Two new secoiridoid glycosides from the roots of picrorhiza scrophulariiflora

Article abstract of DOI:10.1007/s10600-014-0931-y

Two new secoiridoid glycosides, named picrosecoside A (1) and picrosecoside B (2), have been isolated from the underground part of Picrorhiza scrophulariiflora. Their structures were elucidated on the basis of spectroscopic evidence.

Full text of DOI:10.1007/s10600-014-0931-y

Chemistry of Natural Compounds, Vol. 50, No. 2, May, 2014 [Russian original No. 2, March–April, 2014]
TWO NEW SECOIRIDOID GLYCOSIDES FROM THE ROOTS
OF Picrorhiza scrophulariiflora
1
1
1
1
Tong-Fei Zhu, Zong-Fa Yang, Yuan-Juan Yang, Li-Shu Chen,
1
1*
2*
Juan-Juan Hu, Zhi-Hui Yan, and Ke Jiang
Two new secoiridoid glycosides, named picrosecoside A (1) and picrosecoside B (2), have been isolated
from the underground part of Picrorhiza scrophulariiflora. Their structures were elucidated on the basis of
spectroscopic evidence.
Keywords: Picrorhiza scrophulariiflora, secoiridoid glycosides, picrosecosides A and B.
Picrorhiza scrophulariiflora grows in the high altitude regions (over 4,400 m) in the southeast of Tibet and the
northwest of Yunnan in China. The roots of this plant are used in traditional chinese medicine for the treatment of "damp-heat"
dysentery, jaundice, and "steaming of bone" [1]. This paper describes the structural elucidation and identification of two new
secoiridoid glycosides, named picrosecoside A (1) and picrosecoside B (2).
Compound 1, a pale yellow amorphous powder, has the molecular formula C H O on the basis of HR-ESI-MS
3
1 38 17
+
–1
(
m/z 705.1944 [M + Na] ). IR absorptions (KBr, ꢀmax, cm ): 3436, 1693, 1628, 1611, and 1509 suggested the existence of a
hydroxyl, an ꢁ,ꢂ-unsaturated ester, and aromatic groups in compound 1. The H NMR and C NMR spectra of compound 1
1
13
were quite similar to those of picrosecosides I and II [2].
1
The H NMR spectrum of compound 1 (Table 1) showed the presence of an acetal proton [ꢃ 5.37 (1H, d, J = 1.2 Hz)]
(
the J value for H-1 indicated that it was ꢂ-positioned [3]), an oxygenated methylene proton [3.98 (1H, m), 4.25 (1H, d,
J = 9.2 Hz)], an olefinic proton [7.38 (1H, d, J = 2.4 Hz)], a methylene protons [1.42 (1H, ddd, J = 3.6, 12.0, 16.4 Hz), 1.70 (1H,
d, J = 12.0 Hz)], two methine protons [2.69 (1H, m); 2.65 (1H, dd, J = 8.0, 12.0 Hz)], and one terminal vinyl group [5.22 (1H,
dd, J = 2.0, 9.0 Hz), 5.31 (1H, dd, J = 2.0, 16.8 Hz); 5.41 (1H, m)]. The above results indicated the presence of a sweroside
moiety [3], a 1,3,4-trisubstituted aromatic ring [7.09 (1H, br.s); 7.05 (2H, br.d, J = 8.0)], and a pair of trans olefinic protons at
ꢃ 7.48 and 6.24 with a coupling constant of 16.0 Hz; these signals indicated the presence of a trans-caffeoyl moiety [4, 5]. The
two signals at [ꢃꢄ4.82 (1H, d, J = 8.0 Hz)] and [4.64 (1H, d, J = 8.4 Hz)] were assigned to the anomeric proton of glucose,
indicating that compound 1 have two glucose moieties.Acid hydrolysis of 1 liberated D-glucose, which was identified by TLC
comparison with the authentic sugars. The relatively large J value for the two anomeric protons indicated that the glucoside
linkage was ꢂ (Table 1).
O
11
O
7
4
6
3
1
0
1
O
9
OH
8
R =
OH
O
O
5
''
HO
HO
O
O
R
2
O
HO
OH 1'''
1
'
3''
1''
OR
1
HO
9
''
7
''
1
, 2
O
1
2
: R = R, R = H
1 2
: R = H, R = R
1
2
1
) Chongqing Medical and Pharmaceutical College, 401331, Chongqing, P. R. China, fax: +86 23 65317958,
e-mail: chuanqichuanqi@163.com; 2) No. 324 Hospital of PLA, 400020, Chongqing, P. R. China, fax: +86 23 68762106,
e-mail: 45032009@qq.com. Published in Khimiya Prirodnykh Soedinenii, No. 2, March–April, 2014, pp. 248–250. Original
article submitted December 8, 2012.
0
0
009-3130/14/5002-0281 2014 Springer Science+Business Media New York
281

