A phytochemical study of the ethyl acetate extract (EtOAc) of Styrax annamensis leaves resulted in the isolation
and determination of six known compounds, including three nor-neolignans type 2-phenylbenzofurans egonol (1),
egonoic acid (2) and (–)-machicendiol (3), two lignans styraxin (4) and vladinol D (5), and a triterpenoid pomolic acid
(6). The chemical structures of these compounds were determined by NMR spectroscopies, and MS data. This is the
first time to isolate these compounds from S. annamensis species. Compounds 3 and 5 have also been observed from
genus Styrax for the first time.
7 trang |
Chia sẻ: thuyduongbt11 | Ngày: 17/06/2022 | Lượt xem: 290 | Lượt tải: 0
Bạn đang xem nội dung tài liệu Chemical constituents from the leaves of Styrax annamensis Guill, để tải tài liệu về máy bạn click vào nút DOWNLOAD ở trên
Cite this paper: Vietnam J. Chem., 2020, 58(5), 630-636 Article
DOI: 10.1002/vjch.202000052
630 Wiley Online Library © 2020 Vietnam Academy of Science and Technology, Hanoi & Wiley-VCH GmbH
Chemical constituents from the leaves of Styrax annamensis Guill
Nguyen Thanh Tra
1,2
, Tran Dang Anh
1
, Pham Van Cuong
3
, Nguyen Thi Thu Ha
1,2
, Le Thi Tu Anh
1
,
Ba Thi Cham
1
, Ninh The Son
1*
1
Institute of Chemistry, Vietnam Academy Science and Technology (VAST),
18 Hoang Quoc Viet, Cau Giay district, Hanoi 10000, Viet Nam
2
Graduate University of Science and Technology, VAST,
18 Hoang Quoc Viet, Cau Giay district, Hanoi 10000, Viet Nam
3
Institute of Marine Biochemistry, VAST, 18 Hoang Quoc Viet, Cau Giay district, Hanoi 10000, Viet Nam
Received April 6, 2020; Accepted April 9, 2020
Abstract
A phytochemical study of the ethyl acetate extract (EtOAc) of Styrax annamensis leaves resulted in the isolation
and determination of six known compounds, including three nor-neolignans type 2-phenylbenzofurans egonol (1),
egonoic acid (2) and (–)-machicendiol (3), two lignans styraxin (4) and vladinol D (5), and a triterpenoid pomolic acid
(6). The chemical structures of these compounds were determined by NMR spectroscopies, and MS data. This is the
first time to isolate these compounds from S. annamensis species. Compounds 3 and 5 have also been observed from
genus Styrax for the first time.
Keywords. Styrax annamensis, leaves, nor-neolignan, lignan, triterpenoid.
1. INTRODUCTION
Genus Styrax, also known as Storax or Snowbell, is
one of the largest genera in the family Styracaceae,
comprising of about 130 species of small trees and
shrubs.
[1]
Styrax plants were native to tropical and
subtropical areas, especially available in Eastern and
Southeastern Asia.
[2]
The dried exudative gums
derived from pierced bark of the various Styrax
species are currently seen as commercial products,
e.g, for a long history, three species S. tonkinensis
(Siam benzoin), S. benzoin (Sumatra benzoin), and
S. benzoides were being well-known employed for
perfume, incense, and medicine.
[3,4]
Phytochemical
investigations of Styrax species have resulted in the
isolation and structural elucidation of various classes
of compounds, and lignans and triterpenoids are
major components. Crude extracts, fractions as well
as isolated compounds obtained from this genus
have a wide range of biomedical features. As
examples, Park et al. (2009, 2010) used isolated
lignans from Styrax japonica stem bark to combat
the pathogenic fungus Candida albicans,
[5-7]
meanwhile glycoprotein from this plant caused for
oxidative inhibitory and anti-inflammatory actions in
HCT116 colonic epithelial cell.
[8]
Oliveira et al.
(2012) suggested that S. camporum extract can lead
to significantly decrease the extent of DNA damage
in liver cells induced by methanesulfonate.
[9]
There are about thirteen Styrax plants in
Vietnam,
[10]
and several species have already been
studied in both phytochemical and biological
aspects. S. annamensis Guill, locally called Bo De
Trung Bo, was mostly distributed from Hagiang to
Khanhhoa.
[10]
To the best of our knowledge, there
were no documents to research phytochemistry for
this species. In the current paper, we firstly report
the isolation and structural determination of six
compounds, including three nor-neolignans, two
lignans, and a triterpenoid from the leaves of S.
annamensis.
