Antineurodegenerative Labdane Diterpenoid Glycosides from the Twigs of Pinus koraiensis

Article abstract of DOI:10.1021/acs.jnatprod.9b01158

Eleven new labdane-type diterpenoid glycosides, koraiensides A-K (1-11), together with two known analogues were isolated from the twigs of Pinus koraiensis. Their structures were elucidated via NMR, HRMS, and ECD data, DP4+ statistical analysis, and hydrolysis. The metabolites were tested for induction of nerve growth factor in C6 glioma cells to evaluate their potential neuroprotective activity. The compounds were measured for production of nitric oxide levels in lipopolysaccharide (LPS)-activated murine microglia BV2 cells to assess their antineuroinflammatory activity. Compounds 10 and 13 showed NGF secretion inducing effects from C6 glioma cells (162.3 ± 13.9percent and 162.7 ± 6.9percent, respectively). Compound 6 showed an IC₅₀ value of 24.1 μM, implying significant inhibition of NO production.

Full text of DOI:10.1021/acs.jnatprod.9b01158

pubs.acs.org/jnp
Article
Antineurodegenerative Labdane Diterpenoid Glycosides from the
Twigs of Pinus koraiensis
Kyoung Jin Park, Zahra Khan, Lalita Subedi, Sun Yeou Kim, and Kang Ro Lee*
Cite This: https://dx.doi.org/10.1021/acs.jnatprod.9b01158
Read Online
sı
*
Metrics & More
Article Recommendations
Supporting Information
ACCESS
ABSTRACT: Eleven new labdane-type diterpenoid glycosides,
koraiensides A−K (1−11), together with two known analogues
were isolated from the twigs of Pinus koraiensis. Their structures
were elucidated via NMR, HRMS, and ECD data, DP4+ statistical
analysis, and hydrolysis. The metabolites were tested for induction
of nerve growth factor in C6 glioma cells to evaluate their potential
neuroprotective activity. The compounds were measured for
production of nitric oxide levels in lipopolysaccharide (LPS)-
activated murine microglia BV2 cells to assess their antineuroin-
flammatory activity. Compounds 10 and 13 showed NGF
secretion inducing effects from C6 glioma cells (162.3
13.9%
and 162.7 6.9%, respectively). Compound 6 showed an IC50
value of 24.1 μM, implying significant inhibition of NO production.
In ongoing research on bioactive substances from Korean
native plants, the EtOAc layer of the MeOH extract from P.
koraiensis twigs showed that the solvent layer induces NGF
release in C6 glioma cells (EtOAc-soluble layer, 153.8
15.2%; positive control, 6-shogaol, 150.8 8.9%). In contrast,
eurotrophic factors, such as nerve growth factor (NGF),
Nplay an important role in neuronal survival, develop-
ment, and central network formation. NGF is produced by the
brain cells in the nervous system for maintenance, migration,
and differentiation of cells.1 The loss of neurotrophic factors
and production of neuroinflammation may contribute to the
development of neurodegenerative disorders, including Par-
kinson’s and Alzheimer’s diseases.2,3 Uncontrolled activation of
microglial cells can release pro-inflammatory cytokines such as
NO due to excessive formation of inducible nitric oxide
synthase (iNOS).4 Overproduction of NO can result in
neuroinflammation, and it is vital to explore novel bioactive
phytochemicals that can protect brain cells by initiating the
production of NGF and mitigate neuroinflammation-targeting
activated microglia.
Pinus koraiensis Siebold et Zucc., belonging to the Pinaceae
family, is commonly known as “Korean pine” and mainly
distributed in Korea, Russia, China, and Japan. Pine nuts, the
seed crop of this tree, have been utilized as a supplementary
health food and dessert all over the world.5 Phytochemical
studies have reported various pharmacological activities
associated with the components of pine nuts and pine cones
of P. koraiensis. Fatty acids, peptides, and polysaccharides from
the pine nuts were shown as the main components displaying
antifatigue, antiaging, anti-inflammatory, antioxidant, and
hepatoprotective effects.6−8 Further, cytotoxic and angio-
genesis inhibitory diterpenoids,5,9 antioxidant polysacchar-
ides,10 and antitumor, antioxidant, and immunoregulatory
polyphenols11,12 were identified from the pine cones of P.
koraiensis.
the n-hexane-soluble layer (57.5
11.4%), CHCl3-soluble
layer (45.8 11.5%), and n-BuOH-soluble layer (150.8
2.8%) showed weak or similar activities when compared with
the positive control. From the active EtOAc layer, 11 new
diterpenoid glycosides (1−10), including a norditerpenoid
glucoside (11), together with the known compounds 12 and
13 were isolated and characterized. The structures of the new
compounds were elucidated based on the analysis of various
NMR (1H and 13C NMR, COSY, HSQC, HMBC, and
NOESY), HRMS, and ECD data, DP4+ computation, and
hydrolysis. The known analogues 12 and 13 were characterized
by comparing the observed spectra with reported data. The
purified compounds (2−13) were evaluated for their neuro-
protective and anti-inflammatory activities.
RESULTS AND DISCUSSION
■
The 80% MeOH extract of the twigs of P. koraiensis was
sequentially fractionated using n-hexane, CHCl3, EtOAc, and
Received: November 20, 2019
© XXXX American Chemical Society and
American Society of Pharmacognosy
https://dx.doi.org/10.1021/acs.jnatprod.9b01158
J. Nat. Prod. XXXX, XXX, XXX−XXX
A

Journal of Natural Products
pubs.acs.org/jnp
Article
Chart 1
n-BuOH. Such fractions were assessed for their neuro-
protective activity. The EtOAc-soluble fraction displayed
considerable NGF secretion effect and thus was subjected to
repeated chromatographic purification. As a result, 11 new
diterpenoid glycosides (1−11) and two known analogues (12
and 13) were purified and identified.
configuration.16 The NOESY correlations of H-5/H-9 and
H3-18, and H2-11/H3-20 indicated a trans-fused A/B ring
junction (Figure 1A). The orientation of the hydroxy group at
C-13 was verified based on a DP4+ computational analysis.17
1
The calculated H and 13C NMR data of (13α-OH)-1a and
(13β-OH)-1a were compared with the experimental values of
1a, the hydrolysate of 1, using DP4+ computational analysis.
The statistical results showed that (13α-OH)-1a is structurally
coincident to 1a with an α-oriented OH group at C-13 (Figure
1B, S123, and S124, Supporting Information). For determi-
nation of the absolute configuration of 1, the experimental
ECD data of 1a was compared with the calculated ECD data of
the two plausible enantiomers of 1a, (4S,5R,9S,10R,13R)-1a
and (4R,5S,9R,10S,13S)-1a. The experimental ECD spectrum
of 1a exhibited a positive Cotton effect at 222 nm, which was
identical to the calculated data for (4S,5R,9S,10R,13R)-1a
(Figure 1C), thus confirming the (13R) absolute configuration
of 1.
