Structural modification, fungicidal and insecticidal activity of 5-arylbenzofuran neolignan from Magnolia officinalis

Article abstract of DOI:10.1016/j.phytol.2019.01.016

As shown in a number of previous researches, the extracts of Magnolia officinalis exhibited broad-spectrum fungicidal and insecticidal activity. In our preliminary study, 5-arylbenzofuran neolignans, the secondary metabolite of Magnolia officinalis, was found to inherit the activity of Magnolia officinalis. For developing novel agrochemicals, natural 5-arylbenzofuran neolignan was selected as lead compound. After structural optimization, the fungicidal and insecticidal activity and selectivity were significantly improved. Compounds 5a, 5b, 6c and 6d displayed similar or equivalent activity compared with the positive controls against corresponding fungi or pests. Especially, compounds 6c and 6d exhibited the most promising insecticidal ability against Aphis fabae with the LC₅₀ values of 3.56 mg/L and 5.96 mg/L, respectively. The preliminary structure-activity relationship was obtained, and the promising derivatives showed low toxicity in the model of human cells. The results of research indicated great potential of 5-arylbenzofuran neolignan derivatives in the field of fungicide and insecticide.

Full text of DOI:10.1016/j.phytol.2019.01.016

Phytochemistry Letters 30 (2019) 53–57
Contents lists available at ScienceDirect
Phytochemistry Letters
journal homepage: www.elsevier.com/locate/phytol
Structural modification, fungicidal and insecticidal activity of 5-
arylbenzofuran neolignan from Magnolia officinalis
a
a
a
a
a
a,⁎
b
Ding Lin , Zhongzhong Yan , Yangjie Yi , Kangming Li , Jiao Ye , Aixi Hu , Chuyun Long ,
b,⁎
Aiping Liu
a
College of Chemistry and Chemical Engineering, Hunan University, Changsha, 410000, China
b
National Engineering Research Center for Agrochemicals, Hunan Research Institute of Chemical Industry, Changsha, 410000, China
A R T I C L E I N F O
A B S T R A C T
Keywords:
As shown in a number of previous researches, the extracts of Magnolia officinalis exhibited broad-spectrum
fungicidal and insecticidal activity. In our preliminary study, 5-arylbenzofuran neolignans, the secondary me-
tabolite of Magnolia officinalis, was found to inherit the activity of Magnolia officinalis. For developing novel
agrochemicals, natural 5-arylbenzofuran neolignan was selected as lead compound. After structural optimiza-
tion, the fungicidal and insecticidal activity and selectivity were significantly improved. Compounds 5a, 5b, 6c
and 6d displayed similar or equivalent activity compared with the positive controls against corresponding fungi
or pests. Especially, compounds 6c and 6d exhibited the most promising insecticidal ability against Aphis fabae
with the LC50 values of 3.56 mg/L and 5.96 mg/L, respectively. The preliminary structure-activity relationship
was obtained, and the promising derivatives showed low toxicity in the model of human cells. The results of
research indicated great potential of 5-arylbenzofuran neolignan derivatives in the field of fungicide and in-
secticide.
5
-Arylbenzofuran neolignan
Fungicidal
Insecticidal
Structural optimization
Structure-activity relationship
1
. Introduction
literatures, the extracts of Magnolia officinalis showed broad-spectrum
inhibitory activity against plant pathogenic fungi and insect pests
Agricultural chemicals have been used all over the world to guar-
(Boulogne et al., 2012; Choi et al., 2009; Hu et al., 2013; Ye et al., 2015;
Vásquez-Morales et al., 2015; Yang et al., 2015). 5-Arylbenzofuran
neolignans are the secondary metabolites produced by Magnolia offici-
nalis and a newfound class of natural compounds (Kuo et al., 2013). In
our preliminary research, 5-arylbenzofuran neolignan (1, Fig. 1) was
also found having moderate to potent fungicidal and insecticidal ac-
tivity. In consideration of the activity and low molecular weight, it’s
appropriate to be used as the lead compound for the development of
agrochemical with novel skeleton, high effect and low toxicity. There-
fore, in this work, a variety of 5-arylbenzofuran neolignan derivatives
were synthesized and investigated for their fungicidal and insecticidal
activity.
antee the food supplies. However, with the emergence of resistance of
harmful organisms and the increasing environmental and toxicological
requirement, a great deal of traditional agrochemicals were faced with
elimination (Paulraj et al., 2017; Shi et al., 2016). It’s important to
develop new agrochemicals with novel skeleton, high activity and low
toxicity.
In the long evolutionary process, plants produced many secondary
metabolites to protect themselves from pathogens, pests and weeds.
Those plant-sourced bioactive substances often have moderate to strong
activity and high safety for crops and environments (Benelli et al.,
2
017). Some secondary metabolites of plants have been directly used in
the agricultural production, such as Toosendanin (Xu et al., 2018) and
nicotine (Yang et al., 2018). Some other secondary metabolites became
the lead compounds of modern agrochemicals (Fig. 1), such as Phy-
sostigmine which was the lead of carbamate insecticides, Pyrethrin I
which was the origin of pyrethroids insecticides, and indole-3-acetic
acid, the lead of auxin herbicides (Sparks et al., 2017).
2. Results and discussion
2.1. Chemistry
As outlined in Scheme 1, natural 5-arylbenzofuran neolignan 1,
which can only be extracted from Magnolia officinalis in a very low yield
Magnolia officinalis is a species of Magnoliaceae. According to the
⁎
Corresponding authors.
E-mail addresses: axhu@hnu.edu.cn (A. Hu), lapliu@yahoo.com (A. Liu).
https://doi.org/10.1016/j.phytol.2019.01.016
Received 27 August 2018; Received in revised form 20 December 2018; Accepted 11 January 2019
1874-3900/ © 2019 Phytochemical Society of Europe. Published by Elsevier Ltd. All rights reserved.

