Synthesis and biological evaluation of calycanthaceous alkaloid analogs

Article abstract of DOI:10.1016/j.bmc.2019.115088

Starting from 9-methyl-1,2,3,4,9,9a-hexahydro-4aH-pyrido[2,3-b]indol-4a-ol, or indole-3-acetonitrile, 40 new calycanthaceous alkaloid analogs were synthesized in excellent yields. The prepared compounds were evaluated for biological activity against acetylcholinesterase and a broad range of plant pathogen fungi. The results of bioassays indicated that the majority of tested compounds displayed comparable or better in vitro bioactivity than the positive control. Notably, compounds b8 and b9 showed higher activity against Verticillium dahlia than chlorothalonil, with MIC values of 62.5 and 7.81 μg mL^?1, respectively. Compound b3 had a higher activity against Bacillus cereus, with a MIC value of 15.63 μg mL^?1. Compounds c2 and c11 revealed potent activity against acetylcholinesterase, with MIC values of 0.01 and 0.1 ng mL^?1, respectively. Analysis of the molecular docking modes of c2 and c11 with Torpedo californica acetylcholinesterase indicated a medium strong hydrogen bond interaction between the hydroxyl groups of both the ligands and the phenolic hydroxyl of Try121 at a distance of approximately 2.4 ?. The results obtained in this study will be useful for the further design and structural optimization of calycanthaceous alkaloids as potential agrochemical lead compounds for plant disease control.

Full text of DOI:10.1016/j.bmc.2019.115088

Bioorganic&MedicinalChemistryxxx(xxxx)xxxx
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry
journal homepage: www.elsevier.com/locate/bmc
Synthesis and biological evaluation of calycanthaceous alkaloid analogs
⁎
⁎
⁎
Shaojun Zhenga, , Rui Zhua, Xinping Zhoub, Lizhuang Chena, Hongjin Baib, , Jiwen Zhangc,
a School of Environmental and Chemical Engineering, Jiangsu University of Science and Technology, Zhenjiang 212003, Jiangsu, China
b Key Laboratory of Protection & Utilization of Biological Resources in Tarim Basin of Xinjiang Production and Construction Corps/College of Life Sciences, Tarim
University, Alar 843300, Xinjiang, China
c Key Laboratory of Botanical Pesticide R & D in Shaanxi Province, Yangling 712100, Shaanxi, China
A R T I C L E I N F O
A B S T R A C T
Keywords:
Starting from 9-methyl-1,2,3,4,9,9a-hexahydro-4aH-pyrido[2,3-b]indol-4a-ol, or indole-3-acetonitrile, 40 new
calycanthaceous alkaloid analogs were synthesized in excellent yields. The prepared compounds were evaluated
for biological activity against acetylcholinesterase and a broad range of plant pathogen fungi. The results of
bioassays indicated that the majority of tested compounds displayed comparable or better in vitro bioactivity
than the positive control. Notably, compounds b8 and b9 showed higher activity against Verticillium dahlia than
chlorothalonil, with MIC values of 62.5 and 7.81 µg mL−1, respectively. Compound b3 had a higher activity
against Bacillus cereus, with a MIC value of 15.63 µg mL−1. Compounds c2 and c11 revealed potent activity
against acetylcholinesterase, with MIC values of 0.01 and 0.1 ng mL−1, respectively. Analysis of the molecular
docking modes of c2 and c11 with Torpedo californica acetylcholinesterase indicated a medium strong hydrogen
bond interaction between the hydroxyl groups of both the ligands and the phenolic hydroxyl of Try121 at a
distance of approximately 2.4 Å. The results obtained in this study will be useful for the further design and
structural optimization of calycanthaceous alkaloids as potential agrochemical lead compounds for plant disease
control.
