A syringic acid derivative and two iridoid glycosides from the roots of Stachys geobombycis and their antioxidant properties

Article abstract of DOI:10.1080/14786419.2017.1405413

A new derivative of syringic acid, stageobester A (1) and two iridoid glycosides which including a new one, stageoboside A (2), were isolated from the roots of Stachys geobombycis. Their structures were elucidated on the basis of spectroscopic methods, including extensive NMR and MS spectra. In addition, all the isolates were tested for their antioxidant capacity. Compounds 1 and 2 showed moderate antioxidant activities against DPPH radical, with IC₅₀ values of 113.33?±?1.53 and 40.33?±?2.08?mg/L, respectively.

Full text of DOI:10.1080/14786419.2017.1405413

Natural Product Research
Formerly Natural Product Letters
ISSN: 1478-6419 (Print) 1478-6427 (Online) Journal homepage: http://www.tandfonline.com/loi/gnpl20
A syringic acid derivative and two iridoid
glycosides from the roots of Stachys geobombycis
and their antioxidant properties
Xianli Zhou, Sixin Huang, Pengcheng Wang, Qin Luo, Xiao Huang, Qin Xu,
Jiangke Qin, Chengqin Liang & Xu Chen
To cite this article: Xianli Zhou, Sixin Huang, Pengcheng Wang, Qin Luo, Xiao Huang, Qin
Xu, Jiangke Qin, Chengqin Liang & Xu Chen (2017): A syringic acid derivative and two iridoid
glycosides from the roots of Stachys geobombycis and their antioxidant properties, Natural Product
Research, DOI: 10.1080/14786419.2017.1405413
To link to this article: https://doi.org/10.1080/14786419.2017.1405413
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Date: 24 November 2017, At: 05:56

Natural Product research, 2017
ꢁꢁpꢂ://ꢃꢄi.ꢄꢅg/10.1080/14786419.2017.1405413
ꢀ
A syringic acid derivative and two iridoid glycosides from the
roots of Stachys geobombycis and their antioxidant properties
a
a
a
a
a
a,b
Xianli Zhou , Sixin Huang , Pengcheng Wang , Qin Luo , Xiao Huang , Qin Xu ,
c
a
a
Jiangke Qin , Chengqin Liang and Xu Chen
ꢆ
b
cꢄꢇꢇꢈgꢈ ꢄf Pꢀꢆꢅmꢆꢉy, Gꢊiꢇin Mꢈꢃiꢉꢆꢇ univꢈꢅꢂiꢁy, Gꢊiꢇin, P. r. cꢀinꢆ; Gꢊꢆngxi Kꢈy lꢆbꢄꢅꢆꢁꢄꢅy ꢄf Mꢄꢇꢈꢉꢊꢇꢆꢅ
ꢉ
Mꢈꢃiꢉinꢈ in livꢈꢅ Injꢊꢅy ꢆnꢃ rꢈpꢆiꢅ, Gꢊiꢇin Mꢈꢃiꢉꢆꢇ univꢈꢅꢂiꢁy, Gꢊiꢇin, P. r. cꢀinꢆ; sꢆꢁꢈ Kꢈy lꢆbꢄꢅꢆꢁꢄꢅy fꢄꢅ
cꢀꢈmiꢂꢁꢅy ꢆnꢃ Mꢄꢇꢈꢉꢊꢇꢆꢅ enginꢈꢈꢅing ꢄf Mꢈꢃiꢉinꢆꢇ rꢈꢂꢄꢊꢅꢉꢈꢂ, Gꢊꢆngxi Nꢄꢅmꢆꢇ univꢈꢅꢂiꢁy, Gꢊiꢇin, P. r. cꢀinꢆ
ABSTRACT
ARTICLE HISTORY
A new derivative of syringic acid, stageobester A (1) and two iridoid
glycosides which including a new one, stageoboside A (2), were
isolated from the roots of Stachys geobombycis. Their structures
were elucidated on the basis of spectroscopic methods, including
extensive NMR and MS spectra. In addition, all the isolates were
tested for their antioxidant capacity. Compounds 1 and 2 showed
moderate antioxidant activities against DPPH radical, with IC values
rꢈꢉꢈivꢈꢃ 12 sꢈpꢁꢈmbꢈꢅ 2017
aꢉꢉꢈpꢁꢈꢃ 7 Nꢄvꢈmbꢈꢅ 2017
KEYWORDS
sꢁꢆꢉꢀyꢂ gꢈꢄbꢄmbyꢉiꢂ;
ꢂyꢅingiꢉ ꢆꢉiꢃ ꢃꢈꢅivꢆꢁivꢈ;
iꢅiꢃꢄiꢃ gꢇyꢉꢄꢂiꢃꢈ; ꢆnꢁiꢄxiꢃꢆnꢁ
5
0
of 113.33 ± 1.53 and ꢀ0.33 ± ±.0ꢁ mgꢂL, respectively.