D. Lin et al.
Phytochemistry Letters 30 (2019) 53–57
Fig. 1. Design strategy of the novel fungicidal and insecticidal agents developed from 5-arylbenzofuran neolignan.
Scheme 1. Reagents and conditions: (a) PdCl
DMA/H O, 60 °C, 86%; (b) NaNO , concentrated hydrochloric
acid(36–38%), MeCN/H O, r.t., 77%; (c) Zn, NH Cl, HOAc,
EtOH/H O, r.t., 73%; (d) chloroacetyl chloride, CO
CH Cl , r.t., 81%; (e) acryloyl chloride, K CO , CH , r.t.,
2
, NaOAc, O
2
,
2
2
2
4
2
K
2
2
3
,
2
2
2
3
2
Cl
4
6%; (f) acetic anhydride, K
2
CO , ethyl acetate, r.t., 88%; (g)
3
dimethylamine, HCHO(37%), MeOH, 60 °C, 53%; (h) appro-
priate cyclic secondary amine, HCHO(37%), MeOH, 60 °C,
5
5–83%; (i) appropriate cyclic secondary amine, NEt , THF,
3
r.t., 48–85%; (j) substituted benzaldehyde, acetic acid, EtOH,
r.t., 29–73%; (k) chloroacetyl chloride, DMAP, NEt , THF/
CH Cl , r.t. to reflux, 44%; (l) oxalyl chloride, NEt , CH Cl
r.t., 42%; (m) triethyl orthoformate, NEt , 60 °C, 76%; (n)
triphosgene, NEt , CH Cl , r.t., 59%.
3
2
2
3
2
2
,
3
3
2
2
before (Kuo et al., 2013), was now semi-synthesized from honokiol, an
easily available natural product, in a high yield by Wacker-type in-
tramolecular cyclization (Mitsudome et al., 2006). Compound 3 was
synthesized by the reduction of compound 2, which was prepared via
the nitrosation of 1. Compounds 4 were obtained from 3 by acylation
reaction with chloroacetyl chloride, acryloyl chloride or acetic anhy-
dride, respectively. Compounds 5 were generated through Mannich
reaction of 1 with formalin and appropriate secondary amine. Com-
pounds 6 were prepared by the substitution reaction between com-
pound 4a and appropriate cyclic secondary amine. Schiff base
derivatives 7 were synthesized through the condensation reaction of
compound
3 with corresponding substituted benzaldehyde. Ad-
ditionally, oxazine and oxazole derivatives 8 were obtained by the
cyclization of compound 3 with chloroacetyl chloride, oxalyl chloride,
triethyl orthoformate or triphosgene, respectively. The synthetic pro-
cedures and characterizations are provided in the Supplementary ma-
terial.
54

