New lignans from the aerial parts of Rudbeckia laciniata

Article abstract of DOI:10.1002/hlca.201200177

Three new furofuran lignans, (+)-4,4′-O-diangeloylpinoresinol (1), (+)-4,4′-O-diangeloylmedioresinol (2), and (+)-4,4′-O- diangeloylsyringaresinol (3), together with the known compound (+)-syringaresinol, were isolated from the MeOH extract of Rudbeckia l

Full text of DOI:10.1002/hlca.201200177

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Helvetica Chimica Acta – Vol. 96 (2013)
New Lignans from the Aerial Parts of Rudbeckia laciniata
a
a
a
b
a
by Seung Young Lee ), Kyeong Wan Woo ), Chung Sub Kim ), Dong Ung Lee ), and Kang Ro Lee* )
a) Natural Products Laboratory, School of Pharmacy, Sungkyunkwan University, Suwon 440-746, Korea
(
phone: þ 82-31-2907710; fax: þ 82-31-2907730; e-mail: krlee@skku.ac.kr)
b) College of Science and Technology, Dongguk University, Gyeong Ju 780-714, Korea
Three new furofuran lignans, (þ)-4,4’-O-diangeloylpinoresinol (1), (þ)-4,4’-O-diangeloylmedio-
resinol (2), and (þ)-4,4’-O-diangeloylsyringaresinol (3), together with the known compound (þ)-
syringaresinol, were isolated from the MeOH extract of Rudbeckia laciniata. The structure elucidation of
these compounds were based on 1D- and 2D-NMR, and HR-ESI-MS data. The additional structural
evidence was obtained from alkaline hydrolysis of the compounds.
Introduction. – Three Rudbeckia species, R. bicolor, R. hirta, and R. laciniata, are
widespread in Korea [1]. Extracts from the plants have been used as traditional Chinese
medicine in the treatment of the common cold and urinary diseases [2]. Various
phytochemical constituents, i.e., sesquiterpene esters [3 – 7], sesquiterpene lactones
[
8 – 11], lignans [10], flavonoids [3][12][13], polyacetylenes [14], and carotenoids [15],
have been reported from the genus Rudbeckia, and a wide range of biological activities,
including antitumour [2 – 4], antioxidant [16], antibacterial, and antifungal [17 – 19]
properties, have been investigated.
In our continuing search for bioactive constituents from the Korean Asteraceae
medicinal plants, we performed a phytochemical investigation of the MeOH extract
from the aerial parts of R. laciniata. By repeated column chromatographic separation of
the extract, three new furofuran lignans, 1 – 3, along with one known lignan were
isolated. The structures were determined using spectroscopic methods including 1D-
and 2D-NMR (COSY, HMQC, HMBC, and NOESY). Here, we describe the structure
elucidation of the new compounds 1 – 3 (Fig. 1).
Fig. 1. Compounds 1 – 3, isolated from R. laciniata
Results and Discussion. – Compound 1 was obtained as a colorless gum. The
molecular formula of 1 was determined as C H O from the molecular-ion peak
30
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2013 Verlag Helvetica Chimica Acta AG, Zꢁrich

Helvetica Chimica Acta – Vol. 96 (2013)
321
þ
[
M þ Na] at m/z 545.2163 in the positive-ion-mode HR-ESI-MS. The IR spectrum of 1
ꢀ1
showed absorption bands at 3358 and 1650 cm ascribable to a OH and a C¼O group,
1
respectively. The H-NMR spectrum (Table) of 1 showed signals of two H-atoms of a
1
,3,4-trisubstituted benzene at d(H) 7.03 (d, J ¼ 8.5, HꢀC(5,5’)), 7.00 (d, J ¼ 1.5,
HꢀC(2,2’)), and 6.89 (dd, J ¼ 8.5, 1.5, HꢀC(6,6’)), of two OꢀCH H-atoms at d(H) 4.80
(
d, J ¼ 4.0, HꢀC(7,7’)), of two OCH H-atoms at d(H) 4.28 (dd, J ¼ 9.0, 7.0,
2
HꢀC(9a,9’a)), and 3.94 (dd, J ¼ 9.0, 3.5, HꢀC(9b,9’b)), and of two CH H-atoms at
d(H) 3.07 – 3.13 (m, HꢀC(8,8’)), and two MeO signals at d(H) 3.87 (s). In the
13
C-NMR spectrum (Table), ten C-atom signals for a symmetrical structure appeared at
d(C) 54.4 (CH), 71.9 (CH O), 85.6 (OCH), 109.9, 117.9, 122.9, 139.2, 139.8, and 151.6
2
Table. 1H- and 13C-NMR (500 and 125 MHz, resp.) Data of Compounds 1 – 3. Recorded in CDCl ; d in
3
ppm, J in Hz.