1
. Introduction
Stachys geobombycis C.Y.Wu (= S. geobombycis var. geobombycis) is widely distributed in
southern China, and the roots of this plant have been used in oriental medicine as a remedy
for the treatment of phthisis and cough, sucking blood, continuous sweating, asthma, weak
and blood deficiency, infantile malnutrition, pulmonary tuberculosis, scald, etc. (Huang et
al. ±00ꢀ; Zhang et al. ±00ꢀ). Previous chemical studies on the plants of S. geobombycis have
led to the isolation and identification of some compounds, such as baicalein, oroxylin
A, wogonin, baicalin, oleanolic acid and hederagenin (Zhang et al. ±00ꢀ). As part of our
programme to study traditional Chinese medicines, an ethanolic extract of the roots of
S. geobombycis was investigated. A new derivative of syringic acid, stageobester A (1) and
a new iridoid glycoside stageoboside A (2), together with a known iridoid glycoside,
CONTACT cꢀꢈngqin liꢆng
ꢉqꢇiꢆng@gꢇmꢉ.ꢈꢃꢊ.ꢉn; Xꢊ cꢀꢈn
ꢉꢀꢈnxꢊ@gꢇmꢉ.ꢈꢃꢊ.ꢉn
sꢊppꢇꢈmꢈnꢁꢆꢇ ꢃꢆꢁꢆ fꢄꢅ ꢁꢀiꢂ ꢆꢅꢁiꢉꢇꢈ ꢉꢆn bꢈ ꢆꢉꢉꢈꢂꢂꢈꢃ ꢆꢁ ꢀꢁꢁpꢂ://ꢃꢄi.ꢄꢅg/10.1080/14786419.2017.1405413.
©
2017 Infꢄꢅmꢆ uK limiꢁꢈꢃ, ꢁꢅꢆꢃing ꢆꢂ tꢆyꢇꢄꢅ & Fꢅꢆnꢉiꢂ Gꢅꢄꢊp

±
X. ZHOU ET AL.
melittoside (3) (Scarpati and Esposito 1967; Haruji and Hiroyuki 19ꢁ1; Cui et al. ±011), were
isolated from this extract. Compounds 2 and 3 are diglucosidic-iridoids which were consid-
ered as important taxonomic mark of Lamiaceae as identified in several related species
(
Venditti et al. ±013, ±016a, ±016b, ±017). In this paper, we report the isolation and structural
elucidation of these new compounds. Furthermore, their antioxidant properties are reported
herein.
