Secoiridoid Glycosides from the Roots of Picrorhiza scrophulariiflora

Article abstract of DOI:10.1007/s10600-018-2444-6

A new secoiridoid glycoside, named picrogentioside D (1), has been isolated from the underground parts of Picrorhiza scrophulariiflora, together with three known compounds, picrogentioside C (2), scroneoside A (3), and scrophuloside B (4). Their structures were elucidated on the basis of spectroscopic evidence.

Full text of DOI:10.1007/s10600-018-2444-6

DOI 10.1007/s10600-018-2444-6
Chemistry of Natural Compounds, Vol. 54, No. 4, July, 2018
SECOIRIDOID GLYCOSIDES FROM THE ROOTS
OF Picrorhiza scrophulariiflora
Tong-Fei Zhu,1 Jih-Jung Chen, Yuan-Juan Yang,
,2
3
1,2
4
1,2
Qing-Wen Sun, Lin-Feng Hu,
1
,2*
1,2*
Zhi-Hui Yan,
and Ping Li
A new secoiridoid glycoside, named picrogentioside D (1), has been isolated from the underground parts
of Picrorhiza scrophulariiflora, together with three known compounds, picrogentioside C (2), scroneoside A
(
3), and scrophuloside B (4). Their structures were elucidated on the basis of spectroscopic evidence.
Keywords: Picrorhiza scrophulariiflora, secoiridoid glycoside, picrogentioside D.
The plant Picrorhiza scrophulariiflora (Scrophulariaceae) 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, known to be rich in terpenoids, iridoid
glycosides, phenolic glycosides, and phenylethanoid glycosides [1–7], are used in traditional Chinese medicine for the treatment
of damp-heat dysentery, jaundice, and steaming of bone [8]. Here we report the isolation and characterization of a new
secoiridoid glycoside, named picrogentioside D (1) (Fig. 1), as well as three known compounds, picrogentioside C (2) [5],
scroneoside A (3) [6], and scrophuloside B (4) [7].
2
5
Picrogentioside D (1) is a yellow amorphous powder, [ꢀ] –130.2ꢁ (c 0.50, MeOH). The molecular formula C H O
D
26 34 14
+
was assigned for 1 on the basis of HR-ESI-MS at m/z 593.1845 [M + Na] (calcd for C H O Na, 593.1841). Structural
2
6 34 14
assessment of 1 was accomplished using a combination of NMR techniques, along with comparisons with the assignments of
picrogentioside C [5].
1
The H NMR spectrum of 1 (Table 1) showed the presence of three methoxyl groups [ꢂ 3.55 (3H, s), 11-OCH ; 3.81
3
(
6H, s), 3ꢃꢃ, 5ꢃꢃ-OCH ], an acetal proton [ꢂ 5.52 (1H, d, J = 7.2 Hz), H-1], protons of an oxygenated methylene [ꢂ 4.28 (1H, m),
3
4
.19 (1H, m, H -7] and a methylene [ꢂ 1.87 (1H, m), 1.96 (1H, m), H -6], two methine protons [ꢂ 2.87 (1H, dd, J = 6.8, 12.0 Hz),
2
2
H-5; 2.62 (1H, dd, J = 7.2, 12.8 Hz), H-9], an olefinic proton [ꢂ 7.50, s, H-3], and one terminal vinyl group [ꢂ 5.25 (1H, br.d,
J = 10.8 Hz), 5.34 (1H, br.d, J = 17.2 Hz, H -10); 5.75 (1H, m, H-8)]. These signals indicated one secologanol moiety [9–11].
2
Furthermore, the spectrum showed the presence of a syringic acid moiety [12], which was evident from two aromatic
H-atoms at ꢂ 7.21 (2H, s, H-2ꢃꢃ, 6ꢃꢃ), and two methoxyl groups at ꢂ 3.81 (6H, s, 3ꢃꢃ, 5ꢃꢃ-OCH ). In addition, one anomeric
3
1
3
H-atom was observed at ꢂ 4.54 (1H, d, J = 8.0 Hz) which, combined with the C NMR signals at ꢂ 98.8–61.2 (Table 1),
is typical for one ꢄ-glucopyranosyl moiety. The sugar component was identified as D-glucopyranoside by co-HPLC
analysis of its 1-[(S)-N-acetyl-ꢀ-methylbenzylamino]-1-deoxyalditol acetate derivative with the same derivative of the standard
sugar [13]. The relatively large J value of the two anomeric protons indicated that the glucoside linkage had a ꢄ-configuration.
Compared with the secologanol moiety [9–11] signals, the syringic acid moiety should be attached at C-7 of the
secologanol moiety by the downfield shift of the C-7 protons at ꢂ 4.19 and 4.28 (H -7) and of the C-7 signal at ꢂ 63.1.
2
1
) Chongqing Medical and Pharmaceutical College, 401331, Chongqing, P. R. China, fax: +86 23 61969190,
e-mail: chuanqichuanqi@163.com; liping653604@sina.com; 2) Chongqing Engineering Research Center of Pharmaceutical
Sciences, 401331, Chongqing, P. R. China; 3) National Yang-Ming University, Taipei, 11221, Taiwan, P. R. China; 4) Guiyang
College of Traditional Chinese Medicine, Guiyang, 550025, Guizhou, P. R. China. Published in Khimiya Prirodnykh Soedinenii,
No. 4, July–August, 2018, pp. 573–575. Original article submitted February 14, 2017.
0
0
009-3130/18/5404-0677 2018 Springer Science+Business Media, LLC
677

