Stilbenes in Carex acuta and Carex lepidocarpa

Abstract

Stilbenes in the roots of Carex acuta and Carex lepidocarpa were studied. Root samples were extracted with 100% methanol and analyzed by HPLC and LC-MS. In this way, trans-resveratrol dimers (m/z 455 Da [M + H]+), trimers (m/z 681 Da [M + H]+) and tetramers (m/z 907 Da [M + H]+) were identified in the extracts. Using LC-NMR in stop-flow mode, pallidol and trans-ε-viniferin as dimers were identified. After the separation of individual peaks and their measurement by 1H NMR, cis and trans-miyabenol A as a tetramer and cis-miyabenol C as a trimer were identified. In the case of miyabenol A, it is a chromatographically inseparable mixture of cis and trans isomers in the ratio of 2:3 according to 1H NMR measurement. In the case of cis-miyabenol C, the Z-trans-trans-miyabenol C configuration was confirmed. The remaining unidentified peak with a practically identical UV-VIS spectrum to that of cis-miyabenol C is most likely another isomer of miyabenol C.

Full text

Citation: Tˇríska, J.; Vrchotová, N.;
Horník, Š.; Sýkora, J.; Kuˇcerová, A.
Stilbenes in Carex acuta and Carex
lepidocarpa.Molecules 2024,29, 3840.
https://doi.org/10.3390/
molecules29163840
Academic Editors: Roberto Fabiani
and Eliana Pereira
Received: 4 July 2024
Revised: 8 August 2024
Accepted: 9 August 2024
Published: 13 August 2024
Copyright: © 2024 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and
conditions of the Creative Commons
Attribution (CC BY) license (https://
creativecommons.org/licenses/by/
4.0/).
molecules
Article
Stilbenes in Carex acuta and Carex lepidocarpa
Jan Tˇríska 1,* , Nadˇežda Vrchotová1, Štˇepán Horník2, Jan Sýkora 3and Andrea Kuˇcerová4
1Laboratory of Metabolomics and Isotope Analyses, Global Change Research Institute, Czech Academy of
Sciences, Bˇelidla 986/4a, 603 00 Brno, Czech Republic; vrchotova.n@czechglobe.cz
2
Department of Environmental Engineering, Institute of Chemical Process Fundamentals, Czech Academy of
Sciences, Rozvojová2/135, 165 02 Prague, Czech Republic; hornik@icpf.cas.cz
3Department of Analytical Chemistry, University of Chemistry and Technology, Technická5,
166 28 Prague, Czech Republic; jan1.sykora@vscht.cz
4Department of Experimental and Functional Morphology, Institute of Botany, Czech Academy of Sciences,
Dukelská135, 379 01 Tˇrebo ˇn, Czech Republic; andrea.trebon@seznam.cz
*Correspondence: triska.j@czechglobe.cz
Abstract: Stilbenes in the roots of Carex acuta and Carex lepidocarpa were studied. Root samples were
extracted with 100% methanol and analyzed by HPLC and LC-MS. In this way, trans-resveratrol
dimers (m/z455 Da [M + H]
+
), trimers (m/z681 Da [M + H]
+
) and tetramers (m/z907 Da [M + H]
+
)
were identified in the extracts. Using LC-NMR in stop-flow mode, pallidol and trans-
ε
-viniferin as
dimers were identified. After the separation of individual peaks and their measurement by
1
H NMR,
cis and trans-miyabenol A as a tetramer and cis-miyabenol C as a trimer were identified. In the case of
miyabenol A, it is a chromatographically inseparable mixture of cis and trans isomers in the ratio of
2:3 according to 1H NMR measurement. In the case of cis-miyabenol C, the Z-trans-trans-miyabenol
C configuration was confirmed. The remaining unidentified peak with a practically identical UV-VIS
spectrum to that of cis-miyabenol C is most likely another isomer of miyabenol C.
Keywords: Carex acuta;Carex lepidocarpa; pallidol; miyabenol A and C; trans-
ε
-viniferin; liquid
chromatography; NMR
1. Introduction
The largest genera in the Cyperaceae family are Carex and Cyperus. The Carex genus
is one of the largest angiosperm genera with worldwide distribution. The total number
of Carex species in the world is estimated to be more than 2000; among those, 222 species
occur in Europe [1].
Carex acuta L. 1753 (syn. Carex gracilis, Curtis 1782) occurs throughout Europe, from
NW Africa to Central Asia. It is a relatively eurytopic species, tolerates strongly acidic to
neutral soils (pH ca. 4–7) and eutrophication and grows at river banks, the shorelines of
lakes and fishponds, and the margins of wet meadows, canals and fens [2].
Carex lepidocarpa Tausch 1834 (syn. C. flava var. lepidocarpa (Tausch) Godron 1844;
C. viridula
Michaux var. lepidocarpa (Tausch) B. Schmid 1983, C. lepidocarpa subsp. lepido-
carpa) is a part of taxonomically problematic C. flava group. C. lepidocarpa was often treated
under the polymorphic C. viridula, e.g., C. viridula subsp. brachyrhyncha
(Schmid 1983);
however, recent studies confirm C. lepidocarpa as a separate species [
3
,
4
], and it was refer-
enced under this name in the recent European checklist of the Carex genus [
1
]. It occurs
throughout Europe, NW Africa and E Canada. It is a relatively stenotypic species, is
sensitive to changes in the water table and overgrowing and prefers base-rich substrates.
It grows in mesotrophic minerotrophic peat bogs or fen meadows [
2
]. C. acuta usually
develops large stands along the margins of standing waters or forms big tufts (up to 1 m
high) in shallow water bodies and in mesotrophic wetlands. It has a high growth rate;
therefore, it produces a relatively high amount of above- and belowground biomass. It is
possible to grow it easily in a simple hydroponic setting at a low cost [
5
] and produce
Molecules 2024,29, 3840. https://doi.org/10.3390/molecules29163840 https://www.mdpi.com/journal/molecules

Molecules 2024,29, 3840 2 of 11
a sufficiently high amount of root biomass (root length up to 0.8 m in a shallow water
body) for the next extraction of valuable biological compounds. In contrast, C. lepidocarpa
forms smaller tufts (0.2–0.5 m high), probably has a lower growth rate and grows only
sporadically under natural conditions. Nevertheless, it is possible to also grow it in a
simple hydroponic setting, as this species can tolerate a high water table and a low con-
tent of nutrients. However, the total available root biomass will probably be lower than
in C. acuta, as a significant relationship between above- and belowground biomass was
reported for many herbs [
6
]. The production of root biomass and growth rate should be
tested and evaluated in terms of space, time and the economic costs of production of these
biologically interesting compounds. Sedges contain a wide range of stilbenes, mainly in
the roots; the set of stilbenes among species differs considerably (Table 1). Stilbenes and
their derivatives, especially trans-resveratrol oligomers, have attracted increasing attention
for potential pharmacological applications due to their promising biological activities.
