Acylglycosides and Acylquinic Acids from Roots of Panax ginseng

Article abstract of DOI:10.1007/s10600-020-03223-8

Glucose esters of sinapic and ferulic acids including a novel O-acylglycoside (1) and coumaroyl- and feruloylquinic acids were found for the first time in roots of Panax ginseng C. A. Mey. (Araliaceae). Compound 1 was 4-O-sinapoyl-α/β-D-glucopyranose according to UV and NMR spectroscopic and mass spectrometric data. A comparison of the biological activities of the isolated compounds found high antiradical activity (IC₅₀ 36.79–37.75 μM) for the sinapic-acid derivatives.

Full text of DOI:10.1007/s10600-020-03223-8

DOI 10.1007/s10600-020-03223-8
Chemistry of Natural Compounds, Vol. 56, No. 6, November, 2020
ACYLGLYCOSIDES AND ACYLQUINIC ACIDS
FROM ROOTS OF Panax ginseng
D. N. Olennikov
Glucose esters of sinapic and ferulic acids including a novel O-acylglycoside (1) and coumaroyl- and
feruloylquinic acids were found for the first time in roots of Panax ginseng C. A. Mey. (Araliaceae). Compound
1 was 4-O-sinapoyl-α/β-D-glucopyranose according to UV and NMR spectroscopic and mass spectrometric
data. A comparison of the biological activities of the isolated compounds found high antiradical activity
(IC 36.79–37.75 μM) for the sinapic-acid derivatives.
50
Keywords: Panax ginseng, Araliaceae, acylglycosides, acylquinic acids, antiradical activity.
Panax ginseng C. A. Mey. is one of the most studied plant species in the family Araliaceae. Many investigations
found that P. ginseng roots are a source of biologically active triterpenoids [1] and polysaccharides [2]. The chemical composition
of phenolic compounds from this species is inadequately studied. Hydroxycinnamic [3] and benzoic acids [4] and flavonoid
aglycons [3] and catechins [5] have been reported. In continuation of studies of phenolic compounds from Panax species [6],
results from studies of phenolic constituents possessing antioxidant activity from the EtOAc fraction of cultivated P. ginseng
are reported herein.
The EtOAc fraction had the greatest antioxidant activity among fractions obtained from the EtOH extract of fresh
P. ginseng roots. Its constituents were separated using column chromatography (CC) over polyamide, Sephadex LH-20, and
silica gel and preparative HPLC. A total of 11 compounds were isolated including the new O-acylglycoside 1 and 10 known
compounds that were identified using UV and NMR spectroscopy and mass spectrometry as 1-O-sinapoylglucose (2) [7],
2-O-sinapoylglucose (3) [8], 6-O-sinapoylglucose (4) [9], 1-O-feruloylglucose (5) [10], 2-O-feruloylglucose (6) [11],
4-O-feruloylglucose (7) [10], 6-O-feruloylglucose (8) [10], 5-O-cumaroylquinic acid (9) [12], 4-O-feruloylquinic acid (10)
[13], and 5-O-feruloylquinic acid (11) [14]. Hydroxycinnamate 11 was found in P. vietnamensis Ha et. Grushv. [6]. However,
compounds 2–11 were isolated from P. ginseng for the first time.
–
Compound 1 had the formula C H O according to mass spectrometry (m/z 385.5211 [M – H] , calcd 385.3170)
17 22 10
13
and C NMR spectroscopy. The mass spectrum (ESI-MS) contained peaks for the deprotonated molecule (m/z 385) and
–
a fragment with m/z 223 that was indicative of the loss of hexose [(M – H) – C H O ] . Acid hydrolysis in TFA (2 M)
6
10 5
13
produced sinapic acid [7] and D-glucose, which was characteristic of O-sinapoyl glucosides. The PMR and C NMR spectra
showed two similar sets of resonances of high and low intensity that were assigned to the β- and α-isomers of 1, respectively.
The intensity ratio of resonances for anomeric protons of the β- (δ 4.51 ppm) and α-isomers (δ 5.21 ppm) in the PMR
H
H
spectrum was 15.1:1, which was close to that (14.8:1) for resonances of the anomeric C atoms of the β- (δ 99.3 ppm) and
C
13
α-isomers (δ 93.5 ppm) in the C NMR spectrum. Weak-field shifts of resonances for H-4 (δ 3.69–3.71→4.81–4.87) [10]
C
H
and C-4 (δ 70.3–70.4→72.5–72.9) [15] as compared to unsubstituted glucose was consistent with a substituent on C-4.
C
This was confirmed by correlations in the HMBC spectrum between H-4 (δ 4.81, 4.87) and the sinapoyl carbonyl C atom
H
(δ 167.3–167.5) (Fig. 1). Thus, compound 1 was a mixture of α- and β-isomers of 4-O-sinapoyl-D-glucopyranose.
C
Monoglycosides of sinapic acid isomeric to 1 with an acyl fragment in the C-1 [7], C-2 [8], and C-6 position of glucose [9]
were previously isolated from Brassica oleracea L. (Brassicaceae). Sinapic acid 4-O-glucoside was observed in Capsicum
annuum L. (Solanaceae) [16].
Institute of General and Experimental Biology, Siberian Branch, Russian Academy of Sciences, 6 Sakh′yanovoi St.,
Ulan-Ude, 670047, e-mail: olennikovdn@mail.ru. Translated from Khimiya Prirodnykh Soedinenii, No. 6, November–December,
2020, pp. 898–900. Original article submitted April 14, 2020.
©
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0009-3130/20/5606-1044 2020 Springer Science+Business Media, LLC