D. Lin et al.
Phytochemistry Letters 30 (2019) 53–57
Fig. 2. Single crystal of compound 7c.
Table 1
Table 2
The fungicidal activities of target compounds tested at the concentration of
The insecticidal activities of target compounds tested at the concentration of
2
5 mg/L for 72 h.
Compd.
500 mg/L for 72 h.
Compd.
Inhibition rate / %
Mortality rate/%
Pc
Aa
Gz
Bc
Ss
Ms
Af
Tu
1
3
26.1
14.5
23.0
19.7
19.7
57.8
50.7
36.2
39.4
18.3
14.5
25.4
4.9
20.0
2.5
28.8
8.5
42.2
31.3
24.1
37.0
48.2
40.0
34.4
46.9
51.1
13.3
31.3
40.0
3.7
40.2
33.8
26.2
37.6
45.6
46.3
35.8
43.3
59.4
23.5
30.2
35.7
5.3
1
75
39
25
45
5
0
0
3
0
0
4
4
4
5
5
5
5
5
5
6
6
6
6
6
7
7
7
7
8
8
8
8
a
b
c
a
b
c
d
e
f
17.1
17.1
19.5
41.3
47.5
27.5
39.1
15.2
10.0
23.9
2.4
27.4
12.9
16.1
9.5
4a
0
0
4b
0
0
4c
0
0
5a
0
7
2
25.4
25.4
25.7
18.9
0
5b
60
90
0
0
0
5c
18
50
13
40
6
0
5d
21
0
5e
0
5f
85
0
0
a
b
c
d
e
a
b
c
d
a
b
c
d
0
6a
0
16.1
14.5
17.6
4.1
6b
65
25
0
5
0
0
4.9
87.0
48.9
6.7
85.8
50.3
4.3
6c
100
100
22
7
0
32.4
19.7
7.3
26.1
17.4
2.5
6d
21
9
6e
0
1.7
23.4
22.2
20.4
23.4
27.8
37.0
47.4
3.7
20.0
20.1
22.4
22.5
28.7
37.6
38.8
4.3
7a
55
70
55
70
80
30
5
0
11.5
3.3
0
4.8
7b
3
0
7.3
12.9
25.4
27.4
16.1
26.9
21.0
14.0
37.0
–
7c
20
13
8
0
7.3
5.0
7d
0
16.4
18.0
18.2
0
9.8
8a
15
0
22.0
30.2
14.6
–
8b
21
28
13
–
8c
0
8d
90
100
–
0
Thifluzamide
Boscalid
63.0
5.3
–
36.9
100
93.5
–
Chlorantraniliprole
Imidacloprid
Spirotetramatα
–
–
–
100
–
–
Azoxystrobin
Dimethachlon
56.1
–
–
47.6
–
–
83
100
–
–
: not determined; Ms: Mythimna separate; Af: Aphis fabae; Tu: Tetranychus ur-
α
–
: not determined; Pc: Phytophythora capsici; Aa: Alternaria alternata; Gz:
ticae; Spirotetramat was tested at the concentration of 20 mg/L.
Gibberella zeae; Bc: Botrytis cinerea; Ss: Sclerotonia sclerotiorum.
2
.3. Biological activities
2
.2. Crystal structure
2.3.1. Fungicidal activity
For well characterization of target compounds, compound 7c was
The in vitro fungicidal activities of target compounds against
determined by single-crystal X-ray diffraction. The data obtained from
X-ray investigation are in good agreement with the structure of com-
pound 7c (Fig. 2). It’s showed that the double bond of compound 7c is
Phytophythora capsici, Alternaria alternate, Gibberella zeae, Botrytis ci-
nerea and Sclerotonia sclerotiorum were tested according to our pre-
viously reported method (Yan et al., 2018) at the concentration of
“
E” configuration. The crystal of compound 7c is made up of triclinic
2
5 mg/L for 72 h. The results of fungicidal activities were listed in
unit cells, each containing two molecules which are stabilized by π-π
conjugation of benzofuran rings. The bond distances and experimental
parameters are supplied in the Supplementary material. Additional data
are available from the Cambridge Crystallographic Data Centre (www.
ccdc.cam.ac.uk) as CCDC 1886118.
Table 1. Thifluzamide, Boscalid, Azoxystrobin and Dimethachlon were
selected as the positive controls. Natural product 1 exhibited moderate
antifungal activity against all tested fungi. With modification, the ac-
tivities and selectivity were changed in some extent. The introduction
of Mannich base always enhanced the inhibitory activity against Pc
(
Phytophythora capsici) and Aa (Alternaria alternate), especially
55