The most promising application field for resveratrol oligomers from sedges is the treatment
of cancer and Alzheimer’s disease. Resveratrol oligomers isolated from Carex folliculata
and Carex gynandra (pallidol,
α
-viniferin, trans-miyabenol C and kobophenols A and B),
along with resveratrol, were evaluated for antiproliferative effects against human colon
cancer (HCT-116, HT-29, Caco-2) and normal human colon (CCD-18Co) cells. The men-
tioned resveratrol oligomers, as well as resveratrol, inhibited the growth of the human
colon cancer cells, and the most active compound was found to be
α
-viniferin, with IC
50
values of 6–32
µ
M [
7
]. Hu et al. [
8
] found that miyabenol C, isolated from the stems and
leaves of the small-leaf grape (Vitis thunbergii var. taiwaniana), can inhibit both
in vitro
and
in vivo β
-secretase activity, which would lead to a reduction in the accumulation of
amyloid-
β
-peptide in the brain as the primary cause of Alzheimer’s disease. Wang et al. [
9
]
described very recently that miyabenol C and trans-
ε
-viniferin, two resveratrol oligomers,
specifically inhibit SARS-CoV-2 entry by targeting host protease cathepsin L. This means
that there is a potential application of these resveratrol oligomers present in Carex sp. as
lead compounds in controlling SARS-CoV-2 infection.
Table 1. Overview of stilbenes found in different Carex species.
Carex Part of the Plant Stilbenes (m/z) [Da] Literature
C. appessa seeds virgatanol [M + H]+471 [10]
resveratrol diglucoside [M + H]+553
piceatannol [M + H]+245
ε-viniferin [M + H]+455
C. buchananii roots kobophenol A [11]
C. capillacea roots (E)-miyabenol A [11]
C. ciliato-marginata (+)-α-viniferin [M + H]+679 [12]
pallidol [M + H]+455
kobophenol A [M + H]+925
C. cuprina roots carexinol A [M + H]+941 [11]
kobophenol A [M + H]+925
C. distachya roots pallidol diglucoside [13]
C. fedia roots, rhizomes ε-viniferin [14]
miyabenol A
miyabenol B
miyabenol C
C. foliosissima (+)-α-viniferin [M + H]+679 [12]
pallidol [M + H]+455
kobophenol A [M + H]+925
C. folliculata seeds pallidol [15]
kobophenol A
C. folliculata seeds pallidol [7]
kobophenol A

Molecules 2024,29, 3840 3 of 11
Table 1. Cont.
Carex Part of the Plant Stilbenes (m/z) [Da] Literature
C. glauca roots (E)-miyabenol C [M + H]+681 [14]
(+)-α-viniferin [M + H]+679
C. gynandra aerial part pallidol [5]
α-viniferin
trans-miyabenol C
kobophenol B
C. hirta roots resveratrol-diglucoside [M + H]+553 [11]
(E)-miyabenol A [M + H]+907
C. humilis roots α-viniferin [16]
C. kobomugi roots kobophenol A [17]
C. morrowii (+)-α-viniferin [M + H]+679 [12]
pallidol [M + H]+455
kobophenol A [M + H]+925
C. multufolia (+)-α-viniferin [M + H]+679 [12]
pallidol [M + H]+455
kobophenol A [M + H]+925
C. pendula seeds cis-miyabenol A [M + H]+907 [18]
cis-miyabenol C [M + H]+681
kobophenol B [M + H]+905
C. pumita roots, rhizomes (−)-ε-viniferin [19]
miyabenols A, C
C. vulpinoidea seeds vulpinoideol A [M + Na]+481 [20]
vulpinoideol B [M + Na]+511
We focused in our study on two species of sedges, Carex acuta and Carex lepidocarpa, first,
due to the content of stilbenes, which has been not studied yet (see Table 1), and second,
due to correlation on a nutrient gradient. C. acuta is more typical of eutrophic pond shores
and eutrophic wetlands, while C. lepidocarpa is more typical of oligotrophic peat bogs or fen
meadows. Another difference is that C. acuta tolerates large water table fluctuations, while
C. lepidocarpa prefers a more balanced water regime.
Since we are also dealing with stilbenes in grape canes, our next goal was to compare the
contents of the main biologically active stilbenes, with the focus of interest being trimers and
tetramers of resveratrol, which are contained in grape canes in smaller amounts compared to
those Carex species studied above, which were selected based not only on the above facts and
literature data but also based on a quick screening in the wetland plants collection.
2. Results and Discussion
Recently, a very extensive review was published [
21
], in which the authors state that
from Carex genera, 17 stilbenes have been isolated so far. Carex acuta and Carex lepidocarpa
are not listed in this review. Another overview was published this year [
22
], but it does not
change anything about the results listed above. From our literature review (see Table 1),
it follows that in all Carex species, mostly in the roots but also in the seeds, the following
resveratrol derivatives are repeatedly present: resveratrol diglucoside, piceatannol,
α-viniferin,
ε
-viniferin, kobophenol A, kobophenol B, miyabenol A, B, C and pallidol. From this group,
three substances are the most important due to the valuable biological properties described so
far: miyabenol C,
ε
-viniferin and pallidol, and all of the mentioned stilbenes are contained
in the Carex spp. The chemical structures of some stilbenes are shown in Figure 1, and a
chromatogram of the LC/MS analysis of C. lepidocarpa extract is shown in Figure 2. We focused
our study, in accordance with the indicated chromatogram, on the following stilbenes, except
resveratrol: pallidol, a mixture of cis- and trans-miyabenol A, trans-
ε
-viniferin, Z-miyabenol C
and peak 6. The molecular masses of the stilbenes were determined by LC/MS in positive
mode and are listed in Table 2together with the retention data. The content of stilbenes in
Carex acuta and Carex lepidocarpa is shown in Table 3. Further detailed analysis was performed
using LC/NMR.

Molecules 2024,29, 3840 4 of 11
Molecules 2024, 29, x FOR PEER REVIEW 5 of 11
Figure 1. Chemical structure of some stilbenes.
Table 3. Content of stilbenes in the roots of Carex acuta and Carex lepidocarpa (µg/g dry maer); R.t.
(drying at room temperature), Lyof. (drying by lyophilization).
Stilbenes
/
Sample
Drying
C. acuta 2016
R. t.
C. acuta 2017
Lyof.
