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Discovery of γ-lactam derivatives containing 1,3-benzodioxole unit as potential anti-phytopathogenic fungus agents
Journal Pre-proofs Discovery of γ-lactam derivatives containing 1,3-benzodioxole unit as potential anti-phytopathogenic fungus agents Di Song, Xiufang Cao, Jingjing Wang, Shaoyong Ke PII: DOI: Reference:
S0960-894X(19)30795-4 https://doi.org/10.1016/j.bmcl.2019.126826 BMCL 126826
To appear in:
Bioorganic & Medicinal Chemistry Letters
Received Date: Revised Date: Accepted Date:
10 October 2019 12 November 2019 14 November 2019
Please cite this article as: Song, D., Cao, X., Wang, J., Ke, S., Discovery of γ-lactam derivatives containing 1,3benzodioxole unit as potential anti-phytopathogenic fungus agents, Bioorganic & Medicinal Chemistry Letters (2019), doi: https://doi.org/10.1016/j.bmcl.2019.126826
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
© 2019 Published by Elsevier Ltd.
Discovery of γ-lactam derivatives containing 1,3-benzodioxole unit as potential anti-phytopathogenic fungus agents Di Songa, Xiufang Caoa,*, Jingjing Wanga, Shaoyong Keb,*
aCollege
bNational
of Science, Huazhong Agricultural University, Wuhan 430070, China
Biopesticide Engineering Research Center, Hubei Biopesticide Engineering Research Center, Hubei Academy of Agricultural Science, Wuhan 430064, China
Address for correspondence: Xiufang Cao, College of Science, Huazhong Agricultural University; Email: [email protected] (X. Cao), or National Biopesticide Engineering Research Center, Hubei Academy of Agricultural Science; Email: [email protected] (S. Ke)
ABSTRACT: A series of γ-lactam analogs containing 1,3-benzodioxole moiety were designed, and these derivatives were synthesized from the lead compound of lactam via a structural diversityoriented synthesis, their structures were confirmed by 1HNMR,13CNMR, ESI-MS spectrum. Their antifungal activities were evaluated against four serious and typically crop-threatening agricultural fungi, including Rhizoctonia solani, Alternaria tenuis Nees, Gloeosporium theae-sinensis, and Fusarium graminearum. Some of these derivatives exhibited activity against Alternaria tenuis Nees higher than that of commercial fungicides carbendazim, such as compounds 7a, 7b, and 7i, compared with the blank control, some of these derivatives showed good antifungal activities against Gloeosporium theae-sinensis and Fusarium graminearum. The systematic study provides evidences for further structural modification and application of lactam analogues as antifungal 1
agents for agriculture. KEYWORDS: γ-lactam, 1,3-benzodioxole, diversity-oriented, antifungal activities, agricultural fungi
2
Over the past decades, a variety of fungi threaten the crops and severely disrupted agricultural production, the emergence of fungicides has solved these problems. However, long-term use of fungicide can cause lots of problems, such as environment pollution, food safety threats and resistance.1-3 Therefore, the development of environmentally-friendly fungicide is important. Natural products play an important role in the source of drugs,4 and many drugs are derived from natural products,5 some derivatives of natural products also have been commercialized successfully.6-7 1,3-Benzodioxole unit is ubiquitous in natural products8 and pharmaceuticals,9 it has been found that its derivatives had antioxidant and antibacterial activity.10 In the field of medicine, several derivatives containing the structure of 1,3-benzodioxole have been used in clinic, such as Oxolinic Acid,11 Cinoxacin12 and Miloxacin (Fig. 1).13 Nitrogen-containing heterocyclic compounds are very important structures in nature, they exist in lots of natural products14 and medicines.15-18 In the family of nitrogen-containing heterocycles, the γ-lactam core, found in many natural products and medicinally significant compounds (Fig. 2), is a very important building block in chemical synthesis. Many γ-lactams in the pronounced diversity of biological activity, such as antibacterial,19 antifungal,20 antitumor,21 anticancer,22 inhibition of HIV.23 It is expected that modification on the γlactam core should generate more derivatives of potential biological activities.
