Marine-Natural-Product Development: First Discovery of Nortopsentin Alkaloids as Novel Antiviral, Anti-phytopathogenic-Fungus, and Insecticidal Agents

Article abstract of DOI:10.1021/acs.jafc.8b00507

Nortopsentin alkaloids were found to have potent antiviral, anti-phytopathogenic-fungus, and insecticidal activities for the first time. Antiviral-activity tests revealed that these compounds were very sensitive to substituents, so a series of nortopsentin derivatives were designed, synthesized, and systematically evaluated for their antiviral activities against TMV, their fungicidal activities, and their insecticidal activities on the basis of a structural-diversity-derivation strategy. Compounds 2e (in vivo inactivation-, curative-, and protective-activity inhibitory rates of 50, 59, and 56%, respectively, at 500 μg/mL) and 2k (in vivo inactivation-, curative-, and protective-activity inhibitory rates of 60, 58, and 52%, respectively, at 500 μg/mL), with excellent antiviral activities and good physicochemical properties, emerged as new lead compounds for novel-antiviral-agent development. Further fungicidal-activity tests revealed that these alkaloids displayed broad-spectrum fungicidal activities. Compounds 2f, 2h, and 2j emerged as new lead compounds for antifungal-activity research. Additionally, all the compounds displayed good insecticidal activities against five kinds of insects, including Mythimna separate, Helicoverpa armigera, Ostrinia nubilalis, Plutella xylostella, and Culex pipiens pallens.

Full text of DOI:10.1021/acs.jafc.8b00507

Article
pubs.acs.org/JAFC
Cite This: J. Agric. Food Chem. XXXX, XXX, XXX−XXX
Marine-Natural-Product Development: First Discovery of
Nortopsentin Alkaloids as Novel Antiviral, Anti-phytopathogenic-
Fungus, and Insecticidal Agents
Xiaofei Ji,† Jincheng Guo,† Yuxiu Liu,† Aidang Lu,† Ziwen Wang,*,‡ Yongqiang Li,† Shaoxiang Yang,§
and Qingmin Wang*,†
†State Key Laboratory of Elemento-Organic Chemistry, Research Institute of Elemento-Organic Chemistry, College of Chemistry,
Collaborative Innovation Center of Chemical Science and Engineering, Nankai University, Tianjin 300071, China
‡Tianjin Key Laboratory of Structure and Performance for Functional Molecules, Key Laboratory of Inorganic−Organic Hybrid
Functional Materials Chemistry, Ministry of Education, College of Chemistry, Tianjin Normal University, Tianjin 300387, China
§Beijing Key Laboratory of Flavor Chemistry, Beijing Technology and Business University, Beijing 100048, China
S
* Supporting Information
ABSTRACT: Nortopsentin alkaloids were found to have potent antiviral, anti-phytopathogenic-fungus, and insecticidal activities
for the first time. Antiviral-activity tests revealed that these compounds were very sensitive to substituents, so a series of
nortopsentin derivatives were designed, synthesized, and systematically evaluated for their antiviral activities against TMV, their
fungicidal activities, and their insecticidal activities on the basis of a structural-diversity-derivation strategy. Compounds 2e
(in vivo inactivation-, curative-, and protective-activity inhibitory rates of 50, 59, and 56%, respectively, at 500 μg/mL) and 2k
(in vivo inactivation-, curative-, and protective-activity inhibitory rates of 60, 58, and 52%, respectively, at 500 μg/mL), with
excellent antiviral activities and good physicochemical properties, emerged as new lead compounds for novel-antiviral-agent
development. Further fungicidal-activity tests revealed that these alkaloids displayed broad-spectrum fungicidal activities.
Compounds 2f, 2h, and 2j emerged as new lead compounds for antifungal-activity research. Additionally, all the compounds
displayed good insecticidal activities against five kinds of insects, including Mythimna separate, Helicoverpa armigera, Ostrinia
nubilalis, Plutella xylostella, and Culex pipiens pallens.
KEYWORDS: nortopsentin alkaloids, natural product, antiviral activity, antifungal activity, insecticidal activity
Spongosorites ruetzleri.12 Nortopsentins A−C and the debromi-
INTRODUCTION
Natural products are substances produced by living organisms
■
nated derivative, nortopsentin D (Figure 1), were found to
display in vitro cytotoxicity against P388 cells and antifungal
activities against Candida albicans.12−14 Because of the consid-
erable activities shown, a series of nortopsentin analogues con-
taining five-membered heterocycles, such as bis-indolyl-
thiophenes,15 -furans,16 -pyrroles,17 -isoxazoles,16 and -thiazoles,18
were reported. Most of these analogues displayed good
antitumor activities. However, the application of these alkaloids
in plant-disease prevention has not been reported.
and are found in nature. Throughout history, natural products
have been used in a variety of roles, including as pest-control
agents,1−3 medicines4−6 and dyes. In addition, they can also be
used as inspiration in developing novel synthetic pesticides7,8
that possess improved efficacies beyond those of the natural
products.9−11
Nortopsentins A−C (Figure 1), a series of bis(indolyl)-
imidazoles, were isolated from the deep-water marine sponge
Plant diseases caused by viruses, fungi, bacteria, and oomycetes
continuously affect people’s daily lives and health. Tobacco
mosaic virus (TMV), so-called because it was discovered for the
first time on tobacco, was the first plant virus ever discovered. It is
a well-studied plant virus and is known to infect more than 400
plant species belonging to 36 families, including tobacco, tomato,
cucumber, pepper, and ornamental flowers.19 Ribavirin, a widely
used antiviral agent for preventing TMV disease, conveys an
antiviral effect of less than 50% at 500 μg/mL. Therefore, the
development of new, highly efficient antiviral agents is required.
Received: January 27, 2018
Revised: March 18, 2018
Accepted: April 3, 2018
Figure 1. Structures of nortopsentin alkaloids A−D.
© XXXX American Chemical Society
A
DOI: 10.1021/acs.jafc.8b00507
J. Agric. Food Chem. XXXX, XXX, XXX−XXX