2. MATERIALS AND METHODS
2.1. General experimental procedures
ESI-MS data were obtained with a Thermo Scientific
LTQ Orbitrap XL spectrometer (USA). NMR spectra
have been recorded on a Bruker 500 MHz
spectrometer, operating at 125 MHz for
13
C NMR and
at 500 MHz for
1
H NMR. Silica gel 40-63 µm and
Sephadex LH-20 have been employed for column
chromatography (CC). TLC silica gel 60 F254 (Merck)
was used for thin-layer chromatography (TLC).
Vietnam Journal of Chemistry Ninh The Son et al.
© 2020 Vietnam Academy of Science and Technology, Hanoi & Wiley-VCH GmbH www.vjc.wiley-vch.de 631
2.2. Plant material
The leaves of S. annamensis species were collected
in Dienbien province in March 2018. The plant
material was identified by Dr. Nguyen Quoc Binh,
Institute of Ecology and Biological Resources. A
voucher specimen (VN-1547F) was deposited in
Laboratory of Applied Biochemistry, Institute of
Chemistry.
2.3. Extraction and isolation
The dried leaves powder of S. annamensis (1.0 kg)
was ultrasonically extracted with n-hexane (10 L × 3
times) for 1h at 45 °C. After that, the powder was
then extracted with EtOAc (10 L × 3 times) for 1h at
45 °C, and concentrated under vacuum (20~30
mbar) at 50 °C to give a EtOAc residue (55.0 g).
This residue was subjected to silica gel (10 × 50 cm,
350.0 g) column chromatography (CC), eluting with
a gradient of n-hexane-CH3COCH3 (9:1→ 0:10, v/v)
and CH3COCH3-MeOH (9:1→ 0:10, v/v) to yield 13
fractions (Fr.1-Fr.13).
Figure 1: Compounds 1-6 isolated from S. annamensis leaves and their key HMBC and COSY correlations
The Fr.3 (3.8 g) was subjected for Sephadex LH-
20 CC [MeOH-CH2Cl2 (9:1, v/v)] to yield 4
fractions (Fr.3.1-Fr.3.4). Compound 6 (5.0 mg) was
obtained from the fraction Fr.3.4 (0.7 g) by using
Sephadex LH-20 CC [MeOH-CH2Cl2 (9:1, v/v)].
The Fr.4 (3.2 g) was subjected for CC on silica
gel eluting with a gradient solvent of CH2Cl2-
CH3COCH3 (9:1, v/v) to yield 3 fractions (Fr.4.1-
Fr.4.3). Compound 1 (7.0 mg) was isolated from the
fraction Fr.4.2 (1.2 g) by using Sephadex LH-20 CC
[MeOH-CH2Cl2 (9:1, v/v)]. The fraction Fr.5 (4.8 g)
was divided into 4 fractions (Fr.5.1-Fr.5.4) by CC
on silica gel eluting with a gradient solvent of
CH2Cl2-CH3COCH3 (9:1, v/v). Using Sephadex LH-
20 CC [MeOH-CH2Cl2 (9:1, v/v)], compounds 2
(6.0 mg) and 5 (7.0 mg) were separated from the
fraction Fr.5.2 (1.1 g).
The fraction Fr.8 (3.4 g) was chromatographed
on Sephadex LH-20 CC [MeOH-CH2Cl2 (9:1, v/v)]
to yield 3 fractions (Fr.8.1-Fr.8.3). The fraction
Fr.8.1 (1.4 g) was chromatographed on Sephadex
LH-20 CC [MeOH-CH2Cl2 (9:1, v/v)] to afford
compounds 3 (6.0 mg) and 4 (6.0 mg).
Egonol (1): White amorphous powders; ESI-MS
(–): m/z 325 [M–H]–; 1H-NMR (500 MHz, CD3OD,
δH ppm) and
13
C-NMR (125 MHz, CD3OD, δC ppm),
see table 1.
Egonoic acid (2): White amorphous powders;
ESI-MS (-): 339 [M–H]–; 1H-NMR (500 MHz,
CD3OD, δH ppm) and
13
C NMR (125 MHz, CD3OD,
δC ppm), see table 1.
(–)-Machicendiol (3): White amorphous
powders; ESI-MS (+): m/z 343 [M+H]
+
;
1
H-NMR
(500 MHz, CD3OD, δH ppm) and
13
C-NMR (125
MHz, CD3OD, δC ppm), see table 1.
