Nitric oxide inhibitory coumarins from the roots and rhizomes of Notopterygium incisum

Article abstract of DOI:10.1016/j.fitote.2018.10.002

Phytochemical study on the roots and rhizomes of Notopterygium incisum resulted in the isolation of six new coumarins, notoptetherins A ? F (1–6), and 20 known analogues (7–26). Their structures were elucidated on the basis of extensive analyses of NMR an

Full text of DOI:10.1016/j.fitote.2018.10.002

Fitoterapia131(2018)65–72
Contents lists available at ScienceDirect
Fitoterapia
journal homepage: www.elsevier.com/locate/fitote
Nitric oxide inhibitory coumarins from the roots and rhizomes of
Notopterygium incisum
Xikang Zheng, Yuemei Chen, Xiaoli Ma, Chen Zhang, Zhengren Xu, Yong Jiang, Pengfei Tu⁎
State Key Laboratory of Natural and Biomimetic Drugs, School of Pharmaceutical Sciences, Peking University, Beijing 100191, China
A R T I C L E I N F O
A B S T R A C T
Keywords:
Phytochemical study on the roots and rhizomes of Notopterygium incisum resulted in the isolation of six new
coumarins, notoptetherins A − F (1–6), and 20 known analogues (7–26). Their structures were elucidated on the
basis of extensive analyses of NMR and HRMS data, and the absolute configurations of 5 and 6 were established
by Mo2(AcO)4-induced CD and exciton chirality, respectively. Moreover, a biomimetic synthesis of 6 from 21
was employed to confirm its absolute configuration. In a subsequent activity screening, compounds 12 and 17
exhibited potent inhibition against LPS-induced nitric oxide production in RAW 264.7 cells with IC50 values of
12.7 and 10.2 μM, respectively.
Notopterygium incisum
Coumarins
Nitric oxide
1. Introduction
IV automatic polarimeter. ECD spectra were collected on a Jasco J-810
spectrometer. Semipreparative HPLC was performed on a LC3000 ap-
The roots and rhizomes of Notopterygium incisum, known as
“Qianghuo” in traditional Chinese medicine (TCM), have been used as
an anti-inflammatory, anti-pyretic, and analgesic agent [1,2]. Previous
studies on this plant revealed various types of natural products, such as
coumarins [3–5], polyacetylenes [6,7], terpenoids [8,9], and alkaloids
[10], some of which exhibited analgesic [7], anti-inflammatory
[6,11–13], cytotoxic [14,15], anti-tumor [16,17], and im-
munosuppressive [18] activities. Aimed to search for new bioactive
components from N. incisum, a phytochemical investigation was carried
out on its 95% aq. EtOH extract and led to the isolation of 26 cou-
marins, including six new ones, notoptetherins A − F (1–6). Herein, the
isolation and structural elucidation of the new compounds are de-
scribed, along with their nitric oxide (NO) inhibitory effects on LPS-
induced RAW 264.7 cells.
paratus equipped with a UV3000 single channel detector (Beijing Tong
Heng Innovation Technology Co., Ltd., China) using a Thermo Scientific
BDS-C18 column (250 × 10 mm, 5 μm). UPLC/MS analysis was per-
formed on a Waters ACQUITY UPLC apparatus coupled with an AB
Sciex Triple Quad™ 4500 triple quadrupole-linear ion trap (Qtrap) mass
spectrometer using
a
Shimadzu InertSustain C18 column
(150 × 2.1 mm, 3 μm). Column chromatography (CC) was conducted
on Merck silica gel 60 (40–63 μm), Merck Li Chroprep RP-18
(40–63 μm) and Mitsubishi Diaion HP20 (≥ 0.25 mm, ≥ 90%). Thin
layer chromatography (TLC) was performed on pre-coated silica gel
GF254 plates (Qingdao, Haiyang Chemical Co. Ltd., China). Solvents
used in CC and HPLC were analytical grade (Beijing Chemical Reagents
Co. Ltd., Beijing, China) and HPLC grade (Thermo Fisher Scientific Inc.,
Waltham, MA, USA), respectively. Reagents used for chemical com-
munications were purchased from Energy Chemical Co. Ltd. (Shanghai,
China).
2. Experimental
2.1. General experimental procedures
2.2. Plant material
HRESIMS data were obtained on a Shimadzu IT-TOF LC/MS in-
strument. IR spectra were measured on a Thermo Scientific Nicolet
The roots and rhizomes of N. incisum were collected in Ngawa
Tibetan and Qiang Autonomous Prefecture of Sichuan Province, China,
in September 2013, and were authenticated by Prof. Pengfei Tu (one of
the authors in this paper). A voucher specimen (No. QH-201309) has
been deposited in the Herbarium of Modern Research Center for
Traditional Chinese Medicine (TCM), Peking University, Beijing.
Nexus 470 FT-IR spectrometer. UV spectra were recorded on
a
Shimadzu UV-2450 UV–visible spectrometer. 1D and 2D NMR data
were acquired on Agilent VNMRS-500 and Bruker AVANCE III-400
spectrometers. Specific rotations were measured on a Rudolph Autopol
⁎
Corresponding author.
E-mail address: pengfeitu@vip.163.com (P. Tu).
https://doi.org/10.1016/j.fitote.2018.10.002
Received 27 August 2018; Received in revised form 23 September 2018; Accepted 1 October 2018
Availableonline03October2018
0367-326X/©2018PublishedbyElsevierB.V.

X. Zheng et al.
Fitoterapia131(2018)65–72
2.3. Extraction and isolation
(3.86), 220 (3.95), 207 (3.96) nm; IR (KBr) νmax 2960, 2919, 2850,
1739, 1625, 1607, 1580, 1456, 1356, 1201, 1153, 1128, 1019 cm−1
;
The air-dried powders of the roots and rhizomes of N. incisum
(20 kg) were extracted with 95% aq. EtOH (120 L) by refluxing for
thrice, each for 2 h. The combined ethanol extracts were concentrated
in vacuo to obtain 12.6 kg crude extract which was successively parti-
tioned with petroleum ether (PE, 6 L × 3), CHCl3 (6 L × 3) and n-BuOH
(6 L × 3) to give the corresponding portions. The CHCl3 extract
(1570 g) was subjected to silica gel CC and eluted with PE/acetone
(1:0 → 0:1) to afford seven fractions, Frs. C1–C7. Separation of the Fr.
C3 (11.2 g) by silica gel CC using PE/EtOAc solvent system (7:1) led to
four subfractions, Frs. C3A–C3D. Fr. 3B (414 mg) was loaded onto an
ODS column eluting with the mixture of MeOH/H2O (75:25) to give
two fractions, both of which were subjected to silica gel CC (PE/EtOAc,
15:1) to afford 22 (31.7 mg) and 10 (23.1 mg). Fr. C5 (53 g) was
chromatographed on a silica gel column eluting with a gradient of PE/
EtOAc (50:1 → 1:1) to give six fractions, Frs. C5A–C5F. Fr. C5B (2.3 g)
was loaded onto an ODS column and eluted with MeOH/H2O (60:40 →
100:0) to yield five subfractions, Frs. C5BI − C5BV. Fr. C5BII (72.1 mg)
was purified by silica gel CC (PE/acetone, 15:1) to afford 8 (26.5 mg).