Journal of Agricultural and Food Chemistry
Article
13C NMR (100 MHz, CDCl3) δ 186.8, 146.6, 135.4, 134.0, 133.0, 130.6,
128.6, 127.2, 126.4, 124.3, 120.0, 117.8, 116.3, 31.1, 21.7.
Taking into account the above findings, the discovery of novel
antiviral agents from natural products was carried out by our
group. A series of structurally novel natural products, such
as phenanthroindolizidines,20 harmine,21 polycarpine,22 and
matrine,23 have been found to have good antiviral activities. As
part of our ongoing project, nortopsentin alkaloids and their
derivatives were prepared and systematically evaluated for their
antiviral, anti-phytopathogenic-fungus, and insecticidal activities.
3-Cyano-6-bromoindole (7b). To a solution of 6-bromoindole
(19.4 g, 100 mmol) in DMF was added chlorosulfonamide isocyanate
(10.4 mL, 12 mmol) at −50 °C in an Ar atmosphere. The temperature
was raised to −10 °C, and then the solution was brought to room tem-
perature after it was stirred for 1.5 h. The resulting solution was poured
into ice water, let stand for 30 min, and filtered to give 7b. Yellow solid
1
(21.84 g, 99%); mp 189−190 °C; H NMR (400 MHz, DMSO-d6)
δ 12.33 (s, 1H), 8.29 (d, J = 2.8 Hz, 1H), 7.76 (d, J = 1.2 Hz, 1H), 7.61
(d, J = 8.4 Hz, 1H), 7.38 (dd, J = 8.4, 1.6 Hz, 1H).
MATERIALS AND METHODS
■
General Procedures for the Preparation of Compounds 8a
and 8b. Compounds 8a and 8b were prepared using procedures similar
to those used for the preparation of compounds 4a and 4b.
N-Tosyl-3-cyanoindole (8a). Brown solid; yield 99%; mp 159−160 °C;
1H NMR (400 MHz, CDCl3) δ 8.10 (s, 1H), 8.00 (d, J = 8.4 Hz, 1H),
7.83 (d, J = 8.0 Hz, 2H), 7.69 (d, J = 8.0 Hz, 1H), 7.44 (t, J = 7.6 Hz, 1H),
7.37 (t, J = 7.6 Hz, 1H), 7.30 (d, J = 8.4 Hz, 2H), 2.38 (s, 3H);
13C NMR (100 MHz, CDCl3) δ 146.4, 134.1, 133.7, 133.2, 130.4, 128.4,
127.3, 126.6, 124.8, 120.3, 113.8, 113.5, 93.7, 21.7.
N-Tosyl-3-cyano-6-bromoindole (8b). Brown solid; yield 98%; mp
171−172 °C; 1H NMR (400 MHz, CDCl3) δ 8.18 (d, J = 1.2 Hz, 1H),
8.06 (s, 1H), 7.83 (d, J = 8.4 Hz, 2H), 7.56 (d, J = 8.4 Hz, 1H), 7.50 (dd,
J = 8.4, 1.6 Hz, 1H), 7.35 (d, J = 8.4 Hz, 2H), 2.41 (s, 3H); 13C NMR
(100 MHz, CDCl3) δ 146.8, 134.3, 133.8, 133.5, 130.6, 128.3, 127.3,
127.2, 121.4, 120.4, 116.9, 113.0, 93.7, 21.8.
General Procedures for the Preparation of Compounds 9a,
9b, and 9e−9g. To a solution of NH2OH·HCl (30 mmol) in MeOH
(100 mL) was added NaHCO3 (30 mmol); the solution was stirred for
30 min, and then compound 8 (15 mmol) was added. The mixture was
heated at reflux for 5 h. After being cooled to room temperature, the
solution was concentrated in vacuo. Water was added to the residue,
which was then filtered to provide the corresponding compounds, 9a,
9b, and 9e−9g.
Instruments. The melting points of the compounds were tested on
an X-4 binocular microscope (Beijing Tech Instruments Company).
NMR spectra were obtained with a Bruker AV 400 spectrometer with
either CDCl3 or DMSO-d6 as the solvent. The chemical shifts (δ) were
given in parts per million (ppm) and were measured downfield from the
internal standard tetramethylsilane. High-resolution mass spectra were
obtained with an FT-ICR mass spectrometer (Ionspec, 7.0 T).
Compounds 10h−10m were obtained from J&K Scientific.
General Procedures for the Preparation of Compounds 4a
and 4b. To a solution of indole 3 (30 mmol) in CH3CN was added 60%
NaH (42 mmol) at 0 °C. The mixture was stirred for 10 min, and TsCl
(33 mmol) was added. Then, the mixture was allowed to reach room
temperature and was stirred for 4 h. The reaction was quenched with a
saturated aqueous solution of NH4Cl. The resulting solution was
extracted with ethyl acetate (3 × 100 mL). The combined organic
phases were washed with brine (100 mL), dried over anhydrous
Na2SO4, filtered, and concentrated in vacuo to provide the corre-
sponding compounds, 4a and 4b.
N-Tosylindole (4a). Brown solid; yield 99%; mp 76−78 °C; 1H NMR
(400 MHz, CDCl3) δ 7.99 (d, J = 8.4 Hz, 1H), 7.76 (d, J = 8.4 Hz, 2H),
7.56 (d, J = 3.6 Hz, 1H), 7.52 (d, J = 7.6 Hz, 1H), 7.36−7.27 (m, 1H),
7.24−7.18 (m, 3H), 6.65 (d, J = 3.6 Hz, 1H), 2.33 (s, 3H).
N-Tosyl-6-bromoindole (4b). Brown solid; yield 99%; mp 131−
132 °C; 1H NMR (400 MHz, CDCl3) δ 8.17 (s, 1H), 7.76 (d, J = 8.4 Hz,
2H), 7.53 (d, J = 3.6 Hz, 1H), 7.38 (d, J = 8.4 Hz, 1H), 7.33 (dd, J = 8.4,
1.6 Hz, 1H), 7.25 (d, J = 8.4 Hz, 2H), 6.61 (d, J = 3.6 Hz, 1H), 2.36 (s, 3H).
General Procedures for the Preparation of Compounds 5a
and 5b. To a mixture of AlCl3 (300 mmol) in dichloromethane
was added acetic anhydride (150 mmol) at 0 °C; then, compound 4
(50 mmol) was added, and the solution was allowed to reach room
temperature and was stirred for 2 h. The resulting mixture was poured
into ice water and extracted with dichloromethane (3 × 200 mL). The
combined organic phases were washed with brine (200 mL), dried over
anhydrous Na2SO4, filtered, and concentrated in vacuo to provide the
corresponding compounds, 5a and 5b.
N-Tosyl-3-acetylindole (5a). Red-brown solid; yield 99%; mp 143−
145 °C; 1H NMR (400 MHz, CDCl3) δ 8.33 (dd, J = 6.8, 1.6 Hz, 1H),
8.21 (s, 1H), 7.93 (dd, J = 7.0, 1.6 Hz, 1H), 7.84 (d, J = 8.4 Hz, 2H),
7.41−7.31 (m, 2H), 7.29 (d, J = 8.4 Hz, 2H), 2.58 (s, 3H), 2.37 (s, 3H).
N-Tosyl-3-acetyl-6-bromoindole (5b). Brown solid; yield 96%; mp
159−160 °C; 1H NMR (400 MHz, CDCl3) δ 8.19 (d, J = 8.8 Hz, 1H),
8.16 (s, 1H), 8.10 (d, J = 1.6 Hz, 1H), 7.83 (d, J = 8.4 Hz, 2H), 7.45 (dd,
J = 8.4, 1.6 Hz, 1H), 7.32 (d, J = 8.4 Hz, 2H), 2.56 (s, 3H), 2.40 (s, 3H).
General Procedures for the Preparation of Compounds 6a
and 6b. To a solution of 5 (15 mmol) in ethyl acetate was added CuBr2
(20 mmol). The mixture was heated at reflux for 5 h, then cooled to
room temperature, and extracted with dichloromethane (3 × 200 mL).
The combined organic phases were washed with brine (200 mL), dried
over anhydrous Na2SO4, filtered, and concentrated in vacuo. The resi-
due was purified by flash chromatography on a silica gel using petroleum
ether and ethyl acetate (5:1, v/v) as the eluent to give 6a and 6b.
N-Tosyl-3-(α-bromoacetyl)-indole (6a). Yellow solid; yield 89%; mp
118−119 °C; 1H NMR (400 MHz, CDCl3) δ 8.35 (s, 1H), 8.30 (d, J =
7.6 Hz, 1H), 7.93 (d, J = 7.6 Hz, 1H), 7.85 (d, J = 8.0 Hz, 2H), 7.45−7.33
(m, 2H), 7.30 (d, J = 8.0 Hz, 2H), 4.36 (s, 2H), 2.38 (s, 3H).
N′-Hydroxy-N-tosylindole-3-formamidine (9a). Yellow solid; yield
97%; mp 186−188 °C; 1H NMR (400 MHz, DMSO-d6) δ 9.75 (s, 1H),
8.31 (s, 1H), 8.15 (d, J = 8.0 Hz, 1H), 7.93 (d, J = 8.0 Hz, 1H), 7.88 (d,
J = 8.0 Hz, 2H), 7.40 (d, J = 8.0 Hz, 2H), 7.39−7.32 (m, 1H), 7.27 (t, J =
7.8 Hz, 1H), 5.91 (s, 2H), 2.32 (s, 3H); 13C NMR (100 MHz, DMSO-d6)
δ 147.8, 146.2, 135.0, 134.3, 130.8, 128.0, 127.2, 125.8, 125.6, 124.2,
123.9, 116.7, 113.5, 21.5.
N′-Hydroxy-N-tosyl-6-bromoindole-3-formamidine (9b). Yellow
1
solid; yield 99%; mp 178−179 °C; H NMR (400 MHz, DMSO-d6)
δ 9.81 (s, 1H), 8.37 (s, 1H), 8.12 (d, J = 8.4 Hz, 1H), 8.07 (d, J = 1.2 Hz,
1H), 7.91 (d, J = 8.0 Hz, 2H), 7.49 (dd, J = 8.4, 1.2 Hz, 1H), 7.44 (d, J =
8.4 Hz, 2H), 5.97 (s, 2H), 2.33 (s, 3H); 13C NMR (100 MHz, DMSO-d6)
δ 147.0, 146.0, 135.1, 133.6, 130.5, 126.9, 126.7, 126.6, 125.8, 125.2,
117.8, 116.0, 115.4, 21.0.
N-Hydeoxy-p-metoxybenzamidine (9e). White crystal; yield 99%;
mp 123−124 °C; 1H NMR (400 MHz, DMSO-d6) δ 9.47 (s, 1H), 7.61
(d, J = 8.4 Hz, 2H), 6.92 (d, J = 8.8 Hz, 2H), 5.73 (s, 2H), 3.77 (s, 3H);
13C NMR (100 MHz, DMSO-d6) δ 160.3, 151.0, 127.2, 126.2, 113.9, 55.6.
N-Hydeoxy-thiophene-3-formamidine (9f). Washy-blue crystal;
1
yield 99%; mp 81−82 °C; H NMR (400 MHz, DMSO-d6) δ 9.49
(s, 1H), 7.81 (d, J = 2.0 Hz, 1H), 7.50 (dd, J = 4.8, 2.8 Hz, 1H), 7.38−
7.30 (m, 1H), 5.79 (s, 2H); 13C NMR (100 MHz, DMSO-d6) δ 148.4,
135.8, 126.5, 125.7, 122.8.
N-Hydeoxy-hendecylamidine (9g). White solid; yield 99%; mp 79−
80 °C; 1H NMR (400 MHz, CDCl3) δ 8.29 (s, 1H), 4.54 (s, 2H), 2.13
(t, J = 7.6 Hz, 2H), 1.66−1.48 (m, 2H), 1.43−1.17 (m, 14H), 1.01−0.76
(m, 3H); 13C NMR (100 MHz, CDCl3) δ 154.2, 31.9, 31.3, 29.6, 29.5,
29.3, 29.1, 26.8, 22.7, 14.1.
General Procedures for the Preparation of Compounds 10a,
10b, and 10e−10g. To a solution of 9 (3 mmol) in MeOH (40 mL)
was added Raney nickel (0.5 g). The mixture was stirred for 12 h at room
temperature in a H2 atmosphere, concentrated, adjusted to pH 7 with 2
N NaOH, and then filtered to provide the corresponding compounds,
10a, 10b, and 10e−10g.
N-Tosyl-3-(α-bromoacetyl)-6-bromoindole (6b). Brown solid; yield
1
76%; mp 162−163 °C; H NMR (400 MHz, CDCl3) δ 8.30 (s, 1H),
8.16 (d, J = 8.4 Hz, 1H), 8.11 (s, 1H), 7.84 (d, J = 8.4 Hz, 2H), 7.48
(d, J = 8.4 Hz, 1H), 7.34 (d, J = 8.0 Hz, 2H), 4.33 (s, 2H), 2.40 (s, 3H);
N-Tosylindole-3-formamidine (10a). White solid; yield 92%; mp
184−185 °C; 1H NMR (400 MHz, DMSO-d6) δ 8.32 (s, 2H), 7.90 (s, 3H),
B
DOI: 10.1021/acs.jafc.8b00507
J. Agric. Food Chem. XXXX, XXX, XXX−XXX

