A new flavonoid glycoside from Galium verum

Article abstract of DOI:10.1007/s10600-011-9992-3

A new flavonoid glycoside, an apigenin 7-O-(3,4-di-O-acetyl)-α-L- rhamnopyranosyl-(1∈→∈-6)-β-D- glucopyranoside (1), was isolated from the 95% ethanol extract of Galium verum L. Its structure was elucidated by spectroscopic analysis.

Full text of DOI:10.1007/s10600-011-9992-3

Chemistry of Natural Compounds, Vol. 47, No. 4, September, 2011 [Russian original No. 4, July–August, 2011]
A NEW FLAVONOID GLYCOSIDE FROM Galium verum
1
1*
2
Chun-Chao Zhao, Jian-Hua Shao, Chun-Jie Zhao,
and Xian Li
UDC 547.972
2
A new flavonoid glycoside, an apigenin 7-O-(3,4-di-O-acetyl)-ꢀ-L-rhamnopyranosyl-(1ꢁ6)-ꢂ-D-
glucopyranoside (1), was isolated from the 95% ethanol extract of Galium verum L. Its structure was elucidated
by spectroscopic analysis.
Keywords: Rubiaceae, Galium verum L., flavonoid glycoside.
Galium verum L. (Rubiaceae), widely distributed in China, is often used as natural dyestuff and food additive. As
traditional Chinese medicine, it is often used for the treatment of phlebophlogosis and hepatitis [1]. Phytochemical investigations
of G. verum L. have led to the isolation of several kinds of bioactive compounds such as iridoids, anthraquinones, chlorogenic
acids, and flavonoids [2–5].
In our recent research, a new flavonoid glycoside, apigenin 7-O-(3,4-di-O-acetyl)-ꢀ-L-rhamnopyranosyl-(1ꢁ6)-ꢂ-
D-glucopyranoside (1), was obtained. In this paper, we report the isolation and structure elucidation of this rarely acetylated
flavonoid glycoside.
The molecular formula of 1 was determined to be C H O on the basis of the HR-ESI-MS pseudo-ion peak at
31 34 16
+
+
–
m/z 685.1742 [M + Na] (calcd for C H O Na, 685.1745), and ESI-MS m/z: 685.3 [M + Na] , 661.2 [M – H] .
31 34 16
The IR spectrum (KBr) of 1 showed absorption bands for hydroxyl, conjugated carbonyl, and aromatic functional
groups.
1
The H NMR spectrum of 1 exhibited 1,4-disubstituted benzene signals at ꢃ 7.87 (2H, d, J = 8.3, H-2ꢄ, 6ꢄ) and 6.92
(2H, d, J = 8.3, H-3ꢄ, 5ꢄ), meta-coupled aromatic proton signals at ꢃ 6.48 (1H, d, J = 1.9, H-6) and 6.74 (1H, d, J = 1.9, H-8),
13
and an aromatic proton signal at ꢃ 6.64 (1H, s, H-3). The C NMR spectrum disclosed 31 carbon signals, including 15
aromatic carbon signals for the flavone aglycone and 12 signals for the sugar moieties and two acetyl moieties at ꢃ 173.1
(2 ꢅ OCOCH ) and 21.0 (2 ꢅ OCOCH ). Acid hydrolysis of 1 resulted in release of D-glucose and L-rhamnose, which was
3
3
identified by HPTLC comparison of the hydrolysate with an authentic sample. The configurations of the glucose and rhamnose
residues in 1 were assigned as ꢂ- and ꢀ-, based on the coupling constant of the anomeric protons at ꢃ 5.07 (1H, d, J = 7.4,
H-1ꢄꢄ) and 4.70 (1H, d, J = 1.9, H-1ꢄꢄꢄ).
On the basis of the above analyses of spectral data, the flavone aglycone was suggested as 5,7,4ꢄ-trihydroxyflavone.
1
The H NMR spectrum also showed two methyl proton signals at ꢃ 1.99 (3H, s, 3ꢄꢄꢄ-OCOCH ) and 1.92 (3H, s, 4ꢄꢄꢄ-OCOCH ),
3
3
and these methyl groups were assigned to the two acetyl moieties, which were connected to the C-3ꢄꢄꢄ and C-4ꢄꢄꢄ sites of the
rhamnose unit through an oxygen atom by the HMBC correlations of H-3ꢄꢄꢄ/3ꢄꢄꢄ-OCOCH and H-4ꢄꢄꢄ/4ꢄꢄꢄ-OCOCH , respectively.
3
3
In the HMBC spectrum (Fig. 1), long-range correlations of H-1ꢄꢄꢄ/C-6ꢄꢄ and H-6ꢄꢄ/C-1ꢄꢄꢄ established a 1ꢁ6 linkage between
the ꢀ-L-3,4-di-O-acetylrhamnopyranosyl unit and the ꢂ-D-glucopyranosyl moiety, and the correlation of H-1ꢄꢄ/C-7 indicated
1
that the sugar chain was connected to the C-7 position of the flavone aglycone through an oxygen atom. The H NMR and
13
C NMR spectral data of 1, supported by TOCSY, HMQC, and HMBC experiments, permitted assignment of all proton and
carbon resonances. Consequently, compound 1 was determined to be apigenin 7-O-(3,4-di-O-acetyl)-ꢀ-L-rhamnopyranosyl-
(1ꢁ6)-ꢂ-D-glucopyranoside.
1) College of Bioscience and Biotechnology, Yangzhou University, Yangzhou 225009, P. R. China, e-mail:
chunchaozhao@hotmail.com; 2) School of Traditional Chinese Materia Medica, Shenyang Pharmaceutical University, Shenyang,
110016, P. R. China. Published in Khimiya Prirodnykh Soedinenii, No. 4, pp. 485–486, July–August, 2011. Original article
submitted June 4, 2010.
0009-3130/11/4704-0545 02011 Springer Science+Business Media, Inc.
545

O
O
C
6'''
1'''
6''
H C
3
O
O
3'''
O
3'
4'''
O
HO
HO
O
1''
9
O
O
7
1'
OH
2
OH
OH
5'
O
C
10
4
5
OH
CH
3
1
Ha(Ca)
Cb(Hb)
Ha
Cb
Fig. 1. Key HMBC correlations of compound 1.
EXPERIMENTAL
The UV-Vis spectrum was performed on a Shimadzu UV-260 instrument. The IR spectrum was performed on a
Bruker IR S-55 instrument. NMR spectra were recorded on a Bruker-ARX-600 spectrometer, using TMS as an internal standard.
ESI-MS was performed on a Finnigan LCQ mass spectrometer. HR-ESI-MS was performed on a QSTARLCQ mass spectrometer.
The optical rotation was measured on a Perkin–Elmer 241 polarimeter. Silica gel: 200–300 mesh, Qingdao Ocean Chemical
Group Co. Ltd., P. R. China. TLC: HSGF254 precoated silica gel plates, 10–40 m, Yantai Chemical Plant, Yantai, P. R. China.
Sephadex LH-20 gel: Pharmacia.
ACKNOWLEDGMENT
The research work was partially supported by program for the Analytical Detective Center, Shenyang Pharmaceutical
University, and the Analytical Detective Center, Shanghai Second Military Medical University, and the Analytical Detective
Center, Yangzhou University. We are also grateful to Prof. QiShi Sun for identification of the plant.
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1.
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3.
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C. C. Zhao, J. H. Shao, X. Li, J. Xu, and J. H. Wang, Nat. Prod. Res., 20, 981 (2006).
R. Jean and M. Hassan, Sciences Naturelles, 274, 1746 (1972).
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