C. acuta 2017
R. t.
C. lepidocarpa
2016 R. t.
C. lepidocarpa
2017 Lyof.
Pallidol
(peak 1) 308 ± 54 270 ± 16 194 ± 28 14,478 ± 976 13,087 ± 1755
trans-resveratrol
(peak 2) 88 ± 12 78 ± 3 84 ± 10 70 ± 6 66 ± 11
Mixture cis+trans
Miyabenol A (peak 3) 3641 ± 505 4572 ± 586 2603 ± 227 1890 ± 273 847 ± 14
Figure 1. Chemical structure of some stilbenes.
Table 2. Stilbenes in the roots of Carex acuta and Carex lepidocarpa (chromatogram in Figure 2.).
Stilbenes Retention Time [min] m/z[M + H]+[Da]
Pallidol (peak 1) 4.02 455
trans-resveratrol (peak 2) 5.51 229
Mixture cis+trans miyabenol
A (peak 3) 6.99 907
trans-ε-viniferin (peak 4) 7.13 455
Z-miyabenol C (peak 5) 7.45 681
Trimer (peak 6) 7.78 681

Molecules 2024,29, 3840 5 of 11
Molecules 2024, 29, x FOR PEER REVIEW 6 of 11
trans-ɛ-viniferin
(peak 4) n.d. n.d. n.d. 5035 ± 294 3777 ± 332
cis-miyabenol C
(peak 5) 263 ± 5 487 ± 55 342 ± 32 4805 ± 279 3209 ± 185
Trimer
(peak 6) 174 ± 18 102 ± 7 96 ± 9 5060 ± 147 4065 ± 267
n.d.: not detected. LOD for trans-ε-viniferin 0.089 µg/mL, LOQ 0.298 µg/mL.
Figure 2. LC/MS of Carex lepidocarpa extract (PDA; full scan: +APCI). See Table 2 for the description
of the peaks (1–6).
The spectra of the rest of the compounds were more complex and could not be
identified directly from LC-NMR. Therefore, the individual peaks were collected in
repeated HPLC runs, evaporated and dissolved in corresponding deuterated solvents
(acetone-d6, methanol-d4) for a comparison with the available literature data. The LC-MS
analysis revealed that peak 5 and peak 6 from C. lepidocarpa are resveratrol trimers, while
peak 3 from C. acuta is a resveratrol tetramer.
The comparison with the available literature [25] showed that peak 5 from C.
lepidocarpa was represented by Z-miyabenol C (cis-miyabenol C). This compound is
characterized by a Z-conformation on the double bond. This is evident from the signals at
δ 5.83 ppm and 5.78 ppm, which are coupled with a value of the corresponding coupling
constant (J = 12.4 Hz) characteristic for Z-conformation. Both benzodihydrofuran rings
(first, δ 5.29 ppm and 4.22 ppm; second, δ 5.26 ppm and 3.87 ppm) have trans relative
stereochemistry according to the literature data [25]. Therefore, this compound is Z-trans-
trans-miyabenol C. Unfortunately, no match was found for peak 6 from C. lepidocarpa, and
the compound structure could not be elucidated unequivocally. However, we believe that
this compound might be an E-isomer of miyabenol C. This belief comes from a tentative
analysis of 1H NMR and COSY spectra, which showed signals of a double bond with E-
conformation (δ 6.89 and 6.26 ppm with J = 16.3 Hz). Moreover, the compound is probably
represented by two benzodihydrofuran rings (δ 5.30 and 3.70 ppm, coupled with J = 3.6
Hz, and δ 5.03 and 4.58 ppm, coupled with J = 7.3 Hz, for protons on the dihydrofuran
parts of the rings and δ 6.30 and 5.97 ppm, coupled with J = 2.2 Hz, and δ 6.73 and 6.20
ppm, coupled with J = 2.1 Hz for protons on the benzo parts of the rings). Besides that,
there is a 3,5-dihydroxyphenyl ring with signals at δ 6.22 and 5.97 ppm coupled with J =
2.3 Hz and three 4-hydroxyphenyl rings (first, δ 7.07 and 6.81 ppm, coupled with J = 8.6
Hz; second, δ 6.99 and 6.74 ppm, coupled with J = 8.6 Hz; and third, δ 7.00 and 6.80 ppm,
coupled with J = 8.7 Hz). Rotation of the third 4-hydroxyphenyl ring might be slightly
restricted, which is assumed based on the width of its signals. Unfortunately, we have no
other proof for this theory. To the best of our knowledge, this proposed isomer of E-
RT:
1,76 -
10,55
2.0
2.5 3.0
3.5 4.0 4.5 5.0 5.5 6.0
6.5 7.0 7.5 8.0 8.5 9.0
9.5
10.0 10.5
Time
(
min
)
0
20
40
60
80
100
Relative Abundance
0
50000
100000
uAU
7.38
7.70
3.96
7. 08
6.91
1.90
7.92
9.29
8.26
6.71
8.77
6.15
4.24 10.10
9.57
5.97
5.64
5.02
4.64 5.27
2.61 3.63
3.41
3.14
2.38
4.02
7.13
7.45
7.76
6.98
4.28 6.76
2.62
8.32
2.33
6.18
2,76
3,53 5.51 6.04
5.27
4.79
8,85
3,15 9.04
9.33
9.86
10.05
Total Scan PD
A
TIC F: ITMS + c
A
PCI corona Full
ms
2 3
4
5 6
1
RT: 1.76–10.55
Figure 2. LC/MS of Carex lepidocarpa extract (PDA; full scan: +APCI). See Table 2for the description
of the peaks (1–6).
Table 3. Content of stilbenes in the roots of Carex acuta and Carex lepidocarpa (
µ
g/g dry matter); R.t.
(drying at room temperature), Lyof. (drying by lyophilization).
Stilbenes/Sample
Drying
C. acuta 2016
R. t.
C. acuta 2017
Lyof.
C. acuta 2017
R. t.
C. lepidocarpa
2016 R. t.
C. lepidocarpa
2017 Lyof.
Pallidol
(peak 1) 308 ±54 270 ±16 194 ±28 14,478 ±976 13,087 ±1755
trans-resveratrol
(peak 2) 88 ±12 78 ±3 84 ±10 70 ±6 66 ±11
Mixture cis+trans
Miyabenol A
(peak 3) 3641 ±505 4572 ±586 2603 ±227 1890 ±273 847 ±14
trans-ε-viniferin
(peak 4) n.d. n.d. n.d. 5035 ±294 3777 ±332
cis-miyabenol C
(peak 5) 263 ±5 487 ±55 342 ±32 4805 ±279 3209 ±185
Trimer
(peak 6) 174 ±18 102 ±7 96 ±9 5060 ±147 4065 ±267
n.d.: not detected. LOD for trans-ε-viniferin 0.089 µg/mL, LOQ 0.298 µg/mL.