1
13
TABLE 1. H (400 MHz) and C (100 MHz) NMR Data of Compounds 1 and 2 (DMSO-d , ꢃ, ppm, J/Hz)
6
1
2
C atom
ꢃC
ꢃH
ꢃC
ꢃH
Secoiridoid
1
3
4
5
6
7
8
9
95.5
150.7
104.9
27.2
24.1
67.6
5.37 (d, J = 1.2)
7.38 (d, J = 2.4)
95.7
151.3
104.9
26.7
24.2
67.6
5.45 (d, J = 1.2)
7.50 (d, J = 2.4)
2.69 m
1.42 (ddd, J = 3.6, 12.0, 16.4), 1.70 (d, J = 12.0)
3.98 m; 4.25 (d, J = 9.2)
3.06 m
1.52 (ddd, J = 4.0, 12.0, 16.0), 1.78 (d, J = 12.0)
4.28 m; 4.37 (d, J = 8.8)
131.9
41.0
5.41 m
2.65 (dd, J = 8.0, 12.0)
132.3
41.4
5.50 (ddd, J = 8.0, 10.0, 16.8)
2.70 (dd, J = 8.0, 12.0)
1
1
0
1
120.5
163.6
5.22 (dd, J = 2.0, 9.0), 5.31 (dd, J = 2.0, 16.8)
120.3
164.5
5.27 (dd, J = 2.0, 9.0), 5.35 (dd, j = 2.0, 16.8)
Caffeoyl
1
2
3
4
5
6
7
8
9
ꢅꢅ
ꢅꢅ
ꢅꢅ
ꢅꢅ
ꢅꢅ
ꢅꢅ
ꢅꢅ
ꢅꢅ
ꢅꢅ
128.6
115.0
146.6
147.4
115.8
120.8
144.5
115.8
165.6
128.6
115.0
146.8
147.5
116.0
120.8
144.9
115.9
165.7
7.09 br.s
7.17 br.s
7.05 (br.d, J = 8.0)
7.05 (br.d, J = 8.0)
7.48 (d, J = 16.0)
6.24 (d, J = 16.0)
7.12 (br.d, J = 8.0)
7.12 (br.d, J = 8.0)
7.48 (d, J = 16.0)
6.24 (d, J = 16.0)
Glc-1
1
2
3
4
5
6
ꢅ
ꢅ
ꢅ
ꢅ
ꢅ
ꢅ
95.4
73.2
73.5
70.2
77.5
60.8
4.82 (d, J = 8.0)
4.65 (dd, J = 9.2, 8.0)
3.51 m
3.18 (dd, J = 8.8, 9.2)
3.34 m*
98.0
73.2
73.6
71.2
74.9
60.7
4.64 (d, J = 8.0)
3.15 m
3.52 m*
4.66 (dd, J = 9.6, 11.6)
3.52 m*
3.50 m*; 3.71 m*
3.49 m*; 3.71 m*
Glc-2
1
2
3
4
5
6
ꢅꢅꢅ
ꢅꢅꢅ
ꢅꢅꢅ
ꢅꢅꢅ
ꢅꢅꢅ
ꢅꢅꢅ
101.5
75.8
73.2
69.7
77.2
60.7
4.64 (d, J = 8.4)
3.34–3.50 m*
3.34–3.50 m*
3.16 m*
3.34–3.35 m*
3.50 m*; 3.71 m*
101.5
75.8
73.2
69.8
77.2
60.7
4.79 (d, J = 7.2)
3.30 m*
3.31 m*
3.17 m*
3.35 m*
3.49 m*; 3.71 m*
_
_____
*
Signal pattern unclear due to overlapping.
The 13C NMR spectrum of 1 (Table 1) showed the presence of one carbonyl carbon (ꢃ 165.6) of the caffeoyl moiety,
eight olefinic carbons (147.4–115.0), and characteristic signals of two glucopyranosyl groups (101.5–60.7). The chemical
shift of the anomeric carbon (ꢃ 101.5) suggested that glucose 1 was glycosylated with phenol; in addition, the aglycone moiety
containing ten carbon signals showed the presence of the sweroside moiety (95.5, 150.7, 104.9, 27.2, 24.1, 67.6, 131.9, 41.0,
1
20.5, 163.6).
The HMBC (Fig. 1) correlation between 3ꢅꢅ-OH and C-2ꢅꢅ, H-1ꢅꢅꢅ and C-4ꢅꢅ demonstrated that glucose 2 was connected
to the C-4ꢅꢅ oxygen atom. The correlation between H-2ꢅ and the carbonyl carbon and the downfield shift of the oxygenated
methenyl proton at ꢃ 4.65 (H-2ꢅ) suggested that the trans-caffeyl moiety was attached at C-2ꢅ of the glucose 1. The relative
configuration of 1 was determined by analysis of the NOESY spectra. The correlation between H-5 (ꢃ 2.69) and H-9 (2.65)
showed that the two protons were positioned on the same side. Thus, the structure and relative stereochemistry of 1 were
determined to be those shown in Fig. 1.
282

