New compounds from the aerial parts of Calligonum mongolicum

Article abstract of DOI:10.1016/j.phytol.2020.12.002

Previously undescribed compounds, (R)-4-(4-hydroxyphenyl)-2-butanol 2-O-(6-O-galloyl)-β-D-glucopyranoside (1) and (E)-5-(4-hydroxyphenyl)pent-2-enoic acid (2), together with 20 known compounds (3-22) were isolated from the aerial parts of Calligonum mongolicum. Compound 3 was obtained from a natural source for the first time, and all of the compounds (1-22) were reported for the first time in this plant. The structural elucidation of compounds 1 and 2 were performed mainly by HRFABMS, HREIMS, ¹H and ¹³C NMR, ¹H–¹H COSY, HMQC, and HMBC spectroscopy. Some of the enzyme inhibitory activities of the isolated compounds were estimated, and catechin (7) showed ten times higher phenoloxidase inhibitory activity (IC₅₀ 9.1 μM) than epicatechin (8) (IC₅₀ 148.3 μM). Compounds 7 and 8 have a common molecular structure, except for their stereochemistry, and this result was supported by a reproducibility test using pure guaranteed authentic samples.

Full text of DOI:10.1016/j.phytol.2020.12.002

Phytochemistry Letters 41 (2021) 147–151
Contents lists available at ScienceDirect
Phytochemistry Letters
journal homepage: www.elsevier.com/locate/phytol
New compounds from the aerial parts of Calligonum mongolicum
,
Buyanmandakh Buyankhishiga, Toshihiro Murataa *, Batsukh Odonbayara, Javzan Batkhuub,
Kenroh Sasakia
a Department of Pharmacognosy, Tohoku Medical and Pharmaceutical University, Aoba-ku, Sendai 981-8558, Japan
b School of Engineering and Applied Sciences, National University of Mongolia, P.O.B.-617/46A, Ulaanbaatar 14201, Mongolia
A R T I C L E I N F O
A B S T R A C T
Keywords:
Previously undescribed compounds, (R)-4-(4-hydroxyphenyl)-2-butanol 2-O-(6-O-galloyl)-β-D-glucopyranoside
(1) and (E)-5-(4-hydroxyphenyl)pent-2-enoic acid (2), together with 20 known compounds (3-22) were isolated
from the aerial parts of Calligonum mongolicum. Compound 3 was obtained from a natural source for the first
time, and all of the compounds (1-22) were reported for the first time in this plant. The structural elucidation of
compounds 1 and 2 were performed mainly by HRFABMS, HREIMS, 1H and 13C NMR, 1H–1H COSY, HMQC, and
HMBC spectroscopy. Some of the enzyme inhibitory activities of the isolated compounds were estimated, and
Calligonum mongolicum
Phenyl butanoid
Phenyl pentenoic acid
Phenoloxidase
Catechin
catechin (7) showed ten times higher phenoloxidase inhibitory activity (IC50 9.1
148.3 M). Compounds 7 and 8 have a common molecular structure, except for their stereochemistry, and this
result was supported by a reproducibility test using pure guaranteed authentic samples.
μM) than epicatechin (8) (IC50
μ
1. Introduction
the first time. Furthermore, all compounds (1-22) were isolated from
this species for the first time. The inhibitory activities against cholin-
esterase, tyrosinase, and insect phenoloxidase of these isolated com-
pounds were estimated to clarify the biological effects of the
constituents on enzymes.