2
. Results and discussion
Compound 1 was obtained as an amorphous powder. The UV absorption at max ±ꢁ5 nm
suggested the existence of a conjugated system, while the positive HRESIMS displayed an
+
[
M + Na] peak at m/z 365.0ꢁ37 (Calcd. 365.0ꢁꢀ3 for C H O Na) indicating a molecular for-
15
1ꢁ
9
−1
mula C H O . The IR absorption bands indicated the presence of hydroxyl (33ꢁ5 cm ), ester
carbonyl (1739, 17±3 and 1635 cm ) and aromatic rings (16±0, 1516, 1ꢀ60 and 1ꢀꢀ0 cm )
moieties. The H NMR spectrum (Table S1) showed the presence of an aromatic H-atom signal
15
1ꢁ
9
−1
−1
1
at δ 7.±9 (±H, s, H-±, 6), four methoxyls at δ 3.ꢁ6 (6H, s, MeO-3 and -5), δ 3.75 (3H, s, MeO-1′)
H
H
H
and δ 3.70 (3H, s, MeO-ꢀ′), a methylene at δ 3.03 (±H, d, J = 6.1 Hz, H-3′) and an oxygenated
H
H
methine at δ 5.60 (1H, t, J = 6.1 Hz, H-±′). The characteristic proton signals of δ 7.±9 (±H, s,
H
H
H-±, 6) and δ 3.ꢁ6 (6H, s, MeO-3, 5) suggested that there may be a symmetrical benzene
H
1
3
ring in 1. The C NMR and DEPT spectra (Table S1) exhibited 15 carbons, including seven
quaternary carbons (four aromatic and three carbonyl), three methines (two aromatic and
1
one oxygenated), one methylene and four methoxy groups. The H NMR spectrum of δ 7.±9
H
(±H, s, H-±, 6), displayed the existence of a symmetric 1,3,ꢀ,5-tetra-substituted aromatic ring.
The compound 1 was established unambiguously by the HMBC (Figure S1) correlations of
H-±, 6 (δ 7.±9, s) with C-1 (δ 1±0.3), C-ꢀ (δ 1ꢀ±.6) and C-7 (δ 166.ꢁ), MeO-3, 5 (δ 3.ꢁ6, s)
H
C
C
C
H
with C-3, 5 (δ 1ꢀ9.0), H-±′ (δ 5.60, t, J = 6.1 Hz) with C-1′ (δ 171.1), C-±′ (δ 70.±), C-3′
C
H
C
C
(δ 36.9) and C-ꢀ′ (δ 171.5), H -±′ (δ 3.03, d, J = 6.1 Hz) with C-1′, C-±′, C-3′ and C-ꢀ′, MeO-1′
C C ± H
(
δ 3.75, s) with C-1′, and MeO-ꢀ′ (δ 3.70, s) with C-ꢀ′, together with the spin systems of
H
H
1
1
H-±′ꢂH-3′ in the H– H COSY spectrum. In addition, the linkage of the benzoyl group with
C-±′ of dimethyl ±-hydroxysuccinate was supported by the HMBC correlation from H-±′ to
Figure 1. sꢁꢅꢊꢉꢁꢊꢅꢈꢂ ꢄf ꢉꢄmpꢄꢊnꢃꢂ fꢅꢄm S. geobombycis.

NATURAL PRODUCT RESEARCH
3
C-7. The configuration of C-±′ was determined as S based on the negative-specific rotation
in contrast with those of (S)-benzoyl malic acid and (R)-±-O-galloyl malic acid dimethyl ester
(
Ma et al. ±01±). Therefore, the structure of 1, named as stageobester A, was elucidated as
shown.