The primary analysis of the stilbenes’ structures was based on LC-NMR, which pro-
vided spectra of individual peaks. Due to the low concentrations of individual compounds,
only
1
H NMR spectra in stop-flow mode were recorded within a reasonable time. This led
to the identification of pallidol and trans-
ε
-viniferin as peak 1 and peak 4 from C. lepidocarpa,
respectively. The identification of pallidol was achieved by a comparison of the measured
1
H NMR spectrum with the literature data [
23
], whereas the spectrum of the compound
from peak 4 was identical with a previously measured spectrum of trans-
ε
-viniferin [
24
],
which served as proof for the compound identity.
The spectra of the rest of the compounds were more complex and could not be
identified directly from LC-NMR. Therefore, the individual peaks were collected in repeated
HPLC runs, evaporated and dissolved in corresponding deuterated solvents (acetone-d
6
,
methanol-d
4
) for a comparison with the available literature data. The LC-MS analysis
revealed that peak 5 and peak 6 from C. lepidocarpa are resveratrol trimers, while peak
3 from C. acuta is a resveratrol tetramer.
The comparison with the available literature [
25
] showed that peak 5 from C. lepi-
docarpa was represented by Z-miyabenol C (cis-miyabenol C). This compound is charac-
terized by a Z-conformation on the double bond. This is evident from the signals at
δ
5.83 ppm and 5.78 ppm, which are coupled with a value of the corresponding coupling
constant
(J= 12.4 Hz)
characteristic for Z-conformation. Both benzodihydrofuran rings

Molecules 2024,29, 3840 6 of 11
(first,
δ
5.29 ppm and 4.22 ppm; second,
δ
5.26 ppm and 3.87 ppm) have trans rela-
tive stereochemistry according to the literature data [
25
]. Therefore, this compound is
Z-trans-trans-miyabenol C. Unfortunately, no match was found for peak 6 from C. lepido-
carpa, and the compound structure could not be elucidated unequivocally. However, we
believe that this compound might be an E-isomer of miyabenol C. This belief comes from a
tentative analysis of
1
H NMR and COSY spectra, which showed signals of a double bond
with E-conformation (
δ
6.89 and 6.26 ppm with J= 16.3 Hz). Moreover, the compound
is probably represented by two benzodihydrofuran rings (
δ
5.30 and 3.70 ppm, coupled
with
J= 3.6 Hz,
and
δ
5.03 and 4.58 ppm, coupled with J= 7.3 Hz, for protons on the
dihydrofuran parts of the rings and
δ
6.30 and 5.97 ppm, coupled with J= 2.2 Hz, and
δ
6.73
and 6.20 ppm, coupled with J= 2.1 Hz for protons on the benzo parts of the rings). Besides
that, there is a 3,5-dihydroxyphenyl ring with signals at
δ
6.22 and 5.97 ppm coupled
with J= 2.3 Hz and three 4-hydroxyphenyl rings (first,
δ
7.07 and 6.81 ppm, coupled with
J= 8.6 Hz;
second,
δ
6.99 and 6.74 ppm, coupled with J= 8.6 Hz; and third,
δ
7.00 and
6.80 ppm, coupled with J= 8.7 Hz). Rotation of the third 4-hydroxyphenyl ring might be
slightly restricted, which is assumed based on the width of its signals. Unfortunately, we
have no other proof for this theory. To the best of our knowledge, this proposed isomer of
E-miyabenol C has not been identified before. Nevertheless, it is impossible to determine
the stereochemistry without further experiments, for which we have too small an amount
of the compound. The UV-VIS spectrum of the compound represented by peak 6 is shown
in Figure 3, where it is compared with the measured spectrum of cis-miyabenol C, which
was already published by [
14
]. It is obvious that according to the UV-VIS spectra, the
structure of the unknown compound (peak 6) must be very close to that of cis-miyabenol C.
The UV-VIS spectrum of pallidol is also shown for comparison.
Molecules 2024, 29, x FOR PEER REVIEW 7 of 11
miyabenol C has not been identified before. Nevertheless, it is impossible to determine the
stereochemistry without further experiments, for which we have too small an amount of
the compound. The UV-VIS spectrum of the compound represented by peak 6 is shown
in Figure 3, where it is compared with the measured spectrum of cis-miyabenol C, which
was already published by [14]. It is obvious that according to the UV-VIS spectra, the
structure of the unknown compound (peak 6) must be very close to that of cis-miyabenol
C. The UV-VIS spectrum of pallidol is also shown for comparison.
Figure 3. UV spectrum of selected peaks.
The 1H NMR spectrum of Peak 3 revealed that this peak is most likely represented by
a mixture of the trans- and cis-isomers of miyabenol A, as this spectrum was compared to
the literature data [11,18]. The ratio of trans–cis isomers is 3:2 according to the 1H NMR
experiment. Nevertheless, the strongly overlapped signals could not be distinguished,
and the assignment is based on isolated signals and signals of hydrogens bonded to
double-bond carbons. To confirm the elucidation, the solution of Peak 3 was left exposed
for a week at solar radiation, which lead to the transformation of the trans-isomer to the
cis-isomer of miyabenol A. Similarly, to Z-miyabenol C, cis-miyabenol A is characterized
by a Z-conformation on the double bond (δ 5.89 and 5.85 ppm, J = 12.0 Hz). Moreover, the
relative stereochemistry on all three benzodihydrofuran rings is trans according to the
literature data [18].
All of the above-mentioned stilbenes are contained in both C. acuta and C. lepidocarpa,
but in different proportions. In C. acuta, a mixture of cis and trans miyabenol A, which is a
tetramer of resveratrol, predominates, trans-ɛ-viniferin is not present at all, and the
concentrations of other stilbenes vary in the range of hundreds of µg/g d.m. In C.
lepidocarpa, the situation is the opposite. If we do not count trans-resveratrol, the
concentration of which varies in both species in tens of µg/g d.m., then the most
represented substance is pallidol, up to 14.48 mg/g d.m. The content of other substances
is lower and quite balanced, e.g., trans-ɛ-viniferin in a concentration of 3.78–5.04 mg/g
d.m., cis-miyabenol C in a concentration of 3.21–4.81 mg/g d.m. and peak 6 at a
concentration of 4.07–5.06 mg/g d.m. If we summarize the contents of stilbenes in C.
lepidocarpa dried in 2016 at lab. temperature, we reach a relatively high value of 31.28 mg/g
d.m. for the total stilbenes content. The amount about of 3% w/w becomes interesting for
the isolation of these substances from the biomass of C. lepidocarpa roots.