Calycanthaceous alkaloids
Synthesis
Plant pathogen fungi
Acetylcholinesterase
SAR
Recently, fragment-based pesticide discovery methods have become
an increasing focus in agricultural chemistry.1 Fragments with the
features of high modifiability, diversified scaffolds, and small molecular
weights, are an ideal resource for pesticide development. Compared
with traditional pesticide design methods, agrochemists can evolve,
connect, and integrate fragments into pesticide candidates via struc-
ture-based modification.2,3
As a continuation of the development of new natural-product-based
antifungal agents, a series of N-substituted calycanthaceous alkaloid
analogs were designed and synthesized, and the structures were char-
acterized by 1H NMR, 13C NMR, and MS.
To the best of our knowledge, the biological activities of the pre-
pared analogs are reported here for the first time.
The synthetic route to the compounds is given in Scheme 1. The
calycanthaceous alkaloid analogs were prepared according to a pre-
viously reported procedure by our group and the spectral data were
consistent with reported values.19–22 The derivatives of calycanthac-
eous alkaloids were prepared from indole-3-acetonitrile, or 9-methyl-
1,2,3,4,9,9a-hexahydro-4aH-pyrido[2,3-b]indol-4a-ol (4), via acylation
at the N-position. A total of 40 calycanthaceous analogs were prepared,
and characterized by 1H NMR, 13C NMR spectroscopy, and ESI-MS.
The inhibitory effects of the calycanthaceous alkaloid derivatives
against a broad range of plant pathogen fungi are outlined in Tables
1–4. The MIC values were evaluated with chlorothalonil, gentamicin,
streptomycin, amphotericin B, carbendazim, fluconazole, or penicillin
as positive controls, to assay the activities of the prepared caly-
canthaceous alkaloid derivatives against Cytospora juglandis, Aspergillus
flavus, Penicillium citrinum, Fusarium oxysperium sp. vasinfectum,
In nature, hexahydropyrroloindole skeletons are very important
moieties that are widespread in a large family of natural products that
possess potential bioactivity. The Calycanthaceae plants (Fig. 1), which
contain hexahydropyrroloindole skeletons, have been used as tradi-
tional Chinese medicines for the treatment of fungal infection,4 hy-
pertension, tumors, inflammatory conditions, and melanogenesis.5–8
Because of the broad spectrum of biological properties, a number of
studies investigating the synthesis and antimicrobial activity of caly-
canthaceous alkaloids have been reported.7,9–18
Our group has recently reported the preparation and potent anti-
microbial activity of calycanthaceous alkaloid derivatives.19–24 These
findings inspired us to further modify the structure of calycanthaceous
alkaloids with functional motifs so as to acquire potential agrochemical
leads for plant disease control.
⁎ Corresponding authors.
E-mail addresses: sz281cam@just.edu.cn (S. Zheng), bhj67@163.com (H. Bai), nwzjw@nwsuaf.edu.cn (J. Zhang).
https://doi.org/10.1016/j.bmc.2019.115088
Received 12 May 2019; Received in revised form 20 August 2019; Accepted 3 September 2019
0968-0896/©2019ElsevierLtd.Allrightsreserved.
Pleasecitethisarticleas:ShaojunZheng,etal.,Bioorganic&MedicinalChemistry,https://doi.org/10.1016/j.bmc.2019.115088

S. Zheng, et al.
Bioorganic&MedicinalChemistryxxx(xxxx)xxxx
the same MIC value of 62.50 µg mL−1. Compounds c2, c3, and c8
displayed better activity against R. solanacearum compared with gen-
tamicin and streptomycin.
As indicated in Table 3, compounds a2, a5, a6, b1, b2, b5, b7, b8,
c7, and c8 showed some activity against Staphylococcus aureus subsp.
aureus and B. cereus, with compound b3 being the most effective, with a
MIC value of 15.63 µg mL−1
.