Compound 2 was isolated as an amorphous powder, and its molecular formula was estab-
+
lished as C H O on the basis of HRESIMS (m/z 667.1ꢁꢀ9 [M + Na] ). The IR spectrum
±
ꢁ
36 17
−1
showed absorption bands at 33ꢁꢁ, 170±, 165ꢀ, 1631, 1607, 1516 and 1ꢀꢀ5 cm , indicating
the presence of hydroxy, ester carbonyl, olefinic and aromatic functional groups. The H NMR
1
spectrum (Table S1) of 2 exhibited characteristic peaks for an oxygenated methine (δ ꢀ.ꢀ±,
H
br s) and an olefinic proton (δ 5.90, br s), two mutually coupled doublets [δ 6.ꢀ0 and 5.1ꢀ
H
H
(
each d, J = 6.5 Hz)], a pair of A B aromatic system protons [δ 7.90 and 6.ꢁ3 (each d,
± ± H
1
3
J = 9.0 Hz)] and two anomeric doublets [δ ꢀ.6ꢀ and ꢀ.6ꢁ (each d, J = 7.ꢁ Hz)]. The C NMR
H
spectrum showed ±ꢁ carbon signals including 1± for two glucopyranosyl units, seven for a
p-hydroxybenzoyl group, and the remaining nine for an iridoid skeleton. Analysis of its 1D
and ±D NMR spectra indicated that 2 has structural features closely similar to those of
1
0-O-(E)-p-coumaroylmelittoside (2a) (Alipieva et al. ±009). Just like 2a, compound 2 had an
iridoid structure and two glucopyranosyl moieties. The main difference between them was
that the p-coumaroyl moiety of 2a was replaced by a p-hydroxybenzoyl group in 2. The two
spin-spin coupled doublets [δ 7.90 and 6.ꢁ3 (each d, J = ꢁ.ꢁ Hz)], as well as the HMBC cor-
H
relation between δ 7.90 (±H, d, J = ꢁ.ꢁ, Hz, H-1′″, 6″′) and C-1″′, C-ꢀ″′ and C-7″′ suggested
H
the presence of a p-hydroxybenzoyl unit. The connection of p-hydroxybenzoyl group and
C-10 was confirmed by the HMBC correlation of H-10 (δ ꢀ.90) with the ester carbonyl (δ
167.6) of the p-hydroxybenzoyl group. Thus, the structure of 2 (stageoboside A) was eluci-
dated as shown.
Compound 3 was identified as melittoside by comparison of its NMR data with that in
the literature (Scarpati and Esposito 1967; Haruji and Hiroyuki 19ꢁ1; Cui et al. ±011).
In addition, all the isolates were evaluated for their in vitro antioxidant activities of DPPH
radical and hydroxyl radical scavenging activities (Table 1). As a result, compounds 1 and 2
showed moderate antioxidant activities against DPPH radical, with IC values of 113.33 ± 1.53
50
and ꢀ0.33 ± ±.0ꢁ mgꢂL, respectively. And compound 2 was also displayed hydroxyl radical
scavenging activity with IC values of 91.ꢀ0 ± 1.15 mgꢂL.
5
0
3
. Experimental section
3
.1. General experimental procedures
Optical rotations were recorded on a JASCO P-10±0 digital polarimeter (Horiba, Kyoto, Japan).
UV spectra were recorded on a UV-±ꢀ01PC spectrometer (Shimadzu, Kyoto, Japan). IR spectra
Table 1. Fꢅꢈꢈ ꢅꢆꢃiꢉꢆꢇ ꢂꢉꢆvꢈnging ꢆꢉꢁiviꢁiꢈꢂ ꢄf ꢉꢄmpꢄꢊnꢃꢂ.
IC50 (DPPH)ꢂ(mgꢂL)a
IC50 (hydroxyl)ꢂ(mgꢂL)a
Compound
1
2
3
113.33 ± 9.24
40.33 ± 2.08
–
–
91.40 ± 1.15
–
110.30 ± 11.59
b
Vꢉ
25.33 ± 1.53
ꢆ
eꢆꢉꢀ vꢆꢇꢊꢈ iꢂ ꢈxpꢅꢈꢂꢂꢈꢃ ꢆꢂ mꢈꢆn ± sd (n = 3).
Pꢄꢂiꢁivꢈ ꢉꢄnꢁꢅꢄꢇ gꢅꢄꢊp.
b