Enzymatic hydrolysis of 1 with β-glucosidase gave the
aglycone (1a) and a glucosyl unit. The D-configuration of the
glucosyl moiety was established through chiral derivatization
and GC/MS analysis.18 Based on HRESIMS data, the
molecular formula of 1a was confirmed as C20H30O5 and its
1D and 2D NMR spectra showed the absence of a glucosyl
unit when compared with those of 1 (Figures S1 and S2 and
Tables S6 and S7, Supporting Information).19 Thus, 1a was
identified as 13α-hydroxy-8(17)-labden-(15→16)-lacton-19-
oic acid, and the structure of 1 as β-D-glucopyranosyl 13α-
hydroxy-8(17)-labden-(15→16)-lacton-19-oate.
Koraienside A (1) was obtained as a colorless gum, and its
molecular formula was established as C26H40O10 based on the
[M + Na]+ ion in the HRESIMS data. The 1D NMR
spectroscopic data of 1 revealed the characteristic signals for
two tertiary methyls [δC 29.5 (C-18) and 13.9 (C-20); δH 1.19
(3H, s, Me-18) and 0.58 (3H, s, Me-20)], an exocyclic
methylene [δC 107.3 (C-17); δH 4.81 (1H, brs, H-17a) and
4.51 (1H, brs, H-17b)], a γ-lactone group [δC 178.9 (C-16),
80.3 (C-15), 78.2 (C-13), and 42.9 (C-14); δH 4.11 (2H,
overlap, H-15), 2.59 (1H, dd, J = 17.2, 12.6 Hz, H-14a), and
2.37 (1H, dd, J = 17.2, 9.7 Hz, H-14b)], and a glucopyranosyl
moiety [δC 95.7 (C-1′), 78.9 (C-5′), 78.6 (C-3′), 74.2 (C-2′),
71.3 (C-4′), and 62.6 (C-6′); δH 5.37 (1H, d, J = 8.2 Hz, H-
1′), 3.75 (1H, dd, J = 11.9, 1.8 Hz, H-6′a), 3.62 (1H, dd, J =
11.9, 4.6 Hz, H-6′b), and 3.33−3.28 (4H, m, H-2′,3′,4′,5′)],
indicating that compound 1 is a labdane-type diterpenoid
glucoside (Tables 1 and 2).13,14 These data were similar to
those of adenanthoside C (12),15 except for the resonances of
an oxygenated carbon (δC 78.2) and a methylene group [δC
42.9; δH 2.59 (1H, dd, J = 17.2, 12.6 Hz) and 2.37 (1H, dd, J =
17.2, 9.7 Hz)], instead of a Δ13(14) olefinic functionality [δC
146.2; δH 7.35 (1H, brs) and δC 133.3] in 12. Analysis of the
COSY, HSQC, and HMBC spectra corroborated the 2D
structure of 1 (Figure 1A). The location of an oxygenated
carbon and a glucosyl unit was deduced to be at C-13 and C-
19 via the HMBC correlations from H2-14 and H2-15 to C-13
and from H-1′ to C-19, respectively. The characteristic
coupling constant of the anomeric proton (J = 8.2 Hz)
showed that the glucosyl moiety had a β-anomeric
Koraienside B (2), a colorless gum, has a molecular formula
of C26H40O10. Its NMR data resembled those of 12,15 but
oxygenated carbon (δC 73.6) and tertiary methyl [δC 31.0; δH
1.12 (3H, s)] signals were present instead of the exocyclic
double-bond signals [δC 149.1 and δC 107.2; δH 4.91 (1H, s)
and 4.66 (1H, s)] at C-8 and C-17 in 12 (Tables 1 and 2). The
B
https://dx.doi.org/10.1021/acs.jnatprod.9b01158
J. Nat. Prod. XXXX, XXX, XXX−XXX

Journal of Natural Products
pubs.acs.org/jnp
Article
C
https://dx.doi.org/10.1021/acs.jnatprod.9b01158
J. Nat. Prod. XXXX, XXX, XXX−XXX

Journal of Natural Products
pubs.acs.org/jnp
Article
HMBC correlations of H-17/C-7, C-8, and C-9 indicated that
the OH group is located at C-8 (Figure 2). The relative
configuration of C-8 was determined through the NOESY
cross-peak of H-9/H-17, indicating the hydroxy group at C-8 is
β-orientated (Figure 3). The configuration of the glucosyl unit
was confirmed by the same method as described for 1.
Therefore, the structure of compound 2 was assigned as β-D-
glucopyranosyl 8β-hydroxy-labd-13-en-(15→16)-lacton-19-
oate.
Koraienside C (3) was purified as a colorless gum and had
the molecular formula C26H40O10, the same as 2 from the
HRESIMS data. The 1D NMR spectroscopic data of 3 were
close to those of 2, with the main difference in the carbon
chemical shift of the 17-methyl group (δC 23.6, 3; δC 31.0, 2),
suggesting that 3 was an epimer of 2 (Tables 1 and 2). The 2D
NMR spectra were analyzed to corroborate the 2D structure of
3, which confirmed it to be identical to 2. Based on the
NOESY correlation between H-11 and H-17, the hydroxy
group at C-8 was assigned an α-orientation (Figure 3). Thus,
the structure of 3 was elucidated as β-D-glucopyranosyl 8α-
hydroxylabd-13-en-(15→16)-lacton-19-oate.
The molecular formula of koraienside D (4), a colorless
gum, was defined as C26H38O10 from the HRESIMS data.
Comparison of the NMR spectra with data of 1215 displayed
the presence of a C-17 oxygenated methylene [δC 66.2; δH 4.09
(1H, d, J = 12.1 Hz) and 3.86 (1H, d, J = 12.1 Hz)] and Δ7(8)
double-bond signals [δC 126.8; δH 5.69 (m) and δC 138.9] in 4
instead of exocyclic double-bond signals [δC 149.1 and δC
107.2; δH 4.91 (1H, s) and 4.66 (1H, s)] for C-8/C-17 in 12
(Tables 1 and 2). In the HMBC spectrum, the correlations of
H-17/C-7, C-8, and C-9 corroborated the oxygenated
methylene group at C-17 and the Δ7(8) olefinic functionality
(Figure 2). The NOESY data of 4 showed correlations of H-5/
H-9, H-5/H-18, and H-11/H-20, which proved the relative
configuration of 4 (Figure 3). The sugar analysis of 4 was
performed as for 1. Accordingly, compound 4 was defined as β-
D-glucopyranosyl 17-hydroxy-labda-7,13-diene-(15→16)-lac-
ton-19-oate.
Koraienside E (5) gave a molecular formula of C26H38O10
deduced from the molecular ion at m/z 533.2366 [M + Na]+
(calcd for C26H38O10Na, 533.2363) in the HRESIMS data.