3
OMe
O O t uc od pr l a tur Na
O
O
OMe
O
N
OMe O
O
O
OMe Piperine
Glaziovianin A
O 1,3-Benzodioxole P ha rm ac eu tic al
O O
O
O OH
O
OH
O
N Oxolinic Acid
O
O
O N
N
O
O
OH
O
Cinoxacin
N O Miloxacin
Fig. 1. Natural product and drugs containing the structure of 1,3-benzodioxole
R HO OH O N OH CH3
O
O C9H19
N
O
HO
NH HO
MeO OH
HN R
O
OH
R= OH
OMe Pramanici
(-)-Clausenamide
Heliotropamide
Fig. 2. Natural products containing the structure of γ-lactam In our previous work, we found that when the heterocyclic lactam derivatives contained 1,3benzodioxole unit,24 the activity was higher than those without 1,3-benzodioxole unit,25 the result indicated that the 1,3-benzodioxole unit could enhance the activity. It was known that molecular structures determine whether the molecules are bioactive, based on the previous work, we wondered if we could improve or modulate the activities of these compounds by changing the position of 1,3benzodioxole unit. Above all, we designed and synthesized a series of 1,3-benzodioxole analogues containing the γ-lactam core (Fig. 3), the fungicidal activities of these compounds were systematically studied.
4
O R
O
N n
O
Previous work
NH
R1
This work
N
O
n
R2 HO Lactam scaffold
O
O
O
R
1,3-Benzodioxole O Enhance activity
O
O
O
Location migration
Fig. 3. Design strategies for γ-lactam derivatives containing 1,3-benzodioxole structure As shown in the Scheme 1, by using the diversity-oriented synthesis strategy, series of novel γ-lactam analogues containing 1,3-benzodioxole can be easily synthesized through a common precursor. Firstly, amino acid and thionyl chloride react in methanol can get the amino acid ester, then the methyl ester reacts with compound 4 can get the amide 5. Finally, the amide 5 can transform to the lead compound 6 in the presence of appropriate base, and then the compound 6 reacted with different kinds of acyl chloride to produce final compounds, the type of these acyl chloride and the substituents on them directly affected the generation of the final products. n
COOH
SOCl2, MeOH
n
N H HCl
COOMe
2
1
n
N H
O
(COCl)2, CH2Cl2
COOH
COCl Et3N, CH2Cl2
3
O
O
O
4
O
tBuOK, THF
R OH
O
5
O
n
N
O
Cl
Et3N, CH2Cl2
6 n = 1, 2 Lead compound
n=1 n
N
O
O
O 7a:
O O
O
O
O
O
N
O O
;
;
7c:
O
O
O
7b:
; 7d:
O
O
O
; 7e:
CN
;
7f: CF3
R
;
7g: F
n=2 7a-7g n = 1 7h-7o n = 2
O
O 7h:
;
7i:
O
O ;
7j:
;
7k:
O
;
7l:
O
O O
;
O
O
7m: CN
;
7n:
; CF3
7o: F
Scheme 1 General synthetic route for target compounds 7a–7o In addition, many natural products containing 2(5H)-furanone moiety also exhibit broad biological activities, which is the biological isosteric unit of lactams. So, several compounds bearing 2(5H)-furanone moiety have also been synthesized for comparison with the γ-lactam compounds. As shown in the Scheme 2, the prepared acyl chloride 4 reacts with methyl glycolate to get the ester 8, then the ester can be transformed to compound 9 via heterocyclization reaction in the presence of 5
strong base, which reacts with various acyl chloride to produce the 2(5H)-furanone derivatives. O O
O
(COCl)2
COOH
DCM
O
COCl
HO
COOMe
Et3N, DCM
O
3 O O
O OH
O 9
R
O Cl
Et3N, DCM
COOMe
O O
4 O
O
8
O
O R=
O
7p:
O R
O 7p-7s
tBuOK, THF
O ;
7q:
O 7r:
;
7s:
; O O
Scheme 2 General synthetic route for compounds 7p-7s The γ-lactam analogues containing 1,3-benzodioxole 7a-o and the 2(5H)-furanone derivatives 7p-s were evaluated for their antifungal activity against four plant pathogenic fungi (Rhizoctonia solani, Alternaria tenuis Nees, Gloeosporium theae-sinensis, Fusarium graminearum), the commercial fungicides carbendazim and natural product piperine were used as controls in the second screening. The results of antifungal activities of these compounds in vitro are listed in Table 1 and Table 2. As shown in Table 1 and Table 2, most of these compounds displayed broad-spectrum activities on four fungi at 100 mg/L, it was an interesting phenomenon that when the intermediates were different, the activity of its derivatives was also different. Overall, when n = 1, the compounds showed higher activity than the compounds when the n = 2, the compounds 7a, 7b, 7c exhibited higher inhibitory effects against Fusarium graminearum than 7h, 7i and 7j, the inhibition rate of 7a and 7b reached 65.14% and 52.75%, notably, 7b showed higher inhibitory activity against Gloeosporium theae-sinensis than 7i, the inhibition rate of 7b reached 68.59%, however, the inhibition rate of 7i only reached 5.44%. The activity of lactam derivatives and 2(5H)-furanone derivatives was also different, for lactam derivatives, such as the compounds 7a and 7h exhibited higher inhibitory effects against Rhizoctonia solani and Alternaria tenuis Nees than the (5H)furanone derivative 7p, 7p had no activity against these two fungi. However, for the fungi of 6
Gloeosporium theae-sinensis and Fusarium graminearum, the (5H)-furanone derivative 7q showed higher inhibition activity than the lactam derivative 7i. To summarize, the novel γ-lactam derivatives and (5H)-furanone derivatives showed obvious antifungal activity for specific fungi, which emerged as new lead compounds for the development of the new antifungal agents.