TABLE 1. 13C (100 MHz) and H (400 MHz) NMR Data of 1 (DMSO-d , ꢂ, ppm, J/Hz)
1
6
C atom
ꢂC
ꢂH
C atom
ꢂC
ꢂH
1
3
4
5
6
7
8
9
95.7
152.0
109.4
30.4
29.1
63.1
134.7
43.3
118.9
5.52 (d, J = 7.2)
7.50 (s)
2ꢃꢃ
3ꢃꢃ
4ꢃꢃ
5ꢃꢃ
106.8
147.5
140.6
147.5
106.8
165.5
56.0
98.8
76.7
73.0
70.0
7.21 (s)
–
–
–
–
2.87 (dd, J = 6.8, 12.0)
1.96 (m); 1.87 (m)
4.28 (m); 4.19 (m)
5.75 (m)
2.62 (dd, J = 7.2, 12.8)
5.25 (br.d, J = 10.8)
6ꢃꢃ
C=O
3ꢃꢃ, 5ꢃꢃ-OCH3
7.21 (s)
–
3.81 (s)
1ꢃ
2ꢃ
3ꢃ
4ꢃ
5ꢃ
6ꢃ
4.54 (d, J = 8.0)
3.15 (m)
2.95 (t, J = 8.0)
3.02 (t, J = 9.2)
3.25 (m)
3.43 (m); 3.69 (m)
1
0
5
.34 (br.d, J = 17.2)
1
1
166.6
51.0
119.4
–
3.55 (s)
–
1
1-OCH3
ꢃꢃ
77.3
61.2
1
OCH
3
3
''
HO
O
H
OCH
3
H
H 11
1
''
O
5''
H CO
3
6
5
3
7
9
O
10
O
1
H
H
H
O
HO
O
1
OH
'
HO
HO
1
HMBC
NOESY
Fig. 1. Key HMBC and NOESY correlations
of compound 1.
The relative configuration of 1 was determined by analysis of the NMR coupling constants and with the aid of
NOESY experiments (Fig. 1). A J (1, 9) value of 7.2 Hz suggested a trans-diaxial orientation for H-1 and H-9 [14–16], and the
NOESY cross-peaks between H-5 and H-9, as well as between Hꢄ-6 and H-9, revealed that they were on the same side of the
molecular plane (ꢄ). From the above data, the structure of 1 was established as shown in Fig. 1.
EXPERIMENTAL
General Experimetal Procedures. Optical rotations were obtained using a PerkinElmer 241-MC polarimeter.
1
H NMR (400 MHz) and 13C NMR (100 MHz) spectra were obtained on a Bruker AV400 spectrometer with DMSO-d as
6
solvent and TMS as internal standard. HR-ESI-MS data were measured with a Bruker 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
2
system. Colum chromatography was carried out on silica gel (Qingdao Marine Chemical Company, China, 200–300 mesh)
and Sephadex LH-20 (Amersham Pharmacia BiotechAB). Silica GF254 for TLC was obtained from Qingdao Marine Chemical
Company, China and Merck.
Plant Material. Roots of Picrorhiza scrophulariiflora were collected in June 2014 in Sichuan Province, China and
identified by Prof. Qing-Wen Sun (Guiyang College of Traditional Chinese Medicine).Avoucher specimen has been deposited
in the Chongqing Medical and Pharmaceutical College, China.
Extraction and Isolation. The dried and ground roots (underground parts) of Picrorhiza scrophulariiflora (2.5 kg)
were successively extracted three times with MeOH under reflux. After removal of the solvent in vacuo, the residue (1.09 kg)
678