Journal of Agricultural and Food Chemistry
Article
7.41 (s, 2H), 7.31 (d, J = 33.2 Hz, 2H), 6.49 (s, 2H), 3.36 (s, 1H), 2.32
(s, 3H); 13C NMR (100 MHz, DMSO-d6) δ 146.4, 134.6, 134.1, 130.9,
130.8, 128.6, 128.3, 127.5, 125.7, 124.3, 123.2, 117.1, 113.4, 21.5.
N-Tosyl-6-bromoindole-3-formamidine (10b). White solid; yield
92%; mp 196−197 °C; 1H NMR (400 MHz, DMSO-d6) δ 9.36 (s, 2H),
8.51 (s, 1H), 8.06−7.95 (m, 3H), 7.92 (d, J = 7.6 Hz, 1H), 7.50−7.40
(m, 3H), 7.37 (t, J = 7.6 Hz, 1H), 2.33 (s, 3H); 13C NMR (100 MHz,
DMSO-d6) δ 159.6, 146.3, 133.9, 133.4, 130.4, 129.67, 127.2, 126.6,
125.7, 124.2, 121.7, 113.6, 113.2, 21.0.
127.5, 127.4, 127.3, 127.2, 127.1, 125.7, 124.7, 123.8, 123.3, 118.9, 118.5,
116.3, 116.1, 21.5, 21.5; HR-MS (ESI): calcd for C33H25Br2N4O4S2
[M + H]+ 762.9678, found (ESI+) 762.9683.
Compound 2e. Yellow solid; yield 58%; mp 151−152 °C; 1H NMR
(400 MHz, DMSO-d6) δ 12.60 (s, 1H), 8.42−8.17 (m, 1H), 8.18−8.05
(m, 1H), 8.04−7.96 (m, 3H), 7.87 (d, J = 8.4 Hz, 2H), 7.85−7.74
(m, 1H), 7.47−7.39 (m, 1H), 7.38−7.31 (m, 3H), 7.07 (d, J = 8.8 Hz,
2H), 3.82 (s, 3H), 2.27 (s, 3H); 13C NMR (100 MHz, DMSO-d6)
δ 159.9, 146.4, 145.9, 135.2, 134.4, 130.7, 127.1, 127.0, 125.5, 124.2,
123.7, 122.3, 121.9, 114.6, 113.8, 55.7, 21.5; HR-MS (ESI): calcd for
C25H22N3O3S [M + H]+ 444.1376, found (ESI+) 444.1380.
4-Methoxybenzimidamide acetate (10e). White solid; yield 93%;
mp 231−233 °C; 1H NMR (400 MHz, CD3OD) δ 7.79 (d, J = 8.8 Hz,
2H), 7.12 (d, J = 8.8 Hz, 2H), 5.02 (s, 4H), 3.90 (s, 3H), 1.91 (s, 3H);
13C NMR (100 MHz, CD3OD) δ 166.3, 164.4, 129.5, 119.9, 114.3 54.9.
Thiophene-3-carboximidamide acetate (10f). Washy-blue crystal;
1
Compound 2f. Pink solid; yield 58%; mp 165−166 °C; H NMR
(400 MHz, DMSO-d6) δ 12.72 (s, 1H), 8.20 (d, J = 4.4 Hz, 1H), 8.12
(s, 1H), 8.06−7.97 (m, 2H), 7.86 (d, J = 8.0 Hz, 2H), 7.80 (s, 1H),
7.76−7.70 (m, 1H), 7.69−7.62 (m, 1H), 7.46−7.39 (m, 1H), 7.39−7.34
(m, 1H), 7.32 (d, J = 8.0 Hz, 2H), 2.25 (s, 3H); 13C NMR (100 MHz,
DMSO-d6) δ 145.9, 143.5, 135.2, 134.4, 133.1, 130.7, 128.7, 127.6,
127.1, 126.3, 125.5, 124.2, 122.2, 122.2, 121.9, 113.8, 21.4; HR-MS
(ESI): calcd for C22H18N3O2S2 [M + H]+ 420.0835, found (ESI+)
420.0832.
1
yield 94%; mp 233−234 °C; H NMR (400 MHz, CD3OD) δ 8.40
(s, 1H), 7.73−7.68 (m, 1H), 7.59 (d, J = 4.8 Hz, 1H), 4.96 (s, 4H), 1.95
(s, 3H); 13C NMR (100 MHz, CD3OD) δ 160.79, 131.95, 129.40,
128.20, 125.48.
Hendecylamidine (10g). White solid; yield 99%; mp 74−75 °C;
1H NMR (400 MHz, DMSO-d6) δ 2.29 (t, J = 7.2 Hz, 2H), 1.91 (s, 3H),
1.57 (s, 2H), 1.39−0.99 (m, 14H), 1.02−0.68 (m, 3H); 13C NMR
(100 MHz, DMSO-d6) δ 171.4, 32.1, 31.3, 28.9, 28.8, 28.7, 28.5, 28.2,
26.2, 22.1, 13.9.
Compound 2g. Yellow solid; yield 43%; mp 195−196 °C; 1H NMR
(400 MHz, DMSO-d6) δ 11.96 (s, 1H), 8.07 (d, J = 7.6 Hz, 1H), 7.97
(d, J = 8.4 Hz, 1H), 7.91 (s, 1H), 7.84 (d, J = 8.0 Hz, 2H), 7.52 (s, 1H),
7.38 (t, J = 7.6 Hz, 1H), 7.35 (d, J = 8.4 Hz, 2H), 7.31 (t, J = 7.6 Hz, 1H),
2.65 (t, J = 7.6 Hz, 2H), 2.28 (s, 3H), 1.76−1.61 (m, 2H), 1.38−1.15
(m, 14H), 0.89−0.78 (m, 3H); 13C NMR (100 MHz, DMSO-d6)
δ 148.9, 145.9, 135.2, 134.5, 130.7, 128.7, 127.1, 125.4, 124.1, 122.1,
121.3, 113.8, 31.8, 29.4, 29.2, 29.2, 29.2, 28.5, 28.4, 22.6, 21.5, 14.4; HR-MS
(ESI): calcd for C28H36N3O2S [M + H]+ 478.2523, found (ESI+) 478.2529.
Compound 2h. Yellow solid; yield 82%; mp 249−251 °C; 1H NMR
(400 MHz, DMSO-d6 + 1% TFA) δ 8.52 (s, 1H), 8.28 (s, 1H), 8.21−
8.08 (m, 3H), 8.05 (d, J = 8.0 Hz, 1H), 7.93 (d, J = 7.6 Hz, 2H), 7.77−
7.58 (m, 3H), 7.53−7.47 (m, 1H), 7.47−7.35 (m, 3H), 2.32 (s, 3H);
13C NMR (100 MHz, DMSO-d6 + 1% TFA) δ 146.2, 145.5, 135.0,
134.2, 130.8, 129.6, 129.5, 127.9, 127.2, 127.0, 126.6, 126.0, 124.5, 124.0,
121.8, 118.1, 113.9, 113.6, 21.5; HR-MS (ESI): calcd for C24H20N3O2S
[M + H]+ 414.1271, found (ESI+) 414.1273.
General Procedures for the Preparation of N,N′-Ditosylnor-
topsentins 2a−2m. To a solution of 6 (3 mmol) in 3:1 THF−H2O
(40 mL), KHCO3 (9 mmol) was added. The mixture was stirred at
reflux, and a solution of compound 10 (3 mmol) in THF was added. The
mixture was heated at reflux for 4 h and then cooled to room tempera-
ture. The resulting solution was extracted with ethyl acetate (3 × 100 mL).
The combined organic phases were washed with brine (200 mL), dried
over anhydrous Na2SO4, filtered, and concentrated in vacuo. The resi-
due was purified by flash chromatography on a silica gel using petroleum
ether and ethyl acetate (3:1, v/v) as the eluent to give 2a−2m.
N,N′-Ditosylnortopsentin D (2a). Yellow solid; yield 56%; mp 163−
164 °C; 1H NMR (400 MHz, DMSO-d6 + 1% TFA) δ 8.60 (s, 1H), 8.51
(d, J = 4.0 Hz, 1H), 8.32 (s, 1H), 8.19 (d, J = 4.4 Hz, 1H), 8.10−7.99
(m, 3H), 7.91 (d, J = 6.8 Hz, 2H), 7.88 (d, J = 6.8 Hz, 1H), 7.54−7.35
(m, 5H), 7.33 (d, J = 6.4 Hz, 2H), 7.28 (d, J = 4.8 Hz, 2H), 2.23 (s, 3H),
2.20 (s, 3H); 13C NMR (100 MHz, DMSO-d6 + 1% TFA) δ 146.3,
146.0, 140.7, 135.2, 134.9, 134.3, 134.1, 130.8, 130.7, 128.3, 127.9, 127.3,
127.2, 126.2, 125.8, 124.6, 124.4, 123.0, 122.8, 121.9, 113.9, 113.7, 21.4,
21.4; HR-MS (ESI): calcd for C33H27N4O4S2 [M + H]+ 607.1468, found
(ESI+) 607.1464.
Compound 2i. Yellow solid; yield 77%; mp 236−237 °C; 1H NMR
(400 MHz, DMSO-d6 + 1% TFA) δ 8.43 (s, 1H), 8.40 (s, 1H), 8.36−
8.32 (m, 3H), 8.23 (d, J = 7.6 Hz, 1H), 8.12 (s, 1H), 8.03 (d, J = 8.0 Hz,
1H), 7.92 (d, J = 8.4 Hz, 2H), 7.50−7.42 (m, 2H), 7.42−7.36 (m, 2H),
2.30 (s, 3H); 13C NMR (100 MHz, DMSO-d6 + 1% TFA) δ 147.8,
146.2, 143.7, 135.0, 134.3, 130.8, 129.4, 128.1, 127.2, 127.0, 125.9, 124.9,
124.5, 123.9, 123.7, 122.0, 119.7, 117.6, 114.7, 113.8, 21.5; HR-MS
(ESI): calcd for C24H19N4O4S [M + H]+ 459.1122, found (ESI+) 459.1121.
Compound 2j. Yellow solid; yield 53%; mp 142−144 °C; 1H NMR
(400 MHz, DMSO-d6 + 1% TFA) δ 8.94 (d, J = 6.0 Hz, 2H), 8.44 (d, J =
6.4 Hz, 2H), 8.39−8.28 (m, 2H), 8.24 (s, 1H), 8.03 (d, J = 8.4 Hz, 1H),
7.91 (d, J = 8.4 Hz, 2H), 7.50−7.43 (m, 1H), 7.43−7.33 (m, 3H), 2.30
(s, 3H); 13C NMR (100 MHz, DMSO-d6 + 1% TFA) δ 146.1, 144.4,
142.8, 141.8, 135.7, 135.1, 134.3, 130.8, 128.4, 127.2, 125.8, 124.4, 123.5,
122.3, 121.0, 118.1, 115.8, 115.1, 113.8, 100.0, 21.5; HR-MS (ESI):
calcd for C23H19N4O2S [M + H]+ 415.1223, found (ESI+) 415.1225.
Compound 2k. White solid; yield 49%; mp 247−248 °C; 1H NMR
(400 MHz, DMSO-d6 + 1% TFA) δ 8.18 (s, 1H), 8.06 (d, J = 8.0 Hz,
1H), 7.98 (d, J = 8.4 Hz, 1H), 7.88 (d, J = 8.4 Hz, 2H), 7.74 (s, 1H),
7.45−7.40 (m, 1H), 7.40−7.33 (m, 3H), 2.30 (s, 3H), 1.41 (s, 9H);
13C NMR (100 MHz, DMSO-d6 + 1% TFA) δ 156.0, 146.1, 135.0,
134.3, 130.8, 128.3, 127.2, 125.7, 124.3, 122.9, 121.9, 113.8, 33.1, 29.5,
21.5; HR-MS (ESI): calcd for C22H24N3O2S [M + H]+ 394.1584, found
(ESI+) 394.1584.
N,N′-Ditosylnortopsentin B (2b). Yellow solid; yield 66%; mp
1
269 °C (dec); H NMR (400 MHz, DMSO-d6 + 1% TFA) δ 8.57
(s, 1H), 8.43 (d, J = 8.4 Hz, 1H), 8.26 (s, 1H), 8.22−8.11 (m, 2H),
8.08−8.00 (m, 2H), 7.97 (d, J = 7.6 Hz, 2H), 7.91 (d, J = 7.6 Hz, 2H),
7.66 (d, J = 8.4 Hz, 1H), 7.52−7.43 (m, 3H), 7.41 (d, J = 8.4 Hz, 1H),
7.38 (d, J = 7.6 Hz, 2H), 2.34 (s, 3H), 2.30 (s, 3H); 13C NMR
(100 MHz, DMSO-d6 + 1% TFA) δ 146.7, 146.0, 140.1, 135.5, 135.1,
134.4, 133.9, 131.0, 130.7, 128.2, 127.8, 127.3, 127.2, 127.0, 126.3, 125.8,
124.6, 124.4, 123.0, 121.8, 119.0, 116.2, 113.9, 112.1, 21.5, 21.4; HR-MS
(ESI): calcd for C33H26BrN4O4S2 [M + H]+ 685.0573, found (ESI+)
685.0580.
N,N′-Ditosylnortopsentin C (2c). Yellow solid; yield 67%; mp 197−
198 °C; 1H NMR (400 MHz, DMSO-d6 + 1% TFA) δ 8.56 (s, 1H), 8.45
(d, J = 6.4 Hz, 1H), 8.31 (s, 1H), 8.19 (s, 1H), 8.13 (d, J = 7.2 Hz, 1H),
8.06 (d, J = 7.2 Hz, 1H), 7.98 (s, 1H), 7.96−7.81 (m, 4H), 7.56 (d, J =
8.0 Hz, 1H), 7.53−7.41 (m, 2H), 7.41−7.31 (m, 4H), 2.29 (s, 6H);
13C NMR (100 MHz, DMSO-d6 + 1% TFA) δ 146.3, 140.5, 135.8,
134.8, 134.2, 134.1, 130.6, 130.5, 127.6, 127.3, 127.2, 127.0, 126.0, 125.8,
124.4, 123.5, 123.3, 122.5, 118.5, 116.3, 113.59, 21.0; HR-MS (ESI):
calcd for C33H26BrN4O4S2 [M + H]+ 685.0573, found (ESI+) 685.0572.
N-,N′-Ditosylnortopsentin A (2d). Yellow solid; yield 59%; mp 293−
294 °C; 1H NMR (400 MHz, DMSO-d6 + 1% TFA) δ 8.52 (s, 1H), 8.44
(d, J = 8.4 Hz, 1H), 8.25 (s, 1H), 8.19−8.09 (m, 3H), 7.96 (d, J = 6.8 Hz,
2H), 7.94−7.88 (m, 3H), 7.61 (dd, J = 8.4, 1.6 Hz, 1H), 7.55 (dd, J = 8.4,
1.6 Hz, 1H), 7.42 (d, J = 8.4 Hz, 2H), 7.37 (d, J = 8.4 Hz, 2H), 2.30
(s, 3H), 2.27 (s, 3H); 13C NMR (100 MHz, DMSO-d6 + 1% TFA)
δ 146.7, 146.4, 140.4, 135.8, 135.5, 134.1, 133.9, 131.1, 130.9, 127.9,
Compound 2l. White solid; yield 77%; mp 265−266 °C; 1H NMR
(400 MHz, DMSO-d6 + 1% TFA) δ 8.17 (s, 1H), 8.01 (d, J = 8.0 Hz,
2H), 7.94−7.81 (m, 3H), 7.49−7.41 (m, 1H), 7.41−7.31 (m, 3H), 2.52
(s, 3H), 2.30 (s, 3H); 13C NMR (100 MHz, DMSO-d6 + 1% TFA)
δ 145.7, 144.6, 134.5, 133.7, 130.3, 127.2, 127.0, 126.7, 125.5, 124.0,
122.7, 121.1, 115.4, 113.4, 21.0, 12.4; HR-MS (ESI): calcd for
C19H18N3O2S [M + H]+ 352.1114, found (ESI+) 352.1121.
Compound 2m. Yellow solid; yield 44%; mp 243−244 °C; 1H NMR
(400 MHz, DMSO-d6 + 1% TFA) δ 8.42 (s, 1H), 8.14−8.09 (m, 1H),
C
DOI: 10.1021/acs.jafc.8b00507
J. Agric. Food Chem. XXXX, XXX, XXX−XXX