Position
1
2
3
d(H)
d(C) d(H)
d(C) d(H)
d(C)
C(1)
139.8
139.9
109.9 6.62 (s)
151. 6
139.2
122.9
139.4
102.3
152.4
128.0
152.4
102.3
85.9
HꢀC(2)
7.00 (d, J ¼ 1.5)
109.9 7.01 (d, J ¼ 1.5)
C(3)
151.6
C(4)
139.2
HꢀC(5)
HꢀC(6)
HꢀC(7)
HꢀC(8)
7.03 (d, J ¼ 8.5)
122.9 7.05 (d, J ¼ 8.5)
6.89 (dd, J ¼ 8.5, 1.5) 117.9 6.92 (dd, J ¼ 8.5, 1.5) 117.9 6.62 (s)
4.80 (d, J ¼ 4.0)
85.6 4.83 (d, J ¼ 4.0)
85.9 4.80 (d, J ¼ 4.0)
3.07 – 3.13 (m)
54.4 3.08 – 3.11 (m)
54.5 3.09 – 3.11 (m)
54.4
CH (9)
4.28 (dd, J ¼ 9.0, 7.0), 71.9 4.31 (dd, J ¼ 9.0, 7.0), 72.0 4.32 (dd, J ¼ 9.0, 7.0), 72.1
2
3.94 (dd, J ¼ 9.0, 3.5)
3.97 (dd, J ¼ 9.0, 3.5)
55.6 3.85 (s)
3.96 (dd, J ¼ 9.0, 3.5)
56.0 3.84 (s)
3.84 (s)
139.3
102.3 6.62 (s)
152.7
MeOꢀC(3) 3.87 (s)
56.3
56.3
MeOꢀC(5)
C(1’)
139.8
109.9 6.63 (s)
151.6
139.2
122.9
139.4
102.3
152.4
128.0
152.4
102.3
85.9
HꢀC(2’)
7.00 (d, J ¼ 1.5)
C(3’)
C(4’)
128.0
152.7
HꢀC(5’)
HꢀC(6’)
HꢀC(7’)
HꢀC(8’)
7.03 (d, J ¼ 8.5)
6.89 (dd, J ¼ 8.5, 1.5) 117.9 6.63 (s)
102.3 6.62 (s)
85.6 4.80 (d, J ¼ 4.0)
54.3 3.09 – 3.11 (m)
4.80 (d, J ¼ 4.0)
85.6 4.79 (d, J ¼ 4.0)
3.07 – 3.13 (m)
54.4 3.08 – 3.11 (m)
54.4
CH (9’)
4.28 (dd, J ¼ 9.0, 7.0), 71.9 4.31 (dd, J ¼ 9.0, 7.0), 71.9 4.32 (dd, J ¼ 9.0, 7.0), 72.1
2
3.94 (dd, J ¼ 9.0, 3.5)
3.95 (dd, J ¼ 9.0, 3.5)
55.6 3.83 (s)
3.83 (s)
3.96 (dd, J ¼ 9.0, 3.5)
56.3 3.84 (s)
56.3 3.84 (s)
166.0
MeOꢀC(3’) 3.87 (s)
MeOꢀC(5’)
C(1’’)
56.3
56.3
165.8
127.3
139.3
15.9
166.0
127.2
C(2’’)
127.3
HꢀC(3’’)
HꢀC(4’’)
HꢀC(5’’)
C(1’’’)
6.20 – 6.25 (m)
139.9 6.18 – 23 (m)
15.9 2.08 (d, J ¼ 1.5)
20.7 2.07 (d, J ¼ 1.5)
166.0
140.0 6.17 – 6.21 (m)
15.9 2.08 (d, J ¼ 1.5)
20.7 2.07 (d, J ¼ 1.5)
165.8
2.06 (d, J ¼ 1.5)
2.05 (d, J ¼ 1.5)
20.7
165.8
127.3
139.3
15.9
C(2’’’)
127.2