Table 1 In vitro fungicidal activity of novel γ-lactam derivatives at 100mg/L O
N
n
O O R
O
Compound
n
7a
1
7b
1
7c
1
7d
1
Fungicidal activity (%)/100 mg/L
R O
O
O
O O
RS a
AT
GT
FG
28.35
37.99
21.82
65.14
34.76
38.64
68.59
52.75
6.10
15.14
46.25
47.25
16.46
15.80
24.96
10.09
29.88
0.00
20.59
16.97
23.48
2.74
32.37
16.06
0.00
0.00
38.48
1.83
22.87
3.39
34.99
33.49
47.56
34.73
5.44
40.83
0.00
13.19
59.86
21.56
0.00
0.00
32.37
13.76
0.00
0.00
12.30
0.00
0.00
0.00
32.37
2.75
O
7e
1 CN O
7f
1 CF3
O
7g
1 F
7h
2
7i
2
7j
2
7k
2
7l
2
7m
2
O
O
O
O O O O O CN
7
O
7n
2
23.48
18.41
41.10
32.57
0.00
15.14
36.30
0.00
CF3
O
7o
2 F
a
Rs, Rhizoctonia solani; At, Alternaria tenuis Nees; Gt, Gloeosporium theae-sinensis; Fg, Fusarium graminearum. Table 2 In vitro fungicidal activity of novel 2(5H)-furanone derivatives at 100mg/L O
O
O O R
O
Compound
Fungicidal activity (100%) at 100mg/L
R
O
7q
O
7r
O
7s
AT
GT
FG
0.00
0.00
35.86
29.82
38.72
12.53
38.79
55.50
0.00
0.00
31.50
7.34
0.00
4.05
42.84
5.50
RS
O
7p
O
a
a
Rs, Rhizoctonia solani; At, Alternaria tenuis Nees; Gt, Gloeosporium theae-sinensis; Fg, Fusarium graminearum.
According to the preliminary screening result, some compounds with obvious activity were chosen for further bioassay screening at different concentration (200, 100, 50, 25, 12.5 mg/L). The IC50 values of compounds were calculated by SPSS25.0 software, and the values were listed in Table 3. Table 3 The IC50 values of the selective compounds against the plant fungi Compound
Structure
n
7a
1 O
7b
n
1
O O
7c
N
O R
1
R
IC50(mg/L) a RS b
O
O
AT
GT
FG
—
121.75
—
205.77
117.43
159.64
64.47
113.47
—
—
130.70
148.67
O
8
7i
2
7j
2 O
7q O
O
Piperine c
O R
71.03
115.99
71.89
156.69
—
—
110.37
—
87.18
—
99.65
140.15
—
—
196.21
—
79.01
114.67
49.43
262.91
O
O
O
7s
O
O O
Carbendazim c
182.47
a Compound
concentration required to inhibit colony growth by 50%. b Rs, Rhizoctonia solani; At, Alternaria tenuis Nees; Gt, Gloeosporium theae-sinensis; Fg, Fusarium graminearum. c The commercial agricultural fungicides carbendazim and natural product piperine were used for the comparisons of the antifungal activities.