Styraxin (4): White amorphous powders; ESI-
MS (+): m/z 371 [M+H]
+
;
1
H-NMR (500 MHz,
CDCl3, δH ppm) and
13
C-NMR (125 MHz, CDCl3,
δC ppm), see table 2.
Vladinol D (5): White amorphous powders;
ESI-MS (+): m/z 375 [M+H]
+
;
1
H-NMR (500 MHz,
CD3OD, δH ppm): and
13
C-NMR (125 MHz,
CD3OD, δC ppm), see table 2.
Pomolic acid (6): White amorphous powders;
ESI-MS (+): m/z 473 [M+H]
+
;
1
H-NMR (500 MHz,
CD3OD, δH ppm): 5.31 (1H, t, 4.0 Hz, H-12), 3.32
(1H, overlap, H-3), 2.55 (1H, s, H-18), 2.53 (1H, m,
H-2a), 2.04 (2H, m, H-11), 1.87 (2H, m, H-9, H-
Vietnam Journal of Chemistry Chemical constituents from the leaves of
© 2020 Vietnam Academy of Science and Technology, Hanoi & Wiley-VCH GmbH www.vjc.wiley-vch.de 632
15a), 1.74 (2H, m, H-21a, H-22a), 1.67 (1H, m, H-
22b), 1.61 (1H, m, H-7a), 1.59 (1H, m, H-1a), 1.58
(4H, m, H-1b, H-21b, H-16), 1.57 (1H, dd, 4.5 Hz,
11.5 Hz, H-2b), 1.47 (2H, m, H-6), 1.37 (3H, brs, H-
27), 1.29 (1H, m, H-20), 1.29 (1H, m, H-7b), 1.28
(2H, m, H-1b, H-7b), 1.22 (3H, brs, H-29), 1.01 (3H,
brs, H-23), 0.99 (1H, m, H-15b), 0.96 (3H, brs, H-
30), 0.94 (3H, brs, H-25), 0.91 (1H, m, H-5), 0.89
(3H, brs, H-24), 0.83 (3H, brs, C-26),
13
C-NMR
(125 MHz, CD3OD, δC ppm): 182.0 (C-28), 140.2
(C-13), 129.3 (C-12), 80.1 (C-3), 73.7 (C-19), 55.2
(C-5), 54.8 (C-18), 48.8 (C-17), 48.2 (C-9), 43.1 (C-
20), 42.8 (C-14), 42.5 (C-1), 41.3 (C-8), 39.5 (C-4),
39.4 (C-10), 39.1 (C-22), 34.1 (C-7), 29.6 (C-15),
29.2 (C-23), 27.4 (C-21, C-16), 27.1 (C-29), 26.7
(C-2), 24.9 (C-27), 24.7 (C-11), 22.5 (C-24), 19.2
(C-6), 17.6 (C-26), 16.8 (C-30), 16.2 (C-25).
Table 1:
1
H and
13
C-NMR data of compounds 1-3
No
1
2 3
δH (J in Hz) δC δH (J in Hz) δC δH (J in Hz) δC
2 157.2 157.2 157.5
3 6.93 (s) 101.4 6.94 (s) 101.5 7.00 (s) 101.6
3a 132.5 132.4 132.2
4 6.98 (d, 1.5) 113.5 7.01 (d, 1.0) 113.4 7.16 (d, 1.0) 111.5
5 139.2 139.0 142.5
6 6.73 (d, 1.5) 108.9 6.78 (d, 1.0) 108.8 6.92 (d, 1.0) 106.1
7 146.1 146.1 146.4
7a 143.8 143.8 144.5
1' 126.2 126.2 126.1
2' 7.34 (d, 1.5) 106.1 7.34 (d, 2.0) 106.2 7.36 (d, 2.0) 106.2
3' 149.6 149.6 149.7
4' 149.5 149.5 149.6
5' 6.91 (d, 8.0) 109.6 6.92 (d, 8.0) 109.6 6.93 (d, 8.0) 109.6
6' 7.42 (dd, 1.5, 8.0) 120.0 7.42 (dd, 1.5, 8.0) 120.3 7.44 (dd, 1.5, 8.0) 120.1
1'' 2.76 (t, 7.5) 33.4 2.99 (t, 7.5) 33.5 4.88 (m) 72.8
2'' 1.92 (m) 35.9 2.58 (t, 7.5) 39.8
2.06 (m)
1.94 (m)
43.1
3'' 3.61 (t, 6.5) 62.3
179.8
3.72 (m)
3.64 (m)
60.2
OCH2O 6.01 (s) 102.7 6.01 (s) 102.7 6.03 (s) 102.8
7-OCH3 4.03 (s) 56.7 4.02 (s) 56.6 4.02 (s) 56.7
3. RESULTS AND DISCUSSION
Compound 1 was obtained as white amorphous
powders. The negative ESI-MS data indicated the
ion loses a proton at m/z 325 [M–H]–, which along
with the
13
C-NMR data is consistent with the
molecular formula of C19H18O5. The
1
H-NMR data
of 1 established the pattern of a nor-neolignan type
of 2-(3',4'-methylenedioxyphenyl)-benzofuran.