Fr. C5BIII (91.7 mg) was subjected to silica gel CC (PE/acetone, 15:1) to
obtain 12 (31.3 mg). Fr. C5BIV (53.3 mg) was loaded onto a silica gel
column eluting with PE/EtOAc (8:1) to give 4 (19.8 mg) and 23
(12.7 mg). Fr. C5BV (83.2 mg) was purified by silica gel CC (PE/EtOAc,
15:1) to afford 9 (12.1 mg) and 13 (22.3 mg). Separation of Fr. C5C
(3.4 g) by ODS CC (MeOH/H2O, 60:40 → 100:0) led to five fractions,
Frs. C5CI − C5CV. Fr. C5CI (33.7 mg) was purified using semi-
preparative HPLC (MeOH/H2O, 55:45, 2 mL/min) to give 15 (12.3 mg,
tR 30.2 min). Fr. C5CII (56.7 mg) was applied to semipreparative HPLC
(MeCN/H2O, 45:55, 2 mL/min) to yield 17 (16.7 mg, tR 36.8 min) and
18 (13.7 mg, tR 38.7 min). Fr. C5CIII (55.3 mg) was purified by semi-
preparative HPLC (MeCN/H2O, 45:55, 2 mL/min) to afford 16
(30.1 mg, tR 36.3 min). Fr. C5CIV (79.3 mg) was subjected to silica gel
CC (PE/acetone, 30:1 → 10:1) to obtain 21 (32.7 mg) and 24 (14.7 mg).
Fr. C5CV (47.6 mg) was loaded onto a silica gel column eluting with a
mixture of PE/acetone (10:1) to yield 26 (39.4 mg). Fr. C5E (4.5 g) was
chromatographed over an ODS column eluting with MeOH/H2O
(60:40 → 100:0) to give four fractions, Frs. C5EI − IV. Fr. C5EII
(730 mg) was subjected to ODS CC (MeCN/H2O, 85:15) to yield three
fractions, Frs. C5EIIa − C5EIIc. Fr. C5EIIb (121 mg) was loaded onto a
silica gel column eluting with a gradient of PE/EtOAc (5:1 → 3:1) to
obtain four subfractions, and the first subfraction was followed by
semipreparative HPLC (MeCN/H2O, 85:15, 2 mL/min) to afford 1
(3.1 mg, tR 23.1 min), 2 (2.4 mg, tR 24.8 min), and 3 (1.3 mg, tR
27.3 min). Fr. C6 (154 g) was treated with PE/CH2Cl2 (7:1) to give 14
(53 g) as while crystals. Separation of Fr. C7 (973 g) by silica gel CC
(PE/EtOAc, 3:1 → 1:3) led to four fractions, Frs. C7A − C7D. Fr. C7A
(340 mg) was chromatographed on an ODS column eluting with MeOH/
H2O in gradient (50:50 → 70:30) and followed by semipreparative
HPLC (MeCN/H2O, 35:65, 2 mL/min) to give 5 (13.7 mg, tR 25.6 min).
Fr. C7B (716 g) was subjected to silica gel CC (PE/acetone 10:1) to
afford 7 (13 g) and 11 (24 g). A solution of Fr. C7D (21 g) in CH2Cl2 was
filtrated to obtain 19 (2.3 g), and the filtrate was concentrated under
reduced pressure and subjected to ODS CC (MeOH/H2O, 75:25 →
100:0) to yield five fractions, Frs. C7DI − C7DV. Fr. C7DI (35.7 mg)
was purified by silica gel CC (PE/EtOAc, 3:1) to give 25 (11.9 mg). Fr.
C7DIII (93.6 mg) was loaded onto an ODS column eluting with MeOH/
H2O (60:40) to afford three subfractions, and the second subfraction
was purified using semipreparative HPLC (MeCN/H2O, 55:45, 2 mL/
min) to obtain 6 (34.2 mg, tR 14.9 min). Separation of the n-BuOH ex-
tract (1356 g) by macroporous adsorption resin (EtOH/H2O, 10:90 →
90:10) led to five fractions, Frs. B1–B5. White crystals of 20 (437 g)
were obtained from Fr. B3 (593 g) by recrystallization in EtOH.
1H and 13C NMR data, see Tables 1 and 2; HRESIMS m/z 475.2094
[M + Na]+ (calcd for C27H32O6Na, 475.2097).
2.3.2. Notoptetherin B (2)
Colorless oil, UV (MeOH) λmax (log ε) 310 (4.04), 258 (4.09), 251
(4.13), 221 (4.22), 207 (4.23) nm; IR (KBr) νmax 2959, 2919, 2872,
2851, 1736, 1626, 1580, 1457, 1359, 1153, 1128, 1073 cm−1
;
1H and
13C NMR data, see Tables 1 and 2; HRESIMS m/z 477.2243 [M + Na]+
(calcd for C27H34O6Na, 477.2253).
2.3.3. Notoptetherin C (3)
Colorless oil, UV (MeOH) λmax (log ε) 308 (3.68), 260 (3.72), 252
(3.74), 220 (3.79), 206 (3.85) nm; IR (KBr) νmax 2957, 2917, 2850,
1730, 1624, 1455, 1375, 1262, 1121, 1020 cm−1
;
1H and 13C NMR
data, see Tables 1 and 2; HRESIMS m/z 477.2260 [M + Na]+ (calcd for
C27H34O6Na, 477.2253).
2.3.4. Notoptetherin D (4)
Colorless oil, UV (MeOH) λmax (log ε) 310 (4.15), 259 (4.22), 250
(4.26), 220 (4.37), 206 (4.39) nm; IR (KBr) νmax 2973, 2919, 1736,
1625, 1579, 1456, 1355, 1201, 1128, 1070 cm−1
;
1H and 13C NMR
data, see Tables 1 and 2; HRESIMS m/z 405.1674 [M + Na]+ (calcd for
C23H26O5Na, 405.1678).
2.3.5. Notoptetherin E (5)
Colorless oil, [α]2D5 + 13.2 (c 0.12, MeOH); UV (MeOH) λmax (log ε)
309 (3.94), 250 (4.05), 219 (4.19), 207 (4.20) nm; Mo2(OAc)4-induced
CD (DMSO) 304 (Δε + 0.31) nm; IR (KBr) νmax 3349, 2926, 2854, 1742,
1593, 1444, 1367, 1217, 1125, 1030 cm−1
;
1H and 13C NMR data, see
Tables
1
and 2; HRESIMS m/z 393.1299 [M + Na]+ (calcd for
C21H22O6Na, 393.1314).
2.3.6. Notoptetherin F (6)
White amorphous powder, [α]2D5 + 186.3 (c 0.23, MeOH); UV
(MeOH) λmax (log ε) 323 (4.58), 235 (4.17), 205 (4.74) nm; ECD (c 0.6,
MeOH) 342 (Δε + 11.35), 300 (Δε − 6.02), 246 (Δε + 2.19) nm; IR
(KBr) νmax 3335, 2926, 2855, 1738, 1616, 1454, 1366, 1217, 1156,
1117, 1029 cm−1
;
1H NMR (500 MHz, CD3OD) δH: 7.73 (1H, d,
J = 9.6 Hz, H-4), 7.40 (1H, d, J = 16.0 Hz, H-7″), 7.38 (1H, d,
J = 8.2 Hz, H-5), 7.07 (1H, d, J = 2.0 Hz, H-2″), 6.95 (1H, dd, J = 8.1,
2.0 Hz, H-6″), 6.80 (1H, d, J = 8.2 Hz, H-6), 6.78 (1H, d, J = 8.1 Hz, H-
5″), 6.14 (1H, d, J = 16.0 Hz, H-8″), 6.04 (1H, d, J = 9.6 Hz, H-3), 5.63
(1H, dd, J = 10.2, 7.3 Hz, H-2′), 5.40 (1H, brs, H-4′a), 5.36 (1H, brs, H-
4′b), 4.99 (1H, d, J = 13.2 Hz, H-5′a), 4.72 (1H, d, J = 13.2 Hz, H-5′b),
3.89 (3H, s, H3-OCH3), 3.66 (1H, dd, J = 16.0, 10.2 Hz, H-1′a), 3.36
(1H, dd, J = 16.0, 7.3 Hz, H-1′b). 13C NMR (125 MHz, CD3OD) δC:
168.3 (C-9″), 165.2 (C-7), 163.0 (C-2), 152.6 (C-8a), 150.8 (C-4″),
149.4 (C-3″), 146.9 (C-7″), 146.0 (C-4), 145.0 (C-3′), 130.5 (C-5), 127.4
(C-1″), 124.3 (C-6″), 116.5 (C-5″), 115.9 (C-4′), 114.7 (C-8), 114.6 (C-
8″), 114.6 (C-4a), 112.4 (C-3), 111.6 (C-2″), 108.0 (C-6), 86.7 (C-2′),
64.7 (C-5′), 56.5 (C-OCH3), 33.4 (C-1′). HRESIMS m/z 419.1134
[M − H]− (calcd for C24H19O7, 419.1131).
