyflavone, isoscutellarein, luteolin, and luteolin-7-O-glucoside, the methanol extract of the aerial parts of Stachys aegyptiaca yielded a new flavone identified as luteolin 3',4'-dimethylether-7-O- β-D-glucoside on the basis of chemical and spectroscopic methods.

Full text of DOI:10.1007/s10600-007-0186-y

Chemistry of Natural Compounds, Vol. 43, No. 5, 2007
A NEW FLAVONE GLUCOSIDE FROM Stachys aegyptiaca
S. K. El-Desoky, Usama W. Hawas, and M. Sharaf
UDC 547.972
In addition to 5,7,3′-trihydroxy-6,4′-dimethoxyflavone, 5,7,3′-trihydroxy-6,8,4′-trimethoxyflavone,
isoscutellarein, luteolin, and luteolin-7-O-glucoside, the methanol extract of the aerial parts of Stachys
aegyptiaca yielded a new flavone identified as luteolin 3′,4′-dimethylether-7-O-β-D-glucoside on the basis
of chemical and spectroscopic methods.
Key words: Stachys aegyptiaca, Lamiaceae, new flavone glucoside.
Stachys aegyptiaca is a perenninal plant growing wild in the Sinai desert [1] and proved to be a rich source for
flavonoids. We have previously reported the isolation and structure elucidation of diapigenin 7-O-(6″-trans-6″-cis-p,p′-
dihydroxy-µ-truxinyl)glucoside [stachysetin] [2] and hypoluetin 7-[6″-acetylallosyl-(1→2)-3″-acetyl-glucoside, along with 24
known flavonoid aglycones and glycosides [3]. Also, the acetylated isoscutellarein glucoside was reported [4]. In continuation
of our study on the phenolic constituents of S. aegyptiaca, the present communication describes the further isolation and
structure elucidation of a new flavone glycoside, the structure of which was identified as luteolin 3′,4′-dimethylether-7-O-
glucoside from the aerial parts of the same plant.
OCH
3
HOH C
OCH3
2
O
HO
HO
O
O
O
OH
OH
1
The methanol extract of the aerial parts of S. ageyptiaca was fractionated on a polyamide column with H O as eluent
2
with increasing amounts of MeOH. Isolation and purification were achieved by combination of PPC, TLC on silica gel and
Sephadex LH-20.
Flavonoid 1 was isolated as a yellowish white amorphous powder. Acid hydrolysis of 1 afforded glucose, which was
identified by co-chromatography with authentic samples and the aglycone 1a. The UV spectral data of 1a with diagnostic shift
reagents [5] indicated a flavone, absence of a free ortho-dihydroxyl pattern, occupation at positions-3′ and -4′, and a free
hydroxyl group at position-7. The UV spectral data of 1 indicated a flavone with occupation at positions-7,3′ and -4′ [5].
The EI-MS spectrum of permethylated [6] 1 gave a molecular ion peak at m/z 546 (66%) in accordance with fully
methylated luteolin glucoside. A fragment at m/z 328 was due to the aglycone luteolin bearing three methoxyl groups. The
+
identity of the glucose moiety was confirmed by the fragment at m/z 218 due to the ion [glucose-H] and the fragment at m/z
+
1
87 for the ion [glucose-MeOH] .
1
The H NMR spectrum of 1 showed that it is a monoglucoside of luteolin dimethylether on the basis of the signal H-1
glucose (δ 5.1), and the coupling constant (J = 7.5 Hz) is characterized for a β-linked glucose. Furthermore, the chemical shift
(
(
δ 5.1) confirmed that the glucose is directly attached to the aglycone [7]. The spectrum also showed signals at δ 7.4 and δ 6.9
m; d, J = 8.0 Hz) assigned for H-2′,6′ and H-5′, confirming the disubstituted pattern at ring-B. Two doublets (J = 2.5 Hz) at
Phytochemistry and Plant Systematic Department, National Research Centre, Dokki-12311, Cairo, Egypt, e-mail:
sharafali58@hotmail.com. Published in Khimiya Prirodnykh Soedinenii, No. 5, pp. 444-445, September-October, 2007.
Original article submitted June 12, 2006.
©
0
009-3130/07/4305-0542 2007 Springer Science+Business Media, Inc.
5
42

δ 6.8 and δ 6.4 were assigned for H-8 and H-6, while H-3 appeared as a singlet at δ 6.75. The two methoxyls groups appeared
as two singlets at δ 3.95 and δ 3.90.
The 13C NMR spectrum confirmed that 1 is a monoglucoside of luteolin on the basis of C-6 glucose (δ 61.0). The
C NMR shifts of the aglycone part of 1 correspond with the shifts of luteolin [8], the only difference being a downfield shift
1
3
ofthe signal assigned to C-3′ and C-4′ byapproximately3.7 ppm, confirming the location ofthe –OCH groups at C-3′ and C-4′.
3
Also the signal assigned to C-7 was shifted upfield by approximately 2 ppm and there was a downfield shift of about 1.8 ppm
for the para-related carbon (C-10). These shifts are analogue to those reported when the hydroxyl group is glycosylated at C-7
in flavonoids [9 – 11]. The assignments of the glucose carbons in 1 are based on those given in the literature [7, 11, 12]. From
the above data, compound 1 is identified as luteolin 3′,4′-dimethylether-7-O-β-D-glucoside.
EXPERIMENTAL
Plant Material. S. aegyptiaca aerial parts were collected around the Suez Canal University guest house at Saint
Catherine, Sinai, in March 2004.
Extraction and Isolation. Dried plant (1.25 kg) was extracted with 80% MeOH. The concentrated extract was
subjected to a polyamide column eluted with a H O-MeOH mixture with increasing amounts of MeOH. PPC using H O, 15%
2
2
AcOH, BAW (n-BuOH–AcOH–H O, 4:1:5, upper phase) afforded pure samples of the known flavonoids and the aglycone 1a.
2
A combination of TLC (CHCl –MeOH–H O, 45:30:2) and Sephadex LH-20 (MeOH) afforded compound 1.
3
2
Luteolin 3′,4′-dimethylether-7-O-β-D-glucoside (1). UV spectra (MeOH, λmax, nm): 255, 267, 352; +NaOMe: 265,
3
97; +AlCl : 273, 297, 330sh, 422; AlCl +HCl: 260, 275, 297, 350, 385; NaOAc: 260, 370; NaOAc+ H BO : 260, 370.
3
3
3
3
1
H NMR (270 MHz, DMSO-d , δ, J/Hz): 7.40 (2H, m, H-2′,6′), 6.90 (1H, d, J = 8.0, H-5′), 6.80 (1H, d, J = 2.5, H-8), 6.75 (1H,
s, H-3), 6.40 (1H, d, J=2.5, H-6), 5.1 (1H, d, J = 7.5 Hz, H-1 glu), 3.95 (3H, s, -OCH ), 3.90 (3H, s, -OCH ). C NMR
6
1
3
3
3
(
270 MHz, DMSO-d , δ): 55.0 (-OCH ), 55.8 (-OCH ), 61.0 (C-6″), 69.6 (C-4″), 73.5 (C-2″), 76.2 (C-3″), 77.2 (C-5),
6 3 3
9
4.5 (C-8), 99.8 (C-6), 100.0 (C-1), 103.0 (C-3), 105.0 (C-10), 111.0 (C-2′),120.0 (C-6′), 124.5 (C-1′), 149.5 (C-3′), 151.5
(C-4′), 152.5 (C-5′), 158.9 (C-9), 161.0 (C-5), 162.7 (C-7), 164.4 (C-2),182.0 (C-4).
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