As shown in Table 3, the further bioassay screening showed that some compounds displayed good antifungal activities, especially compounds 7a, 7b, 7i and piperine showed higher activities against Alternaria tenuis Nees than the commercial antifungal carbendazim, the result indicated 7a, 7b, 7i can be used as new lead compounds for the development of the new antifungal agents. Besides, for the fungi of Fusarium graminearum, these compounds exhibited higher activities than the natural product piperine, the IC50 values of 7b, 7c, 7i and 7q range of 110 –157 mg/L compared with piperine (262.91 mg/L). Compounds 7i and 7q exhibited good antifungal activity against Rhizoctonia solani (Fig. 4), and compounds 7a and 7i indicated better activities against Alternaria tenuis Nees than the commercial anti-phytopathogenic fungus agent carbendazim (Fig. 5).
9
7i
7q
Piperine CK
12.5ppm
25ppm
50ppm
100ppm
200ppm
Fig. 4. Inhibitory effect of compounds 7i, 7q and Piperine on Rhizoctonia solani
7a
7i
Piperine
Carbendazim
CK
12.5ppm
25ppm
50ppm
100ppm
200ppm
Fig. 5. Inhibitory effect of compounds 7a, 7i, Piperine and Carbendazim on Alternaria tenuis Nees According to the Table 1, Table 2, Table 3, we realized that the structure affected activity, different structures displayed different activities, so we decided to discuss the structure-activity relationship of the lactam and (5H)-furanone derivatives. Firstly, we discussed the lactam derivatives with different substituents, as shown in Table 1 and Table 2, when n = 1, focusing on the 7a, 7b, 7c compounds. When the R were alkyl substituents, the antifungal activities higher against Alternaria tenuis Nees and Fusarium graminearum than the 7e, 7f, 7g, which the R were aryl substituents. When the substituents are the same, the antifungal activities of 7a, 7b, 7c higher against Fusarium graminearum than the 7h, 7i, 7j. When the active units were different, the 10
substituents were same, such as 7d, 7k, 7s, the antifungal activity against Gloeosporium theaesinensis: 7s > 7k > 7d, the result indicated that the activity of (5H)-furanone structure was higher than the lactam structure against Gloeosporium theae-sinensis. Above all, a series of novel γ-lactam and 2(5H)-furanone derivatives containing 1,3benzodioxole were designed, synthesized and evaluated for their fungicidal activities against four plant fungi. All structures of compounds were confirmed by 1H NMR, 13C NMR and ESI-MS. Some of the compounds exhibited potent antifungal activity against two phytopathogenic fungi. Compound 7b showed the highest antifungal activity in vitro against Gloeosporium theae-sinensis and Fusarium graminearum with IC50 values of 64.47 and 113.47 mg/L. Moreover, it is noteworthy that compounds 7a, 7b and 7i displayed higher inhibitory activities against Alternaria tenuis Nees than the commercial fungicide carbendazim, which emerged as new lead compounds for the development of the new antifungal agents, we also summarized the potential structure-activity relationship of some compounds, which could lay the foundation for further structural modification and application of lactam analogues as antifungal agents for agriculture.
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Graphical Abstract O R
O
N O
O
n
Previous work
NH
R2 HO Lactam scaffold
O
O
R1
O
1,3-Benzodioxole Enhance activity
This work
O N
O
n O
O
R Location migration
A series of γ-lactam analogs containing 1,3-benzodioxole moiety were designed and synthesized, and their antifungal activities were evaluated against four serious and typically crop-threatening
agricultural
fungi,
Rhizoctonia solani, Alternaria tenuis Nees,
Gloeosporium theae-sinensis, and Fusarium graminearum. Some of these derivatives exhibited activity against Alternaria tenuis Nees higher than that of commercial fungicides carbendazim, such as compounds 7a, 7b, and 7i.
In recent years, the research on novel heterocycles derived from natural scaffold has increased considerably due to their broad bioactivities. As part of 15
our program aimed at searching for potential biorational pesticides derived from natural scaffold, we would like to report herein our effort to explore the synthesis and bioactivities of novel γ-lactam derivatives containing 1,3-benzodioxole unit, and their potential fungicidal activity against four serious and typically cropthreatening agricultural fungi were fully investigated. Some of these derivatives exhibited activity against Alternaria tenuis Nees higher than that of commercial fungicides carbendazim, such as compounds 7a, 7b, and 7i, compared with the blank control, some of these derivatives showed good antifungal activities against Gloeosporium theae-sinensis and Fusarium
graminearum. The systematic study provides evidences for further structural modifications and application of lactam analogues as antifungal agents for agriculture. We believe it would attract considerable interest of the scientists and engineers in the relation fields of chemistry.
