Synthesis and fungicidal activity study of novel daphneolone analogs with 2,6-dimethylmorpholine

Article abstract of DOI:10.1016/j.cclet.2016.01.045

A series of novel daphneolone analogs was designed and synthesized on the basis of natural product 1,5-diphenyl-2-penten-1-one (I) from Stellera chamaejasme L. as lead compound, whereby 2,6-dimethylmorpholine moiety was introduced to replace 1-phenyl group. Their structures were confirmed by IR, ¹H NMR, and HRMS (ESI) or elemental analysis, ¹³C NMR for some representative compounds. The two isomers of target compounds were separated and identified by NOESY technique and chemical method. All of the synthesized compounds have been evaluated for anti-plant pathogenic fungi activities. The results showed that some compounds exhibited moderate to good antifungal activities against tested fungi at the concentration of 50 mg/L. Among them, compound 7d, with a 4-bromine-substituted phenyl group and cis-2,6-dimethylmorpholine moiety, displayed best activity with an EC₅₀ of 23.87 μmol/L against Valsa Mali, superior to lead compound I. In addition, preliminary structure-activity relationship analysis indicated that, between two isomers of target compounds, the antifungal activities of the isomer with cis-2,6-dimethylmorpholine were better than the trans-isomer.

Full text of DOI:10.1016/j.cclet.2016.01.045

Chinese Chemical Letters 27 (2016) 555–558
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Chinese Chemical Letters
journal homepage: www.elsevier.com/locate/cclet
Original article
Synthesis and fungicidal activity study of novel daphneolone analogs
with 2,6-dimethylmorpholine
Gao-Fei Xu a, Xin-Ling Yang a, Peng Lei a, Xi-li Liu b, Xue-Bo Zhang a, Yun Ling a,
*
a Department of Applied Chemistry, College of Science, China Agricultural University, Beijing 100193, China
b Department of Plant Pathology, College of Agronomy and Biotechnology, China Agricultural University, Beijing 100193, China
A R T I C L E I N F O
A B S T R A C T
Article history:
A series of novel daphneolone analogs was designed and synthesized on the basis of natural product 1,5-
diphenyl-2-penten-1-one (I) from Stellera chamaejasme L. as lead compound, whereby 2,6-dimethyl-
morpholine moiety was introduced to replace 1-phenyl group. Their structures were confirmed by IR,
1H NMR, and HRMS (ESI) or elemental analysis, 13C NMR for some representative compounds. The two
isomers of target compounds were separated and identified by NOESY technique and chemical method.
All of the synthesized compounds have been evaluated for anti-plant pathogenic fungi activities. The
results showed that some compounds exhibited moderate to good antifungal activities against tested
fungi at the concentration of 50 mg/L. Among them, compound 7d, with a 4-bromine-substituted phenyl
Received 5 November 2015
Received in revised form 3 December 2015
Accepted 13 January 2016
Available online 2 February 2016
Keywords:
Daphneolone analogs
2,6-Dimethylmorpholine
Stellera chamaejasme L.
Synthesis
group and cis-2,6-dimethylmorpholine moiety, displayed best activity with an EC50 of 23.87
mmol/L
against Valsa mali, superior to lead compound I. In addition, preliminary structure–activity relationship
analysis indicated that, between two isomers of target compounds, the antifungal activities of the isomer
with cis-2,6-dimethylmorpholine were better than the trans-isomer.
Fungicidal activity
ß 2016 Chinese Chemical Society and Institute of Materia Medica, Chinese Academy of Medical Sciences.
Published by Elsevier B.V. All rights reserved.
1. Introduction
synthesized by Hou’s group [6–8]. Our team is also devoted to the
structural modification of I and II in the previous study. We found,
Natural products (NPs) continue to play a highly significant role
in the drug discovery and development process [1]. Natural
products and their analogs, derivatives account for almost half of
the 877 approved drugs all over the world from 1981 to 2010 [2]. In
fact, exploring a range of natural product sources is also an
important means to identify and develop novel lead compounds
and agrochemicals against a range of insect pest and plant diseases
in the recent decades. 1,5-Diphenyl-2-penten-1-one (I) and 1,5-
diphenylpentan-1-one (II) (Fig. 1) were first isolated from Stellera
chamaejasme L. (Thymelaeaceae, used in Chinese traditional
medicine) in 2001 [3]. Laboratory bioassay showed that these
two compounds had strong contact activity and very good
antifeedant activity against Aphis gossypii and Schizaphis
graminum. Moreover, compound I exhibited the similar effects
on ATP-ase found in the three membranes amongst which the
plasma membrane Ca2+-Mg2+-ATPase is the primary target
[4,5]. After that, various analogs with different bioactivities were
beside insecticidal activity, compounds I, II and their analogs also
have antifungal activities [9–12], which indicated that they could
be an interesting lead structure of fungicide.
In continuation of our earlier interest in this field, here it was
planned to synthesize new analogs by introducing 2,6-dimethyl-
morpholine moiety, a functional group of commercial fungicide
fenpropimorph, tridemorph, dodemorph, etc., to replace one side
phenyl group of compound I, with expectation to obtain the new
products with simple structure and better antifungal activities. The
two isomers of target compounds were separated and identified by
NOESY technique and chemical method. Their antifungal activities
against six plant pathogenic fungi were evaluated for the first time.
It is expected that the results of this study might be valuable for the
discovery of new molecules as agrochemicals.
2. Experimental
1H NMR spectra were collected on Bruker AM-300 (300 MHz)
spectrometer with CDCl3 as the solvent and TMS as the internal
standard. IR spectra were recorded on a Perkin Elmer Spectrum
100 FT-IR spectrometer with a KBr disk. High resolution mass
*
Corresponding author.
E-mail address: lyun@cau.edu.cn (Y. Ling).
http://dx.doi.org/10.1016/j.cclet.2016.01.045
1001-8417/ß 2016 Chinese Chemical Society and Institute of Materia Medica, Chinese Academy of Medical Sciences. Published by Elsevier B.V. All rights reserved.