1
The H and 13C NMR spectra of 5 showed similarity with
those of adenanthoside C (12) (Tables 1 and 2).15 The main
distinction was that 5 has an oxygenated methine [δC 79.3; δH
3.22 (1H, dd, J = 12.2, 4.4 Hz)], replacing a methylene in 12.
The hydroxy group at C-3 was verified based on the HMBC
correlation of H-18/C-3 and the COSY correlation of H-2/H-
3 (Figure 2). The β-orientation of the hydroxy group at C-3
was corroborated through the J value of H-3 (JH‑2α/H‑3 = 4.4
1
Hz and JH‑2β/H‑3 = 12.2 Hz) confirmed in the H NMR data
and further identified by the cross-peak of H-3/H-5 in the
NOESY data (Figure 3). Therefore, the structure of compound
5 was assigned as β-D-glucopyranosyl 3β-hydroxylabda-
8(17),13-diene-(15→16)-lacton-19-oate.
Koraienside F (6) was purified as a colorless gum with the
same molecular formula, C26H38O10, as 5. The NMR
spectroscopic data of 6 were highly similar to the data of 5,
except for the C-3 resonances of 6 [δC 71.4; δH 3.94 (1H, brt, J
= 2.8 Hz)], compared with those of 5 [δC 79.3; δH 3.22 (1H,
dd, J = 12.2, 4.4 Hz)], indicating that 6 is an epimer of 5
(Tables 1 and 2). The 2D structure of 6 was defined via
analysis of the NMR data and confirmed to be the same as 5.
The coupling constants of H-3 (JH‑2α/H‑3 = 2.8 Hz and JH‑2β/H‑3
D
https://dx.doi.org/10.1021/acs.jnatprod.9b01158
J. Nat. Prod. XXXX, XXX, XXX−XXX

Journal of Natural Products
pubs.acs.org/jnp
Article
Table 2. 13C NMR Spectroscopic Data of Compounds 1−11 in Methanol-d4
pos
1
2
3
4
5
6
7
8
9
10
11
1
2
3
4
5
6
7
8
40.5
21.3
39.3
45.9
58.0
27.4
40.0
149.4
57.9
41.9
19.2
38.3
78.2
42.9
80.3
178.9
107.3
29.5
177.7
13.9
95.7
74.2
78.6
71.3
78.9
62.6
40.9
20.1
39.2
45.4
58.4
21.1
43.3
73.6
59.6
40.8
24.8
29.8
134.9
147.7
72.2
177.1
31.0
29.3
178.0
14.2
95.6
74.3
78.6
71.1
78.7
62.4
41.3
20.3
39.0
45.4
58.4
23.2
45.3
74.8
61.8
41.0
24.9
29.6
135.2
147.6
72.2
177.3
23.6
29.3
177.7
14.2
95.7
74.3
78.6
71.3
78.8
62.7
40.5
20.8
39.3
45.4
52.9
25.6
126.8
138.9
51.7
38.3
26.4
27.6
134.8
148.1
72.2
177.1
66.2
29.2
177.6
13.8
95.7
74.2
78.6
71.3
78.9
62.6
38.9
29.4
79.3
51.3
57.1
27.1
39.6
148.7
57.0
41.1
23.4
25.6
134.8
147.8
72.2
177.1
107.8
24.6
176.3
13.7
95.8
74.1
78.5
71.3
78.8
62.6
33.6
28.1
71.4
49.8
50.1
27.0
40.0
149.3
56.7
41.4
23.1
25.5
134.8
147.8
72.2
177.1
107.3
25.0
177.3
13.7
95.6
71.4
78.6
74.2
78.9
62.7
40.7
20.9
41.0
46.7
62.6
72.7
49.8
146.4
56.4
41.5
23.5
25.6
134.8
147.8
72.2
177.0
108.9
32.8
177.9
15.4
96.0
74.1
78.3
71.4
78.9
62.6
40.5
21.2
39.4
45.8
57.9
27.5
39.9
149.2
57.1
41.7
23.2
25.6
134.9
147.7
72.2
177.1
107.4
29.3
177.7
14.0
95.5
74.1
78.5
71.9
77.5
68.0
109.9
83.1
79.0
86.0
63.1
39.0
19.7
37.8
44.3
56.4
25.9
38.4
148.1
55.5
40.1
22.1
33.5
141.9
126.1
57.3
58.6
105.6
27.9
176.2
12.4
94.1
72.7
77.1
69.8
77.3
61.1
38.9
19.7
37.8
44.3
56.4
26.3
38.4
148.1
55.3
40.1
22.3
26.3
141.5
124.4
64.8
57.8
105.6
27.9
176.2
12.4
94.1
72.7
77.1
69.8
77.3
61.1
39.5
21.3
39.2
76.6
58.0
25.7
39.4
148.9
57.2
41.9
23.3
25.6
134.8
147.8
72.2
177.1
107.9
9
10
11
12
13
14
15
16
17
18
19
20
1′
2′
3′
4′
5′
6′
1″
2″
3″
4″
5″
174.2
13.6
96.4
74.0
78.1
71.4
78.8
62.7
1
= 2.8 Hz) in the H NMR spectrum of 6 and the NOESY
correlations of H-3/H-18 and H-5/H-18 were confirmed, but
no cross-peak appeared between H-3 and H-5 (Figure 3). This
evidence revealed that the OH group at C-3 is α oriented.
Consequently, the structure of 6 was elucidated as β-D-
glucopyranosyl 3α-hydroxylabda-8(17),13-diene-(15→16)-lac-
ton-19-oate.
overlap, H-4″), 3.76 (1H, dd, J = 5.8, 2.2 Hz, H-3″), 3.68 (1H,
dd, J = 11.9, 3.3 Hz, H-5″a), and 3.58 (1H, dd, J = 11.9, 5.1
Hz, H-5″b)] and a deshielded resonance of C-6′ (δC 68.0, 8;
δC 62.5, 12) (Tables 1 and 2). The small coupling constant of
H-1″ (J = 2.0 Hz) in 8 verified an α-arabinofuranosyl moiety.20
The analysis of additional 2D NMR spectra confirmed the 2D
structure of 8 (Figure 2). The HMBC data confirmed that the
position of the α-arabinofuranosyl unit is C-6′ based on the
correlation of H-1″/C-6′. Sugar analysis of 8 was performed
using the same method as 1, and L-arabinofuranose and D-
glucopyranose were confirmed. However, the acid hydrolysis
led to the generation of labda-8,13-dien-16,15-olid-19-oic acid
(8b) not pinusolidic acid (8a) (Figure S1, Supporting
Information).19 Thus, the enzymatic hydrolysis of 8 was
performed to give the aglycone pinusolidic acid (8a). The
structure of 8a was confirmed by comparison with the reported
1H NMR, MS, and ECD spectra.19,21 Therefore, the structure
of compound 8 was defined as α-L-arabinofuranosyl-(1→6)-O-
β-D-glucopyranosyl labda-8(17),13-diene-(15→16)-lacton-19-
oate.