Quantitative data on the content of stilbenes are relatively rare in the literature.
Suzuki at al. [14] state that the total content of stilbenes in the roots and rhizome of C. fedia
var. miyabei is over 0.15% (w/w f.w.). The amount of kobophenol B in C. gynandra, C.
pendula and C. pumila ranges between 0.1 and 1.27% w/w d.m. [7,18] which means that our
200
250
300
350
400
450
Norm.
0
50
100
150
200
250
300
350
400
pallidol
cis-miyabenol C
peak 6
nm
Figure 3. UV spectrum of selected peaks.
The
1
H NMR spectrum of Peak 3 revealed that this peak is most likely represented
by a mixture of the trans- and cis-isomers of miyabenol A, as this spectrum was com-
pared to the literature data [
11
,
18
]. The ratio of trans–cis isomers is 3:2 according to the
1H NMR experiment.
Nevertheless, the strongly overlapped signals could not be distin-
guished, and the assignment is based on isolated signals and signals of hydrogens bonded
to double-bond carbons. To confirm the elucidation, the solution of Peak 3 was left exposed
for a week at solar radiation, which lead to the transformation of the trans-isomer to the
cis-isomer of miyabenol A. Similarly, to Z-miyabenol C, cis-miyabenol A is characterized
by a Z-conformation on the double bond (
δ
5.89 and 5.85 ppm, J = 12.0 Hz). Moreover,
the relative stereochemistry on all three benzodihydrofuran rings is trans according to the
literature data [18].

Molecules 2024,29, 3840 7 of 11
All of the above-mentioned stilbenes are contained in both C. acuta and C. lepidocarpa,
but in different proportions. In C. acuta, a mixture of cis and trans miyabenol A, which is a
tetramer of resveratrol, predominates, trans-
ε
-viniferin is not present at all, and the concen-
trations of other stilbenes vary in the range of hundreds of
µ
g/g d.m. In C. lepidocarpa, the
situation is the opposite. If we do not count trans-resveratrol, the concentration of which
varies in both species in tens of
µ
g/g d.m., then the most represented substance is pallidol,
up to 14.48 mg/g d.m. The content of other substances is lower and quite balanced, e.g.,
trans-
ε
-viniferin in a concentration of 3.78–5.04 mg/g d.m., cis-miyabenol C in a concen-
tration of 3.21–4.81 mg/g d.m. and peak 6 at a concentration of
4.07–5.06 mg/g d.m.
If we
summarize the contents of stilbenes in C. lepidocarpa dried in 2016 at lab. temperature, we
reach a relatively high value of 31.28 mg/g d.m. for the total stilbenes content. The amount
about of 3% w/wbecomes interesting for the isolation of these substances from the biomass
of C. lepidocarpa roots.
Quantitative data on the content of stilbenes are relatively rare in the literature.
Suzuki at al. [14] state
that the total content of stilbenes in the roots and rhizome of
C. fedia
var. miyabei is over 0.15% (w/wf.w.). The amount of kobophenol B in C. gynandra,
C. pendula
and C. pumila ranges between 0.1 and 1.27% w/wd.m. [
7
,
18
] which means that
our results of the stilbene content in C. lepidocarpa show the highest stilbene content reported
so far.
3. Materials and Methods
3.1. Plant Materials
Roots of Carex acuta (IPEN nr. CZ 0 HBT 2017.03812) and Carex lepidocarpa
(IPEN nr. CZ 0 HBT 2017.03753) were provided by the Collection of Aquatic and Wetlands
Plants in Tˇreboˇn, which is a part of the Institute of Botany of the Czech Academy of Sciences,
Czech Republic. The plant materials were dried at room temperature; in 2017, a part of the
material was dried at room temperature and another part was freeze dried.
The dried material was crushed and extracted with 100% methanol at 50
◦
C for 3 h.
After centrifugation, the sediment was washed twice more with methanol. Three parallel
samples were always prepared. Until measurement, the extracts were stored at −20 ◦C.
3.2. Chemicals
Methanol LiChrosolv gradient grade for LC (Merck, Prague, Czech Republic), ace-
tonitrile Optima LC/MS (Fisher Scientific, Pardubice, Czech Republic), ortho-phosphoric
acid, p.a. (Fluka, Prague, Czech Republic) and formic acid (Merck, Prague, Czech Republic)
were used. Standards of trans-resveratrol and trans-
ε
-viniferin were purchased from Merck
(Prague, Czech Republic).
3.3. HPLC and LC/MS
3.3.1. HPLC
HPLC—the methods described in our previous publication [
24
] were used for HPLC.
The samples were analyzed using an HP 1050 (Ti-series) HPLC instrument (Hewlett
Packard, Palo Alto, CA, USA) on a 3
µ
m, 150 mm
×
2 mm, Luna C18(2) column (Phe-
nomenex, Torrance, CA, USA) with a water-acetonitrile-o-phosphoric acid mobile phase.
Mobile phase A used 5% of acetonitrile + 0.1% of o-phosphoric acid; mobile phase B used
80% of acetonitrile + 0.1% of o-phosphoric acid (vol.%). The gradient was increased from
20% of B to 80% of B during 20 min and from 80% of B to 100% of B during 5 min. The flow
rate was 0.250 mL/min and the column temperature was 25
◦
C. The injection volume was
5
µ
L. A diode array detector (G1315B DAD, Agilent, Prague, Czech Republic) with detection
wavelengths at 220 and 315 nm and a scanning range of 190–600 nm was used, as well as a
G1321A fluorescence detector (FLD, Agilent, Prague, Czech Republic) with an excitation
wavelength of 315 nm, an emission wavelength of 395 nm and a scanning of emissions
in the range of 300–600 nm. Quantification was performed according to the calibration
curve, and the LOD and LOQ values are as follows: trans-resveratrol according to the

Molecules 2024,29, 3840 8 of 11
calibration curve for trans-resveratrol at 315 nm (LOD 0.033
µ
g/mL,
LOQ 0.109 µg/mL),
pallidol according to the calibration curve for trans-resveratrol at 220 nm (LOD 0.056
µ
g/mL,
LOQ 0.187 µg/mL),
other stilbenes according to the calibration curve for trans-
ε
-viniferin
at 315 nm (LOD 0.089 µg/mL, LOQ 0.298 µg/mL).