Journal of Agricultural and Food Chemistry
Article
8.04 (d, J = 8.2 Hz, 1H), 7.97 (d, J = 7.9 Hz, 1H), 7.92 (d, J = 8.2 Hz,
2H), 7.49 (t, J = 7.6 Hz, 1H), 746−7.38 (m, 3H), 2.33 (s, 4H), 1.35−
1.25 (m, 4H); 13C NMR (100 MHz, DMSO-d6 + 1% TFA) δ 150.4,
146.1, 135.0, 134.2, 130.7, 127.9, 127.8, 127.2, 125.8, 124.4, 123.0, 121.7,
115.9, 113.9, 21.5, 8.7, 8.5; HR-MS (ESI): calcd for C21H20N3O2S
[M + H]+ 378.1271, found (ESI+) 378.1274.
General Procedures for the Preparation of Compounds 1a−1d,
1f, 1g, 1l, and 1m. A solution of sodium (9.0 mmol) and naphthalene
(7.5 mmol) in dry THF (20 mL) was stirred for 2 h at room temperature
and then cooled to −78 °C; then, a solution of 2 (1.0 mmol) was added.
The mixture was stirred at −78 °C for 2 h and then extracted with ethyl
acetate (3 × 50 mL). The combined organic phases were washed with
brine (100 mL), dried over anhydrous Na2SO4, filtered, and
concentrated in vacuo. The residue was purified by flash chromatog-
raphy on a silica gel using dichloromethane and methanol (20:1, v/v) as
the eluent to give 1.
116.2, 111.4, 111.3, 107.7, 106.2; HR-MS (ESI): calcd for C19H15N4
[M + H]+ 299.1291, found (ESI+) 299.1293.
Nortopsentin B (1b). Purple solid; yield 97%; mp 224−225 °C;
1H NMR (400 MHz, DMSO-d6) δ 12.20 (s, 1H), 11.48 (s, 1H), 11.20
(s, 1H), 8.41 (d, J = 8.4 Hz, 1H), 8.07−7.90 (m, 2H), 7.74 (s, 1H), 7.65
(s, 1H), 7.51−7.37 (m, 2H), 7.28 (d, J = 8.0 Hz, 1H), 7.19−7.06
(m, 2H); 13C NMR (100 MHz, DMSO-d6) δ 142.1, 137.1, 136.4, 124.7,
124.0, 124.0, 123.1, 122.5, 121.8, 121.3, 120.0, 119.1, 114.6, 114.2, 111.6,
107.7; HR-MS (ESI): calcd for C19H14BrN4 [M + H]+ 377.0496, found
(ESI+) 377.0395.
Nortopsentin C (1c). Purple solid; yield 79%; mp 170−171 °C;
1H NMR (400 MHz, DMSO-d6) δ 12.28 (s, 1H), 11.39 (s, 1H), 11.33
(s, 1H), 8.42 (d, J = 6.8 Hz, 1H), 8.01 (d, J = 4.0 Hz, 1H), 7.93 (s, 1H),
7.77 (s, 1H), 7.62 (s, 1H), 7.50−7.39 (m, 2H), 7.23 (d, J = 8.0 Hz, 1H),
7.20−7.12 (m, 2H); 13C NMR (100 MHz, CD3OD) δ 142.6, 137.6,
136.8, 129.7, 125.7, 124.4, 123.8, 123.4, 122.7, 122.5, 120.5, 120.4, 119.2,
115.2, 114.4, 114.2, 111.6, 106.2, 103.3; HR-MS (ESI): calcd for
C19H14BrN4 [M + H]+ 377.0396, found (ESI+) 377.0394.
Nortopsentin D (1a). Deep-red solid; yield 80%; mp 155−157 °C;
1H NMR (400 MHz, CD3OD) δ 8.21−8.13 (m, 1H), 7.86 (d, J = 7.6 Hz,
1H), 7.78 (s, 1H), 7.69 (s, 1H), 7.48−7.39 (m, 2H), 7.37 (s, 1H), 7.23−
7.11 (m, 4H); 13C NMR (100 MHz, CD3OD) δ 143.3, 136.9, 136.7,
131.1, 125.1, 124.9, 124.1, 122.1, 121.8, 121.6, 120.0, 119.8, 119.4, 119.2,
Nortopsentin A (1d). Purple solid; yield 68%; mp 166−167 °C;
1H NMR (400 MHz, DMSO-d6) δ 12.19 (s, 1H), 11.49 (s, 1H), 11.33
(s, 1H), 8.41 (d, J = 8.4 Hz, 1H), 8.00 (d, J = 6.8 Hz, 1H), 7.94 (s, 1H),
Figure 2. Synthesis of intermediate 6.
Figure 3. Synthesis of intermediates 10a and 10b.
Figure 4. Synthesis of intermediates 10e−10g.
D
DOI: 10.1021/acs.jafc.8b00507
J. Agric. Food Chem. XXXX, XXX, XXX−XXX