127.2
HꢀC(3’’’)
HꢀC(4’’’)
HꢀC(5’’’)
6.20 – 6.25 (m)
2.06 (d, J ¼ 1.5)
2.05 (d, J ¼ 1.5)
139.9 6.18 – 23 (m)
15.9 2.08 (d, J ¼ 1.5)
20.7 2.07 (d, J ¼ 1.5)
139.9 6.17 – 6.21 (m)
15.9 2.08 (d, J ¼ 1.5)
20.7 2.07 (d, J ¼ 1.5)
20.7

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Helvetica Chimica Acta – Vol. 96 (2013)
(
benzene C), including MeO signals at d(C) 55.6. These spectral data implied that 1
1
was a furofuran-type lignan [20]. Additionally, the H-NMR spectrum of 1 showed the
H-atom signals for the two angeloyl groups at d(H) 6.20 – 6.25 (m, HꢀC(3’,3’’)), 2.06 (d,
J ¼ 1.5, HꢀC(4’,4’’)), and 2.05 (d, J ¼ 1.5, HꢀC(5’,5’’)). The corresponding C-atom
resonances of the two angeloyl groups were observed at d(C) 166.0, 139.9, 127.2, 20.7,
and 15.9 in the HMQC spectrum. The H- and C-NMR data of 1 were very similar to
those of pinoresinol [21], except for the signals for additional two angeloyl groups [22].
The two angeloyl groups were at C(4) and C(4’), respectively, based on the comparison
1
13
13
of C-NMR chemical shifts of 1 with those of pinoresinol (d(C) 151.6 (C(3,3’)), 139.2
C(4,4’)), 122.9 (C(5,5’)) in 1; 146.7 (C(3,3’)), 145.3 (C(4,4’)), 114.3 (C(5,5’)) in
pinoresinol). The configuration of 1 was deduced to be same as that of (þ)-pinoresinol
20][23][24] based on the NOESY correlations (Fig. 2) and by comparison of the
(
[
coupling constants and optical rotation. Final evidence was obtained by alkaline
hydrolysis. Treatment of 1 with 0.1m KOH at room temperature afforded (þ)-
2
5
pinoresinol, which was identified by comparison of its optical rotation value ([a] ¼
D
1
þ5.0), and H-NMR and MS data [21]. Thus, the structure of 1 was determined as
(þ)-4,4’-O-diangeloylpinoresinol.