The genus Calligonum belongs to the family Polygonaceae, with
about 80 species distributed in Northern Africa, Southern Europe, and
Western Asia (Okasaka et al., 2004). Calligonum mongolicum is a shrub
plant distributed in Middle Asia, including Mongolia, and is used for
firewood and prevents aeolian erosion. It is an important fodder of
livestock, especially camels (Jigjidsuren and Johnson, 2003). This plant
is traditionally used as a hemostatic, nasal hemorrhagic, and for the
relief of menstruation (Jigjidsuren and Johnson, 2003). Previous
phytochemical investigations on several species of this genus led to the
isolation of flavonoids (Ahmed et al., 2016), steroids (Samejo et al.,
2013a), stilbenes (Okasaka et al., 2004), butanolides (Yawer et al.,
2007), and terpenoids (Samejo et al., 2013b); some of which exhibited
significant pharmacological activities, including cytotoxicity, anti-
oxidative, anti-lipoxygenase, and antibacteria (Okasaka et al., 2004;
Ahmed et al., 2016; Yawer et al., 2007). However, to the best of our
knowledge, there is no previous report on the chemical constituents of a
single species of C. mongolicum.
2. Results and discussion
The acetone-water (4:1) extract of aerial parts of C. mongolicum was
suspended in water and partitioned with diethyl ether to obtain water
and diethylether extracts. The water extract was subjected to the column
using HP-20 resin. From each obtained fraction, compounds 1, 4, 7ꢀ 9,
13, 14, 17, and 18 were purified using preparative high-performance
liquid chromatography (HPLC). The diethyl ether extract was sub-
jected to silica gel column chromatography, and then compounds 2, 3,
5, 6, 10ꢀ 12, 15, 16, 19, and 20ꢀ 22 were isolated using HPLC. The
chemical structures of the isolated compounds were elucidated using
spectroscopic data, including 1H and 13C NMR, HRFABMS, HREIMS, and
specific rotation. Particularly, compounds 3ꢀ 22 were identified by
comparison of their spectral data with literature reported previously,
(2R, 4aS, 8aS)-4a-hydroxy-2-methyl-3,4,4a,8a-tetrahydrobenzo-1 (2 H)-
pyran-7 (8)-one (3) (Barradas et al., 2009), rhododendrin (4) (Kim et al.,
2011), (R)-(ꢀ )-rhododendrol (5) (Kim et al., 2011), 4-(2-oxobutyl)
phenol (6) (Bunce and Reeves, 1989), catechin (7) (Galotta et al., 2008),
As part of our continuing investigation of the phytochemical and
bioactive compounds of Polygonaceae plants, we have succeeded in the
isolation of twenty-two (1-22) compounds from the aerial parts of this
plant. Among these isolated compounds, 1 and 2 were previously
undescribed compounds, and 3 was obtained from a natural source for
* Corresponding author.
E-mail address: murata-t@tohoku-mpu.ac.jp (T. Murata).
https://doi.org/10.1016/j.phytol.2020.12.002
Received 29 July 2020; Received in revised form 2 December 2020; Accepted 2 December 2020
Available online 18 December 2020
1874-3900/© 2020 Phytochemical Society of Europe. Published by Elsevier Ltd. All rights reserved.

B. Buyankhishig et al.
Phytochemistry Letters 41 (2021) 147–151
epicatechin (8) (Davis et al., 1996), dihydrokaempferol (9) (Lee et al.,
2003), dihydroquercetin (10) (Keihlmann and Slade, 2003), kaempferol
(11) (Chang et al., 2000), quercetin (12) (Chang et al., 2000), kaemp-
ferol 3-O-β-D-glucuronopyranoside (13) (Dini et al., 2004), quercetin
˜
3-β-O-glucuronopyranoside (14) (Castillo-Munoz et al., 2009),
N-trans-feruloyltyramine (15) (Kim et al., 2005), N-cis-feruloyltyramine
(16)
(Fukuda
et
al.,
1983),
2-(4-hydroxyphenyl)ethyl--
β-D-glucopyranoside (17) (Shi et al., 2011), isopentyl β-D-glucopyr-
anoside (18) (Kurashima et al., 2004), p-hydroxy-trans-cinnamic acid
(19) (Satake et al., 1980), p-hydroxybenzoic acid (20) (Chang et al.,
2000), protocatechuic acid (21) (Zhang et al., 1998), and gallic acid (22)
(Gottlieb et al., 1991), as shown in Fig. S18. Compound 1 and 2 were
obtained as new compounds. Therefore, the structure determination
procedures of them are described below.