13
TABLE 1. PMR (500 MHz) and C NMR Spectra (125 MHz) of 1 (MeOH-d , 298 K, δ, ppm, J/Hz)
4
δH
δC
C atom
β-isomer
α-isomer
β-isomer
α-isomer
1
2
3
4
5
6
4.51 (1H, d, J = 7.5)
5.21 (1H, d, J = 4.1)
3.44 (1H, m)
3.92 (1H, m)
4.81 (1H, m)
4.01 (1H, m)
3.63 (1H, m, ÍÀ),
3.51 (1H, m, ÍÂ)
–
99.3
75.8
77.2
72.5
76.3
62.7
93.5
74.1
73.5
72.9
71.0
62.4
3.20 (1H, m)
3.58 (1H, m)
4.87 (1H, m)
3.47 (1H, m)
3.89 (1H, dd, J = 11.9, 2.1, ÍÀ),
3.72 (1H, dd, J = 11.9, 5.0, ÍÂ)
–
123.7
105.7
148.0
137.9
144.9
114.7
167.3
56.7
123.8
105.9
147.8
138.2
145.1
114.5
167.5
56.5
′
1
6.92 (2H, s)
6.90 (2H, s)
2′, 6′
3′, 5′
4′
7′
8′
9′
–
–
–
–
7.63 (1H, d, J = 16.1)
6.47 (1H, d, J = 16.1)
–
7.61 (1H, d, J = 16.0)
6.44 (1H, d, J = 16.0)
–
3.91 (6H, s)
3.89 (6H, s)
3′, 5′-ÎÑÍ3
HO
O
7'
O
H CO
3
OH, H
9'
O
8'
1'
OH1
3'
HO
3
HO
OCH
3
1
Fig. 1. Structure and HMBC correlations of 1.
•
A study of the antiradical activities of 1–11 against DPPH free radical showed that the activities of the sinapic acid
derivatives (IC of 1, 37.75 μM; 2, 36.79; 3, 37.28; 4, 36.81) were greater than those of the feruloylglycosides (IC of 5,
50
50
78.96 μM; 6, 78.43; 7, 77.11; 8, 76.99) and acylquinic acids (IC of 9, 8218.28 μM; 10, 76.88; 11, 75.89). The antioxidant
50
activity of P. ginseng extracts was previously explained by the presence of p-coumaric and ferulic acids [3], triterpenoids [17],
and polysaccharides [18]. Sinapic-acid derivatives were shown for the first time to be antioxidant constituents of P. ginseng.
EXPERIMENTAL
CC used polyamide, Sephadex LH-20, and silica gel (SiO ; Sigma-Aldrich, St. Louis, MO, USA). Spectrophotometric
2
studies used an SF-2000 spectrophotometer (OKB Spectr, St. Petersburg, Russia). Mass spectrometry was performed in an
LCMS-8050 TQ-mass spectrometer (Shimadzu, Columbia, MD, USA) [19]. NMR spectra were recorded on a VXR 500S
spectrometer (Varian, Palo Alto, CA, USA). Separation by preparative HPLC used a Summit liquid chromatograph (Dionex,
Sunnyvale, CA, USA) equipped with a LiChrospher RP-18 column (250 × 10 mm, ∅ 10 μm; Supelco, Bellefonte, PA, USA)
using mobile phases H O (A) and MeCN (B) at flow rate 0.8 mL/min, column temperature 26°C, and UV detection
2
•
at λ 350 nm. Antiradical activities of extracts and compounds against DPPH free radical (2,2-diphenyl-1-picrylhydrazide,
Sigma-Aldrich) were determined by a microplate method [20] using Trolox as a reference standard
(6-hydroxy-2,5,7,8-tetramethylchromane-2-carboxylic acid; Sigma-Aldrich; IC = 28.12 μM).
50
Roots of cultivated P. ginseng aged 7–10 years were collected in 2019 in Khabarovskii Krai (48°14′52″ N, 135°14′51″ E,
110 m above sea level, humidity 67.9 1.8%). The species was determined by Dr. N. K. Chirikova (North-Eastern Federal