Fig. 2. Key NOE (H $ H) correlations of compounds 1 – 3
Compound 2 was obtained as a colorless gum. The molecular formula of 2 was
þ
determined as C H O from the molecular-ion peak [M þ Na] at m/z 575.2259 in the
31
36
9
positive-ion-mode HR-ESI-MS. The IR spectrum of 2 showed absorption bands at
ꢀ
1
1
3
357 and 1660 cm ascribable to a OH and a C¼O group, respectively. The H- and
13
C-NMR spectra of 2 were similar to those of 1 (Table). The main differences were the
additional NMR signals (d(H) 6.63 (s, HꢀC(2’,6’)) and 3.83 (s, MeOꢀC(3’,5’)); d(C)
1
52.7 (C(3’,5’)), 139.3 (C(1’)), 128.0 (C(4’)), 102.3 (C(2’,6’)), and 56.3 (MeOꢀC(3’,5’)))
in 2, impling that 2 has one 1,3,4-trisubstituted and one 1,3,4,5-tetrasubstituted benzene
ring. The additional MeO group was at C(5’) as deduced from the HMBC between the
1
13
MeO signal at d(H) 3.83 and d(C) 152.7 (C(5’)) (Fig. 3). The H- and C-NMR
spectral data (Table) of 2 were similar to those of medioresinol [21], except for the
presence of signals for the two angeloyl groups. The configuration of 2 was assumed to
be same as that of (þ)-medioresinol [20][21][25] by comparison its coupling constants
and optical-rotation value, and confirmed by NOESY correlations (Fig. 2). Alkaline
hydrolysis of 2 afforded (þ)-medioresinol, which was identified by comparison of its
1
optical-rotation value, and H-NMR and MS data [21]. Thus, the structure of 2 was
determined as (þ)-4,4’-O-diangeloylmedioresinol.

Helvetica Chimica Acta – Vol. 96 (2013)
323
Fig. 3. Key HMBCs (H ! C) of compounds 1 – 3
Compound 3 was obtained as a colorless gum. The molecular formula of 3 was
þ
determined as C H O from the molecular-ion peak [M þ Na] at m/z 605.2377 in the
32
38 10
positive-ion-mode HR-ESI-MS. The IR spectrum of 3 showed an absorption bands at
ꢀ
1
1
3
357 and 1660 cm ascribable to a OH and a C¼O group, respectively. The H- and
1
3
C-NMR spectra of 3 were similar to those of (þ)-syringaresinol (Table), except for
the signals of the additional two angeloyl groups. The configuration of 3 was assumed
to be same as that of (þ)-syringaresinol [20][21][25] by comparison its coupling
constants and optical rotation value, and verified by NOESY correlations (Fig. 2).
Alkaline hydrolysis of 3 yielded (þ)-syringaresinol, which was identified by compar-
1
ison of its optical-rotation value, and H-NMR and MS data [21]. Thus, the structure of
3
was determined as (þ)-4,4’-O-diangeloylsyringaresinol.
Sesquiterpene lactons with angeloyl moieties had been already isolated from this
plant [7], but lignans attached to short organic-acid moieites had not been reported.
Furofuran lignans containing the angeloyl groups were reported from Ligularia [26]
and Cremanthodium species [27].
The structure of the known compound was identified as (þ)-syringaresinol by
comparing its spectroscopic data with those in the literature [21].
This work 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
(
20110028285). We thank Drs. E. J. Bang, S. G. Kim, and J. J. Seo at the Korea Basic Science Institute
for their aid in obtaining the NMR and mass spectra.

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Helvetica Chimica Acta – Vol. 96 (2013)
Experimental Part
General. Column chromatography (CC): silica gel (SiO ; 230 – 400 mesh; Merck, Germany),
2
Lichroprep RP18 gel (40 – 60 mm, Merck, DE-Darmstadt), and Sephadex LH-20 (Amersham Pharmacia
Biotech, UK). TLC: SiO 60 F and RP-18 F254s SiO plates (Merck, Germany); detection under UV
2
254
2
light and by spraying with 10% aq. H SO soln., followed by heating at 1208 for 1 min. HPLC: Prep.
2
4
HPLC Gilson 306 pump, Gilson-101 RI detector, Phenomenex-Luna-C -(2) column (250 mm ꢁ
1
8
1
0.00 mm i.d., 5 mm); tR in min. UV Spectra: Jasco P-1020 polarimeter in CHCl ; l
(log e) in nm.
max
3
ꢀ1
1
13
IR Spectra: Bruker IFS-66/S FT-IR spectrometer; KBr pellets; in cm . H- and C-NMR spectra: Varian
UNITY INOVA 500 FT-NMR instrument; d in ppm rel. to Me Si as internal standard, J in Hz. ESI- and
4
HR-ESI-MS: VG BIOTECH platform LC/MS spectrometer; in m/z.