3.3.2. LC/MS
Low-resolution LC-MS measurement was performed using an LCQ Accela Fleet
(Thermo Fisher Scientific, San Jose, CA, USA) with atmospheric pressure chemical ion-
ization (APCI) in positive ionization mode and a photodiode array detector. Luna C18(2)
column, 3
µ
m, 150 mm
×
2 mm (Phenomenex, Torrance, CA, USA), was used with a
water-acetonitrile-formic acid mobile phase. Mobile phase A used 5% of acetonitrile +
0.1% of formic acid; mobile phase B used 80% of acetonitrile + 0.1% of formic acid (in
vol.%). The gradient was increased from 35% of B to 40% of B during 2 min, from 40% of
B to 60% of B during 10 min, from 60% B to 80% B during 1 min and from 80% B to 100%
B during 1 min. The injection volume was 10
µ
L and the flow rate was 0.400 mL/min.
The APCI capillary
temperature was 275
◦
C, the APCI vaporizer temperature was 400
◦
C,
the sheath gas flow was 58 L/min, the auxiliary gas flow was 10 L/min, the source voltage
was 6 kV, the source current was 5 µA and the capillary voltage was 10 V.
3.3.3. Liquid Chromatography–Nuclear Magnetic Resonance Spectroscopy (LC-NMR)
LC-NMR analysis followed the protocol described in our previous work [
24
]. Briefly,
the analysis was performed using a commercial HPLC system (Dionex UltiMate 3000,
Thermo Fisher Scientific) with a 4.6
×
250 mm HPLC column (Luna C18 (2), Phenomenex,
5
µ
m, 100 Å pore size). The concentrated acetonitrile solution (50
µ
L) was injected into
the HPLC. The sample was separated in isocratic mode using an acetonitrile-deuterium
oxide mobile phase (60% ACN-40% D
2
O) with detection at 254 nm. The flow rate was
set to 0.5 mL/min. For the observation of
1
H NMR spectra, a Varian INOVA 500 MHz
spectrometer (Varian Inc., Palo Alto, CA, USA) equipped with an HCN triple resonance
(60
µ
L active volume) micro-flow probe was used. Separation and experiments were carried
out at ambient temperature (22
◦
C). The
1
H NMR spectra of individual chromatographic
peaks were recorded in the stop-flow mode with an accumulation of at least 256 scans
(acquisition time 2 s, relaxation delay 1 s). In order to suppress residual solvent signals,
the WET (water suppression enhanced through T1 effects) multiple-frequency solvent
suppression method was used during the acquisition. The
1
H-NMR spectra were referenced
to the signal of acetonitrile (δ= 2.00 ppm).
The individual stilbenes were isolated using the same HPLC instrument. The concen-
trated solutions (50
µ
L) were injected repeatedly into the HPLC system, and fractions of
isolated compounds were collected. Each fraction was evaporated to dryness and subse-
quently dissolved in an appropriate deuterated solvent (acetone-d
6
, methanol-d
4
) to enable
comparison with the literature data.
3.3.4. Determination of Stilbenes by NMR
The NMR experiments were conducted on a Varian INOVA 500 MHz spectrometer
(Varian Inc., Palo Alto, CA, USA) operating at 499.87 MHz for
1
H. Only the
1
H NMR spectra
of individual compounds in the corresponding deuterated solvent were recorded due to
the low concentration. The identification was based on a comparison of the measured
1H spectra with the literature data.
The NMR data for pallidol (Carex Lepidocarpa Peak 1) are as follows:
1
H NMR (from
LC-NMR 60% ACN-40% D
2
O, ppm)
δ
: 6.97 (d, 4H, H-2a, H-6a, H-2b, H-6b, J= 8.5 Hz),
6.70 (d, 4H, H-3a, H-5a, H-3b, H-5b J= 8.4 Hz), 6.60 (d, 2H, H-14a, H-14b, J= 1.9 Hz),
6.12 (d, 2H, H-12a, H-12b, J= 2.0 Hz), 4.45 (s, 2H, H-7a, H-7b) and 3.76 (s, 2H, H-8a, H-8b),
and they are in agreement with [10].
The NMR data for trans-
ε
-viniferin (Carex Lepidocarpa Peak 4) are as follows:
1
H
NMR (from LC-NMR 60% ACN-40% D
2
O, ppm)
δ
: 7.19 (d, 2H, H-2a, H-6a, J= 8.5 Hz)

Molecules 2024,29, 3840 9 of 11
7.15 (d, 2H, H-2b, H-6b,
J= 8.6 Hz), 6.92 (d, 1H, H-8b, J= 16.4 Hz), 6.82 (d, 2H, H-3a, H-5a,
J= 8.5 Hz), 6.74 (d, 2H, H-3b, H-5b, J= 8.6 Hz), 6.69 (d, 1H, H-14b, J= 1.8 Hz), 6.61 (d, 1H,
H-7b, J= 16.4 Hz), 6.34 (d, 1H, H-12b, J= 1.8 Hz), 6.19 (d, 2H, H-10a, H-14a, J= 1.9 Hz), 6.17
(t, 1H, H-12a, J= 1.9 Hz), 5.48 (d, 1H, H-7a, J= 6.0 Hz) and 4.49 (d, 1H, H-8a, J= 6.0 Hz),
and they are in accordance with our previously published data [24].
The NMR data for cis-miyabenol C (Z-miyabenol C) (Carex Lepidocarpa Peak 5) are as
follows:
1
H NMR (acetone-d
6
, ppm)
δ
: 7.12 (d, 2H, H-2a, H-6a, J= 8.3 Hz), 6.85 (d, 2H, H-3a,
H-5a, J= 8.5 Hz), 6.72 (d, 2H, H-2c, H-6c, J= 8.5 Hz), 6.56 (d, 2H, H-3b, H-5b,
J= 8.6 Hz),
6.50 (d, 2H, H-3c, H-5c, J= 8.5 Hz), 6.37 (d, 2H, H-2b, H-6b, J= 8.5 Hz), 6.33 (d, 1H, H-12c,
J= 1.9 Hz),
6.26 (d, 1H, H-12b,
J= 2.0 Hz),
6.24 (t, 1H, H-12a, J= 2.0 Hz), 6.12 (d, 1H, H-14c,
J= 2.0 Hz), 6.09 (d, 1H, H-14b, J= 2.1 Hz), 5.91 (d, 2H, H-10a, H-14a, J= 2.1 Hz), 5.83
(d, 1H, H-8c, J= 12.4 Hz),
5.78 (d, 1H, H-7c, J= 12.4 Hz), 5.29 (d, 1H, H-7a, J= 3.1 Hz), 5.26
(d, 1H, H-7b, J= 2.6 Hz), 4.22 (d, 1H, H-8a, J= 3.0 Hz) and 3.87 (d, 1H, H-8b, J= 2.5 Hz).