Compound 1 (Fig. 1) was formulated as C23H29O11 (m/z, 481.1709
[M+H]+; calcd for C23H29O11, 481.1710) by HRFABMS. In the 1H NMR
spectrum of 1, a singlet proton at δ 7.11 (2H, s, H-2′′′ and 6′′′) and a set of
o-coupling doublet methine protons at δ 6.91 (2H, d, J =8.5 Hz, H-2′, H-
6′) and 6.59 (2H, d, J =8.5 Hz, H-3′, H-5′) were observed in its aromatic
field. The singlet proton and its correlated carbons in the HMQC and
Fig. 2. 1H-1H COSY and key HMBC correlations of compound 1.
HMBC spectra (δ 121.6, C-1′′′; 110.3, C-2′′′ and 6′′′; 146.6, C-3′′′ and 5′′′
;
139.9, C-4′′′; 168.5, C-7′′′) showed the presence of a galloyl moiety. The
o-coupling doublet methine protons and remaining aromatic carbon
resonances (δ 134.7, C-1′; 130.4, C-2′ and 6′; 116.0, C-3′ and 5′; 156.1, C-
4′) indicated the presence of a p-substituted benzene ring. The lower
field shifted C-4′ carbon suggested it was oxygenated. The 13C NMR
spectrum of 1 showed 10 carbon resonances in the aliphatic field,
including 1 methyl, 3 methylene, and 6 methine carbons. Among them,
the oxygenated five methine and one methylene carbons (δ 102.6, C-1′′;
75.2, C-2′′; 78.2, C-3′′; 71.9, C-4′′; 75.4, C-5′′; 64.9, C-6′′) indicated the
presence of a 6-acylated glucopyranosyl moiety (Shikishima et al.,
2001). This glucosyl moiety was verified as D-glucose by sugar analysis
using HPLC after acid hydrolysis of 1. The HMBC long-range correlations
from H-6′’ to C-7′” showed that the acyl group was the galloyl group
(Fig. 2). The 1H-1H COSY spectrum of 1 showed a 2-oxygenated butyl
moiety (δ 1.17, 3H, d, J =6.0 Hz, H-1; 3.80, 1H, m, H-2; 1.78, 1H, m,
H-3; 1.65, 1H, m, H-3; 2.52, 2H, m, H-4) (Fig. 2). The HMBC long-range
correlation between H-1′’ (δ 4.34, 1H, d, J =7.5 Hz) and C-2 indicated
that the D-glucopyranosyl moiety was connected to C-2. The coupling
constant (J = 7.5 Hz) of the anomeric proton in the glucosyl moiety
indicated the β-orientation of the sugar moiety. The HMBC spectrum
(Fig. 2) showed long-range correlations of H-4 with C-1’, C-2’, and C-6’,
which established that the p-substituted benzene ring was connected to
C-4. From these data, the chemical structure of 1 was determined to be
4-(4-hydroxyphenyl)-2-butanol 2-O-(6-O-galloyl)-β-D-glucopyranoside.
Although this molecular structure is the same as that of
not identical to that of the compound. The glycosidation shifts rule for
(2R)- and (2S)-pentanol (Seo et al., 1978) was attempted for 1,
comparing it with (S)-4-(4-hydroxyphenyl)-2-butanol 2-O-(6-O-gal-
loyl)-β-D-glucopyranoside and 4-(4-hydroxyphenyl)-2-butanol (Shi-
kishima et al., 2001); the (2R)-configuration of 1 was suggested (Fig. S).
Moreover, the 2R-configuration rhododendron (4) (Kim et al., 2011) and
(R)-(ꢀ )-rhododendrol (5) (Kim et al., 2011) were isolated together with
1. Thus, compound
1
was identified as (R)-4-(4-hydrox-
yphenyl)-2-butanol 2-O-(6-O-galloyl)-β-D-glucopyranoside.