The results of the MIC values of compounds against human patho-
genic fungi are summarized in Table 4. Compounds a2, a5, b8, and b11
had better activity against C. tropicalis than amphotericin B or fluco-
nazole, both with the same MIC value of 125.00 µg mL−1. Compounds
a5, b8, c7, and c8 showed greater activity against C. neoformans than
fluconazole, with MIC values of 62.50, 125.00, 125.00, and
125.00 µg mL−1, respectively. Compounds a5 and b8 showed better
activity against C. krolimus than amphotericin B or fluconazole, both
with the same MIC value of 31.25 µg mL−1. Compounds a5, b8, c7, and
c8, with a long chain at the N-position, showed potent activity. Com-
pounds a6 and b9 also showed potent activity because of the n-benzyl
group at the N-position. These results laid the foundation for the study
of the structure–activity relationship of the alkaloid analogs.
Fig. 1. Structures of calycanthaceous alkaloids.
Fusarium oxysporum, Colletotrichum orbiculare, Aspergillus niger, Curvu-
laria lunata, Escherichia sp., Verticillium dahliae, Pseudomonas aeruginosa,
Ralstonia solanacearum, Bacillus cereus, Staphylococcus aureus subsp.
aureus, Candida krolimus, and Cryptococcus neoformans.
The synthesized series of analogs exhibited better antimicrobial
activity compared with the positive controls. Compounds a4, a5, a16,
b7, and b8 showed moderate activity against F. oxysperium sp.
Vasinfectum, C. juglandis, A. flavus, V. dahliae, P. citrinum, F. oxysporum,
C. orbiculare, A. niger, and C. lunata. Thirty-six compounds exhibited
activity against V. dahliae. In particular, compounds a2, a5, b8, b9,
b11, and b14 showed more effective activity against V. dahliae com-
pared with chlorothalonil. Compounds b8 and b9 displayed the most
effective activity among the tested analogs, with MIC values of 62.5 and
7.81 µg mL−1, respectively. Compounds b7, b9, and c7 displayed
slightly better activity against C. lunata than carbendazim or chlor-
othalonil, with the same MIC value of 62.50 µg mL−1. Compounds b14
and b16 had improved activity compared with the positive control
chlorothalonil against F. oxysperium, both with the same MIC value of
As shown in Fig. 2, compound c7 exhibited a better inhibitory effect
against the mycelium of C. lunata at 250.00 µg mL−1 than carbendazim
or chlorothalonil, and the inhibition rate was positively correlated with
the concentration. When the concentrations of compound c7 were
62.50, 125.00, and 250.00 µg mL−1, the inhibition rates of the myce-
lium were 15.50%, 31.32%, and 77.73%, respectively.
As shown in Fig. 3, compound a5 exhibited better inhibitory activity
against V. dahlia than the positive control chlorothalonil at
250.00 µg mL−1. When the concentrations of compound a5 were 31.25,
62.50, 125.00, and 250.00 µg mL−1, the inhibition rates of mycelium
were 46.24%, 46.95%, 63.44%, and 67.74%, respectively.
Fig. 4 shows that the inhibitory rate of compound b8 on the spore
germination of C. krolimus was 87.46% at 500.00 µg mL−1
.
62.50 µg mL−1
.
Fig. 5 shows that compound a8 exhibited potent inhibitory activity
As shown in Table 2, 15 analogs displayed potent in vitro anti-
microbial activity against Escherichia sp., P. aeruginosa, and R. solana-
cearum. Compounds a5, b8, c5, c7, c12, and c14 exhibited improved
activity against R. solanacearum compared with streptomycin, all with
against C. lunata at 125.00 µg mL−1
.
Fig. 6 shows that the inhibitory rate of compound c7 on the spore
germination of C. lunata was 76.23% at 125.00 µg mL−1, which was
superior to chlorothalonil.
Scheme 1. Synthetic route to the compounds a1–a10, b1–b16, and c1–c14.
2

S. Zheng, et al.
Bioorganic&MedicinalChemistryxxx(xxxx)xxxx
Table 1
MIC values of compounds against plant pathogenic fungi.
Comp.
V.d.
F.v.
C.j.
A.f.
P.c.
F.o.
C.o.
A.n.
C.l.