The NMR data for cis-miyabenol C (Z-miyabenol C) were in agreement with [25].
The NMR data for the compound from Carex lepidocarpa Peak 6 are as follows:
1
H
NMR (acetone-d
6
, ppm)
δ
: 7.07 (d, 2H, J= 8.6 Hz), 7.00 (d, 2H, J= 8.7 Hz), 6.99
(d, 2H, J= 8.6 Hz),
6.89
(d, 1H, J= 16.3 Hz),
6.81 (d, 2H, J= 8.6 Hz), 6.80 (brs, 2H), 6.74
(d, 2H, J= 8.6 Hz),
6.73 (d,
1H, J= 2.1 Hz), 6.30 (d, 1H, J= 2.2 Hz), 6.26 (d, 1H, J= 16.3 Hz), 6.22 (t, 1H, J= 2.3 Hz), 6.20
(d, 1H, J= 2.1 Hz), 5.97 (d, 1H, J= 2.2 Hz), 5.97 (d, 2H, J= 2.3 Hz), 5.30 (d, 1H, J= 3.6 Hz),
5.03 (d, 1H, J= 7.3 Hz), 4.58 (d, 1H, J= 7.3 Hz) and 3.70 (d, 1H, J= 3.6 Hz). The NMR data
for cis-miyabenol A (Carex Acuta Peak 1) are as follows:
1
H NMR (methanol-d
4
, ppm)
δ
:
6.72 (d, 2H, H-2d, H-6d, J= 8.5 Hz), 6.61 (d, 2H, H-2a, H-6a, J= 8.6 Hz), 6.60 (d, 2H, H-3c,
H-5c, J= 8.6 Hz), 6.51 (d, 2H, H-3a, H-5a, J= 8.6 Hz), 6.48 (d, 2H, H-2c, H-6c, J= 8.7 Hz),
6.45 (d, 2H, H-3d, H-5d, J= 8.6 Hz), 6.44 (d, 2H, H-2b, H-6b, J= 8.6 Hz), 6.40 (d, 2H, H-3b,
H-5b,
J= 8.7 Hz),
6.30 (brs, 1H, H-12d), 6.28 (d, 1H, H-12b,
J= 2.2 Hz),
6.25 (d, 1H, H-14c, J
= 2.2 Hz), 6.17 (d, 1H, H-12c, J= 2.0 Hz), 6.05 (d, 1H, H-14b, J= 2.2 Hz), 6.00 (d, 1H, H-14d,
J= 2.2 Hz),
5.92 (brs, 1H, H-12a), 5.89 (d, 1H, H-7d, J= 12.0 Hz), 5.85 (d, 1H, H-8d, J= 12.0
Hz), 5.78 (brs, 2H, H-10a, H-14a), 5.40 (d, 1H, H-7c, J= 2.7 Hz), 5.12 (d, 1H, H-7b, J= 2.0
Hz), 5.02 (d, 1H, H-7a, J= 6.3 Hz) 4.40 (d, 1H, H-8b, J= 2.0 Hz) 3.98 (d, 1H, H-8a, J= 6.3 Hz)
and 3.87 (d, 1H, H-8c, J= 2.8 Hz). The NMR data for cis-miyabenol A were in accordance
with [18].
4. Conclusions
We focused our study on two species of sedges, Carex acuta and Carex lepidocarpa,
which have been not studied yet, based on our previous screening of stilbenes in the
Collection of Aquatic and Wetlands Plants in Tˇreboˇn, Institute of Botany of the Czech
Academy of Sciences, Czech Republic. Pallidol, trans-
ε
-viniferin, cis and trans-miyabenol
A and cis-miyabenol C were identified in the extracts. In C. acuta, the mixture of cis and
trans miyabenol A predominates, reaching almost 5 mg/g d.m., while in C. lepidocarpa,
the highest number of stilbenes is attributed to pallidol (up to 14.5 mg/g d.m.) and
to cis-miyabenol C (up to 4.8 mg/g d.m.). The content of all stilbenes reaches almost
3% w/w, which is interesting for the isolation of these substances from the biomass of
C. lepidocarpa roots and is very interesting in terms of recent literature data regarding
resveratrol oligomers—specifically, the inhibition of SARS-CoV-2 entry by targeting host
protease cathepsin L.
Author Contributions: J.T. conceived and designed the experiments; N.V., Š.H. and J.S. performed
the research; J.T., N.V., Š.H. and J.S. performed the data analysis and identification of stilbenes; J.T.,
N.V. and A.K. wrote the paper. J.T. edited the final manuscript. All authors have read and agreed to
the published version of the manuscript.
Funding: This research was funded by the Ministry of Education, Youth and Sports of the Czech
Republic (AdAgriF; CZ.02.01.01/00/22_008/0004635) and partially funded by project Long-term
research development Nr. RVO 67985939.
Institutional Review Board Statement: Not applicable.

Molecules 2024,29, 3840 10 of 11
Informed Consent Statement: Not applicable.
Data Availability Statement: The data used to support the findings of this study can be made
available by the corresponding author upon request.
Acknowledgments: The plants were provided by Hortus Botanicus Tˇreboˇn, Department of Experi-
mental Garden and Collection of Aquatic and Wetlands Plants, Institute of Botany of Czech Academy
of Sciences. We thank Štˇepánka Kuncováfor the original sampling of the Carex species.
Conflicts of Interest: The authors declare no conflicts of interest.
References
1.
Koopman, J. Carex Europaea. The Genus Carex L. (Cyperaceae) in Europe, 1: Accepted Names, Hybrids, Synonyms, Distribution,
Chromosome Numbers; Margraf Publishers: Weikersheim, Germany, 2011.
2.
Schweingruber, F.H.; Kuˇcerová, A.; Adamec, L.; Doležal, J. Anatomic Atlas of Aquatic and Wetland Plant Stems; Springer: Berlin,
Germany, 2020.
3.
Hedrén, M. Patterns of allozyme and morphological differentiation in the Carex flava complex (Cyperaceae) in Fennoscandia. Nord.
J. Bot. 2002,22, 257–301. [CrossRef]
4.
Blackstock, N. A reassessment of Yellow Sedges—Carex flava agg. (Cyperaceae) in the British Isles. Ph.D. Thesis, University of
Lancaster, Lancaster, UK, 2007.
5.
de Moraes, K.R.; Souza, A.T.; Muška, M.; Hladík, M.; ˇ
Ctvrtlíková, M.; Draštík, V.; Kolaˇrík, T.; Kuˇcerová, A.; Krolová, M.; Sajdlová,
Z.; et al. Artificial floating islands: A promising tool to support juvenile fish in lacustrine systems. Hydrobiologia 2023,850,
1969–1984. [CrossRef]
6.