2.4. Chemical transformation
2.4.1. Synthesis of (5′S) hydroxyangenomalin (28)
According to the procedures described previously [19,20] with
slight modifications, to a solution of 21 (10 mg, 0.044 mmol, 1.0 equiv)
in CH2Cl2 (5 mL) was added SeO2 (2.4 mg, 0.022 mmol, 0.5 equiv),
potassium tert-butanolate (TBHP, 20 μL, 0.11 mmol, 2.5 equiv, from
5.5 M toluene solution), and AcOH (0.8 mL). The mixture was stirred at
room temperature for 24 h and filtered to remove the SeO2. The filtrate
was then washed with 10 mL brine and dried with MgSO4, filtered and
concentrated in vacuo to afford the residue, which was purified by
2.3.1. Notoptetherin A (1)
Colorless oil, UV (MeOH) λmax (log ε) 308 (3.76), 259 (3.81), 251
66

X. Zheng et al.
Fitoterapia131(2018)65–72
preparative TLC using PE/EtOAc (3:1, Rf = 0.4) to give the product 28
(2.5 mg, 23% yield) and the starting material 21 (4.8 mg, recovered in
48%). [α]D25 + 186.1 (c 0.06, MeOH); 1H NMR (500 MHz, CDCl3) δH:
7.64 (1H, d, J = 9.5 Hz), 7.28 (1H, d, J = 8.3 Hz), 6.77 (1H, d,
J = 8.3 Hz), 6.22 (1H, d, J = 9.5 Hz), 5.52 (1H, t, J = 9.0 Hz), 5.31
(1H, brs), 5.30 (1H, brs), 4.29 (2H, m), 3.59 (1H, dd, J = 16.1, 9.8 Hz),
3.30 (1H, dd, J = 16.1, 8.2 Hz); HRESIMS m/z 245.0815 [M + H]+
(calcd for C14H13O4, 245.0814).
2.5. Liquid chromatography and mass spectrometry
The powders (80 mesh, 100 mg) of the roots and rhizomes of N.
incisum were extracted with 10 mL of MeOH by ultrasonification at
40 kHz for 30 min. Then 1.5 mL of the MeOH extract was filtrated
through a 0.22 μm membrane and 5 μL of the filtrate was injected into
the UPLC device eluting with MeCN/H2O in gradient (60:40 → 100:0)
within 20 min at 0.4 mL/min. ESIMS data were acquired in the positive
ion mode and the ion source parameters were set as follows: source
temperature 550 °C; ion spray voltage (IS) 4500 V; ion source gas I
(GSI), gas II (GSII), and curtain gas (CUR) were at 55, 55, and 35 psi,
respectively; the collision gas (CAD) was high.
2.4.2. Synthesis of trans-4-O-tertbutyldimethylsilylferulic acid (30)
According to a procedure reported previously [21], to a 50 mL
round-bottom flask charged with 29 (100 mg, 0.52 mmol, 1.0 equiv) in
20 mL CH2Cl2 was added tert-butyldimethylsilyl chloride (TBSCl,
194 mg, 1.3 mmol, 2.5 equiv) and N,N-diisopropylethylamine (DIPEA,
270 μL, 1.5 mmol, 3.0 equiv). The resulting mixture was stirred at room
temperature for 5 h and then quenched by adding 5 mL water and di-
luted with 40 mL EtOAc. The organic phase was washed with 20 mL
1.0 M aqueous HCl and 15 mL brine, dried by MgSO4 and concentrated
to afford the bis-TBS product as yellowish oil. The intermediate was
dissolved in a mixture of 25 mL of THF/H2O (5:1) followed by adding
K2CO3 (178 mg, 1.3 mmol, 2.5 equiv) in a single portion. The resultant
slurry was stirred vigorously for 2 h at room temperature and then di-
luted with 40 mL of EtOAc. The organic phase washed with 20 mL
water, 20 mL 1.0 M aqueous HCl and 15 mL brine, dried (MgSO4) and
concentrated to obtain a white solid, which was further dried in high
vacuum at 80 °C for 6 h to drive off the residual TBSOH to give 30 as
white solid (156 mg, 98% yield). 1H NMR (500 MHz, CDCl3) δH: 7.72
(1H, d, J = 15.8 Hz), 7.06 (1H, dd, J = 8.5, 2.1 Hz), 7.05 (1H, brs),
6.86 (1H, d, J = 8.5 Hz), 6.31 (1H, d, J = 15.8 Hz), 3.85 (3H, s), 1.00
(9H, s), 0.18 (6H, s); 13C NMR (125 MHz, CDCl3) δC: 172.4, 151.4,
148.2, 147.3, 128.1, 122.9, 121.3, 115.0, 111.2, 55.6, 25.8, 18.6, −4.4.
2.6. Bioassay
2.6.1. Cell culture
The murine macrophage RAW 264.7 cells were purchased from
Beijing Union Medical University (Beijing, China) and maintained in
DMEM medium supplemented with 10% FBS, 100 U/mL penicillin, and
100 μg/mL streptomycin at 37 °C under 5% CO2.
2.6.2. NO assay
NO production and cell viability were measured as the procotols
described previously [22,23]. For detailed procedures, see Supple-
mentary data.
3. Results and discussion
The 95% aq. EtOH extract of the roots and rhizomes of N. incisum
was suspended in water and successively partitioned with PE, CHCl3,
and n-BuOH. The resultant CHCl3 and n-BuOH fractions were subjected
to various CC and reverse phase HPLC to yield compounds 1–26
(Fig. 1).