Koraienside G (7) was obtained as a colorless gum, and its
molecular formula was defined as identical to that of 6
(C26H38O10) based on the HRESIMS data. The NMR data of
7 showed that this molecule is closely similar to 6, with the
main differences in resonances at C-3 (δC 41.0, 7; δC 71.4, 6)
and C-6 (δC 72.7, 7; δC 27.0, 6), implying that the OH
functionality at C-3 in 6 is shifted to C-6 in 7 (Tables 1 and 2).
The location of the hydroxy group was corroborated to be at
C-6 based on signals of H-5/H-6 and H-6/H-7 in the COSY
data (Figure 2). The NOESY cross-peak between H-6 and H3-
20 suggested that the hydroxy group at C-6 is α oriented
(Figure 3). Thus, the structure of compound 7 was assigned as
β-D-glucopyranosyl 6α-hydroxylabda-8(17),13-diene-(15→
16)-lacton-19-oate.
The molecular formula of koraienside H (8) was confirmed
as C31H46O13 based on the HRESIMS ion at m/z 649.2832 [M
+ Na]+ (calcd for C31H46O13Na, 649.2836). The 1D NMR
spectra of 8 was comparable with the data of 12,15 except for
the additional arabinofuranose signals [δC 109.9 (C-1″), 86.0
(C-4″), 83.1 (C-2″), 79.0 (C-3″), and 63.1 (C-5″); δH 4.84
(1H, d, J = 2.0 Hz, H-1″), 3.91 (1H, overlap, H-2″), 3.90 (1H,
Koraienside I (9) was obtained as a colorless gum and
identified as C26H42O9, showing a positive-ion signal [M +
Na]+ at m/z 521.2725 based on the HRESIMS data.
Assignments of the 1D NMR data of 9 indicated characteristic
resonances of a labdane diterpenoid glycoside (Tables 1 and
2).13,14 The main differences in NMR data of 9 compared with
those of 1215 were attributed to the presence of two
oxygenated methylenes [δC 57.3; δH 4.16 (2H, d, J = 6.6
E
https://dx.doi.org/10.1021/acs.jnatprod.9b01158
J. Nat. Prod. XXXX, XXX, XXX−XXX

Journal of Natural Products
pubs.acs.org/jnp
Article
Figure 1. Structural elucidation of 1. (A) Key COSY, HMBC, and NOESY correlations. (B) Results of DP4+ analysis for (13α-OH)-1a and (13β-
OH)-1a. (C) Comparison of the experimental and calculated ECD spectra of 1a.
Figure 2. Key COSY and HMBC correlations of 2−5, 7−9, and 11.
Hz) and δC 58.6; δH 4.13 (1H, d, J = 12.4 Hz) and 4.09 (1H, d,
J = 12.4 Hz)] in 9, instead of the α,β-unsaturated lactone
signals [δC 72.1; δH 4.84 (2H, overlap) and δC 177.0] in 12.
The 2D structure of 9 was established via full NMR
assignments and confirmed to be identical with the ent-
labdane diterpenoid andrographatoside, which was isolated
F
https://dx.doi.org/10.1021/acs.jnatprod.9b01158
J. Nat. Prod. XXXX, XXX, XXX−XXX

Journal of Natural Products
pubs.acs.org/jnp
Article
Figure 3. Key NOESY correlations of 2, 3, 5−7, and 9−11.
from Andrographis paniculata.22 The geometry of the Δ13(14)
double bond was corroborated through NOESY correlation of
H-12/H-14, which implied a Z-geometry (Figure 3). The
experimental ECD spectrum showed that 9 has the same
absolute configuration as 1. Consequently, compound 9 was
established as β-D-glucopyranosyl labda-8(17),13Z-diene-
15,16-diol-19-oate.
glucoside was established for 11 (Figure 2). The presence of
rare 18-norditerpenoids in natural products was additionally
confirmed through previous reports.23−25 The relative
configuration of C-4 in 1−10 was established by NOESY
correlations of H3-20/H-1′ and H-5/H3-18 (Figures 1A and
3). The same NOESY correlation of H3-20/H-1′ was observed
in 11, indicating that C-19 was in a β-axial position as in 1−10
(Figure 3). This initial assignment was supported by the
calculated interproton distance between H3-20 and H-1′ in two
C-4 epimers (11r and 11s). The Boltzmann-averaged
interproton distances between H3-20 and H-1′ were 3.94
and 6.83 Å in 11r and 11s, respectively (Figures S125 and
S126, Supporting Information). Since the maximum distance
between two protons that allows for the NOESY cross-peak
observation is ∼5 Å,26 only 11r could be the possible epimer
for 11. Hence, the structure of 11 was defined as β-D-
glucopyranosyl 18-norlabda-8(17),13-diene-(15→16)-lacton-
19-oate.
The other two known analogues were characterized as
adenanthoside C (12)15 and β-D-glucopyranosyl
(4S,5R,9S,10R)-labda-8(17),13-dien-15,16-olid-19-oate (13)19
by comparing the experimental spectra reported data.
In order to evaluate the neuroprotective effects of
compounds 2−13, their efficacy on NGF release in C6 cells
was tested (Table 3). Treatment with 10 and 13 considerably
induced NGF secretion, with values of NGF stimulated at
162.3 13.9% and 162.7 6.9%, respectively (6-shogaol, a
Koraienside J (10) had the same molecular formula,
C26H42O9, as 9. The NMR assignments of 10 also exhibited
close similarities with those of 9, with significant differences in
chemical shifts at C-12 (δC 26.3, 10; δC 33.5, 9), C-14 (δC
124.4, 10; δC 126.1, 9), and C-15 (δC 64.8, 10; δC 57.3, 9),
suggesting that 10 is a geometric isomer of 9 (Tables 1 and 2).
The NOESY cross-peak of H-14/H-16 indicated the E-
geometry of the Δ13(14) olefinic bond (Figure 3). Enzymatic
hydrolysis of 10 yielded the aglycone 10a and D-glucose. The
sugar moiety was analyzed using the same method as 1. The
structure of 10a was implied through HRESIMS data analysis.
Thus, the structure of compound 10 was assigned as β-D-
glucopyranosyl labda-8(17),13E-diene-15,16-diol-19-oate.
Koraienside K (11) was purified as a colorless gum. Its
molecular formula was determined as C25H36O10 by
HRESIMS, displaying a positive-ion peak [M + Na]+ at m/z
519.2208 (calcd for C25H36O10Na, 519.2206). Comparison of
the 1D NMR spectra indicated that 11 has an oxygenated
tertiary carbon (δC 76.6) instead of a methyl group [δC 29.4;
δH 1.27 (3H, s)] and a quaternary carbon (δC 45.7) in 12.15
The HMBC correlations of H-3/C-4 and H-5/C-4 verified that
the hydroxy group is positioned at C-4 (Figure 2). Based on
2D NMR and HRESIMS data, the skeleton of a norditerpenoid
positive control, 150.9
8.9%), without any cytotoxicity
toward normal cells at a 20 μM concentration. Interestingly,
despite the structural similarity, 10 exhibited considerable
G
https://dx.doi.org/10.1021/acs.jnatprod.9b01158
J. Nat. Prod. XXXX, XXX, XXX−XXX

Journal of Natural Products
pubs.acs.org/jnp
Article
play a substantial role in inhibition of inflammation.