16
S0960-894X(19)30795-4 https://doi.org/10.1016/j.bmcl.2019.126826 BMCL 126826
To appear in:
Bioorganic & Medicinal Chemistry Letters
Received Date: Revised Date: Accepted Date:
10 October 2019 12 November 2019 14 November 2019
Please cite this article as: Song, D., Cao, X., Wang, J., Ke, S., Discovery of γ-lactam derivatives containing 1,3benzodioxole unit as potential anti-phytopathogenic fungus agents, Bioorganic & Medicinal Chemistry Letters (2019), doi: https://doi.org/10.1016/j.bmcl.2019.126826
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
© 2019 Published by Elsevier Ltd.
Discovery of γ-lactam derivatives containing 1,3-benzodioxole unit as potential anti-phytopathogenic fungus agents Di Songa, Xiufang Caoa,*, Jingjing Wanga, Shaoyong Keb,*
aCollege
bNational
of Science, Huazhong Agricultural University, Wuhan 430070, China
Biopesticide Engineering Research Center, Hubei Biopesticide Engineering Research Center, Hubei Academy of Agricultural Science, Wuhan 430064, China
Address for correspondence: Xiufang Cao, College of Science, Huazhong Agricultural University; Email: [email protected] (X. Cao), or National Biopesticide Engineering Research Center, Hubei Academy of Agricultural Science; Email: [email protected] (S. Ke)
ABSTRACT: A series of γ-lactam analogs containing 1,3-benzodioxole moiety were designed, and these derivatives were synthesized from the lead compound of lactam via a structural diversityoriented synthesis, their structures were confirmed by 1HNMR,13CNMR, ESI-MS spectrum. Their antifungal activities were evaluated against four serious and typically crop-threatening agricultural fungi, including Rhizoctonia solani, Alternaria tenuis Nees, Gloeosporium theae-sinensis, and Fusarium graminearum. Some of these derivatives exhibited activity against Alternaria tenuis Nees higher than that of commercial fungicides carbendazim, such as compounds 7a, 7b, and 7i, compared with the blank control, some of these derivatives showed good antifungal activities against Gloeosporium theae-sinensis and Fusarium graminearum. The systematic study provides evidences for further structural modification and application of lactam analogues as antifungal 1
agents for agriculture. KEYWORDS: γ-lactam, 1,3-benzodioxole, diversity-oriented, antifungal activities, agricultural fungi
2
Over the past decades, a variety of fungi threaten the crops and severely disrupted agricultural production, the emergence of fungicides has solved these problems. However, long-term use of fungicide can cause lots of problems, such as environment pollution, food safety threats and resistance.1-3 Therefore, the development of environmentally-friendly fungicide is important. Natural products play an important role in the source of drugs,4 and many drugs are derived from natural products,5 some derivatives of natural products also have been commercialized successfully.6-7 1,3-Benzodioxole unit is ubiquitous in natural products8 and pharmaceuticals,9 it has been found that its derivatives had antioxidant and antibacterial activity.10 In the field of medicine, several derivatives containing the structure of 1,3-benzodioxole have been used in clinic, such as Oxolinic Acid,11 Cinoxacin12 and Miloxacin (Fig. 1).13 Nitrogen-containing heterocyclic compounds are very important structures in nature, they exist in lots of natural products14 and medicines.15-18 In the family of nitrogen-containing heterocycles, the γ-lactam core, found in many natural products and medicinally significant compounds (Fig. 2), is a very important building block in chemical synthesis. Many γ-lactams in the pronounced diversity of biological activity, such as antibacterial,19 antifungal,20 antitumor,21 anticancer,22 inhibition of HIV.23 It is expected that modification on the γlactam core should generate more derivatives of potential biological activities.
3
OMe
O O t uc od pr l a tur Na
O
O
OMe
O
N
OMe O
O
O
OMe Piperine
Glaziovianin A
O 1,3-Benzodioxole P ha rm ac eu tic al
O O
O
O OH
O
OH
O
N Oxolinic Acid
O
O
O N
N
O
O
OH
O
Cinoxacin
N O Miloxacin
Fig. 1. Natural product and drugs containing the structure of 1,3-benzodioxole
R HO OH O N OH CH3
O
O C9H19
N
O
HO
NH HO
MeO OH
HN R
O
OH
R= OH
OMe Pramanici
(-)-Clausenamide
Heliotropamide
Fig. 2. Natural products containing the structure of γ-lactam In our previous work, we found that when the heterocyclic lactam derivatives contained 1,3benzodioxole unit,24 the activity was higher than those without 1,3-benzodioxole unit,25 the result indicated that the 1,3-benzodioxole unit could enhance the activity. It was known that molecular structures determine whether the molecules are bioactive, based on the previous work, we wondered if we could improve or modulate the activities of these compounds by changing the position of 1,3benzodioxole unit. Above all, we designed and synthesized a series of 1,3-benzodioxole analogues containing the γ-lactam core (Fig. 3), the fungicidal activities of these compounds were systematically studied.