Three aromatic proton signals H-3 (δH 6.93, s), H-4
(δH 6.98, d, 1.5 Hz), and H-6 (δH 6.73, d, 1.5 Hz)
were assigned to benzofuran nuclear, whereas ABX
spin system [H-2' (δH 7.34, d, 1.5 Hz), H-6' (δH 7.42,
dd, 1.5, 8.0 Hz), and H-5' (δH 6.91, 8.0 Hz)], and
dioxygenated methylene (δH 6.01) were
characteristic of 3',4'-methylenedioxyphenyl unit.
The
1
H-NMR spectrum also identified the
presence of three other aliphatic methylenes of
hydroxypropyl unit [H-1'' (δH 2.76, t, 7.5 Hz), H-2''
(δH 1.92, m), and H-3'' (δH 3.61, t, 6.5 Hz)], and a
methoxy group 7-OCH3 (δH 4.03, s). The
13
C-NMR
data of 1 were composed of six aromatic methine
carbons, four methylene carbons, eight quaternary
carbons, and one methoxy carbon (table 1 and figure
1). The chemical structure of 1 was further
confirmed by 2D-NMR data (HSQC and HMBC).
Benzofuran nuclear was established with the key
HMBC cross-peaks H-3/C-2, C-3a, and C-7a, H-
4/C-3, C-6, and C-7a, while the key HMBC
correlations OCH2O/C-3', and C-4', H-2'/C-3', H-
5'/C-4', and H-6'/C-2', and C-4' were presented for
3',4'-methylenedioxyphenyl unit. The HMBC
correlations H-2' and H-6'/C-2 showed that phenyl
unit connected to benzofuran nuclear at carbon C-2.
Vietnam Journal of Chemistry Ninh The Son et al.
© 2020 Vietnam Academy of Science and Technology, Hanoi & Wiley-VCH GmbH www.vjc.wiley-vch.de 633
The important HMBC correlation OCH3/C-7 pointed
out that methoxy group directly substituted at carbon
C-7. The correlations H-2''/C-1'', and C-3'', H-3''/C-
1'', and H-1''/C-4, C-5, and C-6 in the HMBC
spectrum also identified that hydroxypropyl side
chain linked to carbon C-5. In comparison with
literature data, compound 1 was determined to be
egonol.
[11,12]
This compound is now available in
Styrax plants, and is becoming a useful agent in anti-
inflammatory,
[11]
antioxidative,
[12]
anti-cancer,
[13]
and
anti-bacterial treatments.
[14]
Compound 2 was isolated as white amorphous
powders, and its molecular formula C19H16O6 was
identified basing on the ion loses a proton at m/z 339
[M–H]– in the negative ESI-MS spectrum. The 1H
and
13
C-NMR data of 2 were similar to those of 1,
except for hydroxypropyl side chain in 1 was
replaced by carboxyethyl unit [H-1'' (δH 2.99, t, 7.5
Hz) and C-1'' (δC 33.5); H-2'' (δH 2.58, t, 7.5 Hz) and
C-2'' (δC 39.8); and C-3'' (δC 179.8)] in 2 (table 1).
The HMBC evidence H-2''/C-1'', and C-3'', and H-
1''/C-4, C-5, and C-6 (figure 1) also affirmed that
carboxyethyl unit substituted at carbon C-5 in 2. The
structure of 2 was further confirmed by comparison
with literature data as known compound egonoic
acid.
[15]
Compound 3 was separated as white amorphous
powders. The
1
H and
13
C-NMR data of 3 were very
similar to those of 1. The difference between 1 and 3
occurred at carbon C-1'' since a proton of methylene
H-1'' in 1 was replaced by hydroxy group in 3. This
phenomenon has been so far confirmed by 2D-NMR
(figure 1), especially MS data. The molecular mass
of 3 is higher than that of 1 by 12 Da. From these
findings and comparison with literature data,
compound 3 was elucidated as (–)-machicendiol.[16]
This is the first time to observe this compound in
genus Styrax, to date.