ꢀ
X. ZHOU ET AL.
were measured with a Bruker Tensor ±7 infrared spectrometer with KBr pellets (Bruker,
Karlsruhe, Germany). 1D and ±D NMR spectra were performed on Bruker AM-500 MHz spec
-
trometers (Bruker Optics, Ettlingen, Germany). High-resolution electrospray-ionisation mass
spectra (HR-ESI-MS) was obtained on an Agilent 6±10 ESIꢂTOF mass spectrometer (Agilent,
Santa Clara, CA, USA). Column chromatography (CC) was carried out on silica gel (100–
±00 and ±00–300 mesh, Qingdao Marine Chemical, Inc., Qingdao, China), MCI gel (75–150 μM,
Mitsubishi Chemical Corporation, Tokyo, Japan), Sephadex LH-±0 (Amersham Pharmacia
Biotech, Uppsala, Sweden) and Lichroprep RP-1ꢁ gel (ꢀ0–63 μM, Merck, Merck & Co Inc,
Darmstadt, Germany). Semi-preparative HPLC was carried out on an Agilent 1±60 liquid
chromatography (LC) with a Zorbax SB-C1ꢁ column (5 μM, 9.ꢀ mm × ±5 cm) (Agilent, Santa
Clara, CA, USA). Absorbance was recorded on an Infinite M±00 Pro multifunctional microplate
tester (Tecan, Austria). TLC was carried out on silica gel 60 F±5ꢀ on glass plates (Qingdao
Marine Chemical, Inc., Qingdao, China) using various solvent systems and spots were visual-
ised by heating the silica gel plates sprayed with 10% H SO in EtOH (VꢂV = 10:90). Glucose
±
ꢀ
was obtained from J&K Scientific Ltd. (Beijing, China). Vitamin C, Ethanol, H O , Tris and HCl
±
±
were obtained from XiLong Scientific Ltd. (Guangdong, China). DPPH and salicylic acid were
obtained from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China).
3
.2. Materials
The roots (10.0 kg) of S. geobombycis C.Y.Wu (= S. geobombycis var. geobombycis) were col-
lected in Guigang county of Guangxi province, People’s Republic of China, in September
±01ꢀ, and was identified by Mr. De-Qing Huang, College of Pharmacy, Guilin Medical
University. The voucher specimen (No. ±01ꢀ09001) has been deposited in the College of
Pharmacy, Guilin Medical University, People’s Republic of China.
3
.3. Extraction and isolation
The powder-dried roots of S. geobombycis (10.0 kg) were extracted with 95% EtOH (30 L × 3)
at room temperature (each 7± h). After concentrated in vacuo to get a residue, the extract
was suspended in H O and partitioned successively with ethylthe acetate (EtOAc) and n-bu-
±
tanol (BuOH), to obtain a EtOAc extract (103.0 g) and a BuOH extract (133.0 g). The EtOAc
part was subjected to silica gel column chromatograph (100–±00 mesh, 10 × 70 cm, 1.5 kg)
eluted with CHCl –MeOH (1:0, 9:1, ꢁ:±, ±:1, 1:1, and 0:1, vꢂv) to afford fractions A–G based on
3
the TLC characteristics. The further separation of fraction B (ꢁ.5 g) by MCI gel column chro-
matography, eluted with MeOH-H O (30, 50, 70 and 100%), yielded fractions B1–Bꢀ. Fraction
±
B1 finally purified by semi-preparative HPLC eluted with MeOH-H O (76%, flow rate 3 mLꢂ
±
min) to yield compound 1 (±6.ꢁ mg). The BuOH extract was chromatographed using silica
gel column (100–±00 mesh, 10 × 70 cm, 1.5 kg), eluting with a CHCl –MeOH gradient system
3
(
1:0, 9:1, ꢁ:±, ±:1, 1:1, and 0:1, vꢂv), to give fractions I–VI. Fraction II (9.3 g) was separated by
Sephadex LH-±0 column (100% MeOH) to yield five subfractions (IIa–IIe). Fractions IIc was
subjected to semi-preparative HPLC (eluted with ±5% MeOH-H O, 3 mLꢂmin) to afford com-
±
pound 3 (71.9 mg). Fraction V (6.3 g) was fractionated by Sephadex LH-±0 column (100%
MeOH) to yield five subfractions (Va–Ve). Fractions Vc was purified by semi-preparative HPLC
(
eluted with 10% MeOH-H O, 3 mLꢂmin) to afford compound 2 (±9.7 mg).