Compound 7 exhibited moderate activity (IC50 35.7 μM).
In summary, 11 new labdane-type diterpenoid glycosides
(1−11) were isolated from the twigs of P. koraiensis, together
with two known analogues, 12 and 13. The aglycones 1a−6a
and 9a were identified as new diterpenoid acids via NMR and
HRMS data analysis. Among the isolates, compounds 10 and
13 showed neuroprotective effects, and compound 6 exhibited
antineuroinflammatory activity.
Table 3. Effects of Selected Compounds (2−13) on NGF
Secretion in C6 Cells
a
b
compound
NGF secretion (%)
cell viability (%)
2
3
4
5
6
7
8
9
10
11
12
13
106.1 1.3
84.5 0.2
94.2 2.6
111.2 9.1
101.6 2.3
98.3 7.9
92.8 5.1
101.4 7.5
93.3 3.7
86.5 0.2
104.0 0.1
76.0 6.9
101.0 4.8
105.0 3.8
108.8 0.6
119.4 5.1
134.7 3.9
106.6 4.0
128.7 8.0
112.5 1.3
105.4 1.7
162.3 13.9
98.6 1.7
EXPERIMENTAL SECTION
■
General Experimental Procedures. The experimental proce-
dures were performed as previously described.17
Plant Material. The twigs of P. koraiensis were obtained from
Hongcheon, Korea, in May 2016, and the plant was authenticated by
one of the authors (K.R.L.). A voucher specimen (SKKU-NPL 1414)
of the plant is deposited at the herbarium of the School of Pharmacy,
Sungkyunkwan University, Suwon, Korea.
142.4 6.7
162.7 6.9
150.9 8.9
c
6-shogaol
a
C6 cells were treated with 20 μM of each compound. After 24 h, the
content of NGF secreted into the C6-conditioned medium was
measured by ELISA. The level of secreted NGF is expressed as the
Extraction and Isolation. P. koraiensis (10.0 kg) twigs were
extracted three times with 80% aqueous MeOH under reflux and
filtered. The residue was concentrated under reduced pressure to
obtain a MeOH extract (665 g). The crude extract was suspended in
distilled water and partitioned with n-hexane, CHCl3, EtOAc, and n-
BuOH, yielding 39, 50, 22, and 65 g of residue, respectively. The
EtOAc-soluble fraction (22 g) was separated on a silica gel column
(CHCl3−MeOH−H2O, 7:1:0.1 → 1:1:0.1) to yield eight fractions
(E1−E8). Fraction E2 (3.7 g) was separated on an RP-C18 silica gel
column, eluting with 35% aqueous MeOH, to acquire eight
subfractions (E2A−E2H). Subfraction E2G (440 mg) was purified
by C18 semipreparative HPLC (2 mL/min, 32% aqueous CH3CN) to
obtain compounds 12 (tR: 40.3 min, 136 mg) and 13 (tR: 49.0 min, 18
mg). Fraction E4 (2.8 g) was chromatographed on an RP-C18 silica
gel column with 30% aqueous MeOH to give 11 subfractions (E4A−
E4K). Subfraction E4E (338 mg) was subjected to a LiChroprep
Lobar-A Si gel 60 column (CHCl3−MeOH, 10:1) to acquire three
subfractions (E4E1−E4E3). Subfraction E4E3 (126 mg) was purified
by semipreparative HPLC (2 mL/min, 21% aqueous CH3CN) to
afford compound 3 (tR: 35.3 min, 22 mg). Compounds 4 (tR: 52.2
min, 3 mg), 6 (tR: 54.1 min, 3 mg), 7 (tR: 60.4 min, 5 mg), and 11 (tR:
69.1 min, 3 mg) were obtained from fraction E4F (172 mg) using a
LiChroprep Lobar-A Si gel 60 column (CHCl3−MeOH−H2O,
6.5:1:0.1) followed by semipreparative HPLC (2 mL/min, 22%
aqueous CH3CN). Subfraction E4G (208 mg) was separated on a
LiChroprep Lobar-A Si gel 60 column (CHCl3−MeOH−H2O,
6:1:0.1), followed by semipreparative HPLC (26% aqueous
MeOH), to obtain compound 5 (tR: 35.1 min, 4 mg). Using a
LiChroprep Lobar-A Si gel 60 column with CHCl3−MeOH (10:1),
subfraction E4I (319 mg) was fractionated into three further
subfractions (E4I1−E4I3). Subfraction E4I3 (117 mg) was purified
by semipreparative HPLC (29% aqueous CH3CN) to afford
compounds 1 (tR: 32.1 min, 2 mg), 2 (tR: 33.4 min, 5 mg), and 8
(tR: 50.2 min, 20 mg). Fraction E6 (3.8 g) was subjected to an RP-C18
silica gel column with 35% aqueous MeOH to obtain 12 subfractions
(E6A−E6L). Subfraction E6I (607 mg) was separated on a silica gel
column (CHCl3−MeOH−H2O, 4:1:0.1) to yield two subfractions
(E6I1 and E6I2). Subfraction E6I1 (220 mg) was isolated by
semipreparative HPLC (57% aqueous MeOH) to obtain compounds
9 (tR: 22.7 min, 10 mg) and 10 (tR: 24.3 min, 2 mg).
b
percentage of the untreated control (set as 100%). The cell viability
after treatment with 20 μM of each compound was determined by an
MTT assay and is expressed as a percentage (%). Results are the
means of three independent experiments, and the data are expressed
c
as means SD. Positive control substance.
activity (162.3 13.9%), but the activity of 9, the geometric
isomer, was relatively weak (105.4 1.7%).
The potential antineuroinflammatory activity of compounds
2−13 was tested by measuring NO levels produced in the BV2
cell line (Table 4). Compound 6 strongly inhibited NO
Table 4. Inhibitory Effects of Selected Compounds (2−13)
on NO Production Induced by LPS in BV2 Cells
a
b
compound
IC50 (μM)
cell viability (%)
2
3
4
5
6
7
8
9
10
11
12
13
49.2
402.0
93.2
68.8
24.1
35.7
>500
151.5
65.4
51.6
65.8
54.1
28.8
89.6 4.1
70.4 5.2
87.7 3.1
91.3 2.5
77.5 7.7
99.7 4.1
69.3 1.0
132.6 3.5
134.6 4.6
80.7 5.8
92.1 3.3
107.2 4.5
99.2 1.0
c
L-NMMA
a
The IC50 value of each compound was defined as the concentration
(μM) that caused 50% inhibition of NO production in LPS-activated
b
BV2 cells. The cell viability after treatment with 20 μM of each
compound was measured using the MTT assay and is expressed as a
percentage (%). Results are the means of three independent
c
experiments, and data are expressed as the means
control substance.