Compound 4 was obtained as white amorphous
powders. The molecular formula C20H18O7 deduced
from the proton adduct ion at m/z 371 [M+H]
+
in the
positive ESI-MS. The 1D-NMR data (
1
H and
13
C-
NMR) aided by the 2D-NMR spectroscopic data
(HSQC and HMBC) of 4 revealed that secondary
metabolite 4 is a lignan furofuran. In the
1
H-NMR of
4, the signals of furofuran nuclear resonated at δH
3.45-5.29 ppm, while 3',4'-methylenedioxyphenyl
unit was found to appear in the downfield [OCH2O
(δH 5.97, s), H-2' (δH 7.34, d, 1.5 Hz), H-5' (δH 6.91,
d, 8.0 Hz), and H-6' (δH 7.42, dd, 1.5, 8.0 Hz)]. The
1
H-NMR of 4 also proved the appearance of a 1,3,4-
trisubstitutedphenyl unit [ABX spin system H-2'' (δH
6.81, d, 2.0 Hz), H-6'' (δH 6.77, dd, 2.0, 7.5 Hz), and
H-5'' (δH 6.98, d, 7.5 Hz)], and a methoxy group 3''-
OCH3 (δH 3.95, s). Meanwhile, the
13
C-NMR data of
lignan 4 contained twenty carbon signals, including
six aromatic methines, four aliphatic methine
carbons, two oxygenated methylene carbons, six
quaternary carbons, one methoxy carbon 3''-OCH3
(δC 56.0), and one carbonyl carbon C-8 (δC 176.8).
The 2D-NMR data (HSQC and HMBC) is in
accordance with this. As shown in figure 1,
furofuran nuclear was established with the key HBC
correlations H-1/C-2, and C-8, H-5/C-4, and C-6, H-
2/C-5, H-1/C-4, and H-6/C-1, and C-8. In the same
manner, 3',4'-methylenedioxyphenyl unit has
associated with the representative HMBC evidence
OCH2O/C-3', and C-4', H-2'/C-3', and H-6'/C-2', and
C-4'. The remaining 1,3,4-trisubstituted unit was
characterized by the important HMBC correlations
H-2''/C-3'', H-6''/C-2'', and C-4''. It turned out that
OCH3 substituted at carbon C-3'' due to HMBC
correlation OCH3/C-3''. The linkage between
furofuran nuclear and 3',4'-methylenedioxyphenyl
unit at carbon C-2 was identified by HMBC
correlations H-2' and H-6'/C-2, as well as the
connection between furofuran nuclear and 1,3,4-
trisubstituted phenyl unit was determined by H-2''
and H-6''/C-6. The structure of compound 4 has
coincided with an isolated compound, namely
styraxin.
[17]
However, to the best of our knowledge,
the NMR data of this compound have not yet
assigned fully. This is the second time we isolated
and provided full NMR results since it was only
found in S. officinalis aerial part.
[17]
Compound 5 was precipitated out of EtOAc
extract as white amorphous powders. The molecular
formula of 5 was to be C20H22O7, deducing from the
proton adduct ion at m/z 375 [M+H]
+
in the positive
ESI-MS spectrum. The comprehensive analysis of
1D-NMR data (
1
H and
13
C) and 2D-NMR data
(HSQC, HMBC, and COSY) can lead to identifying
that secondary metabolite 5 was a tetrahydrofuran
lignan, which named vladinol D.