Journal of Agricultural and Food Chemistry
Article
Figure 5. Synthesis of nortopsentin alkaloids A−D (1a−1d).
Figure 6. Synthesis of 1e−1m.
Table 1. In Vitro Antiviral Activities of Ribavirin and Nortopsentins in Series 1 and 2 against TMV
a
a
compd
concn (μg/mL)
inhibition rate (%)
compd
2b
concn (μg/mL)
inhibition rate (%)
1a
500
100
500
100
500
100
500
100
500
100
500
100
500
100
500
100
500
100
500
100
500
100
500
100
500
100
500
100
36
11
14
0
2
1
2
500
100
500
100
500
100
500
100
500
100
500
100
500
100
500
100
500
100
500
100
500
100
500
100
500
100
48
0
2
1b
1c
1d
1e
1f
2c
42
21
20
0
1
2
2
44
0
3
2d
2e
35
17
39
14
58
14
40
0
2
2
1
2
3
1
2
53
18
40
0
1
1
2
2f
2g
29
0
1
1g
1h
1i
2h
2i
59
12
25
0
2
2
1
41
0
2
1
1
34
0
2j
19
0
2
1j
22
0
2k
41
17
43
25
53
4
2
1
2
2
1
1
1
2
1k
1l
35
13
51
19
36
8
3
1
2
1
2
1
2
2l
2m
ribavirin
1m
2a
41
9
19
0
a
Averages of three replicates. All the results are expressed as means SD.
7.76 (s, 1H), 7.64 (d, J = 13.6 Hz, 2H), 7.44 (s, 1H), 7.29 (d, J = 8.4 Hz, 1H),
7.23 (d, J = 8.0 Hz, 1H); 13C NMR (100 MHz, CD3OD) δ 142.8, 137.8,
137.6, 124.5, 124.4, 123.2, 123.0, 122.4, 115.1, 114.7, 114.6, 108.1; HR-MS
(ESI): calcd for C19H13Br2N4 [M + H]+ 454.9501, found (ESI+) 454.9493.
General Procedures for the Preparation of Compounds 1e
and 1h−1k. To a solution of compound 2 (1 mmol) in MeOH
(50 mL) and THF (20 mL) was added 2 N NaOH (30 mL). The
mixture was heated at reflux for 2 h in an Ar atmosphere, cooled to room
E
DOI: 10.1021/acs.jafc.8b00507
J. Agric. Food Chem. XXXX, XXX, XXX−XXX