MIC (µg/mL)
a1
125.00
31.25
62.50
62.50
31.25
250.00
250.00
125.00
62.50
250.00
250.00
62.50
250.00
–
–
250.00
250.00
125.00
62.50
125.00
250.00
250.00
250.00
250.00
250.00
62.50
62.50
250.00
250.00
250.00
125.00
62.50
125.00
125.00
125.00
250.00
250.00
250.00
62.50
250.00
250.00
–
250.00
250.00
250.00
250.00
250.00
250.00
250.00
250.00
250.00
250.00
250.00
250.00
250.00
250.00
250.00
250.00
250.00
250.00
250.00
250.00
250.00
250.00
250.00
250.00
250.00
250.00
–
–
250.00
125.00
125.00
125.00
125.00
250.00
250.00
250.00
250.00
250.00
125.00
125.00
125.00
250.00
125.00
125.00
125.00
125.00
125.00
250.00
250.00
250.00
250.00
250.00
250.00
250.00
–
250.00
–
250.00
250.00
250.00
250.00
250.00
125.00
250.00
250.00
250.00
250.00
125.00
125.00
250.00
–
250.00
a2
–
250.00
–
a3
–
250.00
250.00
250.00
250.00
–
125.00
a4
250.00
125.00
125.00
a5
250.00
250.00
125.00
a6
250.00
250.00
62.50
a7
–
125.00
250.00
250.00
250.00
–
–
a8
250.00
–
–
a9
250.00
–
–
a10
b1
–
–
–
–
–
250.00
250.00
250.00
–
250.00
b2
–
–
–
b3
–
–
–
b4
–
–
–
b5
31.25
15.63
125.00
62.50
7.81
–
250.00
–
250.00
250.00
250.00
250.00
250.00
250.00
250.00
250.00
250.00
250.00
250.00
–
–
b6
–
250.00
250.00
250.00
250.00
250.00
250.00
250.00
250.00
–
–
b7
250.00
250.00
125.00
250.00
250.00
125.00
–
250.00
62.50
b8
250.00
125.00
b9
–
62.50
b10
b11
b12
b13
b14
b15
b16
c1
250.00
31.25
62.50
125.00
31.25
250.00
–
250.00
–
–
–
–
–
250.00
–
62.50
125.00
62.50
–
250.00
250.00
–
–
250.00
–
–
–
–
–
–
–
–
–
c2
250.00
250.00
250.00
250.00
125.00
62.50
62.50
125.00
250.00
250.00
250.00
250.00
–
–
–
–
–
–
–
–
–
c3
–
–
–
–
–
–
–
–
c4
–
–
–
–
–
–
–
–
c5
–
–
–
–
–
–
–
–
c6
250.00
250.00
250.00
–
125.00
125.00
125.00
–
–
–
250.00
250.00
–
250.00
250.00
250.00
–
250.00
250.00
250.00
–
250.00
c7
–
–
62.50
c8
125.00
–
–
125.00
c9
–
–
–
c10
c11
c12
c13
c14
Ca
–
–
–
–
–
–
–
–
250.00
–
250.00
–
250.00
–
250.00
250.00
–
250.00
–
–
125.00
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
7.81
62.50
250.00
31.25
62.50
7.81
1.96
15.63
125.00
62.50
125.00
250.00
–
250.00
125.00
Ch
31.25
7.81
15.63
Note: Carbendazim and chlorothalonil were used as the positive controls; “−” means no inhibition effect. MIC: minimal inhibitory concentration; V.d.: V. dahliae;
F.v.: F. oxysperium sp. Vasinfectum; C.j.: C. juglandis; A.f.: A. flavus; P.c.: P. citrinum; F.o.: F. oxysporum; C.o.: C. orbiculare: A.n.: A. niger; C.l.: C. lunata; Ca: carbendazim;
Ch: chlorothalonil.
Table 2
MIC values against Gram-negative bacteria.
Comp.
E.s.
P.a.
R.s.
Comp.
E.s.
P.a.
R.s.
Comp.
E.s.
P.a.
R.s.