2.4.3. Synthesis of 4″-O-tertbutyldimethylsilynotoptetherin F (31)
1-Ethyl-3-(3-dimethylaminopropyl)carbodiimide
hydrochloride
Notoptetherin A (1) was obtained as a colorless oil. The molecular
formula of 1 was established as C27H32O6 by the positive HRESIMS ion
at m/z 475.2094 [M + Na]+ (calcd for C27H32O6Na, 475.2097), cor-
responding to 12 indices of hydrogen deficiency. The 1H NMR signals of
two pairs of ortho-coupled olefinic doublets at δH 8.27 (1H, d,
J = 9.7 Hz), 6.29 (1H, d, J = 9.7 Hz) and 7.79 (1H, d, J = 2.3 Hz), 7.16
(1H, d, J = 2.3 Hz) and a phenyl singlet at δH 7.21 (1H, s) (Table 1)
indicated that 1 was a linear furocoumarin with a side-chain substituted
at C-5 [24], which was confirmed by the HMBC correlation from H2–1′
(δH 5.04) to C-5 (δC 150.4) and the NOE enhancement between H-10
(δH 7.16) and H2–1′ (δH 5.04). Analysis of the 13C NMR data (Table 2) in
combination with the HSQC correlations revealed that the residue
substituted at C-5 was composed of 16 carbon resonances attributable
to one bisubstituted double bond (δC 139.0 and 127.2), one trisub-
stituted double bond (δC 143.3 and 121.1), two sp3 oxygenated tertiary
carbons (δC 90.8 and 80.5), six sp3 methylenes (δC 70.9, 43.2, 38.0 × 2,
and 25.5 × 2), and four methyls (δC 16.8, 24.7, and 25.6 × 2). The
aforementioned spectroscopic data suggested that 1 was a derivative of
notoptol (7) [4,24] with an additional C6 ring moiety accounting for the
remaining one index of hydrogen deficiency, which was deduced to be a
1-methylcyclopentyl hydroxyl group [25] by the 1H−1H COSY and
HMBC correlations (Fig. 2). By comparison with the NMR data of no-
toptol (7) [4,24] and 1-methylcyclopentanol [25], the deshielded re-
sonances of C-7′ (δC 80.5 for 1 and δC 70.6 for 7) and C-1″ (δC 90.8 for 1
and δC 79.7 for 1-methylcyclopentanol) in 1 indicated that these two
moieties were linked via a peroxy bond between C-7′ and C-1″, which
was supported by the molecular composition and the similar C-1″ re-
sonance value to 1-methylcyclopentyl hydroperoxide (δC 92.1) [25]. In
the 1D NOE experiment, when irradiation of H2–1′ (δH 5.04), H3–9′ (δH
1.65) showed an enhancement, indicating a 2′E-configuration for the
double bond (Fig. 2). Meanwhile, the 5′E-configuration was determined
from the coupling constant of 15.8 Hz between H-5′ and H-6′. Thus, the
structure of notoptetherin A (1) was determined as shown.
(EDCl, 2.7 mg, 0.014 mmol, 1.5 equiv) and catalytic amount of 4-di-
methylaminopyridine (DMAP) were added to a solution of 30 (4.4 mg,
0.014 mmol, 1.5 equiv) in CH2Cl2 (2 mL) followed by dropping the
solution of 28 (2.3 mg, 0.0094 mmol, 1.0 equiv) in 0.5 mL of CH2Cl2.
The mixture was allowed to stirred overnight at room temperature and
directly purified by preparative TLC (PE/EtOAc, 3:1, Rf = 0.5) to afford
the product 31 (2.8 mg, 56% yield). [α]D25 + 187.3 (c 0.05, MeOH); 1H
NMR (500 MHz, CDCl3) δH: 7.59 (1H, d, J = 9.5 Hz), 7.55 (1H, d,
J = 15.6 Hz), 7.26 (1H, overlapped), 6.99 (2H, m), 6.85 (1H, d,
J = 8.6 Hz), 6.78 (1H, d, J = 8.3 Hz), 6.23 (1H, d, J = 15.6 Hz), 6.16
(1H, d, J = 9.5 Hz), 5.54 (1H, t, J = 8.9 Hz), 5.41 (1H, brs), 5.38 (1H,
brs), 4.89 (1H, d, J = 13.4 Hz), 4.80 (1H, d, J = 13.4 Hz), 3.85 (3H, s),
3.64 (1H, dd, J = 16.1, 9.9 Hz), 3.38 (1H, dd, J = 16.1, 7.7 Hz), 1.01
(9H, s), 0.18 (6H, s); HRESIMS m/z 535.2159 [M + H]+ (calcd for
C
30H35O7Si, 535.2152).
2.4.4. Synthesis of notoptetherin F (6)
To a solution of 31 (2.5 mg, 0.0047 mmol, 1.0 equiv) in 2 mL of THF
stirred at room temperature, the 1.0 M solution of tetra-n-butylammo-
nium fluoride (TBAF) in THF (10 μL, 2.1 equiv) was added dropwise.
The reaction was monitored by TLC and upon completion, the product
(1.4 mg, 73% yield) was purified by preparative TLC (PE/EtOAc, 1:1,
Rf = 0.4). [α]D25 + 183.1 (c 0.04, MeOH); ECD (c 0.04 MeOH) 342
(Δε + 10.12), 300 (Δε
−
5.06), 253 (Δε + 2.51) nm; 1H NMR
(400 MHz, CD3OD) δH: 7.75 (1H, d, J = 9.5 Hz), 7.41 (1H, d,
J = 15.9 Hz), 7.41 (1H, d, J = 8.3 Hz), 7.09 (1H, d, J = 1.9 Hz), 6.96
(1H, dd, J = 8.2, 1.9 Hz), 6.82 (1H, d, J = 8.3 Hz), 6.79 (1H, d,
J = 8.2 Hz) 6.16 (1H, d, J = 15.9 Hz), 6.06 (1H, d, J = 9.5 Hz), 5.66
(1H, dd, J = 10.3, 7.3 Hz), 5.42 (1H, brs), 5.38 (1H, brs), 5.01 (1H, d,
J = 13.2 Hz), 4.73 (1H, d, J = 13.2 Hz), 3.69 (1H, dd, J = 16.1,
10.3 Hz), 3.39 (1H, dd, J = 16.1, 7.3 Hz); HRESIMS m/z 419.1133 [M
− H]− (calcd for C24H19O7, 419.1131).
67

X. Zheng et al.
Fitoterapia131(2018)65–72
Fig. 1. Structures of compounds 1–27.
Notoptetherin B (2), isolated as a colorless oil, had a molecular
formula of C27H34O6 determined by the HRESIMS ion at m/z 477.2260
[M + Na]+ (calcd for C27H34O6Na, 477.2253). The 1H and 13C NMR
data of 3 (Tables 1 and 2) were similar to those of 1 and 2 except for the
different substituent group attached at C-7′-OH, which was deduced to
be a 2,3-dimethyl-2-butanyl hydroxyl group based on the 1He1H COSY
correlations of H-2″/H3–3″ (H3–6″) and the HMBC correlations from
H3–3″ (H3–6″) to C-1″ and C-2″, from H-2″ to C-1″ and C-4″ (C-5″), and
from H3–4″ (H3–5″) to C-1″. The presence of the peroxy bond between
C-7′ and C-1″ was established by the molecular composition and the C-
1″ resonance (δC 83.9 for 3 and δC 85.1 for 2,3-dimethyl-2-butanyl
hydroperoxide [25]). Thus, the structure of notoptetherin C (3) was
characterized unequivocally.
formula of C27H34O6 determined by the positive HRESIMS ion at m/z
477.2243 [M + Na]+ (calcd for C27H34O6Na, 477.2253), processing 11
indices of hydrogen deficiency. The NMR data of 2 (Tables 1 and 2)
were similar to those of 1, except that the 1-methylcyclopentyl hy-
droxyl group located at C-7′-OH in 1 was substituted by a 2-methyl-2-
pentanyl hydroxyl group in 2, which was supported by the 1H−1H
COSY correlations of H2–2″/H2–3″/H3–4″ and the HMBC correlations of
H2–3″/C-1″ and H3–5″ (H3–6″)/C-1″and C-2″ (Fig. 2). The connection
between C-7′ and C-1″ via a peroxy bond was confirmed by the mole-
cular composition and the C-1″ resonance (δC 81.5 for 2 and δC 80.1 for
tert-butyl 2-methyl-2-pentanyl peroxide [26]). Therefore, the structure
of notoptetherin B (2) was established.
Peroxy natural products usually possess hydroperoxy groups or
peroxide bridges generated intramolecularly [27,28]. However, acyclic
Notoptetherin C (3) was obtained as a colorless oil with a molecular
68

X. Zheng et al.
Fitoterapia131(2018)65–72
Table 1
1H NMR data of compounds 1–5 (500 MHz, δ in ppm, J in Hz).