±

NATURAL PRODUCT RESEARCH
5
3
.3.1. Stageobester A (1)
24
Amorphous powder; [ꢀ]D − 233.3 (c = 0.70, MeOH); UV (MeOH) λmax (log ε): ±±0 (ꢀ.10), ±ꢁ5
(
1
3.ꢁ6) nm; IR (KBr) ν 33ꢁ5, ±957, 1739, 17±3, 1635, 16±0, 1516, 1ꢀ60, 1ꢀꢀ0, 1339, 1±1±,
max
−
1
1
13
11±, 60± cm ; H and C NMR data, see Table S1 and Figures Sꢀ–S7; ESI-MS: m/z 365
+
+
[
M + Na] ; HR-ESI-MS m/z 365.0ꢁ37 [M + Na] (Calcd for C H O Na, 365.0ꢁꢀ3) (Figure S3).
15 1ꢁ 9
3
.3.2. Stageoboside A (2)
24
Amorphous powder; [ꢀ]D − 73.3 (c = ±.50, MeOH); UV (MeOH) λmax (log ε): ±10 (ꢀ.31), ±60
(
1
6
ꢀ.01), 335 (3.6±) nm; IR (KBr) ν 33ꢁꢁ, ±9±5, 170±, 165ꢀ, 1631, 1607, 1516, 1ꢀꢀ5, 137±, 1±75,
max
13
−1 1
166, 109ꢁ, 103ꢀ cm ; H and C NMR data, see Table S1 and Figures S1±–S15; ESI-MS: m/z
+
+
67 [M + Na] ; HR-ESI-MS m/z 667.1ꢁꢀ9 [M + Na] (Calcd for C H O Na, 667.1ꢁꢀ5) (Figure
±ꢁ 36 17
S11).
3
.4. Acid hydrolysis of compound 2
The absolute configuration of the d-glucose of compound 2 was determined by the method
reported by Wang et al. (±006). Compound 2 (5 mg) was hydrolysed with ± M HCl (1.0 mL)
by refluxing on a boiling water bath for ± h. The hydrolysate was partitioned between H O
±
and AcOEt. The aqueous layer was concentrated in vacuo to give a residue. Glucose was
identified from the residue by TLC comparison with an authentic sample with BuOHꢂAcOHꢂ
H O 5 :1:5 (upper layer).
±
3
.5. Evaluation of antioxidant activity
3
.5.1. DPPH radical scavenging activity
The capacities of the isolates to clear DPPH were examined using the method of (Chen
et al. ±011). The scavenging ability was calculated as follows: scavenging activity (%) =
[
1 − (A − A )／A ] × 100. Where A is the absorbance of DPPH solution without sample, A
1 ± 0 0 1
is the absorbance of the test sample mixed with DPPH solution and A is the absorbance of
±
the sample without DPPH solution. Vitamin C (Vc) was used as a positive control.
3
.5.2. Hydroxyl radical scavenging activity
Hydroxyl radical scavenging assay was performed as described in (Pu et al. ±016), and vitamin
C was used as a positive control. Scavenging activity was determined by the following equa-
tion: scavenging activity (%) = [1 − (A − A )／A ] × 100. Where A is the absorbance of blank
1
±
0
0
(
water instead of sample), A is the absorbance of sample and A is the absorbance of back-
1
±
ground (water instead of H O ).
±
±
4
. Conclusion
In summary, two new compounds stageobester A (1) and stageoboside A (2), and a known
iridoid glycoside melittoside, were isolated from the roots of S. geobombycis for the first time.
All isolates were also evaluated for their in vitro antioxidant activities (Table 1). Compounds
1
and 2 showed moderate effects in the DPPH radical scavenging assay, but compound 3
was little. This may be for the reason of that the compounds 1 and 2 own phenolic hydroxyl

6
X. ZHOU ET AL.
groups, which have been reported that they had high eliminating capacity of the DPPH
radical (Shahidi et al. 199±).
Disclosure statement
No potential conflict of interest was reported by the authors.
Funding
This work was supported by the National Natural Science Foundation of China [grant number 31560100];
the Science and Technology Research Project of Guangxi University [grant number YB±01ꢀ±7±]; the
project was funded by State Key Laboratory for Chemistry and Molecular Engineering of Medicinal
Resources (Guangxi Normal University) [grant number CHEMR±017-B15].
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