Journal of Agricultural and Food Chemistry
Article
temperature, and extracted with ethyl acetate (3 × 50 mL). The
combined organic phases were washed with brine (100 mL), dried over
anhydrous Na2SO4, filtered, and concentrated in vacuo. The residue was
purified by flash chromatography on a silica gel using dichloromethane
and methanol (50:1, v/v) as the eluent to give 1.
132.3, 129.9, 127.4, 125.6, 124.5, 123.7, 122.8, 120.7, 119.7, 117.4, 114.6,
112.7, 102.7; HR-MS (ESI): calcd for C17H14N3 [M + H]+ 260.1182,
found (ESI+) 260.1184.
1
Compound 1i. Red solid; yield 90%; mp 244−246 °C; H NMR
(400 MHz, DMSO-d6 + 1% TFA) δ 11.55 (s, 1H), 8.42 (d, J = 8.4 Hz,
2H), 8.32 (d, J = 8.4 Hz, 2H), 8.01 (d, J = 7.6 Hz, 1H), 7.94 (s, 1H), 7.92
(s, 1H), 7.50 (d, J = 7.6 Hz, 1H), 7.29−7.19 (m, 1H), 7.19−7.11
(m, 1H); 13C NMR (100 MHz, DMSO-d6 + 1% TFA) δ 147.5, 142.4,
136.9, 134.1, 133.7, 126.8, 124.9, 124.2, 122.4, 120.3, 120.2, 112.5, 106.1,
100.0; HR-MS (ESI): calcd for C17H13N4O2 [M + H]+ 305.1033, found
(ESI+) 305.1035.
Compound 1e. Brown solid; yield 86%; mp 217−218 °C; 1H NMR
(400 MHz, DMSO-d6 + 1% TFA) δ 14.47 (s, TFA and NH) 11.73
(s, 1H), 8.16−8.06 (m, 3H), 8.05 (d, J = 2.0 Hz, 1H), 7.94 (d, J = 8.0 Hz,
1H), 7.53 (d, J = 8.0 Hz, 1H), 7.30−7.23 (m, 3H), 7.22−7.15 (m, 1H),
3.89 (s, 3H); 13C NMR (100 MHz, DMSO-d6 + 1% TFA) δ 160.3,
144.1, 136.4, 131.0, 127.3, 124.4, 123.3, 121.7, 120.2, 119.7, 119.6, 115.4,
114.4, 111.9, 105.9, 55.4; HR-MS (ESI): calcd for C18H16N3O [M + H]+
290.1288, found (ESI+) 290.1294.
Compound 1j. Orange-yellow solid; yield 74%; mp 244−246 °C;
1H NMR (400 MHz, DMSO-d6) δ 12.87 (s, 1H), 11.31 (s, 1H), 8.88−
8.50 (m, 2H), 8.03 (s, 1H), 8.00−7.90 (m, 2H), 7.81 (s, 1H), 7.64
(s, 1H), 7.46 (d, J = 7.6 Hz, 1H), 7.22−7.15 (m, 1H), 7.15−7.08
(m, 1H); 13C NMR (100 MHz, DMSO-d6) δ 150.1, 142.3, 137.3, 136.4,
124.7, 122.6, 121.5, 120.0, 119.4, 118.7, 111.7; HR-MS (ESI): calcd for
C16H13N4 [M + H]+ 261.1135, found (ESI+) 261.1137.
Compound 1f. Brown oil; yield 93%; 1H NMR (400 MHz, CD3OD)
δ 7.92 (d, J = 2.0 Hz, 1H), 7.83 (d, J = 8.0 Hz, 1H), 7.69 (s, 1H), 7.67
(d, J = 5.2 Hz, 1H), 7.47 (dd, J = 4.8, 2.8 Hz, 1H), 7.43 (d, J = 8.0 Hz,
1H), 7.36 (s, 1H), 7.21−7.15 (m, 1H), 7.15−7.08 (m, 1H); 13C NMR
(100 MHz, CD3OD) δ 142.6, 136.9, 131.6, 131.6, 126.4, 125.4, 125.1,
122.0, 121.8, 121.7, 119.5, 119.2, 117.4, 111.4, 107.3; HR-MS (ESI):
calcd for C15H12N3S [M + H]+ 266.0746, found (ESI+) 266.0748.
Compound 1g. Brown oil; yield 84%; 1H NMR (400 MHz, CD3OD)
δ 7.68−7.57 (m, 1H), 7.44 (d, J = 2.8 Hz, 1H), 7.30−7.21 (m, 1H), 7.04
(d, J = 3.2 Hz, 1H), 7.02−6.88 (m, 2H), 2.55 (s, 2H), 1.54 (s, 2H), 1.05
(s, 14H), 0.76−0.66 (m, 3H); 13C NMR (100 MHz, CD3OD) δ 148.0,
136.9, 130.7, 124.9, 121.5, 119.3, 119.2, 115.1, 111.3, 107.7, 31.8, 29.4,
29.4, 29.2, 29.1, 29.1, 28.5, 27.6, 22.5, 13.3; HR-MS (ESI): calcd for
C21H30N3 [M + H]+ 324.2434, found (ESI+) 324.2436.
Compound 1k. Orange-yellow solid; yield 77%; mp 106−108 °C;
1H NMR (400 MHz, DMSO-d6) δ 11.15 (s, 1H), 7.91 (d, J = 7.6 Hz,
1H), 7.64 (s, 1H), 7.42 (d, J = 8.0 Hz, 1H), 7.22 (s, 1H), 7.14 (t, J =
7.2 Hz, 1H), 7.08 (t, J = 7.2 Hz, 1H), 1.39 (s, 9H); 13C NMR (100 MHz,
DMSO-d6) δ 154.5, 136.4, 124.8, 121.6, 121.1, 119.9, 118.9, 111.5, 32.5,
29.6; HR-MS (ESI): calcd for C15H18N3 [M + H]+ 240.1595, found
(ESI+) 240.1496.
1
Compound 1l. Brown solid; yield 87%; mp 96−98 °C; H NMR
(400 MHz, DMSO-d6) δ 12.03 (s, 1H), 11.43 (s, 1H), 7.87 (d, J =
8.0 Hz, 1H), 7.73 (s, 1H), 7.52 (s, 1H), 7.46 (d, J = 8.0 Hz, 1H), 7.23−
7.14 (m, 1H), 7.14−7.06 (m, 1H), 2.49 (s, 3H); 13C NMR (100 MHz,
DMSO-d6) δ 143.7, 136.9, 130.0, 124.7, 123.1, 122.2, 120.0, 114.0,
112.3, 106.5, 13.0; HR-MS (ESI): calcd for C12H12N3 [M + H]+
198.1026, found (ESI+) 198.1026.
Compound 1h. White solid; yield 82%; mp 205 °C (dec); 1H NMR
(400 MHz, DMSO-d6 + 1% TFA) δ 11.79 (s, 1H), 8.17 (s, 1H), 8.16−
8.12 (m, 2H), 8.10 (d, J = 2.0 Hz, 1H), 7.97 (d, J = 7.6 Hz, 1H), 7.80−
7.64 (m, 3H), 7.55 (d, J = 7.6 Hz, 1H), 7.31−7.24 (m, 1H), 7.24−7.18
(m, 1H); 13C NMR (100 MHz, DMSO-d6 + 1% TFA) δ 143.5, 136.9,
Table 2. In Vivo Antiviral Activities of Ribavirin and Nortopsentins in Series 1 and 2 against TMV
inactivation
a
curative effect
protective
inactivation
a
curative effect
protective
a
a
a
a
compd concn (μg/mL)
effect (%)
(%)
effect (%)
compd
2b
concn (μg/mL)
effect (%)
(%)
effect (%)
1a
1b
1c
1d
1e
1f
500
100
500
100
500
100
500
100
500
100
500
100
500
100
500
100
500
100
500
100
500
100
500
100
500
100
500
100
54
26
32
0
3
3
2
47
18
25
0
4
1
3
49
13
37
5
1
2
1
1
2
1
4
3
2
3
2
1
2
5
5
1
5
500
100
500
100
500
100
500
100
500
100
500
100
500
100
500
100
500
100
500
100
500
100
500
100
500
100
43
7
2
1
4
4
3
35
8
5
2
2
1
5
47
16
50
12
33
0
3
1
3
1
1
2c
58
15
28
0
56
21
23
0
35
0
1
31
0
2
37
9
2d
2e
48
16
49
9
3
1
3
1
3
2
1
1
4
2
1
51
12
45
12
51
30
48
10
46
18
37
5
2
1
5
2
1
1
3
4
3
1
4
1
1
2
2
3
1
2
4
44
10
51
19
49
16
46
11
43
24
41
0
50
18
44
0
3
1
3
59
21
41
15
39
0
4
2
4
3
1
56
30
50
17
45
0
2
1
5
1
2
2f
58
22
54
20
54
27
43
0
2g
42
4
3
1
3
1
2
2
5
1g
1h
1i
2h
2i
58
20
35
6
50
17
32
0
4
1
2
54
27
40
0
4
3
3
2j
29
0
34
0
3
26
0
3
1j
41
15
51
17
51
19
36
8
4
1
4
1
3
1
5
2
1
33
9
34
0
2
2k
60
26
53
8
3
1
3
4
5
1
1
2
58
18
49
17
48
13
37
13
3
2
2
1
3
1
1
1
52
29
57
19
40
0
4
2
1
1
2
1k
1l
44
15
55
17
41
0
48
23
59
25
39
11
29
0
3
3
4
4
3
1
3
2l
2m
ribavirin
40
7
1m
2a
41
9
38
15
2
2
31
0
25
4
3
1
a
Averages of three replicates. All the results are expressed as means SD.
F
DOI: 10.1021/acs.jafc.8b00507
J. Agric. Food Chem. XXXX, XXX, XXX−XXX

Journal of Agricultural and Food Chemistry
Article
G
DOI: 10.1021/acs.jafc.8b00507
J. Agric. Food Chem. XXXX, XXX, XXX−XXX

Journal of Agricultural and Food Chemistry
Article
1
Compound 1m. Brown solid; yield 92%; mp 96−98 °C; H NMR
(400 MHz, CD3OD) δ 7.77 (d, J = 8.0 Hz, 1H), 7.56 (s, 1H), 7.40 (d, J =
8.0 Hz, 1H), 7.18−7.12 (m, 2H), 7.1−7.07 (m, 1H), 2.06−1.96
(m, 1H), 0.97−0.92 (m, 4H); 13C NMR (100 MHz, CD3OD) δ 149.5,
136.8, 130.5, 127.4, 125.4, 125.0, 121.5, 121.4, 119.3, 119.1, 115.6, 111.2,
107.9, 8.3, 6.5; HR-MS (ESI): calcd for C14H14N3 [M + H]+ 224.1182,
found (ESI+) 224.1187.
others, which indicated that the substituents at the 7-position and
20-position exhibited synergistic effects. When the 7-position is
bromine, and the 20-position is hydrogen, the structure is bad for
antiviral activity. However, the introduction of Ts groups at the
1-position and 17-position changed this activity law (antiviral
effects: 1a > 2a, 1b < 2b, 1c ≈ 2c, 1d > 2d), which indicated that
these compounds were very sensitive to substituents, thus increas-
ing the molecular regulation. The above results also showed that
the influence of indole unit at the 10-position is more significant
than that at the 12-position. A series of 10-position-indole-unit-
replaced derivatives, 1e−1m, were prepared and evaluated for
their antiviral activities. Compounds 1e and 1h showed activities
similar to that of 1a and slightly higher than that of 1i. Com-
pounds 2e and 2h showed activities significantly higher than
those of 2a and 2i. The electron-deficient aryl group is bad for
antiviral activity (antiviral effects: 1i < 1e and 1h, 2i < 2e and 2h).
The replacement of the indole unit with thiophene is favorable
(antiviral effect: 1f > 1a), but its replacement with pyridine is
unfavorable (antiviral effect: 1j < 1a). The introduction of an
alkyl at the 10-position is favorable for activity (antiviral effects:
1g and 1l > 1a, 2g and 2k−2m > 2a).
Biological Assay. Each bioassay was repeated three times at 25
1 °C. The activity results were estimated according to a percentage scale
of 0−100 (0 indicating no activity and 100 indicating total mortality).
Detailed bioassay procedures for the anti-TMV,20 fungicidal,24 and
insecticidal24 activities are described in our published literature.
RESULTS AND DISCUSSION
■
Chemistry. Although nortopsentins have been synthesized
by the palladium-catalyzed coupling of 3-indolylboronic acids
with halogenated imidazoles,14,25 and the corresponding bis-
(indolyl)thiazole analogues have been prepared,26 the reported
methods cannot be used for structure−activity-relationship stud-
ies because they result in low yields and harsh conditions, com-
plex materials, and many steps are required. A novel route for the
preparation of nortopsentin derivatives is needed. As shown in
Figure 2, commercially available indoles (3) were reacted with
tosyl chloride to give the protected indoles (4), which were
treated with acetic anhydride and brominated to give the key
intermediate α-bromoketones (6). As depicted in Figures 3
and 4, treatment of the indoles (3) with chlorosulfonyl isocyanate
(CSI) and protection with tosyl chloride gave the 3-cyano
indoles (8), which were reacted with hydroxylamine and then
reduced with hydrogen to give the key intermediate amidines
(10). As depicted in Figure 5, condensation of the α-bromoketones
(6) with the amidines (10) gave protected nortopsentins 2a−2d.
Experiments on various conditions, such as CH3ONa, KOH,
SmI2, and Cs2CO3, were carried out for the removal of the Ts
group. Only Na/naphthalene could successfully give nortop-
sentins 1a−1d. To investigate the influence of the indole unit on
bioactivity, indole-imidazole compounds 2e−2m and 1e−1m, in
which one indole unit per compound was replaced with another
substituent, were designed and synthesized. As shown in Figure 6,
a similar procedure for the preparation of the nortopsentins was
used. The removal of the Ts group was carried out under refluxing
conditions in a solution of 2 N NaOH or in Na/naphthalene
conditions. As mentioned in the literature,27 the imidazole
rings of nortopsentins have two types of mutual variations.
Nortopsentins in series 1 existed as tautomers. 1H NMR spectra
of the nortopsentins in series 1 showed splitting of all the signals,
which could be suppressed by the addition of 1% CF3COOH to
the deuterated solvent.
In Vivo Anti-TMV Activity. As depicted in Table 2, the
nortopsentins in series 1 and their derivatives in series 2 also
showed good in vivo antiviral activities. Most of the compounds
had activities similar to that of the plant virucide ribavirin. Among
Table 4. In Vivo Fungicidal Activities of Nortopsentins in
Series 1 and 2 against Five Kinds of Fungi
a
inhibition rate (%) at 200 mg/kg
b
compd
Cc
13
Pc
Ss
Rs
Bc
1a
1b
1c
1d
1e
1f
2
1
1
2
1
2
2
1
3
1
2
1
1
2
1
1
2
1
1
2
1
1
1
2
1
1
0
13
20
15
8
1
2
1
2
1
1
2
1
1
2
2
1
2
1
1
1
2
1
2
1
2
1
1
1
1
1
2
3
1
1
1
1
6
1
3
1
1
3
1
1
1
2
1
1
1
1
2
1
1
1
2
1
1
1
1
1
1
1
1
2
20
15
10
11
18
20
13
18
10
10
16
18
16
12
11
10
18
16
12
13
16
14
7
0
0
4
10
13
0
13
8
0
9
2
15
3
8
6
1
1
1
1
1
1
1
1
1
2
1
1
1
1
10
11
11
0
1
1
2
12
13
6
1g
1h
1i
7
20
13
10
10
18
16
13
16
7
11
7
12
2
1j
7
3
1
1
1
1
1
1k
1l
8
8
3
5
6
9
1m
2a
2b
2c
2d
2e
2f
9
3
12
9
2
10
0
8
9
12
8
11
10
9
6
1
1
1
1
1
1
1
1
1
2
1
1
4
Phytotoxic Activity. The phytotoxic-activity tests showed
that the nortopsentins in series 1 and their derivatives in series 2
were safe for testing on plants at 500 μg/mL.
8
3
9
6
12
9
5
16
12
33
8
6
Antiviral Activity. The results of the anti-TMV activities of
the nortopsentins in series 1 and 2 are listed in Tables 1 and 2
with the commercial plant virucide ribavirin as the control.
In Vitro Anti-TMV Activity. As shown in Table 1, most of these
compounds displayed good antiviral activities, especially com-
pounds 1e, 1g, 1h, 2f, and 2k, which exhibited the same level of
antiviral activity as the plant virucide ribavirin (41% in vitro
activity at 500 μg/mL). Compounds 1f, 1l, 2b, 2e, 2h, 2l, and 2m
exhibited higher antiviral activities than the plant virucide
ribavirin at 500 μg/mL. Among the compounds, 1f, 2h, and 2m
exhibited much higher antiviral activities than ribavirin. The main
differences among 1a−1d lie in the bromine. Nortopsentin B
(1b) displayed significantly lower antiviral activity than the
2g
2h
2i
0
4
4
8
1
2
1
8
6
14
12
0
6
9
2j
14
4
6
7
2k
2l
8
12
12
5
16
12
100
13
10
100
1
2
13
12
83
6
2m
11
81
c
azoxystrobin
82
a
b
Averages of five replicates. Cc, Corynespora cassiicola (cucumber pro-
tection); Pc, Phytophthora capsici (pepper protection); Ss, Sclerotinia
sclerotiorum (rape protection); Rs, Rhizoctonia solani (rice protection);
c
Bc, Botrytis cinerea (cucumber protection). The dilution of
azoxystrobin is 1000×.
H
DOI: 10.1021/acs.jafc.8b00507
J. Agric. Food Chem. XXXX, XXX, XXX−XXX