University, Yakutsk, Russia). A specimen of the raw material is preserved in the herbarium of the IGEB, SB, RAS
(No. CHA/ARA-0919/10-637).
Extraction and Isolation of 1–11 from P. ginseng. Fresh roots (2.2 kg) were ground in a blender and extracted (2×)
with EtOH (95%, 1:5) at 25°C for 48 h. The EtOH extract was concentrated to dryness. The dry solid (134 g) was suspended
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in H O and extracted with CHCl , EtOAc, and BuOH to produce CHCl (F-1, 8 g), EtOAc (F-2, 26 g), and BuOH fractions
2
3
3
•
(F-3, 67 g). Fraction F-2 showed the greatest antiradical activity against the DPPH radical (IC 83.74 2.07 μg/mL) and was
50
separated over polyamide (3 kg) with elution by H O (F-2-1; IC > 100 μg/mL), EtOH (40%) (F-2-2; IC > 100 μg/mL),
2
50
50
EtOH (90%) (F-2-3; IC > 100 μg/mL), and NH solution (0.5%) in EtOH (90%) (F-2-4; IC 48.11 0.92 μg/mL). Next,
50
3
50
active fraction F-2-4 was chromatographed over Sephadex LH-20 (CC, 4 × 90 cm, EtOH-–H O eluent, 90:10→50:10) and
2
SiO (CC, 2 × 40 cm, EtOAc–Me CO eluent, 80:20→50:50) and by prep. HPLC [gradient mode (%B): 0–90 min, 7–45%] to
2
2
isolate the following compounds (ratio of α:β-isomers): 1 (25 mg), 1-O-sinapoylglucose (11 mg, 2) [7], 2-O-sinapoylglucose
(14 mg, mixture of α- and β-isomers, 1:27, 3) [8], 6-O-sinapoylglucose (21 mg, mixture of α- and β-isomers, 1:14, 4) [9],
1-O-feruloylglucose (5 mg, 5) [10], 2-O-feruloylglucose (12 mg, mixture of α- and β-isomers, 1:39, 6) [11], 4-O-feruloylglucose
(5 mg, mixture of α-and β-isomers, 1:11, 7) [10], 6-O-feruloylglucose (29 mg, mixture of α- and β-isomers, 1:27, 8) [10],
5-O-coumaroylquinic acid (37 mg, 9) [12], 4-O-feruloylquinic acid (11 mg, 10) [13], and 5-O-feruloylquinic acid (19 mg, 11)
[14], which were identified using UV and NMR spectroscopy and mass spectrometry and comparisons with known compounds
and the literature.
4-O-Sinapoyl-α/β-D-glucopyranose (1). C H O . UV spectrum (50% MeOH, λ , nm): 326. HR-ESI-MS,
17 22 10
–
max
–
–
–
m/z: 358.5211 (calcd for C H O , 385.3170 [M – H] ). ESI-MS, m/z (%): 385 [M – H] (100), 223 [(M – H) – C H O ]
17 21 10
–
6 10 5
13
(52), 179 [(M – H) – C H O ] (6). Table 1 lists the PMR (500 MHz, MeOH-d , 298 K, δ, ppm) and C NMR spectra
11 10
4
4
(125 MHz, δ, ppm).
Acid hydrolysis of the compounds was performed in TFA(2 M). The reaction products were separated over polyamide
[21]. Phenolic compounds were analyzed by GC-MS [22]; monosaccharides, after derivatization with 3-methyl-1-phenyl-2-
pyrazolin-5-one [23]. Compounds were assigned to D/L-series after reductive amination with L-tryptophan [24]. Hydrolysis
of 1 produced sinapic acid [7] and D-glucose.
ACKNOWLEDGMENT
The studies were sponsored by FASO Russia (AAAA-AA17-117011810037-0).
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