Position
1a
2a
3a
4b
5a
3
6.29, d (9.7)
8.27, d (9.7)
7.21, s
6.28, d (9.8)
8.27, d (9.8)
7.21, s
6.29, d (9.7)
8.26, d (9.7)
7.21, s
6.25, d (9.8)
8.13, d (9.8)
7.12, s
6.28, d (9.8)
8.26, d (9.8)
7.19, s
4
8
9
7.79, d (2.3)
7.16, d (2.3)
5.04, d (6.9)
5.59, t (6.9)
2.74, d (6.8)
5.48, dt (15.8, 6.8)
5.59, d (15.8)
1.24, s
7.79, d (2.4)
7.16, d (2.4)
5.04, d (7.0)
5.59, t (7.0)
2.74, d (6.8)
5.48, dt (15.7, 6.8)
5.59, d (15.7)
1.24, s
7.80, d (2.3)
7.16, d (2.3)
5.04, d (7.0)
5.60, t (7.0)
2.74, d (6.8)
5.48, dt (15.8, 6.8)
5.59, d (15.8)
1.24, s
7.59, d (2.3)
6.94, d (9.3)
4.95, d (6.8)
5.55, t (6.8)
2.78, d (5.9)
5.46, dd (15.8, 5.9)
5.51, d (15.8)
1.25, s
7.79, d (2.4)
7.16, dd (2.4, 1.1)
5.03, d (6.9)
5.61, t (6.9)
2.78, d (6.7)
5.65, dt (15.6, 6.7)
5.57, d (15.6)
3.35, d (2.7)
1.67, s
10
1′
2′
4′
5′
6′
8′
9′
1.65, s
1.65, s
1.65, s
1.67, s
10′
1.24, s
1.24, s
1.24, s
1.25, s
1.21, s
2″a
1.85, m
1.45, m
1.85, m
b
1.38, m
3″a
1.66, m
1.32, m
0.87, t (7.3)
1.13, s
0.85, d (6.9)
1.09, s
b
1.55, m
4″a
1.66, m
b
5″a
1.55, m
1.85, m
1.09, s
b
1.38, m
6″
1.30, s
1.13, s
0.85, d (6.9)
OCH2CH3
OCH2CH3
3.31, q (7.0)
1.13, t (7.0)
a
b
measured in CD3OD.
measured in CDCl3.
Table 2
hydroperoxy group (Scheme. S1, Supplementary Data). The hydro-
peroxy intermediate iv could be formed by oxidation of 10 followed by
trapping the generated vinyl free radicals i/ii with molecule oxygen
(O2). Nucleophilic substitution of cations A, produced by oxidation of
the corresponding C6 alkanes, with iv afforded the dialkyl peroxides
1–3. On the other hand, 1–3 could also be formed by reaction of hy-
droperoxy intermediate B with cation v. The hydroperoxy intermediate
B could come from the C6 alkanes via a process similar to that for the
formation of iv, while the counterpart cation v could be obtained from
7.
13C NMR data of compounds 1–5 (125 MHz, δ in ppm).
Position
1a
2a
3a
4b
5a
2
163.2, C
163.2, C
163.2, C
113.1, CH
141.5, CH
109.1, C
150.4, C
116.3, C
159.7, C
95.0, CH
153.8, C
146.9, CH
106.2, CH
70.9, CH2
121.1, CH
143.3, C
43.2, CH2
127.1, CH
139.1, CH
80.5, C
161.3, C
112.7, CH
139.6, CH
107.6, C
148.9, C
114.3, C
158.2, C
94.3, CH
152.7, C
145.0, CH
105.1, CH
69.8, CH2
119.8, CH
141.8, C
42.5, CH2
126.1, CH
138.9, CH
74.6, C
163.2, C
113.1, CH
141.5, CH
108.9, C
150.4, C
116.1, C
159.7, C
94.9, CH
153.8, C
146.9, CH
106.2, CH
70.9, CH2
121.0, CH
143.2, C
43.3, CH2
127.3, CH
138.0, CH
73.9, C
3
113.1, CH
141.5, CH
109.1, C
113.1, CH
141.5, CH
109.1, C
4
4a
5
150.4, C
150.4, C
6
116.1, C
116.3, C
7
159.7, C
159.7, C
8
95.0, CH
153.8, C
95.0, CH
153.8, C
Notoptetherin D (4), obtained as a colorless oil, had a molecular
formula of C23H26O5 according to its sodium adduct ion at m/z
405.1674 [M + Na]+ (calcd for C23H26O5Na, 405.1678) in the
HRESIMS spectrum. The NMR data of 4 (Tables 1 and 2) were similar to
those of 7 [4,24] except for the presence of an additional ethyl group
(δH 3.31, q, J = 7.01 Hz, δC 57.8 and δH 1.13, t, J = 7.01 Hz, δC 16.2),
indicating that 4 was an ethyl etherificated derivative of notoptol (7).
This deduction was confirmed by the HMBC correlation from the pro-
tons of ethoxy group (δH 3.31) to C-7′ (δC 74.6) (Fig. S1, Supplementary
Data). To clarify whether compound 4 was an artificial product, the
MeOH extract of N. incisum was analyzed by using UPLC/MS. The
chromatographic peak at 6.01 min with a sodium additive ion peak at
m/z 405.2 was consistent with the case of 4 under the same analytical
conditions (Fig. S66, Supplementary Data). This indicated that com-
pound 4 occurred naturally.
8a
9
146.9, CH
106.2, CH
70.9, CH2
121.1, CH
143.3, C
146.9, CH
106.2, CH
70.9, CH2
121.0, CH
143.3, C
10
1′
2′
3′
4′
43.2, CH2
127.2, CH
139.0, CH
80.5, C
43.2, CH2
127.2, CH
139.0, CH
80.5, C
5′
6′
7′
8′
25.6, CH3
16.8, CH3
25.6, CH3
90.8, C
25.5, CH3
16.8, CH3
25.5, CH3
81.5, C
25.5, CH3
16.8, CH3
25.5, CH3
83.9, C
26.5, CH3
16.8, CH3
26.5, CH3
70.9, CH2
16.8, CH3
24.6, CH3
9′
10′
1″
2″
38.0, CH2
25.5, CH2
25.5, CH2
38.0, CH2
24.7, CH3
43.0, CH2
18.3, CH2
15.1, CH3
25.1, CH3
25.1, CH3
36.1, CH
17.9, CH3
22.0, CH3
22.0, CH3
17.9, CH3
3″
4″
5″
Notoptetherin E (5) was isolated as a colorless oil. Its molecular
formula was deduced as C21H22O6 from a sodium additive ion peak at
m/z 393.1299 [M + Na]+ (calcd for C21H22O6Na, 393.1314) in the
HRESIMS spectrum, 16 mass units more than that of notoptol (7)
[4,24]. Analyses of the NMR data (Tables 1 and 2) indicated that 5 was
8′-hydroxynotoptol, which was confirmed by the HMBC correlations
from H2–8′ to C-6′, C-7′, and C-10′, from H-6′ to C-8′, and from H3–10 to
C-8′ (Fig. S1, Supplementary Data). To establish the absolute config-
uration of the 7′,8′-diol moiety, the in situ Mo2(OAc)4-induced circular
dichroism (ICD) method [40–42] was employed. Compound 5 was
mixed with Mo2(OAc)4 in anhydrous DMSO to form a metal complex,
which gave a positive Cotton effect at 304 nm (Fig. 3), suggesting the
(7′S) configuration for 5.
6″
OCH2CH3
OCH2CH3
57.8, CH2
16.2, CH3
a
b
measured in CD3OD.
measured in CDCl3.
dialkyl peroxides [29–34], especially those with two different alkyl
groups [35,36], such as notoptetherins A-C (1–3), are rare examples
from natural source. A putative biosynthetic pathway to 1–3 is pro-
posed to be derived from compounds 7 or 10 and volatile C6 alkanes,
including methylcyclopentane [37], 2-methylpentane [38], and 2,3-
dimethylbutane [39] via a SN1-type nucleophilic substitution by the
69

X. Zheng et al.
Fitoterapia131(2018)65–72
Fig. 2. Selected 1H−1H COSY, HMBC and NOE correlations of compounds 1–3 and 6.