was suspended in H O and then extracted successively with n-hexane, EtOAc, and n-BuOH. The EtOAc layer was concentrated
2
in vacuo to give a viscous residue (175 g), which was subjected to silica gel column chromatography eluting with mixtures of
CH Cl –MeOH of increasing polarity to give eight fractions (Frs. 1–8). Fraction 7 (19.0 g) was further separated by silica gel
2
2
column chromatography using CH Cl –MeOH gradient as eluent to afford five fractions (Frs. 6A–6E). Fraction 6B (2.3 g)
2
3
was further purified by Sephadex LH-20 and further separated by preparative thin-layer chromatogram to yield compounds 1
4.2 mg), 3 (3.3 mg), and 4 (4.7 mg). Fraction 6C was purified by Sephadex LH-20 and further separated by preparative
(
thin-layer chromatogram to afford compound 2 (5.4 mg).
Compound 1. Yellow amorphous powder; [ꢀ] –130.2ꢁ (c 0.50, MeOH). For H and 13C NMR spectra, see Table 1.
2
5
1
D
+
HR-ESI-MS m/z 593.1845 [M + Na] (calcd for C H O Na, 593.1841).
2
6 34 14
Acid Hydrolysis of 1. A solution of compound 1 (6 mg) in 2 N TFA (3 mL) was refluxed at 100ꢁC for 3 h. The
reaction mixture was extracted with EtOAc. D-Glucose was found to be the only sugar present in the water part following the
procedure of Oshima, Yamauchi, and Kumanotani [13]. The H O layer was neutralized by passing through an ion exchange
2
resin (Amberlite MB-3) column and concentrated under reduced pressure to dryness. The residue was dissolved in H O (1 mL),
2
to which L-(–)-ꢀ-methylbenzylamine (5 mg) and NaBH CN (8 mg) in EtOH (1 mL) were added. The mixture was stirred at
3
4
0ꢁC for 4 h, then acidified by addition of glacial AcOH (0.2 mL) and evaporated to dryness. The resulting solid was acetylated
with Ac O (0.3 mL) in pyridine (0.3 mL) for 24 h at room temperature. After evaporation, H O (1 mL) was added to the
2
2
residue. The solution was passed through a Sep-Pak C18 cartridge and washed with H O and CH CN. The CH CN eluate was
2
3
3
analyzed by HPLC under the following conditions: solvent, MeCN–H O (2:3); flow rate, 0.8 mL/min; detection, UV 230 nm.
2
The derivative of D-glucopyranose was detected with t 17.3 min.
R
ACKNOWLEDGMENT
This study was supported by the Science and Technology Research Project of Chongqing Municipal Education
Commission (No. KJ1502701) and the Traditional Chinese Medicine Science and Technology Project of Chongqing City
Health and Family Planning Commission (No. ZY201702127).
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