MIC (µg/mL)
MIC (µg/mL)
MIC (µg/mL)
a1
a2
a3
a4
a5
a6
a7
a8
a9
a10
b1
b2
b3
b4
–
–
–
b5
250.00
125.00
250.00
c3
–
250.00
250.00
250.00
250.00
250.00
250.00
250.00
250.00
250.00
250.00
250.00
250.00
1.96
31.25
–
250.00
250.00
250.00
b6
–
125.00
250.00
c4
–
–
125.00
250.00
b7
250.00
125.00
125.00
c5
250.00
250.00
125.00
62.50
250.00
250.00
250.00
–
62.50
125.00
62.50
31.25
125.00
250.00
125.00
62.50
–
250.00
250.00
125.00
b8
250.00
125.00
62.50
c6
125.00
125.00
62.50
b9
–
–
125.00
c7
–
–
125.00
b10
b11
b12
b13
b14
b15
b16
c1
–
–
–
c8
–
–
–
250.00
125.00
–
c9
–
–
–
–
–
–
–
–
–
–
–
–
c10
c11
c12
c13
c14
g
250.00
–
–
250.00
–
–
–
–
–
–
250.00
250.00
250.00
–
–
–
–
–
–
250.00
250.00
–
–
250.00
1.96
62.50
62.50
250.00
–
–
–
–
250.00
250.00
250.00
31.25
c2
s
31.25
–
Note: Gentamicin and streptomycin were used as the positive controls; “−” means no inhibition effect. MIC: minimal inhibitory concentration; E.s.: Escherichia sp.;
P.a.: P. aeruginosa; R.s.: R. solanacearum; g: gentamicin; s: streptomycin.
3

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Bioorganic&MedicinalChemistryxxx(xxxx)xxxx
Table 3
MIC values against Gram-positive bacteria.
Comp.
B.c.
S.a.
Comp.
B.c.
S.a.
Comp.
B.c.
S.a.
Comp.
B.c.
S.a.
MIC(µg/mL)
MIC(µg/mL)
MIC(µg/mL)
MIC(µg/mL)
a1
a2
a3
a4
a5
a6
a7
a8
a9
a10
p
–
–
b1
b2
b3
b4
b5
b6
b7
b8
b9
b10
31.25
250.00
15.63
–
62.50
b11
b12
b13
b14
b15
b16
c1
125.00
–
c5
–
125.00
125.00
62.50
62.50
–
250.00
–
250.00
250.00
125.00
–
c6
–
–
–
–
–
–
–
–
–
–
–
–
c7
250.00
–
–
–
–
c8
250.00
62.50
250.00
250.00
125.00
–
125.00
250.00
–
250.00
250.00
125.00
62.50
125.00
250.00
250.00
–
c9
–
–
–
–
–
–
–
–
c10
c11
c12
c13
c14
–
250.00
250.00
250.00
250.00
–
–
125.00
c2
–
–
–
250.00
–
–
–
c3
–
c4
250.00
7.81
15.63
Note: Gentamicin and streptomycin were used as the positive controls; “−” means no inhibition effect. MIC: minimal inhibitory concentration; p: penicillin; B.c.: B.
cereus; S.a.: S. aureus.
Table 4
MIC values of compounds against human pathogenic fungi.
Comp.
C.k
C.N.
C.t
Comp.
C.k
C.N.
C.t
Comp.
C.k
C.N.