Notoptetherin F (6) was obtained as a white amorphous powder. A
deprotonated ion [M − H]− at m/z 419.1134 from the HRESIMS data
determined its molecular formula as C24H20O7 (calcd for C24H19O7,
419.1131). The 1H NMR spectrum of 6 displayed a pair of characteristic
doublets for H-3 and H-4 of a coumarin skeleton (δH 7.73 and 6.04,
each 1H, d, J = 9.6 Hz) and two ortho-coupled phenyl protons at δH
7.38 and 6.80 (each 1H, d, J = 8.2 Hz), suggesting that 6 was a 7,8-
disubstituted coumarin derivative [19]. Further inspection of the 1H
NMR spectrum, combining with the 1H−1H COSY correlations, re-
vealed the presence of additional 13 proton signals attributable to two
sp3 geminal methylenes (δH 3.66, 1H, dd, J = 16.0, 10.2 Hz, 3.36, 1H,
dd, J = 16.0, 7.3 Hz; 4.99 and 4.72, each 1H, d, J = 13.2 Hz), a sp3
oxygenated methine (δH 5.63, 1H, dd, J = 10.2, 7.3 Hz), a trisubstituted
aromatic ring with an AMX system (δH 7.07, 1H, d, J = 2.0 Hz, 6.95,
1H, dd, J = 8.1, 2.0 Hz, and 6.78, 1H, d, J = 8.1 Hz), a trans-double
bond (δH 7.40 and 6.14, each 1H, d, J = 16.0 Hz), a terminal vinyl (δH
5.40 and 5.36, each 1H, brs), and a methoxy group (δH 3.89, 3H, s).
Taking the esterified carbon resonance at δC 168.3 into consideration,
Fig. 3. Mo2(OAc)4-ICD spectrum of compound 5 in DMSO and conformations of
the Mo24+complex of compound 5.
the above mentioned NMR data indicated that
6 was an ester
Fig. 4. ECD and UV spectra of compound 6 (A) and the positive chirality for compound 6 (B).
70

X. Zheng et al.
Fitoterapia131(2018)65–72
Scheme. 1. Chemical transformation of 6 from 21 and trans-ferulic acid (29).
the synthetic product and [α]2D5 + 186.3 for the natural product. Thus,
the S absolute configuration of 6 was determined unambiguously, and
the structure of 6 was defined as shown.
Table 3
Inhibitory effects of compounds 1–26 on NO production in RAW 264.7 cells
induced by LPS.
Compounds
The other 20 known compounds were identified as notoptol (7)
[24], methylnotoptol (8) [4], anhydronotoptol (9) [4], bergamottin
(10) [45], notopterol (11) [7], methylnotopterol (12) [46], ethylno-
topterol (13) [47], isoimperatorin (14) [47], bergapten (15) [48], im-
peratorin (16) [49], isobergapten (17) [48], pimpinellin (18) [48],
nodakenetin (19) [3,50], nodakenin (20) [3,51], (S)-angenomalin (21)
[19,44], seselin (22) [45], aurapten (23) [45], 7-O-prenylumbeliferone
(24) [45], scopoletin (25) [52], and (S)-6-O-methylscorzocreticin (26)
[53–56] by comparison of their physical and spectroscopic data with
those in the literature. Compound 26, reported as a synthetic racemate
previously [53,54], was isolated firstly as a natural product with S
absolute configuration. The absolute configuration of 26 was de-
termined by comparison of its ECD spectrum with that of mellein
[55,56] (Fig. S56, Supplementary Data). Since compound 26 showed a
positive Cotton effect at 236 nm and a negative Cotton effect at 256 nm,
similar to the case of mellein, the absolute configuration of 26 was
assigned as S. 6-Methoxyhydrangenol (27) [57], an analogue of 26
isolated from N. franchetii, gave a specific rotation data ([α]2D0 + 11 in
MeOH), which was in agreement with that of 26 ([α]2D5 + 9.1 in
MeOH). Thus, compound 27 processed an S absolute configuration as
well.
IC50 (μM)a
Compounds
IC50 (μM)a
1
−
−
−
14
15
16
17
18
19
20
21
22
23
24
25
26
−
−
2
3
26.3
10.2
−
1.2
4
20.4
49.5
−
1.3
1.2
5
2.6
6
−
7
−
−
8
23.9
36.6
28.6
29.1
12.7
18.1
10.1
2.9
2.1
2.3
1.0
0.9
0.1
0.4
27.0
27.9
−
1.6
1.1
9
10
11
−
12
−
13
19.8
0.5
Dexamethasoneb
a
Values were displayed as means SD from triplicate experiments. “−”
meant compounds inactive (inhibition rate < 50% at 100 μM).
b
Positive control.
comprising of an angenomalin moiety [19] and a trans-feruloyl group
[3]. The linkage of C-5′ − O − C-9″ was established on the basis of the
HMBC correlation from H2–5′ (δH 4.99 and 4.72) to C-9″ (δC 168.3).
Thus, the 2D structure of 6 was elucidated as trans-feruloylangenomalin
(Fig.2). In the ECD spectrum of 6 (Fig. 4), the sequential negative and
positive Cotton effects at 300 nm and 342 nm, causing by the exciton
coupling between the electric transition dipoles of coumarin nucleus
and the trans-feruloyl moiety, implied a positive chirality (+) and an S
absolute configuration for 6.
According to the clinical application of N. incisum, which is used in
TCM for treating the common cold and inflammatory diseases [2], in-
hibition against LPS-induced NO production in RAW 264.7 cells was
employed to evaluate the anti-inflammatory activities of compounds
1–26, and their IC50 values are presented in Table 3. It could be ob-
served that most of the furocoumarins with a linear prenyl side-chain,
except for compounds 1–3, 7, and 14, exhibited moderate inhibitory
effects with IC50 values ranging from 12.7 to 49.5 μM. This indicated
that compounds processing a peroxy group, such as 1–3, or an exposed
hydroxy group at C-7′, e.g. 5 and 7, might decrease the inhibitory ac-
tivity. Furthermore, compounds with an O-isopentenyl group at C-8
(16, IC50 = 26.3 μM) showed moderate inhibitory effects; but when the
substituent group was at C-5, compounds became inactive (14,
IC50 > 100 μM). Among the angular furocoumarins, 17 and 21 re-
vealed similar NO inhibitory activities to those discussed above with
IC50 values of 10.2 and 27.0 μM, respectively. Compound 17 exerted
the most potent inhibitory effect among all the test compounds.
Even though the exciton chirality rule is nonempirical due to its
well-established theoretical basis, the way to predict the sign and in-
tensity of an exciton couplet essentially depending on the geometry of
transition dipoles is not completely accurate [43]. Thus, a biomimetic
synthesis of 6 from 21, a known compound with the S absolute con-
figuration assigned by comparison its specific rotation ([α]D25 + 189.3
in MeOH) with the literature data [44] ([α]D23 + 181.0 in EtOH), and
trans-ferulic acid (29) was carried out to further confirm the absolute
configuration of 6 (Scheme 1). 28 was prepared by allylic oxidation of
21 using SeO2 and TBHP [19,20] in 23% yield with 21 recovered in
48%. Esterification of the oxidation product 28 with the mon-TBS
protected trans-ferulic acid using EDCl in the presence of a catalytic
amount of DMAP afforded 31 in a yield of 56%. 6 was easily obtained
by treatment 31 with TBAF to remove the TBS group. As shown in
Fig.4, the ECD spectrum of the synthetic product 6 presented the same
Cotton effects as those of the natural product 6. Moreover, both of them
had the consistent specific rotation data in MeOH, [α]D25 + 183.1 for
Conflict of interest
The authors declare no conflict of interest.