Compound 2 was formulated as C11H12O3 (m/z 192.0790 [M]+;
calcd for C11H12O3, 192.0786) by HREIMS. The 1H NMR spectrum of 2
exhibited 10 proton resonances. The 1H–1H COSY spectrum of 2 (Fig. 3)
suggested the presence of a butyl aliphatic chain [δ 5.78 (1H, d, J =15.5
Hz, H-2); 6.91 (1H, dt, J = 16.0, 7.0 Hz, H-3); 2.46 (2H, m, H-4); 2.67
(2H, t, J =7.0 Hz, H-5)] and p-substituted benzene ring [δ 7.00 (2H, d, J
=8.5 Hz, H-2′, 6′) and δ 6.69 (2H, d, J = 8.5, H-3′, 5′)]. The coupling
constant of the two olefinic proton resonances (J =15.5 Hz) between H-2
and H-3 indicated their E configuration. In the 13C NMR spectrum, one of
the quaternary carbons at δ 171.0 (C-1) suggested the presence of the
carboxylic acid moiety, and it was long-range coupled with H-2 and H-3
in its HMBC spectra (Fig. 3). Additionally, aromatic carbons at δ 133.2
(C-1′), 130.4 (C-2′ and 6′), 116.2 (C-3′ and 5′), and 156.6 (C-4′) were
assigned to the 4-oxygenated benzene ring. These NMR data and the
molecular formula determined by HRFABMS indicated that 2 had one
(S)-4-(4-hydroxyphenyl)-2-butanol
2-O-(6-O-gal-
loyl)-β-D-glucopyranoside (Shikishima et al., 2001), the NMR data was
Fig. 1. Structures of compounds 1–3.
Fig. 3. 1H-1H COSY, key HMBC, and NOE correlations of compound 2.
148

B. Buyankhishig et al.
Phytochemistry Letters 41 (2021) 147–151
hydroxy and one carboxylic acid group. The HMBC correlations from H-
5 to C-1′, C-2′, and C-6′ established that the 4-hydroxy phenyl moiety
was connected to C-5. Hence, 2 was identified as 5-(4-hydroxyphenyl) 2-
pentenoic acid.
TSKgel ODS-120 T (Tosoh, Tokyo, Japan, 21.5 × 300 mm), Mightysil
RP-18 GP (Kanto Chemical, Tokyo, Japan, 10 × 250 mm), Cosmosil 5C18
AR-II (Nacalai Tesque, Kyoto, Japan, 20 × 250 mm) and Develosil C30
UG-5 (Nomura Chemical, Aichi, Japan, 20 × 250 mm).
-
To estimate the biological activities of the isolated compounds,
acetylcholinesterase, tyrosinase, and insect phenoloxidase inhibitory
activities were tested. Although electric eel acetylcholinesterase (0.8
mM) and mushroom tyrosinase (1 mM) inhibitor was not found, com-
pounds 7 and 8 affected the enzymatic activities of phenoloxidase from
Acyrthosiphon pisum (Table 1). Other tested compounds 1–6, 13, 15, 17,
19, 20 did not show significant activity. Phenoloxidase is an important
component in an insect’s immune system, and it contributes to the
elimination of phatogens by producing melanin (Stączek et al., 2020).
Melanization involves oxidative steps. Catechin (7) from C. mongolicum
3.2. Plant material
The aerial parts of Calligonum mongolicum were collected at Segs
Tsagaan Bogd Mountain, Shine Jinst soum, Bayankhongor province,
Mongolia, at 958 m above sea level, in July 2012 and identified by Prof.
Ch. Sanchir, Institute of Botany, Mongolian Academy of Sciences. A
voucher specimen (No.31.05.03.12A) was deposited at the Laboratory
of Bioorganic Chemistry and Pharmacognosy, National University of
Mongolia.