C.t
MIC (µg/mL)
MIC (µg/mL)
MIC (µg/mL)
a1
a2
a3
a4
a5
a6
a7
a8
a9
a10
b1
b2
b3
b4
250.00
250.00
125.00
250.00
31.25
250.00
250.00
250.00
250.00
–
–
125.00
125.00
–
b5
250.00
250.00
250.00
31.25
250.00
250.00
250.00
250.00
–
–
250.00
c3
–
–
–
–
b6
–
250.00
c4
–
–
–
–
b7
–
250.00
c5
–
–
–
–
250.00
125.00
250.00
250.00
–
b8
125.00
125.00
c6
–
250.00
–
62.50
b9
–
–
–
–
–
–
–
–
–
–
250.00
c7
–
125.00
250.00
–
–
–
–
–
–
–
–
–
b10
b11
b12
b13
b14
b15
b16
c1
125.00
c8
–
125.00
–
125.00
c9
–
–
–
–
–
–
–
–
–
–
c10
c11
c12
c13
c14
A
–
–
–
250.00
–
–
–
250.00
250.00
–
–
–
–
250.00
250.00
250.00
–
250.00
125.00
250.00
–
–
–
–
–
–
–
250.00
–
250.00
62.50
1.96
c2
–
F
250.00
Note: Gentamicin and streptomycin were used as the positive controls; “−” means no inhibition effect. MIC: minimal inhibitory concentration; C.k: C. krolimus; C.N.:
C. neoformans; C.t.: C. tropicalis; A: amphotericin B; F: fluconazole.
Fig. 2. Inhibitory effect of compound c7 on the mycelium of C. lunata.
Fig. 3. Inhibitory effect of compound a5 on the mycelium of V. dahlia.
The inhibitory rate of compound c7 on the spore germination of C.
lunata was 43.68% at 250.00 µg mL−1, which was better than carben-
dazim or chlorothalonil (Fig 7).
a slow upward trend from 1 to 6 h. However, the bacterial growth
proliferated quickly from 12 to 20 h, and then stabilized, indicating that
the growth of R. solanacearum was inhibited, and this was positively
correlated with the sample concentration. The growth of bacteria was
Fig. 8 shows that bacteria in the control group proliferated quickly
within 20 h. However, the bacteria proliferated relatively slowly after
20 h indicating that the bacteria grew slowly into a stable state with
typical bacterial growth characteristics. Bacterial reproduction showed
almost completely inhibited at 500 µg mL−1
.
The acetylcholinesterase activity of the compounds was determined
by Ellman colorimetry. The inhibition rates of seven different
4

S. Zheng, et al.
Bioorganic&MedicinalChemistryxxx(xxxx)xxxx
Fig. 7. Effect of compound c7 on the spore germination of C. lunata.
Fig. 4. Effect of compound b8 on the spore germination of C. krolimus.
Fig. 8. Effect of compound c8 on the growth curve of R. solanacearum.
Table 5
Inhibition of acetylcholinesterase.
Fig. 5. Effect of compound a8 on the spore germination of C. juglandis.
Compd. IC50
Compd. IC50
Compd. IC50
(μg/mL)
Compd. IC50
(μg/mL)
(μg/mL) (μg/mL)
a1
a2
a3
a4
a5
a6
a7
a8
a9
a10
3.29
b1
b2
b3
b4
b5
b6
b7
b8
b9
b10
0.39
b11
b12
b13
b14
b15
b16
c1
1.43
c5
7.90
148.50
101.10
43.64
8.14
2.86
5.96
1.57
0.06
66.12
8.74
43.50
54.29
3.14
6.70
c6
2.29
1.33
0.12
0.32
0.11
0.0001
1.78
0.92
0.08
1.41
c7
21.31
220.50
0.002
0.30
c8
c9
111.40
395.80
0.14
c10
c11
c12
c13
c14
c2
0.00001
33.35
0.14
0.11
c3
63.21
c4
concentrations and the IC50 values of the test compounds indicated that
the inhibition rate of acetylcholinesterase increased with an increase in
sample concentrations.
Table 5 shows the activity of compounds a8, a9, b11, c2, c4, c6,
c11, c13, and c14 against acetylcholinesterase. The results indicated
that these compounds had potent activity at 1 mg mL−1 against acet-
ylcholinesterase. The rate of inhibition of acetylcholinesterase was
more than 80%. Compounds c2 and c11 were the most effective, with
MIC values of 0.01 and 0.1 ng mL−1, respectively.
Fig. 6. Effect of compound c7 on the spore germination of C. lunata.