556
G.-F. Xu et al. / Chinese Chemical Letters 27 (2016) 555–558
(18 mmol) and one to two drop of N,N-dimethyl formamide (DMF)
was added, the resulted mixture was refluxed for 1 h. Then the
solvent and remaining thionyl chloride was removed under reduced
pressure, theresiduewasdissolvedindichloromethane(DCM)toget
the stock solution of 6 without further purification. The solution of
6 was dropped slowly into the solution of 2,6-dimethylmorpholine
(6 mmol) and TEA (6.6 mmol) in DCM at 0 8C, the resulted mixture
was stirred for 1 h. After the reaction completed, the mixture was
washed with water. Organic layer was dried over anhydrous MgSO4
and concentrated in vacuo. Then the residue was separated by
chromatography on silica-gel column (n-hexane:ethyl acetate = 4:1,
v/v) to obtain the corresponding 7a–7g, 8a–8g.
Fig. 1. The chemical structure of compounds I and II, originally isolated from Stellera
chamaejasme L.
spectrometry (HRMS) data were recorded on an FTICR-MS Varian
7.0 TFTICR-MSinstrument. Elemental analysis wasdetermined on an
ST-Carloerba. Co elemental analyser. All the reagents were obtained
commercially and used without further purification. Column
chromatography purification was carried out by using silica gel.
The general synthetic scheme for representative compounds
7a–7g, 8a–8g is shown in Scheme 1. Substituted cinnamic acids 2
were prepared from substituted benzaldehyde 1 through knoe-
venagel reaction according to the method in the literature
[13]. Compounds 2a–2g were reduced by lithium aluminum
hydride (LiAlH4) to afford substituted phenylpropanol 3a–3g. Next,
compounds 3a–3g were oxidized by PCC to afford substituted
benzenepropanal 4. (E)-5-(Substituted phenyl)pent-2-enoic acids
5 were obtained through the same process as compound 2. The
general procedure of compounds 2a–2g to 5a–5g is described in
the Supporting information.
3. Results and discussion
As shown in Scheme 1, the target compounds 7a–7g, 8a–8g
were synthesized via six steps, including Knoevenagel reaction,
reduction, oxidation, and amidation, with substituted benzalde-
hyde as starting material. Characterization data of all the target
compounds are included in the Supporting information. The
material 2,6-dimethylmorpholine we used in the last step was
consisted of a mixture of cis-form and trans-form, due to the two
methyl group could be on the same side or the different side of
morpholine ring, namely cis-2,6-dimethylmorpholine and trans-
2,6-dimethylmorpholine. Therefore we obtained our target com-
pounds with two isomers (7 and 8) as well, which can be separated
easily by silica-gel column but very complicated to be identified.
Clear difference could be seen on the 1H NMR spectra of two
representative compounds 7f and 8f (Fig. 2). First, NOESY
Target compounds 7a–7g and 8a–8g were prepared by the
acylchloriration of compounds 5a–5g followed by a condensation
reaction with 2,6-dimethylmorpholine at the presence of triethy-
lamine (TEA). The general procedure describe as below: To a stirred
solution of compounds 5 (6 mmol) in chloroform, thionyl chloride
Scheme 1. Synthetic route of title compounds. (i) piperidine, pyridine, 85 8C, 6 h; (ii) LiAlH4, THF, reflux, 4 h; (iii) PCC, CH2Cl2, r.t. 1 h; (iv) piperidine, pyridine, 85 8C, 6 h; (v)
SOCl2, DMF, CHCl3, reflux 1 h; (vi) TEA, CH2Cl2, r.t. 2 h.
Fig. 2. The 1H NMR spectra of compound 7f, 8f and 9.