(9.1
catechin (8) (148.3
test using guaranteed pure substances (+)-catechin hydrate (>97.0 %,
Tokyo Chemical Industry, Tokyo, Japan): 18.6 M and (ꢀ )-epicatechin,
from green tea (>98.0 %, Fujifilm, Osaka, Japan): 195.8 M. Because
μ
M) showed a ten times stronger IC50 value compared with epi-
μM). This result was confirmed by a repeatability
3.3. Extraction and isolation
μ
The dried aerial parts (250 g) were extracted with acetone-water
(4:1) (3 × 2.5 L). The extracts were combined and evaporated in vacuo
at 50 ◦C. The evaporated extract (42 g) was suspended in water (0.5 L)
and then partitioned with diethyl ether (3 × 0.5 L). The aqueous extract
(37.8 g) was subjected to DIAION HP-20 column chromatography with a
gradient eluent of water-methanol (1:0 to 0:1, v/v) to afford five frac-
tions (1A-1E). Fraction 1C (4.0 g) was chromatographed over a reverse-
phase ODS-SM-50C-M column eluted with water-methanol (gradient
system from 4:1 to 3:2, v/v) to give subfractions 2A-2L. Subfraction 2C
(82.5 mg) was separated by preparative HPLC to obtain compounds 7
(10.3 mg) and 17 (6.0 mg) [TSKgel ODS-120 T, CH3CN–H2O (3:17, v/v)
containing 0.2 % TFA; Develosil C30-UG-5, CH3CN–H2O (3:17, v/v)
containing 0.2 % TFA]. Subfractions 2F-H (622.0 mg) were purified by
preparative HPLC to isolate compounds 4 (113.4 mg), 8 (0.9 mg), 9 (4.5
mg), and 18 (1.9 mg) [TSKgel ODS-120 T, CH3CN–H2O (4:16, v/v)
containing 0.2 % TFA; Develosil C30-UG-5, CH3CN–H2O (6:14, v/v)
containing 0.2 % TFA]. Fraction 1D (12.5 g) was loaded on a reverse-
phase ODS-SM-50C-M column eluted with water-methanol (gradient
system from 4:1 to 1:1, v/v) to give subfractions 3A-T. Subfractions 3J-K
(172.4 mg) were separated by preparative HPLC to obtain compounds 1
(3.5 mg) and 13 (54.5 mg) [TSKgel ODS-120 T, CH3CN–H2O (1:4, v/v)
containing 0.2 % TFA; Develosil C30-UG-5, CH3CN–H2O (1:4, v/v)
containing 0.2 % TFA] and subfractions 3H-I (169.9 mg) were subjected
to preparative HPLC to isolate compound 14 (87.4 mg) [TSKgel ODS-
μ
compounds 7 and 8 have a common molecular structure, it was expected
that the stereochemistry of C-2 and C-3 was an important key structure
for the inhibitory activity against this enzyme. According to previously
reported literature data (Odonbayar et al., 2016), gallocatechin showed
an inhibitory effect on phenoloxidase, and it was stronger than that of
epigallocatechin. Although Odonbayar et al. (2016) suggested that the
inhibitory activity of pyrogallol B-ring is stronger than that of catechol
B-ring, catechin (7) with catechol B-ring showed stronger activity than
gallocatechins in this study. Therefore, further studies are needed on
structure-activity relationship of catechin derivatives. N-phenylthiourea
was used as positive control. Although the activities of (+)-catechin and
(-)-epicatechin were lower compared to positive control, the catechins
are included in many plants. Therefore, the study of catechins as insect
phenoloxidase inhibitors seems to be useful for the control of pests and
may enable understanding of the interactions between insect immune
systems and plant chemicals.
3. Experimental section
3.1. General experimental procedures
Specific rotation was taken on a JASCO P-2300 polarimeter (JASCO,
Tokyo, Japan). NMR experiments were carried out using a JEOL JNM-
AL400 FT-NMR spectrometer (JEOL, Tokyo, Japan) operating at 400
MHz for 1H and at 100 MHz for 13C, and chemical shifts were given as δ
values with TMS as an internal standard at 25 ◦C (measured in methanol-
120 T, CH3CN–H2O (1:4, v/v) containing 0.2 % TFA; Develosil C30
UG-5, CH3CN–H2O (1:4, v/v) containing 0.2 % TFA].
