A new flavanone glucoside from the flowers of carthamus tinctorius and assignment of absolute configuration

Article abstract of DOI:10.1007/s10600-014-0977-x

A new flavanone glucoside was isolated from the flowers of Carthamus tinctorius. The structural elucidation was performed mainly by mean of FAB-MS, NMR, and acid hydrolysis; the absolute configuration was also determined by circular dichroism spectroscopy.

Full text of DOI:10.1007/s10600-014-0977-x

Chemistry of Natural Compounds, Vol. 50, No. 3, July, 2014 [Russian original No. 3, May–June, 2014]
A NEW FLAVANONE GLUCOSIDE FROM THE FLOWERS
OF Carthamus tinctorius AND ASSIGNMENT
OF ABSOLUTE CONFIGURATION
Jiang Liu, Jing Zhang, and Feng Wang1
1
2*
A new flavanone glucoside was isolated from the flowers of Carthamus tinctorius. The structural elucidation
was performed mainly by mean of FAB-MS, NMR, and acid hydrolysis; the absolute configuration was also
determined by circular dichroism spectroscopy.
Keywords: Carthamus tinctorius, Compositae, flavanone glucoside.
Carthamus is one of the most important genera in the Compositae family. The dried flower of Carthamus tinctorius
(
safflower) has long been used traditionally in China and southeast Asia. It showed therapeutic potential for treating coronary
heart disease, stroke, gynecological disease, angina, and hypertension [1–7]. Many studies concerning the chemical constituents
of Carthamus tinctorius have been carried out, which have led to the isolation of a series of secondary metabolites, including
flavonoids, alkaloids, lignans, and fatty acids. These constituents were found to be responsible for the overall curative effects
of safflower [8–18]. In this article, we present the isolation and structure elucidation of a new flavanone glucoside based on
extensive spectroscopic and chemical studies.
3
0
Compound 1 was obtained as white needles, [ꢀ] –20.2ꢁ in MeOH; its IR spectrum (KBr) showed absorption bands
D
–
1
–1
–1
for hydroxyl (3390 cm ), conjugated carbonyl (1645 cm ) groups, and aromatic rings (1616 and 1520 cm ). HR-FAB-MS
+
showed an m/z 473.1062 (M + Na) corresponding to the molecular formula C H O .
2
1 22 11
1
The H NMR spectrum of compound 1 exhibited doublets at ꢂ 5.80 and 5.89 (each 1H, d, J =2.10 Hz) due to meta
coupling of two protons of the A-ring. The specific dihydropyrone core of a flavanone aglycone was confirmed by the
1
H NMR spectrum, in which the signals due to the H-2, H-3a, and H-3b protons were observed as an ABX type at ꢂ 5.44
(
dd, JXA = 12.36, J = 3.42 Hz), 2.71 (dd, JAB = 17.16, JBX = 3.42 Hz, cis), and 3.21 (dd, JAB = 17.16, JAX = 12.36 Hz, trans),
XB
1
respectively. The H NMR data also showed signals attributed to an anomeric proton at ꢂ 4.69 (1H, d, J = 7.56 Hz, H-1ꢃꢃ),
1
3
together with five glycosyl protons in the range ꢂ 3.8–3.4. The C NMR and DEPT spectra of 1 displayed 21 carbon signals
consisting of six carbons of the glycosyl moiety. All of the above data revealed that 1 is a flavanone monoglycoside with a ꢄ
sugar unit; acid hydrolysis of compound 1 also indicates that the monosaccharide moiety was a D-glucose.
The signals in the H and C NMR spectra were unambiguously assigned by HMQC, HMBC, H–H COSY, and
NOESY experiments (Fig. 1). Long-range correlation from the anomeric proton ꢂ 4.69 (d, J = 7.56 Hz) to C-4ꢃ (ꢂ 145.4) in the
HMBC spectrum and the correlation between ꢂ 7.12 (d, J = 8.22 Hz, H-5ꢃ) and 4.69 (d, J = 7.56 Hz, H-1ꢃꢃ) in the NOESY
spectrum unequivocally established that the sugar linkage to the aglycone in 1 was at C-4ꢃ.
1
13
Additionally, the absolute configuration at C-2 was found to be S as it showed a negative Cotton effect at 290 nm
–
5
–5
(
ꢅꢆ = –11.2, c = 11.10 ꢇ 10 M) and positive Cotton effect (ꢅꢆ = + 8.2, c = 11.10 ꢇ 10 M) at 334 nm in the CD spectrum.
Accordingly, the structure of 1 was determined as (2S)-5,7,3ꢃ-trihydroxyflavanone-4ꢃ-O-ꢄ-D-glucopyranoside [19].
1
) College of Agronomy, Sichuan Agricultural University, 611130, Chengdu, P. R. China; 2) College of Horticulture,
SichuanAgricultural University, 625014, Yaꢃan, P. R. China, fax: +86 28 86290870, e-mail: liuzhang916@yeah.net. Published
in Khimiya Prirodnykh Soedinenii, No. 3, May–June, 2014, pp. 370–371. Original article submitted December 1, 2012.
0
0
009-3130/14/5003-0427 2014 Springer Science+Business Media New York
427