Journal of Agricultural and Food Chemistry
Article
Table 5. Larvicidal Activities of Nortopsentins in Series 1 and 2 against Oriental Armyworm (Mythimna separate), Cotton
Bollworm (Helicoverpa armigera), Corn Borer (Ostrinia nubilalis), Diamond Back Moth (Plutella xylostella), and Mosquito
(Culex pipiens pallens)
larvicidal activities (% mortality) at concn (μg/mL)
M. separat
H. armigera
O. nubilalis
P. xylostella
C. pipiens pallens
compd
1a
600 μg/mL
200 μg/mL
600 μg/mL
600 μg/mL
600 μg/mL
200 μg/mL
10 μg/mL
5 μg/mL
2 μg/mL
45
20
0










20











0
25
25
0
30
30
0
50
0



40

50






70







40

50
30
30

100
35
100
70




65


















40



35
1b
1c
45
0

100









45








100

45
65
60
1d
1e
1f
15
0
5
20
0
100
0
100
40
0
20
15
15
20
15
100
45
0
10
10
10
20
10
80
30
0
10
15
20
25
25
75
25
0
100
0
20
1g
1h
1i
35
75
0
35
35
1j
0
60
1k
1l
0
55
0
5
1m
2a
100
70
0
15
0
0
0
100
20
2b
2c
45
15
5
20
10
5
30
20
5
0
35
2d
2e
2f
50
0
40
15
25
20
5
10
15
5
10
15
10
5
55
0
15
2g
2h
2i
0
20
5
90
0
35
0
0
0
35
2j
100
15
0
75
10
0
85
15
0
100
80
90
40
100
100
45
2k
2l




100
100
100
2m
rotenone
0
0
0
65
45
35
the compounds, 1f, 1l, 2c, 2e, 2h, 2k, and 2l exhibited antiviral
activities much higher than that of ribavirin (the inactivation,
curative, and protective effects in vivo were 41, 37, and 38%,
respectively). Compounds 2e and 2k, with excellent activities
and good physicochemical properties, emerged as new lead com-
pounds for the development of novel antiviral agents. The in vivo
antiviral activities of most of the compounds were higher than
those in vitro, which indicated that these alkaloids might be able
to induce disease resistance in plants. The natural product
nortopsentin A and its analogue nortopsentin D exhibited higher
activities than nortopsentin B and nortopsentin C. However, the
introduction of Ts groups reverses this (antiviral effects: 2b and
2c > 2a and 2d). The 10-position-indole-unit-replaced
derivatives, 1e−1m, displayed activities similar to that of 1a.
However, the replacement of the indole unit at the 10-position of
2a significantly increased the antiviral activity (antiviral effects:
2e−2m > 2a). The other structure−activity relationships in vivo
were similar to those in vitro.
Fungicidal Activity. The nortopsentins in series 1 and their
derivatives were also evaluated for their fungicidal activities with
the commercial fungicides chlorothalonil and carbendazim as the
controls.
In Vitro Fungicidal Activity. First, the in vitro antifungal-
activity tests showed that the nortopsentins in series 1 and their
derivatives in series 2 exhibited broad-spectrum fungicidal activi-
ties against 14 kinds of phytopathogenic fungi at 50 mg/kg
(Table 3). Some of the compounds showed levels of antifungal
activity similar to that of the commercial fungicide carbendazim.
Nortopsentin D showed higher activity than carbendazim against
Physalospora piricola. Compounds 2f and 2j exhibited excellent
fungicidal activities against Rhizoctonia cerealis (fungicidal activi-
ties of 90 and 89%, respectively), which were higher than those of
the commercial fungicides, chlorothalonil and carbendazim.
Compound 2h exhibited excellent fungicidal activity (fungicidal
activity of 95%) against Sclerotinia sclerotiorum, which was higher
than those of the commercial fungicides, chlorothalonil and
carbendazim. Compounds 2f, 2h, and 2j emerged as new lead
compounds for antifungal-activity research.
In Vivo Fungicidal Activity. The nortopsentins in series 1 and
their derivatives in series 2 were further evaluated for their in vivo
fungicidal activities against a series of plant pathogens. Their
abilities to protect cucumbers from Corynespora cassiicola,
peppers from Phytophthora capsici, rape from Sclerotinia
sclerotiorum, rice from Rhizoctonia solani, and cucumbers from
Botrytis cinerea were determined, and the results (Table 4)
revealed that the nortopsentins in series 1 and their derivatives in
series 2 also displayed good in vivo fungicidal activities.
Insecticidal Activity. The nortopsentins in series 1 and their
derivatives were also evaluated for their insecticidal activities with
the commercial insecticide rotenone as the control. Some
compounds exhibited excellent insecticidal activities (Table 5).
Compounds 1k and 2j exhibited broad-spectrum insecticidal
activities that induced >70% mortality in Mythimna separate,
Helicoverpa armigera Hubner, and Ostrinia nubilalis at 600 mg/kg.
Compounds 1d, 1f, 1m, 2h, 2j, and 2l exhibited >90% insec-
ticidal activities against Plutella xylostella at 600 mg/kg, and some
I
DOI: 10.1021/acs.jafc.8b00507
J. Agric. Food Chem. XXXX, XXX, XXX−XXX