Plant Material. The aerial parts of R. laciniata (7.0 kg) were collected at the Taebaek Mountain in
Gangwon-Do Province, Korea, in May 2009, and the plant was identified by one of the authors
(
K. R. L.). A voucher specimen of the plant (SKK-09-06) was deposited with the School of Pharmacy in
Sungkyunkwan University.
Extraction and Isolation. Half-dried aerial parts of R. laciniata (Asteraceae) (7.0 kg) were extracted
with 80% MeOH three times at r.t. (6 ꢁ 12 l, overnignt). The resulting MeOH extracts (400 g) were
suspended in dist. H O (800 ml ꢁ 4), and then successively partitioned with hexane, CHCl , AcOEt, and
2
3
BuOH, yielding residues of 37, 1, 5, and 30 g, resp. The hexane-soluble extract (37 g) was subjected to CC
(
RP-18 (400 g), 90% MeOH): Frs. 1 – 7. Fr. 2 (2 g) was subjected again to CC (SiO (20 g); hexane/
2
CHCl /MeOH 2.5 :3 :0.1): Frs. 2.1 – 2.7. Fr. 2.4 was purified by prep. HPLC (RP-C ; MeOH/H O 85 :15;
3
18
2
2
ml/min): 1 (tR 20 min; 5 mg). Fr. 2.5 (1 g) was subjected to CC (Sephadex LH-20 (100 g); 100%
MeOH): Frs 2.5.1 – 2.5.2. Fr. 2.5.2 (40 mg) was purified by prep. HPLC (RP-C ; MeOH/H O 85 :15;
18
2
2
ml/min): 2 (tR 19 min; 5 mg) and 3 (tR 18 min; 5 mg). Fr. 2.9 was purified by prep. HPLC (RP-C18,
MeOH/H O 60 :40; 2 ml/min): (þ)-syringaresinol (t 15 min; 5 mg).
2
R
(
þ)-4,4’-O-Diangeloylpinoresinol (¼(1S,3aR,4S,6aR)-Tetrahydro-1H,3H-furo[3,4-c]furan-1,4-diyl-
25
bis-[2-methoxybenzene-4,1-diyl] Bis[(2Z)-2-methylbut-2-enoate); 1). Colorless gum. [a]
.17, CHCl ). UV (MeOH): 216 (4.0), 276 (3.9). IR (KBr): 3358, 2942, 2833, 1650, 1453, 1122, 1033.
D
¼ þ14.0 (c ¼
0
3
1
13
þ
þ
8
H- and C-NMR: Table. HR-ESI-MS: 545.2163 ([M þ Na] , C H NaO ; calc. 545.2151).
30
34
(
þ)-4,4’-O-Diangeloylmedioresinol (¼2,6-Dimethoxy-4-[(1S,3aR,4S,6aR)-4-(3-methoxy-4-{[(2Z)-
2
-methylbut-2-enoyl]oxy}phenyl)tetrahydro-1H,3H-furo[3,4-c]furan-1-yl]phenyl (2Z)-2-Methylbut-2-
enoate; 2). Colorless gum. [a]
2
5
D
¼ þ52 (c ¼ 0.15, CHCl ). UV (MeOH): 223 (4.0), 275 (4.1). IR
3
1
13
(
KBr): 3357, 2945, 2832, 1660, 1451, 1118, 1031. H- and C-NMR: Table. HR-ESI-MS: 575.2259 ([M þ
þ þ
Na] , C H NaO ; calc. 575.2257).
31
36
9
(
þ)-4,4’-O-Diangeloylsyringaresinol (¼(1S,3aR,4S,6aR)-Tetrahydro-1H,3H-furo[3,4-c]furan-1,4-
25
diylbis-[2,6-dimethoxybenzene-4,1-diyl] Bis[(2Z)-(2-Methylbut-2-enoate]; 3). Colorless gum. [a]
¼
D
þ71.0 (c ¼ 0.15, MeOH). UV (MeOH): 216 (4.0), 272 (3.9). IR (KBr): 3357, 2945, 2832, 1660,
1
13
þ
þ
10
1
6
451, 1116, 10311. H- and C-NMR: Table. HR-ESI-MS: 605.2377 ([M þ Na] , C H NaO ; calc.