71

X. Zheng et al.
Fitoterapia131(2018)65–72
Acknowledgments
[24] P.C. Stevenson, M.S.J. Simmonds, M.A. Yule, N.C. Veitch, G.C. Kite, D. Irwin,
M. Legg, Insect antifeedant furanocoumarins from Tetradium daniellii,
Phytochemistry 63 (2003) 41–46.
This work was financially supported by the National Key
Technology R&D Program “New Drug Innovation” of China (No.
2018ZX09711001-008-003).
[25] G.A. Olah, D.G. Parker, N. Yoneda, F. Pelizza, Oxyfunctionalization of hydro-
carbons. 1. Protolytic cleavage-rearrangement reactions of tertiary alkyl hydro-
peroxides with magic acid, J. Am. Chem. Soc. 98 (1976) 2245–2250.
[26] X. Su, H. Huang, W. Hong, J. Cui, M. Yu, Y. Li, Alkyl radical triggered in situ SO2-
capture cascades, Chem. Commun. 53 (2017) 13324–13327.
Appendix A. Supplementary data
[27] D.A. Casteel, Peroxy natural products, Nat. Prod. Rep. 9 (1992) 289–312.
[28] D.A. Casteel, Peroxy natural products, Nat. Prod. Rep. 16 (1999) 55–73.
[29] M. Hiroi, D. Takaoka, Studies on the peel oil of Citrus iyo, Nippon Kagaku Kaishi
(1973) (1973) 1339–1344.
Supplementary data to this article can be found online at https://
doi.org/10.1016/j.fitote.2018.10.002.
[30] A. Kobayashi, K. Nohara, E. Ohsumi, T. Yamanishi, Identification of di(1-oxyalkyl)-
peroxides in the essential oil of Citrus iyo, Agric. Biol. Chem. 54 (1990) 561–562.
[31] H. Kameoka, K. Kubo, M. Miyazawa, Volatile flavor components of Malabar-
nightshade (Basella rubra L.), J. Food Compos. Anal. 4 (1991) 315–321.
[32] J.J.K. Wright, Y. Merill, M.S. Puar, A.T. McPhail, Structure of oxanthromicin (an-
tibiotic 16–550), a novel dimeric anthrone peroxide, J. Chem. Soc. Chem. Commun.
(1984) 473–474.
References
[1] Chinese Pharmacopoeia Commission, Chinese Pharmacopeia (2015 Edition), China
Medical Science Press, Beijing, 2015, pp. 182–183.
[33] H. Yang, A. Hou, S. Mei, H. Sun, C. Che, Constituents of Clerodendrum bungei, J.
Asian Nat. Prod. Res. 4 (2002) 165–169.
[2] Editorial Committee of Chinese Materia Medica of State Administration of
Traditional Chinese Medicine, Chinese Materia Medica, Shanghai Scientific &
Technical Publishers, Shanghai, 1999, pp. 992–997.
[34] A. Lavaud, P. Richomme, J. Gatto, M.-C. Aumond, C. Poullain, M. Litaudon,
R. Andriantsitohaina, D. Guilet, A tocotrienol series with an oxidative terminal
prenyl unit from Garcinia amplexicaulis, Phytochemistry 109 (2015) 103–110.
[35] T. Koiwa, T. Nakano, S. Takahashi, H. Koshino, M. Yamazaki, T. Takashi,
A. Nakagawa, Adxanthromycin: a new inhibitor of ICAM-l/LFA-1 mediated cell
adhesion from Streptomyces sp. NA-148, J. Antibiot. 52 (1999) 198–200.
[36] T. Nakano, T. Koiwa, S. Takahashi, A. Nakagawa, Adxanthromycins A and B, new
inhibitors of ICAM-1/LFA-1 mediated cell adhesion molecule from Streptomyces sp.
NA-148, J. Antibiot. 53 (2000) 12–18.
[3] Z. Gu, D. Zhang, X. Yang, M. Hattori, T. Namba, Isolation of two new coumarin
glycosides from Notopterygium forbesii and evaluation of a Chinese crude drug,
Qiang-Huo, the underground parts of N. incisum and N. forbesii, by high-perfor-
mance liquid chromatography, Chem. Pharm. Bull. 38 (1990) 2498–2502.
[4] M. Kozawa, M. Fukumoto, Y. Matsuyama, K. Baba, Chemical studies on the con-
stituents of the Chinese crude drug “Quiang Huo”, Chem. Pharm. Bull. 31 (1983)
2712–2717.
[5] S. Wu, Y. Yu, Y. Hu, J. Hu, A new dimeric furanocoumarin from Notopterygium
incisum, Chin. Chem. Lett. 19 (2008) 940–942.
[37] B. Tirillini, G. Verdelli, F. Paolocci, P. Ciccioli, M. Frattoni, The volatile organic
compounds from the mycelium of Tuber borchii Vitt, Phytochemistry 55 (2000)
983–985.
[6] X. Liu, O. Kunert, M. Blunder, N. Fakhrudin, S.M. Noha, C. Malainer, A. Schinkovitz,
E.H. Heiss, A.G. Atanasov, M. Kollroser, D. Schuster, V.M. Dirsch, R. Bauer, Polyyne
hybrid compounds from Notopterygium incisum with peroxisome proliferator-acti-
vated receptor gamma agonistic effects, J. Nat. Prod. 77 (2014) 2513–2521.
[7] E. Okuyama, S. Nishimura, S. Ohmori, Y. Ozaki, M. Satake, M. Yamazaki, Analgesic
component of Notopterygium incisum Ting, Chem. Pharm. Bull. 41 (1993) 926–929.
[8] S. Wu, Y. Zhao, H. Fan, Y. Hu, M.T. Hamann, J. Peng, C.M. Starks, M. O'Neil-
Johnson, J. Hu, New guaiane sesquiterpenes and furanocoumarins from
Notopterygium incisum, Planta Med. 74 (2008) 1812–1817.
[38] G. MacLeod, J.M. Ames, Gas chromatography-mass spectrometry of the volatile
components of cooked scorzonera, Phytochemistry 30 (1991) 883–888.
[39] E.D. Jordan, T.C.Y. Hsieh, N.H. Fischer, Volatiles from litter and soil associated with
Ceratiola ericoides, Phytochemistry 33 (1993) 299–302.
[40] G. Snatzke, U. Wagner, H.P. Wolff, Circulardichroism—LXXV: cottonogenic deri-
vatives of chiral bidentate ligands with the complex, Mo2(O2CCH3)4, Tetrahedron
37 (1981) 349–361.
[41] J. Frelek, M. Geiger, W. Voelter, Transition metal complexes as auxiliary chromo-
phores in chiroptical studies on carbohydrates, Curr. Org. Chem. 3 (1999) 117–146.
[42] L. Di Bari, G. Pescitelli, C. Pratelli, D. Pini, P. Salvadori, Determination of absolute
configuration of acyclic 1,2-diols with Mo2(OAc)4. 1. Snatzke's method revisited, J.
Organomet. Chem. 66 (2001) 4819–4825.
[9] M. You, J. Xiong, Y. Zhao, L. Cao, S. Wu, G. Xia, J. Hu, Glycosides from the me-
thanol extract of Notopterygium incisum, Planta Med. 77 (2011) 1939–1943.
[10] K. Xu, S. Jiang, H. Sun, Y. Zhou, X. Xu, S. Peng, L. Ding, New alkaloids from the
seeds of Notopterygium incisum, Nat. Prod. Res. 26 (2012) 1898–1903.