-
The diethyl ether extract (3.7 g) that was subjected to silica gel
column chromatography was eluted with n-hexane-acetone (gradient
system from 1:0 to 0:1, v/v) and aqueous methanol (1:1 and 0:1, v/v) to
produce 37 fractions (4A-4K1). Fractions 4M-P (150.8 mg) were applied
to the column using HP-20 resin with a gradient eluent of water-
methanol (1:4 and 0:5, v/v) to generate two subfractions (5A-5B). 5A
(39.9 mg) was purified by HPLC on the 5C18-AR-II column with
CH3CN–H2O (1:4, v/v) to yield compounds 3 (10.1 mg) and 6 (3.7 mg).
Fractions 4S-T (118.2 mg), 4U (213.4 mg), and 4X (315.8 mg) were
isolated using the same procedure as 4M-P to achieve compounds 2 (2.7
mg), 5 (119.0 mg), 10 (12.7 mg), 11 (3.3 mg), 12 (2.3 mg), 15 (27.7
mg), 16 (1.3 mg), 19 (2.6 mg), 20 (13.7 mg), 21 (9.6 mg), and 22 (20.9
mg).
1
d4, chloroform-d, and pyridine-d5). HMQC (optimized for JC–H =145
n
Hz) and HMBC (optimized for JC–H =8 Hz) pulse sequences with a
pulsed field gradient. HRFABMS, and HREIMS data were processed
using a JEOL JMS700 mass spectrometer (JEOL), with a glycerol matrix.
Preparative and analytical HPLC was performed using a JASCO 2089
(JASCO) with UV detection at 210 nm, using the following columns:
Ultra Pack ODS-SM-50C-M (Yamazen, Osaka, Japan, 37 × 100 mm),
Table 1
Insect phenoloxidase inhibitory activities for identified
compounds from the aerial parts of C. mongolicum.
Compound
IC50 (μM)
3.3.1. (R)-4-(4-hydroxyphenyl)-2-butanol 2-O-(6-O-galloyl)-β-D-
7a
9.1 ± 0.3
glucopyranoside (1)
catechinb
18.6 ± 0.6
148.3 ± 2.6
195.8 ± 4.8
0.053 ± 0.001
22
Yellowish, amorphous solid; [
α]
D –15.7◦ (c 0.05, MeOH); 1H NMR
8a
(methanol-d4, 400 MHz): δ 7.11 (2H, s, H-2′′′, 6′′′), 6.91 (2H, d, J =8.5
Hz, H-2′, 6′), 6.59 (2H, d, J =8.5 Hz, H-3′, 5′), 4.50 (1H, dd, J = 12.5, 2.5
Hz, H-6′′), 4.45 (1H, dd, J =12.5, 5.5 Hz, H-6′′), 4.34 (1H, d, J =7.5 Hz,
H-1′′), 3.80 (1H, m, H-2), 3.53 (1H, m, H-5′′), 3.45 (1H, t, J =9.0 Hz, H-
4′′), 3.39 (1H, t, J =9.0 Hz, H-3′′), 3.22 (1H, dd, J = 7.5, 9.0 Hz, H-2′′),
2.52 (1H, m, H-4), 1.78 (1H, m, H-3), 1.65 (1H, m, H-3), 1.17 (1H, d, J
epicatechinc
N-phenylthiourea
a
Compounds were isolated from C. mongolicum.
b
The compound was guaranteed by the Tokyo chemical
industry.
c
The compound was guaranteed by the Fujifilm.