32
38
05.2363).
Alkaline Hydrolysis of 1 – 3. Compound 1 (1.7 mg) was hydrolyzed with 0.1m KOH (1 ml) at r.t. for
3
h. After adding H O (3 ml), the mixture was extracted with CHCl three times, and the CHCl extract
2
3
3
was evaporated in vacuo. The CHCl extract was purified through a SiO Waters Sep-pak Vac 12cc
3
2
cartridge (Milford, MA, USA; with CHCl /MeOH 20 :1) to give (þ)-pinoresinol, which was identified by
3
1
H-NMR, MS, and optical-rotation data. Compounds 2 (1.0 mg) and 3 (1.0 mg) were treated by the same
method. The CHCl extract was purified through a SiO Waters Sep-pak Vac 12cc cartridge to give (þ)-
3
2
1
medioresinol, and (þ)-syringaresinol, which were identified by H-NMR, MS, and optical-rotation data.
2
5
1
(
þ)-Pinoresinol. [a] ¼ þ5.0 (c ¼ 0.03, CHCl ). H-NMR (CDCl , 500 MHz): 6.89 (d, J ¼ 2.0,
D
3
3
HꢀC(2,2’)); 6.88 (d, J ¼ 8.0, HꢀC(5,5’)); 6.82 (dd, J ¼ 8.0, 2.0, HꢀC(6,6’)); 4.74 (d, J ¼ 4.0, HꢀC(7,7’));
4
(
.24 (dd, J ¼ 9.0, 7.0, HꢀC(9a,9a’)); 3.91 (s, MeOꢀC(3,3’)); 3.88 (dd, J ¼ 9.0, 3.5, HꢀC(9b,9b’)); 3.09 – 3.11
ꢀ
m, HꢀC(8,8’)). ESI-MS: 357 ([M ꢀ H] ).
2
5
1
(
þ)-Medioresinol. [a]
D
¼ þ20.0 (c ¼ 0.01, CHCl ). H-NMR (CDCl , 500 MHz): 6.87 (d, J ¼ 2.0,
3
3
HꢀC(2)); 6.86 (d, J ¼ 8.0, HꢀC(5)); 6.83 (dd, J ¼ 8.0, 2.0, HꢀC(6)); 6.54 (s, HꢀC(2’,6’)); 4.74 (d, J ¼ 4.0,
HꢀC(7)); 4.70 (d, J ¼ 4.0, HꢀC(7’)); 4.24 (dd, J ¼ 9.0, 7.0, HꢀC(9a,9a’)); 3.91 (s, MeOꢀC(3)); 3.88 (s,

Helvetica Chimica Acta – Vol. 96 (2013)
325
MeOꢀC(3’,5’)); 3.88 (dd, J ¼ 9.0, 3.5, HꢀC(9b)); 3.85 (dd, J ¼ 9.0, 3.5, HꢀC(9b’)); 3.08 – 3.11 (m, HꢀC(8,
ꢀ
8
’)). ESI-MS: 387 ([M ꢀ H] ).
2
5
1
(
þ)-Syringaresinol. [a] ¼ þ56.0 (c ¼ 0.01, CHCl ). H-NMR (CDCl , 500 MHz): 6.58 (s,
D
3
3
HꢀC(2,6,2’,6’)); 4.74 (d, J ¼ 4.0, HꢀC(7,7’)); 4.24 (dd, J ¼ 9.0, 7.0, HꢀC(9a,9a’)); 3.90 (s,
MeOꢀC(3,5,3’,5’)); 3.88 (dd, J ¼ 9.0, 3.5, HꢀC(9b,9b’)); 3.10 – 3.13 (m, HꢀC(8, 8’)). ESI-MS: 417
ꢀ
(
[M ꢀ H] ).
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Received April 6, 2012