5

S. Zheng, et al.
Bioorganic&MedicinalChemistryxxx(xxxx)xxxx
Fig. 9. The stereoisomer for each compound with the best docking score is circled. The top-scoring pose of c2 and c11 obtained by docking into the active site of
acetylcholinesterase is shown. Hydrogen bonds are shown by red dotted lines.
Analysis of the molecular docking modes of compounds c2 and c11
with Torpedo californica acetylcholinesterase indicated a medium to
strong hydrogen bond (HB) interaction between the hydroxyl groups of
both ligands and the phenolic hydroxyl of Try121 at a distance of ap-
proximately 2.4 Å (Fig. 9). The quantitative HB interaction energy of
A1-TcAChE and B2-Tc acetylcholinesterase, calculated based on the
AutoDock scoring function, showed slight differences of −1.39 and
−1.37 kcal/mol, respectively. Van der Waals (Vdw) interactions be-
tween the ligands and TcAChE was the key difference, these interac-
tions benefited from replacing the methyl group with a p-fluorophenyl
group, which allows a new π-π interaction between the p-fluorophenyl
ring and Trp279 to be formed, which had −8.23 kcal/mol Vdw inter-
action energy in the B2-TcAChE complex, while the corresponding
energy in the A1-TcAChE complex was −7.11 kcal/mol. The total
binding energy difference was −1.27 kcal/mol (−8.07 kcal/mol in B2-
TcAChE and −6.80 kcal/mol in A1-TcAChE), which is very close to the
theoretical free-energy change of −1.36 kcal/mol, while the bioactivity
was improved 10-fold.
activity against V. dahliae compared with chlorothalonil, with MIC
values of 62.5 and 7.81 µg mL−1, respectively. The activity of com-
pound b3 was more potent against B. cereus, with a MIC value of
15.63 µg mL−1. Notably, compounds c2 and c11 had potent activity
against acetylcholinesterase, with MIC values of 0.01 and 0.1 ng mL−1
,
respectively. These results will pave the way for the further design,
structural optimization, and development of calycanthaceous alkaloids
as potential agrochemical leads for plant disease control.
Declaration of Competing Interest
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influ-
ence the work reported in this paper.
Acknowledgements
This work was supported by the National Natural Science
Foundation of China (21502073 and 31360079), the Natural Science
Foundation of Jiangsu Province (Grants No BK 20150465 and
BK20180978), and the Key Research and Development Program
(Modern Agriculture) of Zhenjiang City (NY2018002). We thank
Victoria Muir from Liwen Bianji, Edanz Editing China (www.
liwenbianji.cn/ac), for editing the English text of a draft of this
manuscript.
In summary, 40 novel tetrahydropyrroloindole-based calycanthac-
eous alkaloids analogs were prepared using 9-methyl-1,2,3,4,9,9a-
hexahydro-4aH-pyrido[2,3-b]indol-4a-ol(4), or indole-3-acetonitrile as
the starting material via acylation at the N-position, and the activity
against acetylcholinesterase, as well as a broad range of plant pathogen
fungi was screened. The results of bioassays revealed that most of the
compounds had moderate to potent activity against acet-
ylcholinesterase as well as a broad variety of plant pathogen fungi, and
were more effective than the positive controls. Compounds in the a and
b series exhibited potent inhibition activity against plant pathogen
fungi. The reason for this activity was the substitutions at the 1- and 3-
positions and the presence of a long chain without fluorine at the N-
position. Compounds in the c series exhibited potent inhibition activity
against plant pathogen fungi and Gram-negative bacteria. The reason
for this activity was that the structures contained hexahy-
dropyrroloindole skeletons. Compounds a5, b8, c7, and c8, with a long
chain at the N-position, also showed potent activity. Compounds a6 and
b9 also showed potent activity because of the n-benzyl group at the N-
position. Compounds a10, b13, and c13, with m-methoxybenzoyl and
m-methylbenzoyl groups at the N-position showed no activity against
bacteria or plant pathogen fungi.
Appendix A. Supplementary data
Supplementary data to this article can be found online at https://
doi.org/10.1016/j.bmc.2019.115088.
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