4
O R
O
N n
O
Previous work
NH
R1
This work
N
O
n
R2 HO Lactam scaffold
O
O
O
R
1,3-Benzodioxole O Enhance activity
O
O
O
Location migration
Fig. 3. Design strategies for γ-lactam derivatives containing 1,3-benzodioxole structure As shown in the Scheme 1, by using the diversity-oriented synthesis strategy, series of novel γ-lactam analogues containing 1,3-benzodioxole can be easily synthesized through a common precursor. Firstly, amino acid and thionyl chloride react in methanol can get the amino acid ester, then the methyl ester reacts with compound 4 can get the amide 5. Finally, the amide 5 can transform to the lead compound 6 in the presence of appropriate base, and then the compound 6 reacted with different kinds of acyl chloride to produce final compounds, the type of these acyl chloride and the substituents on them directly affected the generation of the final products. n
COOH
SOCl2, MeOH
n
N H HCl
COOMe
2
1
n
N H
O
(COCl)2, CH2Cl2
COOH
COCl Et3N, CH2Cl2
3
O
O
O
4
O
tBuOK, THF
R OH
O
5
O
n
N
O
Cl
Et3N, CH2Cl2
6 n = 1, 2 Lead compound
n=1 n
N
O
O
O 7a:
O O
O
O
O
O
N
O O
;
;
7c:
O
O
O
7b:
; 7d:
O
O
O
; 7e:
CN
;
7f: CF3
R
;
7g: F
n=2 7a-7g n = 1 7h-7o n = 2
O
O 7h:
;
7i:
O
O ;
7j:
;
7k:
O
;
7l:
O
O O
;
O
O
7m: CN
;
7n:
; CF3
7o: F
Scheme 1 General synthetic route for target compounds 7a–7o In addition, many natural products containing 2(5H)-furanone moiety also exhibit broad biological activities, which is the biological isosteric unit of lactams. So, several compounds bearing 2(5H)-furanone moiety have also been synthesized for comparison with the γ-lactam compounds. As shown in the Scheme 2, the prepared acyl chloride 4 reacts with methyl glycolate to get the ester 8, then the ester can be transformed to compound 9 via heterocyclization reaction in the presence of 5
strong base, which reacts with various acyl chloride to produce the 2(5H)-furanone derivatives. O O
O
(COCl)2
COOH
DCM
O
COCl
HO
COOMe
Et3N, DCM
O
3 O O
O OH
O 9
R
O Cl
Et3N, DCM
COOMe
O O
4 O
O
8
O
O R=
O
7p:
O R
O 7p-7s
tBuOK, THF
O ;
7q:
O 7r:
;
7s:
; O O
Scheme 2 General synthetic route for compounds 7p-7s The γ-lactam analogues containing 1,3-benzodioxole 7a-o and the 2(5H)-furanone derivatives 7p-s were evaluated for their antifungal activity against four plant pathogenic fungi (Rhizoctonia solani, Alternaria tenuis Nees, Gloeosporium theae-sinensis, Fusarium graminearum), the commercial fungicides carbendazim and natural product piperine were used as controls in the second screening. The results of antifungal activities of these compounds in vitro are listed in Table 1 and Table 2. As shown in Table 1 and Table 2, most of these compounds displayed broad-spectrum activities on four fungi at 100 mg/L, it was an interesting phenomenon that when the intermediates were different, the activity of its derivatives was also different. Overall, when n = 1, the compounds showed higher activity than the compounds when the n = 2, the compounds 7a, 7b, 7c exhibited higher inhibitory effects against Fusarium graminearum than 7h, 7i and 7j, the inhibition rate of 7a and 7b reached 65.14% and 52.75%, notably, 7b showed higher inhibitory activity against Gloeosporium theae-sinensis than 7i, the inhibition rate of 7b reached 68.59%, however, the inhibition rate of 7i only reached 5.44%. The activity of lactam derivatives and 2(5H)-furanone derivatives was also different, for lactam derivatives, such as the compounds 7a and 7h exhibited higher inhibitory effects against Rhizoctonia solani and Alternaria tenuis Nees than the (5H)furanone derivative 7p, 7p had no activity against these two fungi. However, for the fungi of 6
Gloeosporium theae-sinensis and Fusarium graminearum, the (5H)-furanone derivative 7q showed higher inhibition activity than the lactam derivative 7i. To summarize, the novel γ-lactam derivatives and (5H)-furanone derivatives showed obvious antifungal activity for specific fungi, which emerged as new lead compounds for the development of the new antifungal agents.