OH
H
OH
H 3''
H
HO
5
'' 6''
O
OH
6
'
4'
2''
H
O
H 1''
8
HO
9
O
O
2
1
'
OH
2
'
3
6
1
0
OH
1
H-H COSY
HMBC
NOESY
Fig. 1. Structure of compound 1.
EXPERIMENTAL
General. NMR spectra were recorded on a Varian InovaAS 600 system; CD spectra were measured on a Jasco J-720
W spectrometer; FAB-MS spectra were recorded with a JEOL JMS-SX 102A mass spectrometer. Diaion HP-20 (Mitsubishi
Chemical Corporation) and Chromatorex ODS DM1020T (100–200 mesh, Fuji Silysia Chemical Ltd.) were used for column
chromatography. Preparative HPLC: Shimadzu LC-10AD with refractive index detector; preparative column: YMC-Pack
ODS-A (250 ꢇ 20 mm i.d., S-5 ꢈm, 12 nm); sugar identification HPLC: optical rotation detector (Shodex OR-2), Kaseisorb LC
NH -60-5, 250 ꢇ 4.6 mm.
2
Plant Material. The flowers of Carthamus tinctorius were collected from Xinjiang, China in 2011. A voucher specimen
of this plant was deposited at the College of Agronomy, Sichuan Agricultural University.
Extraction and Isolation. The flowers of Carthamus tinctorius (2 kg) were extracted three times with MeOH under
reflux for 3 h. Evaporation of the solvent under reduced pressure provided the MeOH extract (40.1 g). The MeOH extract
was passed through a Diaion HP-20 column chromatograph and sequentially eluted twice with H O and MeOH to give an
2
H O-eluted fraction (15.5 g) and an MeOH-eluted fraction (24.5 g). The MeOH-eluted fraction (24.5 g) was chromatographed
2
on ODS columns using a gradient of MeOH–H O (20: 80ꢉ40: 60ꢉ60: 40ꢉ80: 20)ꢉMeOH to give 10 fractions (1–10).
2
Fraction 4 (2.0 g) was repeatedly chromatographed on RP-C [MeOH–H O (45:55)] to give 1 (6.0 mg).
1
8
2
1
Compound 1. White needles. H NMR (600 MHz, DMSO-d , ꢂ, ppm, J/Hz): 2.71 (1H, dd, J = 3.42, 17.16, H-3a),
6
3
.21 (1H, dd, J = 12.36, 17.16, H-3b), 3.40 (2H, m, H-4ꢃꢃ, 5ꢃꢃ), 3.46 (2H, m, H-2ꢃꢃ, 3ꢃꢃ), 3.71 (2H, dd, J = 3.42, 11.7, H-6ꢃꢃ), 4.69
(
1H, d, J = 7.56, H-1ꢃꢃ), 5.44 (1H, dd, J = 3.42, 12.36, H-2), 5.80 (1H, d, J = 2.10, H-6), 5.89 (1H, d, J = 2.10, H-8), 6.85 (1H,
1
3
dd, J = 2.04, 8.22, H-6ꢃ), 6.95 (1H, d, J = 2.04, H-2ꢃ), 7.12 (1H, d, J = 8.22, H-5ꢃ). C NMR (150 MHz, DMSO-d , ꢂ, ppm):
6
7
1
8.1 (C-2), 42.0 (C-3), 196.1 (C-4), 163.4 (C-5), 95.8 (C-6), 166.6 (C-7), 95.0 (C-8), 162.7 (C-9), 101.8 (C-10), 133.2 (C-1ꢃ),
14.4 (C-2ꢃ), 146.7 (C-3ꢃ), 145.4 (C-4ꢃ), 116.6 (C-5ꢃ), 117.7 (C-6ꢃ), 102.2 (C-1ꢃꢃ), 73.3 (C-2ꢃꢃ), 75.8 (C-3ꢃꢃ), 69.8 (C-4ꢃꢃ), 77.2
(
C-5ꢃꢃ), 60.7 (C-6ꢃꢃ).
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