G.-F. Xu et al. / Chinese Chemical Letters 27 (2016) 555–558
557
Scheme 2. Synthesis of compound 9.
Fig. 3. NOE in cis- and trans-configuration.
spectrum of 9 coincided exactly with the 1H NMR spectrum of
compound 7f (Fig. 4). Therefore 7f should be the isomer with cis-
configuration. This result is same with the previous deduction. On
the basis of the above results, we can identify both isomers of all
the other target compounds.
technique was used to identify the two isomers. As shown in Fig. 3,
in the case of cis-form, there are two equatorial CH3-groups at 2,6-
position, NOEs between the protons of H2ax and H6ax, H3ax and
H5ax should occur. While in the case of trans-form, there is one
equatorial and one axial CH3-group, NOE should only occur
between the protons of H2ax and H6ax. Therefore we expected two
observable NOEs in the cis-configuration but only one NOE in the
trans (Fig. 3). Experimentally, as shown in Fig. 4, for 7f, the signal at
4.47 ppm shows NOE with the signal at 3.58 ppm, the signal at
2.74 ppm shows NOE with the signal at 2.33 ppm, therefore this
correspond to the cis-configuration. For 8f, the signal at 3.82 ppm
shows NOE with the signal at 3.47 ppm, and therefore this
correspond to the trans-configuration.
The target compounds were evaluated for fungicidal activities
against six plant pathogenic fungi (Valsa mali, Pythium aphani-
dermatum, Rhizoctorzia solani, Alternaria solani, Bipolaris maydis and
Sclerotinia sclerotiorum) at the concentration of 50 mg/L according
to the method reported in the literature [14]. Difenoconazole, a
commercial fungicide, was used as positive control. The results
were summarized in Table 1. Data in Table 1 indicated that these
compounds showed fungicidal activities at different degree.
Generally, these compounds exhibited better activities against
V. mali than the other tested fungi. Among them, the inhibitory
rates of 7c and 7d against V. mali reached 76.8% and 90.7%,
respectively, obviously superior to that of the lead compound (I)
(45.1%). This result indicated that an electron-withdrawing substit-
uent is more desirable than an electron-donating substituent to
Finally, in order to verify this deduction, we further chose
commercial available cis-2,6-dimethylmorpholine reacted with
(E)-5-(4-ethoxyphenyl)pent-2-enoyl chloride (6f) to obtain com-
pound 9 (Scheme 2) with cis-configuration. As a result, the 1H NMR
Fig. 4. NOESY spectrum of compound 7f and 8f.
Table 1
Fungicidal activities of the target compoundsa.
Compd.
Inhibitory %
V. mali
P. aphanidermatum
R. solani
A. solani
B. maydis
S. sclerotiorum
7a
18.3
16.3
24.0
25.6
76.8
51.6
90.7
59.8
53.3
33.3
33.3
27.2
19.5
22.0
45.1
100.0
13.3
11.7
23.8
11.3
31.3
29.6
40.4
29.6
25.4
14.2
20.4
20.0
15.4
12.5
30.4
57.9
32.9
23.3
32.5
27.3
60.6
48.6
70.7
57.4
61.8
36.5
43.0
45.4
44.2
29.7
83.5
88.0
19.0
16.8
23.9
23.1
40.0
31.0
45.3
23.9
26.9
19.8
23.5
13.0
19.8
16.0
33.3
88.4
13.8
26.3
19.8
15.0
49.1
44.9
51.5
34.1
44.3
42.5
30.5
33.5
35.9
21.0
44.9
65.3
36.1
36.1
40.7
27.4
53.9
34.0
33.2
30.3
28.2
57.3
12.0
17.8
16.6
36.1
41.5
96.7
8a
7b
8b
7c
8c
7d
8d
7e
8e
7f
8f
7g
8g
Compound I
Difenoconazoleb
a
The inhibitory data were measured at concentration of 50 mg/L.
Difenoconazole was used as the positive control.
b