Table 1 In vitro fungicidal activity of novel γ-lactam derivatives at 100mg/L O
N
n
O O R
O
Compound
n
7a
1
7b
1
7c
1
7d
1
Fungicidal activity (%)/100 mg/L
R O
O
O
O O
RS a
AT
GT
FG
28.35
37.99
21.82
65.14
34.76
38.64
68.59
52.75
6.10
15.14
46.25
47.25
16.46
15.80
24.96
10.09
29.88
0.00
20.59
16.97
23.48
2.74
32.37
16.06
0.00
0.00
38.48
1.83
22.87
3.39
34.99
33.49
47.56
34.73
5.44
40.83
0.00
13.19
59.86
21.56
0.00
0.00
32.37
13.76
0.00
0.00
12.30
0.00
0.00
0.00
32.37
2.75
O
7e
1 CN O
7f
1 CF3
O
7g
1 F
7h
2
7i
2
7j
2
7k
2
7l
2
7m
2
O
O
O
O O O O O CN
7
O
7n
2
23.48
18.41
41.10
32.57
0.00
15.14
36.30
0.00
CF3
O
7o
2 F
a
Rs, Rhizoctonia solani; At, Alternaria tenuis Nees; Gt, Gloeosporium theae-sinensis; Fg, Fusarium graminearum. Table 2 In vitro fungicidal activity of novel 2(5H)-furanone derivatives at 100mg/L O
O
O O R
O
Compound
Fungicidal activity (100%) at 100mg/L
R
O
7q
O
7r
O
7s
AT
GT
FG
0.00
0.00
35.86
29.82
38.72
12.53
38.79
55.50
0.00
0.00
31.50
7.34
0.00
4.05
42.84
5.50
RS
O
7p
O
a
a
Rs, Rhizoctonia solani; At, Alternaria tenuis Nees; Gt, Gloeosporium theae-sinensis; Fg, Fusarium graminearum.
According to the preliminary screening result, some compounds with obvious activity were chosen for further bioassay screening at different concentration (200, 100, 50, 25, 12.5 mg/L). The IC50 values of compounds were calculated by SPSS25.0 software, and the values were listed in Table 3. Table 3 The IC50 values of the selective compounds against the plant fungi Compound
Structure
n
7a
1 O
7b
n
1
O O
7c
N
O R
1
R
IC50(mg/L) a RS b
O
O
AT
GT
FG
—
121.75
—
205.77
117.43
159.64
64.47
113.47
—
—
130.70
148.67
O
8
7i
2
7j
2 O
7q O
O
Piperine c
O R
71.03
115.99
71.89
156.69
—
—
110.37
—
87.18
—
99.65
140.15
—
—
196.21
—
79.01
114.67
49.43
262.91
O
O
O
7s
O
O O
Carbendazim c
182.47
a Compound
concentration required to inhibit colony growth by 50%. b Rs, Rhizoctonia solani; At, Alternaria tenuis Nees; Gt, Gloeosporium theae-sinensis; Fg, Fusarium graminearum. c The commercial agricultural fungicides carbendazim and natural product piperine were used for the comparisons of the antifungal activities.
As shown in Table 3, the further bioassay screening showed that some compounds displayed good antifungal activities, especially compounds 7a, 7b, 7i and piperine showed higher activities against Alternaria tenuis Nees than the commercial antifungal carbendazim, the result indicated 7a, 7b, 7i can be used as new lead compounds for the development of the new antifungal agents. Besides, for the fungi of Fusarium graminearum, these compounds exhibited higher activities than the natural product piperine, the IC50 values of 7b, 7c, 7i and 7q range of 110 –157 mg/L compared with piperine (262.91 mg/L). Compounds 7i and 7q exhibited good antifungal activity against Rhizoctonia solani (Fig. 4), and compounds 7a and 7i indicated better activities against Alternaria tenuis Nees than the commercial anti-phytopathogenic fungus agent carbendazim (Fig. 5).