O
H
O
O
H
OH
1
O
O
O
OH
2
HO
O
HO
O
HO
HO
OH
HO
O
1
HMBC (H
C), NOESY (H
H)
Fig. 1. Key HMBC and NOESY correlations of 1.
Compound 2 was obtained as a pale yellow amorphous powder. Its molecular formula was determined as C H O
1 38 17
3
+
1
13
from the [M + Na] quasi-ion peak at m/z 705.1994 in the HR-ESI-MS spectra. The H NMR and C NMR spectra of
compound 2 were quite similar to those of 1 (Table 1), except for the signals originating from the linkage between the carbonyl
carbon and the glucose 1. The HMBC correlation between H-4ꢅ and the carbonyl carbon, and the downfield shift of the
oxygenated methenyl proton at ꢃ 4.66 (H-4ꢅ), suggested that the trans-caffeyl moiety was attached at the C-4ꢅ oxygen atom.
Accordingly, picrosecoside II was determined to have the structure 2.
EXPERIMENTAL
General Experimetal Procedures. UV spectra were recorded on a Milton Roy Spectronic 1201 spectrophotometer,
and FTIR spectra were measured on a PerkinElmer 157G infrared spectrophotometer. Optical rotations were obtained using a
1
13
PerkinElmer 241-MC polarimeter. H NMR (400 MHz) and C NMR (100 MHz) spectra were obtained on a Bruker AV 400
spectrometer with DMSO-d as the solvent and TMS as an internal standard. HR-ESI-MS data were measured with a Bruker
6
AOEXIII 7.0 TESLA FTMS. HPLC was conducted using reverse-phase columns (Mightysil RP-18 and 8, Kantho Chemical
Co. Ltd.) with the MeOH–H O solvent system. Column chromatography was carried out on silica gel (Qingdao Marine
2
Chemical Company China, 200–300 mesh) and Sephadex LH-20 (Amersham Pharmacia Biotech AB). Silica GF254 for TLC
was produced by Qingdao Marine Chemical Company, China and Merck.
Plant Material. Roots of Picrorhiza scrophulariiflora were collected in October 2006 in Sichuan Province, China
and identified by Prof. Qi-shi Sun (Shenyang Pharmaceutical University). A voucher specimen has been deposited in the
Herbarium of the School of Traditional Chinese Medicine of Shenyang Pharmaceutical University, China.
Extraction and Isolation. The dried and ground roots (underground parts) of Picrorhiza scrophulariiflora (3.0 kg)
were successively extracted three times with 90% EtOH under reflux. After removal of the solvent in vacuo, the residue
(
1.6 kg) was suspended in H O and then extracted successively with petroleum ether (br 60–90ꢆC), EtOAc, and n-BuOH. The
2
n-BuOH layer was concentrated in vacuo to give a viscous residue (500 g), which was then dissolved in water (2 L) and
subjected to macroporous D-101 resin column chromatography and eluted successively with water and ethanol (water, 30%,
5
0%, and 100% ethanol). The 50% EtOH eluted fraction was evaporated in vacuo to yield a residue (140 g) that was subjected
to silica gel column chromatography and eluted with mixtures of CHCl –MeOH of increasing polarity to give eight fractions
3
(
Frs.1–8).
Fraction 3 (28.5 g) was chromatographed over silica gel using a EtOAc–MeOH gradient system as the eluent to yield
five fractions 3A–3E. Fraction 3B (276.6 mg) was purified by Sephadex LH-20 chromatography and further separated by
reverse-phase HPLC using MeOH–H O (57:43/48:52) as the mobile phase to yield compounds 1 (18.4 mg) and 2 (15.6 mg).
2
2
5
–1
Compound 1. Yellow amorphous powder. [ꢁ] –140.3ꢆ (c 0.45, MeOH). IR (KBr, ꢀmax, cm ): 3527, 3436, 3300,
893, 1693, 1628, 1611, 1509, 1403. For H and C NMR spectra, see Table 1. HR-ESI-MS m/z 705.1944 ([M + Na] ) (calcd
D
1
13
+
2
for C H O Na 705.1939).
3
1 36 17
283