Journal of Agricultural and Food Chemistry
Article
Discovery; Buss, A. D., Butler, M. S., Eds.; Royal Society of Chemistry
Publishing: Cambridge, U.K., 2010; pp 3−27.
(6) Newman, D. J.; Cragg, G. M. Natural products as sources for new
drugs over the 30 years from 1981 to 2010. J. Nat. Prod. 2012, 75, 311−
335.
mortalities reached 100%. Compounds 1b, 1d, 2a, 2j, 2l, and 2m
exhibited good insecticidal activities against mosquito larvae,
especially compounds 1d and 2j, which exhibited 100% mortality
at 5 mg/kg.
In summary, nortopsentins A−D and a series of derivatives
were designed, synthesized, and evaluated for their antiviral, anti-
phytopathogenic-fungus, and insecticidal activities for the first
time. Most of these compounds displayed good to excellent
antiviral activities. The structure−activity-relationship study
revealed that these compounds were very sensitive to sub-
stituents. Compounds 2e and 2k, which had excellent antiviral
activities and good physicochemical properties, emerged as new
lead compounds for the development of novel antiviral agents.
Further fungicidal-activity tests revealed that these alkaloids
displayed broad-spectrum fungicidal activities. Compounds 2f,
2h, and 2j emerged as new lead compounds for antifungal-
activity research. Insecticidal-activity tests revealed that these
alkaloids also displayed good insecticidal activities. The above
results provide fundamental support for the development of
nortopsentins as potential agrochemical bioregulators.
(7) Song, B. A.; Yang, S.; Jin, L. H.; Bhadury, P. S. Environment-friendly
anti-plant viral agents; Chemical Industry Press: Beijing, China, 2009; pp
1−305.
(8) Rimando, A.; Duke, S. O. Natural products for pest management.
In Natural Products for Pest Management; Rimando, A., Duke, S. O., Eds.;
American Chemical Society: Washington, DC, 2006; Vol. 927, pp 2−21.
(9) Zhang, G. P.; Hao, G. F.; Pan, J. K.; Zhang, J.; Hu, D. Y.; Song, B. A.
Asymmetric synthesis and bioselective activities of α-aminophospho-
nates based on the dufulin motif. J. Agric. Food Chem. 2016, 64, 4207−
4213.
(10) Gan, X. H.; Hu, D. Y.; Wang, Y. J.; Yu, L.; Song, B. A. Novel trans-
ferulic acid derivatives containing a chalcone moiety as potential
activator for plant resistance induction. J. Agric. Food Chem. 2017, 65,
4367−4377.
(11) Zhang, J.; Zhao, L.; Zhu, C.; Wu, Z. X.; Zhang, G. P.; Gan, X. H.;
Liu, D. Y.; Pan, J. K.; Hu, D. Y.; Song, B. A. Facile synthesis of novel
vanillin derivatives incorporating a bis(2-hydroxyethyl)dithhioacetal
moiety as antiviral agents. J. Agric. Food Chem. 2017, 65, 4582−4588.
(12) Sakemi, S.; Sun, H. H. Nortopsentins A, B, and C. cytotoxic and
antifungal imidazolediylbis[indoles] from the Sponge Spongosorites
ruetzleri. J. Org. Chem. 1991, 56, 4304−4307.
(13) Sun, H. H.; Sakemi, S., Gunasekera, S.; Kashman, Y.; Lui, M.;
Burres, N.; McCarthy, P. Isolation of nortopsentin A, B, and C from
marine sponges as antitumor and antimicrobial agents. U.S. Patent
US4970226, 1990; Chem. Abstr. 1991, 115, 35701z.
(14) Kawasaki, I.; Yamashita, M.; Ohta, S. Total synthesis of
nortopsentins A−D, marine alkaloids. Chem. Pharm. Bull. 1996, 44,
1831−1839.
(15) Diana, P.; Carbone, A.; Barraja, P.; Montalbano, A.; Martorana,
A.; Dattolo, G.; Gia, O.; Dalla Via, L.; Cirrincione, G. Synthesis and
antitumor properties of 2,5-bis(3′-indolyl)thiophenes: Analogues of
marine alkaloid nortopsentin. Bioorg. Med. Chem. Lett. 2007, 17, 2342−
2346.
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.jafc.8b00507.
■
S
1H and 13C NMR and HRMS spectra of nortopsentins in
series 1 and 2 and 1H NMR spectra of compounds 4−10
(PDF)
AUTHOR INFORMATION
Corresponding Authors
*E-mail: wangziwen2725@163.com. Tel.: 0086-22-23503792.
Fax: 0086-22-23503792 (Z.W.).
■
*E-mail: wangqm@nankai.edu.cn. Tel.: 0086-22-23503952.
Fax: 0086-22-23503952 (Q.W.).
(16) Diana, P.; Carbone, A.; Barraja, P.; Kelter, G.; Fiebig, H. H.;
Cirrincione, G. Synthesis and antitumor activity of 2,5-bis(3′-indolyl)-
furans and 3,5-bis(3′-indolyl)-isoxazoles, nortopsentin analogues.
Bioorg. Med. Chem. 2010, 18, 4524−4529.
ORCID
Shaoxiang Yang: 0000-0002-9944-7472
Qingmin Wang: 0000-0002-6062-3766
Funding
We gratefully acknowledge assistance from the National
Natural Science Foundation of China (21732002, 21672117,
and 21772145), the Tianjin Natural Science Foundation
(16JCZDJC32400 and 15JCQNJC05600), the Training Pro-
gram of Outstanding Youth Innovation Team of Tianjin Normal
University, and the Open Project Program of Beijing Key
Laboratory of Flavor Chemistry of Beijing Technology and
Business University (SPFW-2017-YB07).
̀
(17) Carbone, A.; Parrino, B.; Barraja, P.; Spano, V.; Cirrincione, G.;
Diana, P.; Maier, A.; Kelter, G.; Fiebig, H. H. Synthesis and
antiproliferative activity of 2,5-bis(3′-indolyl)pyrroles, analogues of
the marine alkaloid nortopsentin. Mar. Drugs 2013, 11, 643−654.
̀
(18) Spano, V.; Attanzio, A.; Cascioferro, S.; Carbone, A.; Montalbano,
A.; Barraja, P.; Tesoriere, L.; Cirrincione, G.; Diana, P.; Parrino, B.
Synthesis and antitumor activity of new thiazole nortopsentin analogs.
Mar. Drugs 2016, 14, No. e226.
(19) Liu, L. R. The control of disease and pests of tobacco; Science Press:
Beijing, China, 1998.
(20) Wang, Z. W.; Wei, P.; Wang, L. Z.; Wang, Q. M. Design, synthesis,
and anti-tobacco mosaic virus (TMV) activity of phenanthroindolizi-
dines and their analogues. J. Agric. Food Chem. 2012, 60, 10212−10219.
(21) Song, H. J.; Liu, Y. X.; Liu, Y. X.; Wang, L. Z.; Wang, Q. M.
Synthesis and antiviral and fungicidal activity evaluation of β-carboline,
dihydro-β-carboline, tetrahydro-β-carboline alkaloids, and their deriv-
atives. J. Agric. Food Chem. 2014, 62, 1010−1018.
(22) Guo, P. B.; Wang, Z. W.; Li, G.; Liu, Y. X.; Xie, Y. F.; Wang, Q. M.
First discovery of polycarpine, polycarpaurines A and C, and their
derivatives as novel antiviral and anti-phytopathogenic fungi agents. J.
Agric. Food Chem. 2016, 64, 4264−4272.
(23) Ni, W. J.; Li, C. J.; Liu, Y. X.; Song, H. J.; Wang, L. Z.; Song, H. B.;
Wang, Q. M. Various bioactivity and relationship of structure−activity of
matrine analogues. J. Agric. Food Chem. 2017, 65, 2039−2047.
(24) Zhao, H. P.; Liu, Y. X.; Cui, Z. P.; Beattie, D.; Gu, Y. C.; Wang, Q.
M. Design, synthesis, and biological activities of arylmethylamine
Notes
The authors declare no competing financial interest.
REFERENCES
■
(1) Godfrey, C. R. A. Fungicides and bactericides. In Agrochemicals
from Natural Products; Godfrey, C. R. A., Ed.; Marcel Dekker: NewYork,
1995; pp 311−339.
(2) Dayan, F. E.; Cantrell, C. L.; Duke, S. O. Natural products in crop
protection. Bioorg. Med. Chem. 2009, 17, 4022−4034.
(3) Cantrell, C. L.; Dayan, F. E.; Duke, S. O. Natural products as source
for new pesticides. J. Nat. Prod. 2012, 75, 1231−1242.
(4) Dias, D. A.; Urban, S.; Roessner, U. A historical overview of natural
products in drug discovery. Metabolites 2012, 2, 303−336.
(5) Newman, D. J.; Cragg, G. M. Natural products as drugs and leads to
drugs: the historical perspective. In Natural Product Chemistry for Drug
J
DOI: 10.1021/acs.jafc.8b00507
J. Agric. Food Chem. XXXX, XXX, XXX−XXX

Journal of Agricultural and Food Chemistry
Article
substituted chlorotriazine and methylthiotriazine compounds. J. Agric.
Food Chem. 2011, 59, 11711−11717.
(25) Tan, J.; Chen, Y.; Li, H.; Yasuda, N. Suzuki-Miyaura cross-
coupling reactions of unprotected haloimidazoles. J. Org. Chem. 2014,
79, 8871−8876.
(26) Gu, X. H.; Wan, X. Z.; Jiang, B. Syntheses and biological activities
of bis(3-indolyl)thiazoles, analogues of marine bis(indole)alkaloid
nortopsentins. Bioorg. Med. Chem. Lett. 1999, 9, 569−572.
́
(27) Guinchard, X.; Vallee, Y.; Denis, J. N. Total synthesis of marine
sponge bis(indole) alkaloids of the topsentin class. J. Org. Chem. 2007,
72, 3972−3975.
K
DOI: 10.1021/acs.jafc.8b00507
J. Agric. Food Chem. XXXX, XXX, XXX−XXX