Harris, T.; Klimeš, A.; Martínková, J.; Klimešová, J. Herbs are not just small plants: What biomass allocation to rhizomes tells us
about differences between trees and herbs. Am. J. Bot. 2023,110, e16202. [CrossRef] [PubMed]
7.
González-Sarrías, A.; Gromek, S.; Niesen, D.; Seeram, N.P.; Henry, G.E. Resveratrol oligomers isolated from Carex species inhibit
growth of human colon tumorigenic cells mediated by cell cycle arrest. J. Agric. Food Chem. 2011,59, 8632–8638. [CrossRef]
[PubMed]
8.
Hu, J.; Lin, T.; Gao, Y.; Xu, J.; Jiang, C.; Wang, G.; Bu, G.; Xu, H.; Chen, H.; Zhang, Y. The resveratrol trimer miyabenol C inhibits
β-secretase activity and β-amyloid generation. PLoS ONE 2015,10, e0115973. [CrossRef] [PubMed]
9.
Wang, C.; Ye, X.; Ding, C.; Zhou, M.; Li, W.; Wang, Y.; You, Q.; Zong, S.; Peng, Q.; Duanmu, D.; et al. Two resveratrol oligomers
inhibit cathepsin L activity to suppress SARS-CoV-2 entry. J. Agric. Food Chem. 2023,71, 5535–5546. [CrossRef]
10.
Arraki, K.; Totoson, P.; Decendit, A.; Badoc, A.; Zedet, A.; Jolibois, J.; Pudlo, M.; Demougeot, C.; Girard-Thernier, C. Cyperaceae
species are potential sources of natural mammalian arginase inhibitors with positive effects on vascular function. J. Nat. Prod.
2017,80, 2432–2438. [CrossRef] [PubMed]
11.
Arraki, K.; Richard, T.; Badoc, A.; Pédrot, E.; Bisson, J.; Waffo-Téguo, P.; Mahjoub, A.; Mérillon, J.M.; Decendit, A. Isolation,
characterization and quantification of stilbenes from some Carex species. Rec. Nat. Prod. 2013,7, 281–291.
12.
Senda, N.; Kubota, Y.; Hoshino, T.; Nozaki, H.; Hayashi, H.; Nakayama, M. Mass spectra of some stilbene oligomers from Carex
species. J. Mass Spectrom. Soc. Jpn. 1995,43, 45–51. [CrossRef]
13.
Fiorentino, A.; Ricci, A.; D’Abrosca, B.; Pacifico, S.; Golino, A.; Letizia, M.; Picolella, S.; Monaco, P. Potential food additives from
Carex distachya roots: Identification and in vitro antioxidant properties. J. Agric. Food Chem. 2008,56, 8218–8225. [CrossRef]
14.
Suzuki, K.; Shimizu, T.; Kawabata, J.; Mizutani, J. New 3,5,4
′
-trihydroxystilbene (resveratrol) oligomers from Carex fedia Nees var.
miyabei (Franchet) T. Koyama (Cyperaceae).Agric. Biol. Chem. 1987,51, 1003–1008.
15.
Li, L.; Henry, G.E.; Seerman, N.P. Identification and bioactivities of resveratrol oligomers and flavonoids from Carex folliculata
seeds. J. Agric. Food Chem. 2009,57, 7282–7287. [CrossRef] [PubMed]
16.
Seo, H.; Kim, M.; Kim, S.; Mahmud, H.A.; Islam, M.I.; Nam, K.W.; Cho, M.L.; Kwon, H.-S.; Song, H.Y.
In vitro
activity of
alpha-viniferin isolated from the roots of Carex humulis against Mycobacterium tuberculosis.Pulm. Pharmacol. Ther. 2017,46, 41–47.
[CrossRef] [PubMed]
17.
Kawabata, J.; Ichikawa, S.; Kurihara, H.; Mizunati, J. Kobophenol-A, a unique tetrastilbene from Carex kobomugi Ohwi (Cyperaceae).
Tetrahedron Lett. 1989,30, 3785–3788. [CrossRef]
18.
Meng, Y.; Bourne, P.C.; Whiting, P.; Šik, V.; Dinan, L. Identification and ecdysteroid antagonist activity of three oligostilbenes from
the seeds of Carex pendula (Cyperaceae). Phytochemistry 2001,57, 393–400. [CrossRef]
19.
Kurihara, H.; Kawabata, J.; Ichikawa, S.; Mizutani, J. (-)-
ε
-viniferin and related oligostilbenes from Carex pumita Thunb. (Cyper-
aceae). Agric. Biol. Chem. 1990,54, 1097–1099.
20.
Niesen, D.B.; Ma, H.; Yuan, T.; Bach, A.C.; Henry, G.E.; Seeram, N.P. Phenolic constituents of Carex vulpinoidea seeds and their
tyrosinase inhibitory activities. Nat. Prod. Commun. 2015,10, 491–493. [CrossRef]
21.
Dávid, C.Z.; Hohmann, J.; Vasas, A. Chemistry and pharmacology of Cyperaceae stilbenoids: A review. Molecules 2021,26, 2794.
[CrossRef]
22.
Gajbhiye, R.; Sarma, S.S.; Kumar, D.; Singh, S. The treasure trove of the genus Carex: A phytochemical and pharmacological
review. Health Sci. Rev. 2024,10, 100151. [CrossRef]

Molecules 2024,29, 3840 11 of 11
23.
Biais, B.; Krisa, S.; Cluzet, S.; Costa, G.D.; Waffo-Teguo, P.; Mérillon, J.M.; Richard, T. Antioxidant and cytoprotective activities of
grapevine stilbenes. J. Agric. Food Chem. 2017,65, 4952–4960. [CrossRef]
24.
Soural, I.; Vrchotová, N.; Tˇríska, J.; Balík, J.; Horník, Š.; Cuˇrínová, P.; Sýkora, J. Various extraction methods for obtaining stilbenes
from grape cane of Vitis vinifera L. Molecules 2015,20, 6093–6112. [CrossRef] [PubMed]
25.
Mattivi, F.; Vrhovsek, U.; Malacarne, G.; Masuero, D.; Zulini, L.; Stefanini, M.; Moser, C.; Velasco, R.; Guella, G. Profiling of
resveratrol oligomers, important stress metabolites, accumulating in the leaves of hybrid Vitis vinifera (Merzling
×
Toroldego)
genotypes infected with Plasmopara viticola.J. Agric. Food Chem. 2011,59, 5364–5375. [CrossRef] [PubMed]
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