2
5
–1
Compound 2. Yellow amorphous powder. [ꢁ] –185.6ꢆ (c 0.39; MeOH). IR (KBr, ꢀ , cm ): 3530, 3436, 3298,
D
max
1
13
+
2
889, 1701, 1628, 1609, 1509, 1413. For H and C NMR spectra, see Table 1. HR-ESI-MS m/z 705.1994 ([M + Na] ) (calcd
for C H O Na 705.1981).
3
1
36 17
Acid Hydrolysis of 1 and 2. A solution of each compound (1 and 2) (6 mg) in 2 N TFA (3 mL) was refluxed at 100ꢆC
for 3 h. The reaction mixture was extracted with EtOAc. The EtOAc extract of compounds 1 and 2 was proved to contain
caffeic acid by direct TLC comparison with authentic samples. D-glucose was found to be the only sugar present in the water
part following the procedure of Oshima, Yamauchi, and Kumanotani [6].
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1
.
State Pharmacopeia Commission of P. R. China, Pharmacopeia of the P. R. China, Peopleꢅs Health Publishing House,
Beijing, P. R. China, 1995, Vol. I, p. 204.
2
3
4
5
6
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.
L. C. Zou, T. F. Zhu, S. C. Gan, D. C. Wang, Y. Zhang, and X. M. Deng, Chin. Chem. Lett., 19, 1224 (2008).
S. Kumar, O. P. Sati, V. D. Semwal, M. Nautiyal, S. Sati, and Y. Takeda, Phytochemistry, 53, 499 (2000).
T. F. Zhu, K. Y. Huang, X. M. Deng, Y. Zhang, H. Xiang, H. Y. Gao, and D. C. Wang, Molecules, 13, 729 (2008).
J. Tian, Y. M. Zhao, and X. H. Luan, Nat. Prod. Res. Dev., 19, 247 (2007).
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