[11] S.Y. Tang, I.K. Cheah, H. Wang, B. Halliwell, Notopterygium forbesii Boiss extract and
its active constituent phenethyl ferulate attenuate pro-inflammatory responses to
lipopolysaccharide in RAW 264.7 macrophages. A “protective” role for oxidative
stress? Chem. Res. Toxicol. 22 (2009) 1473–1482.
[43] G. Pescitelli, L. Di Bari, Revision of the absolute configuration of preussilides a−F
established by the exciton chirality method, J. Nat. Prod. 80 (2017) 2855–2859.
[44] S. Yamaguchi, S. Muro, M. Kobayashi, M. Miyazawa, Y. Hirai, Absolute structures of
some naturally occurring isopropenyldihydrobenzofurans, remirol, remiridiol, an-
genomalin, and isoangenomalin, J. Organomet. Chem. 68 (2003) 6274–6278.
[45] S. Marumoto, M. Miyazawa, Structure–activity relationships for naturally occurring
coumarins as β-secretase inhibitor, Bioorg. Med. Chem. 20 (2012) 784–788.
[46] G. Kou, Y. Zhang, X. Yang, R. Rong, O-Methylnotopterol, a new natural product
from the roots and rhizomes of Notopterygium incisum, Zhongguo Zhong Yao Za Zhi
35 (2010) 1134–1136.
[12] H. Cao, R. Yu, Y. Choi, Z. Ma, H. Zhang, W. Xiang, D.Y. Lee, B.M. Berman,
K.D. Moudgil, H.H.S. Fong, R.B. van Breemen, Discovery of cyclooxygenase in-
hibitors from medicinal plants used to treat inflammation, Pharmacol. Res. 61
(2010) 519–524.
[13] M. Blunder, X. Liu, O. Kunert, N.A. Winkler, A. Schinkovitz, C. Schmiderer,
J. Novak, R. Bauer, Polyacetylenes from radix et rhizoma Notopterygii incisi with
an inhibitory effect on nitric oxide production in vitro, Planta Med. 80 (2014)
415–418.
[47] Y.Q. Xiao, X.H. Liu, Y.F. Sun, K. Baba, M. Taniguchi, M. Kozawa, Three new fur-
ocoumarins from Notopterygium incisum Ting, Chin. Chem. Lett. 5 (1994) 593–596.
[48] T. ONeill, J.A. Johnson, D. Webster, C.A. Gray, The Canadian medicinal plant
Heracleum maximum contains antimycobacterial diynes and furanocoumarins, J.
Ethnopharmacol. 147 (2013) 232–237.
[14] S. Wu, F. Pang, Y. Wen, H. Zhang, Z. Zhao, J. Hu, Antiproliferative and apoptotic
activities of linear furocoumarins from Notopterygium incisum on cancer cell lines,
Planta Med. 76 (2010) 82–85.
[15] Q.C. Chen, J.P. Lee, W.Y. Jin, U.J. Youn, H.J. Kim, I.S. Lee, X.F. Zhang, K.S. Song,
Y.H. Seong, K.H. Bae, Cytotoxic constituents from Angelicae sinensis radix, Arch.
Pharm. Res. 30 (2007) 565–569.
[49] T. Masuda, M. Takasugi, M. Anetai, Psoralen and other linear furanocoumarins as
phytoalexins in Glehnia littoralis, Phytochemistry 47 (1998) 13–16.
[50] R. Liu, Q. Sun, Y. Shi, L. Kong, Isolation and purification of coumarin compounds
from the root of Peucedanum decursivum (Miq.) Maxim by high-speed counter-cur-
rent chromatography, J. Chromatogr. A 1076 (2005) 127–132.
[16] H.R. Jin, J. Zhao, Z. Zhang, Y. Liao, C.Z. Wang, W.H. Huang, S.P. Li, T.C. He,
C.S. Yuan, W. Du, The antitumor natural compound falcarindiol promotes cancer
cell death by inducing endoplasmic reticulum stress, Cell Death Dis. 3 (2012) e376.
[17] C.Z. Wang, Z. Zhang, W.H. Huang, G.J. Du, X.D. Wen, T. Calway, C. Yu, R. Nass,
J. Zhao, W. Du, S.P. Li, C.S. Yuan, Identification of potential anticancer compounds
from Oplopanax horridus, Phytomedicine 20 (2013) 999–1006.
[51] J. Lemmich, S. Havelund, O. Thastrup, Dihydrofurocoumarin glucosides from
Angelica archangelica and Angelica silvestris, Phytochemistry 22 (1983) 553–555.
[52] O.S. Chaves, Y.C. Teles, M.M. Monteiro, L.D. Mendes Junior, M.F. Agra, V.A. Braga,
T.M. Silva, M.F. Souza, Alkaloids and phenolic compounds from Sida rhombifolia L.
(Malvaceae) and vasorelaxant activity of two indoquinoline alkaloids, Molecules 22
(2017) 94.
[18] S. Mitsui, K. Torii, H. Fukui, K. Tsujimura, A. Maeda, M. Nose, A. Nagatsu,
H. Mizukami, A. Morita, The herbal medicine compound falcarindiol from
Notopterygii rhizoma suppresses dendritic cell maturation, J. Pharmacol. Exp. Ther.
333 (2010) 954–960.
[53] R.S. Mali, K.N. Babu, P.G. Jagtap, Expedient syntheses of naturally occurring
(
)-3-benzylphthalides and ( )-3-aryl-8-hydroxy-3,4-dihydroisocoumarins:
[19] S. Yamaguchi, R. Miyakawa, S. Yonezawa, Y. Kawase, The synthesis of some di-
methylpyranocoumarins and isopropenyldihydrofuranocoumarins, Bull. Chem. Soc.
Jpn. 62 (1989) 3593–3597.
structure revision of the ( )-3-benzylphthalide isolated from Frullania falciloba, J.
Chem. Soc. Perkin Trans. 1 (2001) 3017–3019.
[54] A. Saeed, Synthesis of 6-O-methyl ether of scorzocreticin and scorzocreticoside I,
metabolites from Sorzonera cretica, J. Asian Nat. Prod. Res. 8 (2006) 417–423.
[55] S. Paraschos, P. Magiatis, E. Kalpoutzakis, C. Harvala, A. Skaltsounis, Three new
dihydroisocoumarins from the Greek endemic species Scorzonera cretica, J. Nat.
Prod. 64 (2001) 1585–1587.
[20] R.A. Heald, T.S. Dexheimer, H. Vankayalapati, A. Siddiqui-Jain, L.Z. Szabo,
M.C. Gleason-Guzman, L.H. Hurley, Conformationally restricted analogues of
psorospermin: design, synthesis, and bioactivity of natural-product-related bisfur-
anoxanthones, J. Med. Chem. 48 (2005) 2993–3004.
[21] A.K.F. Albertson, J. Lumb, A bio-inspired total synthesis of tetrahydrofuran lignans,
Angew. Chem. Int. Ed. 54 (2015) 2204–2208.
[56] A. Hisao, Die absolutkonfiguration des melleins, Bull. Chem. Soc. Jpn. 41 (1968)
2541.
[22] S. He, K. Zeng, Y. Jiang, P. Tu, Nitric oxide inhibitory constituents from the barks of
Cinnamomum cassia, Fitoterapia 112 (2016) 153–160.
[57] Y. Li, F. Luo, S. Peng, J. Liang, L. Ding, A new dihydroisocoumarin from the rhi-
zomes of Notopterygium forbesii, Nat. Prod. Res. 20 (2006) 860–865.
[23] Y. Jiang, K.W. Zeng, B. David, G. Massiot, Constituents of Vigna angularis and their
in vitro anti-inflammatory activity, Phytochemistry 107 (2014) 111–118.
72