9
7i
7q
Piperine CK
12.5ppm
25ppm
50ppm
100ppm
200ppm
Fig. 4. Inhibitory effect of compounds 7i, 7q and Piperine on Rhizoctonia solani
7a
7i
Piperine
Carbendazim
CK
12.5ppm
25ppm
50ppm
100ppm
200ppm
Fig. 5. Inhibitory effect of compounds 7a, 7i, Piperine and Carbendazim on Alternaria tenuis Nees According to the Table 1, Table 2, Table 3, we realized that the structure affected activity, different structures displayed different activities, so we decided to discuss the structure-activity relationship of the lactam and (5H)-furanone derivatives. Firstly, we discussed the lactam derivatives with different substituents, as shown in Table 1 and Table 2, when n = 1, focusing on the 7a, 7b, 7c compounds. When the R were alkyl substituents, the antifungal activities higher against Alternaria tenuis Nees and Fusarium graminearum than the 7e, 7f, 7g, which the R were aryl substituents. When the substituents are the same, the antifungal activities of 7a, 7b, 7c higher against Fusarium graminearum than the 7h, 7i, 7j. When the active units were different, the 10
substituents were same, such as 7d, 7k, 7s, the antifungal activity against Gloeosporium theaesinensis: 7s > 7k > 7d, the result indicated that the activity of (5H)-furanone structure was higher than the lactam structure against Gloeosporium theae-sinensis. Above all, a series of novel γ-lactam and 2(5H)-furanone derivatives containing 1,3benzodioxole were designed, synthesized and evaluated for their fungicidal activities against four plant fungi. All structures of compounds were confirmed by 1H NMR, 13C NMR and ESI-MS. Some of the compounds exhibited potent antifungal activity against two phytopathogenic fungi. Compound 7b showed the highest antifungal activity in vitro against Gloeosporium theae-sinensis and Fusarium graminearum with IC50 values of 64.47 and 113.47 mg/L. Moreover, it is noteworthy that compounds 7a, 7b and 7i displayed higher inhibitory activities against Alternaria tenuis Nees than the commercial fungicide carbendazim, which emerged as new lead compounds for the development of the new antifungal agents, we also summarized the potential structure-activity relationship of some compounds, which could lay the foundation for further structural modification and application of lactam analogues as antifungal agents for agriculture.
Acknowledgements We gratefully acknowledge the support of this work by the Program for Leading Talents of Hubei Academy of Agricultural Sciences and Hubei Agricultural Science Innovation Centre (2019-620000-001-27). REFERENCE （1） Yoon, M.-Y.; Kim, Y. S.; Ryu, S. Y.; Choi, G. J.; Choi, Y. H.; Jang, K. S.; Cha, B.; Han, S.-S.; Kim, J.-C. In vitro and in vivo antifungal activities of decursin and decursinol angelate isolated from Angelica gigas against Magnaporthe oryzae, the causal agent of rice 11
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Graphical Abstract O R
O
N O
O
n
Previous work
NH
R2 HO Lactam scaffold
O
O
R1
O
1,3-Benzodioxole Enhance activity
This work
O N
O
n O
O
R Location migration
A series of γ-lactam analogs containing 1,3-benzodioxole moiety were designed and synthesized, and their antifungal activities were evaluated against four serious and typically crop-threatening
agricultural
fungi,
Rhizoctonia solani, Alternaria tenuis Nees,
Gloeosporium theae-sinensis, and Fusarium graminearum. Some of these derivatives exhibited activity against Alternaria tenuis Nees higher than that of commercial fungicides carbendazim, such as compounds 7a, 7b, and 7i.
In recent years, the research on novel heterocycles derived from natural scaffold has increased considerably due to their broad bioactivities. As part of 15
our program aimed at searching for potential biorational pesticides derived from natural scaffold, we would like to report herein our effort to explore the synthesis and bioactivities of novel γ-lactam derivatives containing 1,3-benzodioxole unit, and their potential fungicidal activity against four serious and typically cropthreatening agricultural fungi were fully investigated. Some of these derivatives exhibited activity against Alternaria tenuis Nees higher than that of commercial fungicides carbendazim, such as compounds 7a, 7b, and 7i, compared with the blank control, some of these derivatives showed good antifungal activities against Gloeosporium theae-sinensis and Fusarium
graminearum. The systematic study provides evidences for further structural modifications and application of lactam analogues as antifungal agents for agriculture. We believe it would attract considerable interest of the scientists and engineers in the relation fields of chemistry.
16