SD. Positive
Koraienside A (1): colorless gum; [α]2D5 +62 (c 0.1, MeOH); ECD
(MeOH) λmax (Δε) 225 (+2.45) nm; IR (KBr) νmax 3864, 3627,
1
3551, 2973, 2869, 1639, 1409, 1051 cm−1; H (700 MHz) and 13C
(175 MHz) NMR data in methanol-d4, see Tables 1 and 2; HRESIMS
(positive-ion mode) m/z 535.2516 [M + Na]+ (calcd for
C26H40O10Na, 535.2519).
production (IC50 24.1 μM) and was comparable to L-NMMA,
a positive control (IC50 28.8 μM), with insignificant
cytotoxicity at 20 μM. Even if compounds 5 and 6 have
similar structures, they showed different inhibitory effects on
NO production (IC50 68.8 μM, 5; IC50 24.1 μM, 6), indicating
that the orientation of the hydroxy functionality at C-3 may
Koraienside B (2): colorless gum; [α]2D5 +28 (c 0.1, MeOH); UV
(MeOH) λmax (log ε) 218 (2.11) nm; ECD (MeOH) λmax (Δε) 225
(+3.11) nm; IR (KBr) νmax 3552, 3160, 2975, 2869, 2358, 1644, 1404,
1053 cm−1; 1H (700 MHz) and 13C (175 MHz) NMR data in
H
https://dx.doi.org/10.1021/acs.jnatprod.9b01158
J. Nat. Prod. XXXX, XXX, XXX−XXX

Journal of Natural Products
pubs.acs.org/jnp
Article
methanol-d4, see Tables 1 and 2; HRESIMS (positive-ion mode) m/z
535.2520 [M + Na]+ (calcd for C26H40O10Na, 535.2519).
8β-Hydroxylabd-13-en-(15→16)-lacton-19-oic acid (2a): color-
less gum; [α]2D5 +117 (c 0.1, MeOH); UV (MeOH) λmax (log ε) 218
(1.31) nm; ECD (MeOH) λmax (Δε) 218 (+0.71) nm; 1H (700
MHz) and 13C (175 MHz) NMR data in methanol-d4, see Tables S6
and S7, Supporting Information; HRESIMS (positive-ion mode) m/z
373.1990 [M + Na]+ (calcd for C20H30O5Na, 373.1991).
8α-Hydroxylabd-13-en-(15→16)-lacton-19-oic acid (3a): color-
less gum; [α]2D5 +11 (c 0.1, MeOH); UV (MeOH) λmax (log ε) 218
(1.28) nm; ECD (MeOH) λmax (Δε) 227 (+1.20) nm; 1H (700
MHz) and 13C (175 MHz) NMR data in methanol-d4, see Tables S6
and S7, Supporting Information; HRESIMS (positive-ion mode) m/z
373.1990 [M + Na]+ (calcd for C20H30O5Na, 373.1991).
Koraienside C (3): colorless gum; [α]2D5 +22 (c 0.1, MeOH); UV
(MeOH) λmax (log ε) 218 (1.90) nm; ECD (MeOH) λmax (Δε) 227
1
(+2.67) nm; IR (KBr) νmax 3550, 3172, 1660, 1398, 1053 cm−1; H
(700 MHz) and 13C (175 MHz) NMR data in methanol-d4, see
Tables 1 and 2; HRESIMS (positive-ion mode) m/z 535.2467 [M +
Na]+ (calcd for C26H40O10Na, 535.2519).
Koraienside D (4): colorless gum; [α]2D5 +12 (c 0.1, MeOH); UV
(MeOH) λmax (log ε) 220 (1.82) nm; ECD (MeOH) λmax (Δε) 224
(+2.43) nm; IR (KBr) νmax 3553, 3481, 3194, 1654, 1402, 1054 cm−1;
1H (700 MHz) and 13C (175 MHz) NMR data in methanol-d4, see
Tables 1 and 2; HRESIMS (positive-ion mode) m/z 533.2363 [M +
Na]+ (calcd for C26H38O10Na, 533.2363).
17-Hydroxylabda-7,13-diene-(15→16)-lacton-19-oic acid (4a):
colorless gum; [α]D25 +16 (c 0.1, MeOH); UV (MeOH) λmax (log ε)
Koraienside E (5): colorless gum; [α]2D5 +2 (c 0.1, MeOH); UV
(MeOH) λmax (log ε) 217 (2.01) nm; ECD (MeOH) λmax (Δε) 225
(+2.97) nm; IR (KBr) νmax 3678, 3602, 2974, 2869, 2350, 1643, 1338,
1054 cm−1; 1H (700 MHz) and 13C (175 MHz) NMR data in
methanol-d4, see Tables 1 and 2; HRESIMS (positive-ion mode) m/z
533.2366 [M + Na]+ (calcd for C26H38O10Na, 533.2363).
1
220 (1.33) nm; ECD (MeOH) λmax (Δε) 224 (+0.67) nm; H (700
MHz) and 13C (175 MHz) NMR data in methanol-d4, see Tables S6
and S7, Supporting Information; HRESIMS (positive-ion mode) m/z
371.1834 [M + Na]+ (calcd for C20H28O5Na, 371.1834).
3β-Hydroxylabda-8(17),13-diene-(15→16)-lacton-19-oic acid
(5a): colorless gum; [α]2D5 +91 (c 0.1, MeOH); UV (MeOH) λmax
(log ε) 217 (1.10) nm; ECD (MeOH) λmax (Δε) 220 (+1.43) nm; 1H
(700 MHz) and 13C (175 MHz) NMR data in methanol-d4, see
Tables S6 and S7, Supporting Information; HRESIMS (positive-ion
mode) m/z 371.1836 [M + Na]+ (calcd for C20H28O5Na, 371.1834).
3α-Hydroxylabda-8(17),13-diene-(15→16)-lacton-19-oic acid
(6a): colorless gum; [α]2D5 +75 (c 0.1, MeOH); UV (MeOH) λmax
(log ε) 217 (1.21) nm; ECD (MeOH) λmax (Δε) 220 (+0.81) nm; 1H
(700 MHz) and 13C (175 MHz) NMR data in methanol-d4, see
Tables S6 and S7, Supporting Information; HRESIMS (positive-ion
mode) m/z 371.1835 [M + Na]+ (calcd for C20H28O5Na, 371.1834).