[18,19]
Considering
the
1
H-NMR data of 5, three aliphatic methines H-8,
H-7' and H-8', and an oxygenated methylene H-9 of
furan ring resonated in the region of 2.72-4.66 ppm,
and induced serial COSY cross-peaks H-9/H-8/H-
8'/H-7'. Oxygenated methylene H-9' (δH 3.62 and δH
3.67) correlated to C-8' (δC 54.6) suggests that this
group substituted at carbon C-8'. The
1
H-NMR data
also showed the presence of a 1,3,4-trisubstituted
benzoyl unit [ABX spin system H-2 (δH 7.61, d, 2.0
Hz), H-6 (δH 7.63, dd, 2.0, 9.0 Hz), and H-5 (δH
6.91, d, 9.0 Hz)], and a 1,3,4-trisubstituted phenyl
unit [ABX spin system H-2' (δH 7.08, d, 2.0 Hz), H-
6' (δH 6.87, dd, 2.0, 8.0 Hz), and H-5' (δH 6.78, d, 8.0
Hz)]. Two methoxy groups at δH 3.93 and δH 3.90
directly substituted at carbons C-3 (δC 149.2) and C-
3' (δC 149.1) can be explained by the HMBC
Vietnam Journal of Chemistry Chemical constituents from the leaves of
© 2020 Vietnam Academy of Science and Technology, Hanoi & Wiley-VCH GmbH www.vjc.wiley-vch.de 634
correlations 3-OCH3/C-3 and 3'-OCH3/C-3',
respectively. Benzoyl moiety connecting to carbon
C-8 of furan nuclear was confirmed by the key
HMBC correlations H-8 and H-9/C-7, while phenyl
unit linked to carbon C-7' due to the crucial HMBC
correlations H-2' and H-6'/C-7'. Vladinol (5) has
been isolated from various high plants, such as
Vladimiria souliei or Forsythia suspensa,
[18,19]
but
this is the first time to observe in genus Styrax.
Table 2:
1
H and
13
C-NMR data of compounds 4-2
No
4
5
δH (J in Hz) δC δH (J in Hz) δC
1 3.45 (dd, 3.5, 9.5) 53.2 130.1
2 5.33 (d, 4.0) 83.4 7.61 (d, 2.0) 112.5
3 149.2
4
4.31 (dd, 3.5, 9.5)
4.32 (dd, 7.0, 9.5)
72.7
153.5
5 3.20 (m) 49.9 6.91 (d, 9.0) 115.9
6 5.29 (d, 4.0) 84.5 7.63 (dd, 2.0, 9.0) 125.0
7 200.3
8 176.8 4.28 (m) 50.3
9 4.19 (m) 71.8
1' 132.3 133.6
2' 6.90 (d, 1.5) 108.2 7.08 (d, 2.0) 111.5
3' 148.0 149.1
4' 148.4 147.5
5' 6.76 (d, 8.0) 105.7 6.78 (d, 8.0) 116.0
6' 6.86 (dd, 1.5, 8.0) 118.0 6.87 (dd, 2.0, 8.0) 121.0
7' 4.66 (d, 9.0) 85.3
8' 2.72 (m) 54.6
9'
3.62 (dd, 5.5, 11.5)
3.67 (dd, 4.5, 11.5)
61.3
1'' 133.1
2'' 6.81 (d, 2.0) 108.5
3'' 146.8
4'' 145.4
5'' 6.98 (d, 7.5) 114.5
6'' 6.77 (dd, 2.0, 7.5) 119.0
OCH2O 5.97 (s) 101.5
3-OCH3 3.93 (s) 56.47
3'-OCH3 3.95 (s) 56.0 3.90 (s) 56.41
Compound 6 was obtained as white amorphous
powders. On the basis of the proton adduct ion at
m/z 473 [M+H]
+
in the positive ESI-MS
spectroscopy, the molecular formula of 6 was to be
C30H48O4. 1D-NMR data coulped with 2D-NMR
data (HSQC and HMBC) of 6 corresponded to a
well-known triterpenoid, namely pomolic acid.
[20-22]
1D-NMR revealed that compound 6 contained five
methyl, one methine carbinol, one olefinic bond, one
carbonyl carbon, and remaining aliphatic methines
and methylenes. Hydroxygenation occurred at
carbon carbinol C-3 (δC 80.1) with the key HMBC
correlations H-1, H-23, and H-24/C-3. Double bond
located at carbons C-12 (δC 129.3) and C-13 (δC
140.2), with the characteristic HMBC correlations
H-12/C-11 and C-13, H-18/C-12. Carboxyl group
substituted at carbon C-17, which can be visible by
HMBC correlations H-18 and H-22/C-28. The direct
correlations H-23 and H-24/C-4, H-25/C-10, H-
26/C-9, H-27/C-14, H-29/C-19, and H-30/C-20 in
the HMBC spectrum established the positions of
methyl groups. Pomolic acid (6) is now abundant in
Vietnam Journal of Chemistry Ninh The Son et al.
© 2020 Vietnam Academy of Science and Technology, Hanoi & Wiley-VCH GmbH www.vjc.wiley-vch.de 635
nature, but regarding genus Styrax, here is the
second time we have successfully isolated and
identified since it was only found in the leaves of S.
tonkinensis.
[ 23]
4. CONCLUSION
This is the first time that three nor-neolignans type
2-phenylbenzofurans egonol (1), egonoic acid (2)
and (–)-machicendi