558
G.-F. Xu et al. / Chinese Chemical Letters 27 (2016) 555–558
Table 2
exhibited good fungicidal activities against tested fungi at the
concentration of 50 mg/L. Compound 7d, with a 4-bromine-
substituted benzyl group and cis-2,6-dimethylmorpholine moiety,
showed the best fungicidal activity against V. mali with 90.7%
inhibition rate at the concentration of 50 mg/L and EC50 value of
The EC50 value of compounds 7c, 8c, 7d and 8d against
Valsa mali.
Compd.
EC50 (mmol/L)
7c
43.56
23.87
66.29
42.79
40.34
7d
23.87
mmol/L. Initial structure-activity relationship revealed that,
8c
the configuration of target compounds had a remarkable effect on
the fungicidal activities of these analogs. Between two isomers of
the target compounds, the fungicidal activities of the isomer with
cis-2,6-dimethylmorpholine were better than the trans-isomer.
Further studies on the structural optimization are in progress in
our laboratory.
8d
Compound I
Difenoconazolea
0.047
a
Commercial difenoconazole was used as positive
control.
generate a compound with better fungicidal activity. What is more,
amongst the analogs containing a halogen substituent on the
benzene ring, the electronegativity of the halogen had a markedly
influence on the fungicidal activities. The compounds containing a
halogen with weaker electronegativity showed better activities
against most of the tested fungi than those compounds containing a
halogen with bigger electronegativity. For example, the order of the
fungicidal activities of compounds 7b (with a fluorine substituent),
7c(witha chlorinesubstituent), and7d(witha brominesubstituent)
could be placed as following: 7d > 7c > 7b. Also, compounds 8b, 8c,
8d, hadthesimilarresults. Andinterestingly,theconfigurationofthe
Acknowledgments
This work was financially supported by the National Natural
Science Foundation of China (No. 21272266) and the National High
Technology Research and Development Program of China (No.
2011AA10A202).
Appendix A. Supplementary data
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.cclet.2016.01.
045.
2,6-dimethylmorpholine moiety of target compounds had
a
remarkable effect on the fungicidal activities of these analogs. As
a whole, thefungicidalactivities against almostallthetestedfungiof
the isomer with cis-2,6-dimethylmorpholine were better than the
trans-isomer, especially against V. mali, P. aphanidermatum, R. solani
and A. solani. Moreover, the activities of compounds 7g and 8g
indicated that the introduction of thiophene group is unfavorable to
the fungicidal activity.
In addition, the EC50 value of comparatively potent compounds
7c, 7d, 8c, and 8d against V. mali were further tested (Table 2).
Compound 7d, with a 4-bromine-substituted benzyl group and cis-
2,6-dimethylmorpholine moiety, exhibited the highest activity
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4. Conclusion
In summary, a series of novel daphneolone analogs containing
2,6-dimethylmorpholine moiety were designed and synthesized
on the basis of natural product 1,5-diphenyl-2-penten-1-one (I)
from S. chamaejasme L. The two isomers of target compounds were
separated and identified. All the compounds were evaluated for
their fungicidal activities against six plant pathogenic fungi.
Bioassay results indicated that some of the target compounds