Pinusolidic acid (8a): colorless gum; [α]2D5 +45 (c 0.1, MeOH);
UV (MeOH) λmax (log ε) 217 (1.35) nm; ECD (MeOH) λmax (Δε)
Koraienside F (6): colorless gum; [α]2D5 +16 (c 0.1, MeOH); UV
(MeOH) λmax (log ε) 217 (2.34) nm; ECD (MeOH) λmax (Δε) 220
(+1.40) nm; IR (KBr) νmax 3553, 3152, 2971, 2837, 1653, 1408, 1040
cm−1; 1H (700 MHz) and 13C (175 MHz) NMR data in methanol-d4,
see Tables 1 and 2; HRESIMS (positive-ion mode) m/z 533.2365 [M
+ Na]+ (calcd for C26H38O10Na, 533.2363).
Koraienside G (7): colorless gum; [α]2D5 +26 (c 0.1, MeOH); UV
(MeOH) λmax (log ε) 219 (1.88) nm; ECD (MeOH) λmax (Δε) 225
(+2.13) nm; IR (KBr) νmax 3662, 3513, 2972, 2836, 1653, 1410, 1042
cm−1; 1H (700 MHz) and 13C (175 MHz) NMR data in methanol-d4,
see Tables 1 and 2; HRESIMS (positive-ion mode) m/z 533.2363 [M
+ Na]+ (calcd for C26H38O10Na, 533.2363).
Koraienside H (8): colorless gum; [α]2D5 +4 (c 0.1, MeOH); UV
(MeOH) λmax (log ε) 217 (1.51) nm; ECD (MeOH) λmax (Δε) 226
(+3.01) nm; IR (KBr) νmax 3719, 3601, 3164, 2972, 2869, 1648, 1406,
1053 cm−1; 1H (700 MHz) and 13C (175 MHz) NMR data in
methanol-d4, see Tables 1 and 2; HRESIMS (positive-ion mode) m/z
649.2832 [M + Na]+ (calcd for C31H46O13Na, 649.2836).
1
222 (+1.33) nm; H NMR (CDCl3, 700 MHz) δ 7.10 (1H, brt, J =
1.4 Hz, H-14), 4.89 (1H, brs, H-17a), 4.77 (2H, overlap, H-15), 4.59
(1H, brs, H-17b), 1.24 (3H, s, H-18), 0.60 (3H, s, H-20); ESIMS
(negative-ion mode) m/z 331.2 [M − H]−.
Labda-8(17),13Z-diene-15,16-diol-19-oic acid (9a): colorless
gum; [α]2D5 +19 (c 0.1, MeOH); ECD (MeOH) λmax (Δε) 220
(+0.75) nm; 1H (700 MHz) and 13C (175 MHz) NMR data in
methanol-d4, see Tables S6 and S7, Supporting Information;
HRESIMS (positive-ion mode) m/z 359.2197 [M + Na]+ (calcd
for C20H32O4Na, 359.2198).
Labda-8(17),13E-diene-15,16-diol-19-oic acid (10a): colorless
gum; [α]2D5 +11 (c 0.1, MeOH); ECD (MeOH) λmax (Δε) 224
(+0.51) nm; HRESIMS (positive-ion mode) m/z 359.2198 [M +
Na]+ (calcd for C20H32O4Na, 359.2198).
Koraienside I (9): colorless gum; [α]2D5 +16 (c 0.1, MeOH); ECD
(MeOH) λmax (Δε) 222 (+2.11) nm; IR (KBr) νmax 3720, 3588,
1
3511, 3178, 2973, 2869, 1340, 1053 cm−1; H (700 MHz) and 13C
(175 MHz) NMR data in methanol-d4, see Tables 1 and 2; HRESIMS
(positive-ion mode) m/z 521.2725 [M + Na]+ (calcd for
C26H42O9Na, 521.2727).
Koraienside J (10): colorless gum; [α]2D5 +3 (c 0.1, MeOH); ECD
(MeOH) λmax (Δε) 223 (+1.87) nm; IR (KBr) νmax 3681, 3600,
3552, 3511, 2973, 2869, 2073, 1407, 1053 cm−1; 1H (700 MHz) and
13C (175 MHz) NMR data in methanol-d4, see Tables 1 and 2;
HRESIMS (positive-ion mode) m/z 521.2728 [M + Na]+ (calcd for
C26H42O9Na, 521.2727).
Acid Hydrolysis of Compound 8. Compound 8 (1.0 mg) was
refluxed with 1 N HCl (1.0 mL) for 2 h at 90 °C. The hydrolysate was
diluted with H2O and extracted with CHCl3. The aqueous layer was
neutralized by passing through an Amberlite IRA-67 column to obtain
the sugar. The organic layer was concentrated under reduced pressure
to yield 8b.
Koraienside K (11): colorless gum; [α]2D5 +15 (c 0.1, MeOH); UV
(MeOH) λmax (log ε) 221 (2.43) nm; ECD (MeOH) λmax (Δε) 225
(+1.35) nm; IR (KBr) νmax 3552, 3516, 3162, 2989, 2841, 1652, 1408,
1043 cm−1; 1H (700 MHz) and 13C (175 MHz) NMR data in
methanol-d4, see Tables 1 and 2; HRESIMS (positive-ion mode) m/z
519.2208 [M + Na]+ (calcd for C25H36O10Na, 519.2206).
Computational Analysis. Information regarding the DP4+ and
ECD calculations are provided in the Supporting Information.
Enzymatic Hydrolysis of Compounds 1−11. A solution of
each sample (0.5−1.0 mg) in H2O (1.0 mL) was individually
hydrolyzed with β-glucosidase (10 mg, from almonds, Sigma-Aldrich,
St. Louis, MO, USA) at 37 °C for 48 h. After hydrolysis, each reaction
mixture was extracted with CHCl3 to obtain aglycones 1a−6a and
8a−10a (0.3−0.5 mg).
1
Labda-8,13-dien-16,15-olid-19-oic acid (8b): colorless gum; H
NMR (methanol-d4, 700 MHz) δ 7.39 (1H, brt, J = 1.5 Hz, H-14),
4.84 (2H, overlap, H-15), 1.68 (3H, s, H-17), 1.24 (3H, s, H-18),
0.94 (3H, s, H-20); ESIMS (negative-ion mode) m/z 331.2 [M −
H]−.
Determination of Absolute Configuration of Sugar Moi-
eties of Compounds 1−11. The experimental procedures were
performed as previously described.16 D-Glucose and L-arabinose were
identified by co-injection with standard silylated samples, giving a
single peak at 11.468 min (D-glucose) and 9.312 min (L-arabinose).
Authentic samples (Sigma-Aldrich, St. Louis, MO, USA) treated in
the same way showed a single peak at 11.467 min (D-glucose) and
9.320 min (L-arabinose), respectively.
13α-Hydroxy-8(17)-labden-(15→16)-lacton-19-oic acid (1a):
colorless gum; [α]D25 +103 (c 0.1, MeOH); ECD (MeOH) λmax
1
(Δε) 222 (+0.27) nm; H (700 MHz) and 13C (175 MHz) NMR
data in methanol-d4, see Tables S6 and S7, Supporting Information;
HRESIMS (positive-ion mode) m/z 373.1989 [M + Na]+ (calcd for
C20H30O5Na, 373.1991).