D. Lin et al.
Phytochemistry Letters 30 (2019) 53–57
Table 3
The LC50 values of compounds 6c and 6d against Aphis fabae.
Compd.
Regression Equation
Correlation
95% Confidence Intervals (mg/L)
MW
LC50
6
6
c
y = 4.7504 + 0.4522x
y = 4.4630 + 0.6918x
y = 4.0389 + 2.2634x
0.9855
0.8912
0.9693
2.61–4.86
2.95–12.11
1.96–3.60
419.52
433.55
373.45
3.56 mg/L
5.96 mg/L
2.66 mg/L
8.48 μM
13.75 μM
7.12 μM
d
Spirotetramat
Table 4
3. Conclusions
Cytotoxicity of natural compound 1 and promising compounds 5a, 5b and 6c.
In conclusion, natural 5-arylbenzofuran neolignan 1 was semi-syn-
thesized and 23 kinds of derivatives were designed and prepared. All
the target compounds were evaluated for their fungicidal and in-
secticidal activity. Several compounds exhibited more potent inhibitory
activity than natural compound 1 against tested fungi and pests.
Thereinto, compounds 5a, 5b and 6c displayed promising antifungal
activity against certain fungi at the concentration of 500 mg/L.
Compounds 6c and 6d showed similar insecticidal ability with the
commercial insecticide against Aphis fabae with the LC50 values of
Compd.
IC50/μM
HepG2
A549
K562
1
125.60 ± 2.26
> 128
115.55 ± 2.05
> 128
126.20 ± 1.56
> 128
5
5
6
a
b
c
> 128
> 128
> 128
98.59 ± 7.80
75.41 ± 2.27
61.27 ± 5.63
compounds 5a and 5b, the activities of which against Pc were similar to
the positive controls Thifluzamide and Azoxystrobin. Compound 6c
displayed the best fungicidal activity and selectivity against Bc (Botrytis
cinerea) and Ss (Sclerotonia sclerotiorum) with the inhibition rates of
8
.48 μM and 13.75 μM, respectively. Additionally, the lead compound 1
and promising compounds showed low toxicity in the model of human
cells. And the further research is underway. All the research results
above suggested great potential of 5-arylbenzofuran neolignan deriva-
tives as novel fungicides or insecticides with high effect and low toxi-
city. The research will also contribute to explore other biological ac-
tivities of 5-arylbenzofuran neolignan and its derivatives.
8
7.0% and 85.8% respectively, which were similar or stronger com-
pared to the positive controls Boscalid and Azoxystrobin. Conversely,
the amide (4a–4c), Schiff base (7a–7d), oxazine (8a,8b) and oxazole
(
8c,8d) derivatives showed low fungicidal activity against all tested
fungi.
Acknowledgement
This work was supported by the National Natural Science
Foundation of China (Nos. 21572050, 21442014).
2
.3.2. Insecticidal activity
The in vivo insecticidal activities of target compounds against
Mythimna separate, Aphis fabae and Tetranychus urticae were evaluated
according to our previously reported method (Huang et al., 2017) at the
concentration of 500 mg/L for 72 h. Chlorantraniliprole, Imidacloprid
and Spirotetramat was selected as the positive control. As shown in
Table 2, natural product 1 displayed potent insecticidal activity against
Ms (Mythimna separate) with the mortality rate of 75%, but have no
effect on Af (Aphis fabae) and Tu (Tetranychus urticae). After modifica-
tion, compounds 5c, 5f, 8a and 8d showed better insecticidal activity
against Ms than natural compound 1. What is more surprising is that
compounds 6c and 6d exhibited 100% kill rate against Af, which is
worthy to be further investigated. Therefore, 6c and 6d were singled
out to evaluate the LC50 against Af. As displayed in Table 3, the LC50
values of 6c and 6d were 3.56 mg/L (8.48 μM) and 5.96 mg/L
Appendix A. Supplementary data
Supplementary material related to this article can be found, in the
online version, at doi:https://doi.org/10.1016/j.phytol.2019.01.016.
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