149

B. Buyankhishig et al.
Phytochemistry Letters 41 (2021) 147–151
=6.0 Hz, H-1); 13C NMR (methanol-d4, 100 MHz): δ 168.5 (C-7′′′), 156.1
(C-4′), 146.6 (C-3′′′, 5′′′), 139.9 (C-4′′′), 134.7 (C-1′), 130.4 (C-2′, 6′),
121.6 (C-1′′′), 116.0 (C-3′, 5′), 110.3 (C-2′′′, 6′′′), 102.6 (C-1′′), 78.2 (C-
3′′), 75.6 (C-2), 75.4 (C-5′′), 75.2 (C-2′′), 71.9 (C-4′′), 64.9 (C-6′′), 40.6
(C-3), 31.8 (C-4), 20.2 (C-1); HMBC (methanol-d4, 400 MHz): from 1.17
(H-1) to 75.6 (C-2), and 40.6 (C-3); from 2.52 (H-4) to 40.6 (C-3), 134.7
(C-1′), and 130.4 (C-2′, 6′); from 6.91 (H-2′) to 31.8 (C-4), 130.4 (C-6′)
and 156.1 (C-4′); from 6.59 (H-3′) to 134.7 (C-1′); from 4.34 (H-1′’) to
75.6 (C-2); from 3.22 (H-2′′) to 102.6 (C-1′′); from 4.45 (H-6′′) to 168.5
(C-7′′′); from 7.11 (H-2′′′) to 121.6 (C-1′′′), 146.6 (C-3′′′), 139.9 (C-4′′′),
110.3 (C-6′′′), and 168.5 (C-7′′′); HRFABMS (positive) m/z 481.1709
[M+H]+ (calcd for C23H29O11, 481.171).
Declaration of Competing Interest
The authors report no declarations of interest.
Acknowledgments
We thank Mr. S. Sato and Mr. T. Matsuki of Tohoku Pharmaceutical
University for assisting with the MS measurements. This work was
supported by a grant from JSPS Kakenhi (grant number JP19K16397),
JICA M-JEED project, JST/JICA SATREPS (grant number JPMJSA1906).
This work was partially supported by the Kanno Foundation of Japan.
Appendix A. Supplementary data
3.3.2. 5-(4-hydroxyphenyl) 2-pentenoic acid (2)
Yellowish, amorphous solid; 1H NMR (methanol-d4, 400 MHz): δ
7.00 (2H, d, J =8.5 Hz, H-2′, 6′), 6.91 (1H, dt, J = 16.0, 7.0 Hz, H-3),
6.69 (2H, d, J =8.5 Hz, H-3′, 5′), 5.78 (1H, d, J =15.5 Hz, H-2), 2.67 (1H,
t, J =7.0 Hz, H-5), 2.46 (1H, m, H-4); 13C NMR (methanol-d4, 100 MHz):
δ 171.0 (C-1), 156.6 (C-4′), 149.4 (C-3), 133.2 (C-1′), 130.4 (C-2′, C-6′),
123.8 (C-2), 116.2 (C-3′, C-5′), 35.4 (C-4), 34.7 (C-5); HMBC (methanol-
d4, 400 MHz): from 5.78 (H-2) to 171.0 (C-1), and 35.4 (C-4); from 6.91
(H-3) to 171.0 (C-1), and 35.4 (C-4); from 2.46 (H-4) to 123.8 (C-2),
149.4 (C-3), 34.7 (C-5) and 133.2 (C-1′); from 2.67 (H-5) to 149.4 (C-3),
35.4 (C-4), 133.2 (C-1′), and 130.4 (C-2′); from 7.0 (H-2′) to 34.7 (C-5),
130.4 (C-6′), 116.2 (C-3′), and 156.6 (C-4′); from 6.69 (H-3′) to 130.4 (C-
2′), 116.2 (C-5′), and 156.6 (C-4′); HREIMS (positive) m/z 192.0790
[M]+ (calcd for C11H12O3, 192.0786).
Supplementary material related to this article can be found, in the
online version, at doi:https://doi.org/10.1016/j.phytol.2020.12.002.
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