NGF and Cell Viability Assays and NO Production and
Viability in LPS-Stressed BV2 Cells. The bioactivity assays were
performed using the methods reported previously.17
I
https://dx.doi.org/10.1021/acs.jnatprod.9b01158
J. Nat. Prod. XXXX, XXX, XXX−XXX

Journal of Natural Products
pubs.acs.org/jnp
Article
(11) Wang, L.; Li, X.; Wang, H. Int. J. Biol. Macromol. 2019, 126,
385−391.
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.jnatprod.9b01158.
■
sı
(12) Yi, J.; Cheng, C.; Li, X.; Zhao, H.; Qu, H.; Wang, Z.; Wang, L.
Food Funct. 2017, 8, 151−166.
(13) Chen, L.-X.; Qiu, F.; Wei, H.; Qu, G.-X.; Yao, X.-S. Helv. Chim.
Acta 2006, 89, 2654−2664.
HRESIMS and NMR data of compounds 1−11, 1a−6a,
and 9a, HRESIMS data of 10a, and computational data
(PDF)
(14) Waridel, P.; Wolfender, J. L.; Lachavanne, J. B.; Hostettmann,
K. Phytochemistry 2004, 65, 945−954.
(15) Wu, L. B.; Xiao, C. J.; Jiang, X.; Qiu, L.; Dong, X.; Jiang, B.
Chem. Biodiversity 2015, 12, 1229−1236.
(16) Kim, C. S.; Subedi, L.; Park, K. J.; Kim, S. Y.; Choi, S. U.; Kim,
K. H.; Lee, K. R. Fitoterapia 2015, 106, 147−152.
(17) Park, K. J.; Kim, C. S.; Khan, Z.; Oh, J.; Kim, S. Y.; Choi, S. U.;
Lee, K. R. J. Nat. Prod. 2019, 82, 1345−1353.
AUTHOR INFORMATION
Corresponding Author
Kang Ro Lee − Natural Products Laboratory, School of
Pharmacy, Sungkyunkwan University, Suwon 16419, Republic
of Korea; orcid.org/0000-0002-3725-5192; Phone: +82-
31-290-7710; Email: krlee@skku.edu; Fax: +82-31-290-
7730
■
(18) Hara, S.; Okabe, H.; Mihashi, K. Chem. Pharm. Bull. 1987, 35,
501−506.
(19) Hu, C.-L.; Xiong, J.; Wang, P.-P.; Ma, G.-L.; Tang, Y.; Yang, G.-
X.; Li, J.; Hu, J.-F. Phytochem. Lett. 2017, 20, 239−245.
(20) Suh, W. S.; Kim, K. H.; Kim, H. K.; Choi, S. U.; Lee, K. R. Helv.
Chim. Acta 2015, 98, 1087−1094.
(21) Chiang, Y.-M.; Liu, H.-K.; Lo, J.-M.; Chien, S.-C.; Chan, Y.-F.;
Lee, T.-H.; Su, J.-K.; Kuo, Y.-H. J. Chin. Chem. Soc. 2003, 50, 161−
166.
(22) Shen, Y. H.; Li, R. T.; Xiao, W. L.; Xu, G.; Lin, Z. W.; Zhao, Q.
S.; Sun, H. D. J. Nat. Prod. 2006, 69, 319−322.
Authors
Kyoung Jin Park − Natural Products Laboratory, School of
Pharmacy, Sungkyunkwan University, Suwon 16419, Republic
of Korea
Zahra Khan − College of Pharmacy and Gachon Institute of
Pharmaceutical Science, Gachon University, Incheon 21936,
Republic of Korea
Lalita Subedi − College of Pharmacy and Gachon Institute of
Pharmaceutical Science, Gachon University, Incheon 21936,
Republic of Korea
Sun Yeou Kim − College of Pharmacy and Gachon Institute of
Pharmaceutical Science, Gachon University, Incheon 21936,
Republic of Korea
(23) Quon, H. H.; Swan, E. P. Can. J. Chem. 1969, 47, 4389−4392.
(24) Bohlmann, F.; Suding, H.; Cuatrecasas, J.; King, R. M.;
Robinson, H. Phytochemistry 1980, 19, 267−271.
(25) Jung, H. A.; Lee, E. J.; Kim, J. S.; Kang, S. S.; Lee, J.-H.; Min,
B.-S.; Choi, J. S. Arch. Pharmacal Res. 2009, 32, 1399−1408.
̌
(26) Pristovsek, P.; Franzoni, L. J. Comput. Chem. 2006, 27, 791−
797.
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.jnatprod.9b01158
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This research was supported by the Basic Science Research
Program through the National Research Foundation of Korea
(NRF), funded by the Ministry of Education, Science and
Technology (2016R1A2B2008380). We are grateful to the
Korea Basic Science Institute (KBSI) for the mass spectro-
metric analysis.
REFERENCES
■
(1) McAllister, A. K. Cell. Mol. Life Sci. 2001, 58, 1054−1060.
(2) Dawbarn, D.; Allen, S. J. Neuropathol. Appl. Neurobiol. 2003, 29,
211−230.
(3) Amor, S.; Puentes, F.; Baker, D.; van der Valk, P. Immunology
2010, 129, 154−169.
(4) Block, M. L.; Zecca, L.; Hong, J. S. Nat. Rev. Neurosci. 2007, 8,
57−69.
(5) Lee, T. K.; Park, J. Y.; Yu, J. S.; Jang, T. S.; Oh, S. T.; Pang, C.;
Ko, Y. J.; Kang, K. S.; Kim, K. H. Bioorg. Med. Chem. Lett. 2018, 28,
1084−1089.
(6) Liang, R.; Cheng, S.; Wang, X. Food Chem. 2018, 254, 170−184.
(7) Qu, H.; Gao, X.; Zhao, H. T.; Wang, Z. Y.; Yi, J. J. Carbohydr.
Polym. 2019, 223, 115056.
(8) Su, X.-Y.; Wang, Z.-Y.; Liu, J.-R. Food Chem. 2009, 117, 681−
686.
(9) Lee, T. K.; Roh, H.-S.; Yu, J. S.; Baek, J.; Lee, S.; Ra, M.; Kim, S.
Y.; Baek, K.-H.; Kim, K. H. Chem. Biodiversity 2017, 14, e1600400.
(10) Zhang, H.; Zhao, H.; Zhou, X.; Yang, X.; Shen, S.; Wang, J.;
Wang, Z.; Geng, L. RSC Adv. 2016, 6, 110706−110721.
J
https://dx.doi.org/10.1021/acs.jnatprod.9b01158
J. Nat. Prod. XXXX, XXX, XXX−XXX