Novel Coumarin 7-Carboxamide/Sulfonamide Derivatives as Potential Fungicidal Agents: Design, Synthesis, and Biological Evaluation

Coumarin compounds have a variety of biological activities such as anti-tumor, anti-coagulation, anti-HIV, anti-fungal, and insecticidal. Amide and sulfonamide compounds have been used as fungicides for half a century, and dozens of varieties have been developed so far. This study focused on the introduction of carboxamide and sulfonamide moieties in a coumarin core to discover novel derivatives. Based on this strategy, we synthesized two series of novel carboxamide and sulfonamide substituted coumarin derivatives, and their fungicidal activity was also investigated. Some designed compounds possessed potential activities against six phytopathogenic fungi in the primary assays, highlighted by compound 6r. Compound 6r exhibited stronger fungicidal activity against Botrytis cinerea (EC50 = 20.52 µg/mL) and will be the lead structure for further study.


Introduction
Agricultural diseases are an important factor causing food crises, and plant pathogenic fungi and bacteria cause about 2/3 losses. Fungicides have become an important measure for comprehensively controlling agricultural diseases [1]. However, long-term irregular use of fungicides has resulted in resistance to many fungal diseases and serious harm to the natural environment. Therefore, developing new, environmentally friendly, efficient, and selective green fungicides is of great significance to ensure the safety of food, crops, and ecological environment and promote the sustainable development of agriculture [2,3]. Natural products provide a large number of synthetic templates for the development of new pharmaceutical and pesticide-active molecules due to their novel structure, unique mode of action, and environmental friendliness [4].
Coumarin and its derivatives are widely distributed in natural plants, such as Rutaceae, Leguminosae, Umbelliferae, and Compositae [5]. Coumarin derivatives display a variety of biological activities, such as anti-virus, anticancer, antioxidant, antimicrobial, and herbicidal activity. They have been found in widespread application in the fields of pesticides and medicine [6][7][8][9]. As a secondary metabolite of phenylpropanoids synthesized by plants, coumarins have good environmental compatibility, unique physiological activity, and structural plasticity. In the agricultural field, coumarin and its derivatives have many important biological activities. For example, many pathogens can induce plants to secrete coumarin compounds, which can prevent the invasion of pathogens at the infection site and play antibacterial roles in vitro. They are a class of phytoalexins and special lead compounds for the synthesis of small molecules of agriculturally active organic compounds, which has attracted the interest of many pesticide chemists [10]. As a commercial coumarin fungicide, Osthole has a good inhibitory effect on Fusarium graminearum and Phytophthora capsici and has a good inhibitory effect on melon powdery mildew [11]. Coumoxystrobin containing a coumarin skeleton shows broad-spectrum fungicidal activity against many Inspired by these facts and using Osthole as a lead structure, our group designed and synthesized a series of coumarin derivatives with high fungicidal activity. Compounds such as pyrano [3,2-c]chromene-2,5-diones, pyrrole/pyrazole-substituted coumairn derivatives, furo [3,2-c]coumarins, coumarin-3-carboxamide derivatives, and fluorinated 7-hydroxycoumarin derivatives containing an oxime ether moiety were studied [13][14][15][16][17]. However, their potency to be used as agricultural fungicide still has a long way to go.
Carboxamide and sulfonamide moieties exhibit many important biological activities in the agricultural field. Carboxamide fungicides are a kind of ancient fungicides, the number of which occupies a large proportion. Bayer, BASF, Syngenta, and other companies have successively developed novel varieties of commercial amide fungicides, such as sopyrazam, fluopyram, and bixafen [18][19][20]. Sulfonamide compounds have various physiological activities and are widely used in pesticides. Amisulbrom, which features a sulfonamide group, was applied to control phytophthora and downy mildew [21]. 4-Hydroxycoumarin sulfonamides hybrids show significant antifungal activity in vitro against M. canis [22] (Figure 2). Based on these encouraging results, we considered that combining the coumarin skeleton with carboxamide and sulfonamides moieties may result in diversified coumarin hybrids with high fungicidal activity ( Figure 3). Herein, we synthesized a novel se- Inspired by these facts and using Osthole as a lead structure, our group designed and synthesized a series of coumarin derivatives with high fungicidal activity. Compounds such as pyrano [3,2-c]chromene-2,5-diones, pyrrole/pyrazole-substituted coumairn derivatives, furo [3,2-c]coumarins, coumarin-3-carboxamide derivatives, and fluorinated 7-hydroxycoumarin derivatives containing an oxime ether moiety were studied [13][14][15][16][17]. However, their potency to be used as agricultural fungicide still has a long way to go.
Carboxamide and sulfonamide moieties exhibit many important biological activities in the agricultural field. Carboxamide fungicides are a kind of ancient fungicides, the number of which occupies a large proportion. Bayer, BASF, Syngenta, and other companies have successively developed novel varieties of commercial amide fungicides, such as sopyrazam, fluopyram, and bixafen [18][19][20]. Sulfonamide compounds have various physiological activities and are widely used in pesticides. Amisulbrom, which features a sulfonamide group, was applied to control phytophthora and downy mildew [21]. 4-Hydroxycoumarin sulfonamides hybrids show significant antifungal activity in vitro against M. canis [22] ( Figure 2). minearum and Phytophthora capsici and has a good inhibitory effect on melon powdery mildew [11]. Coumoxystrobin containing a coumarin skeleton shows broad-spectrum fungicidal activity against many plant diseases and has been observed in field trials against cucumber downy mildew with a good inhibitory effect [12] (Figure 1). Inspired by these facts and using Osthole as a lead structure, our group designed and synthesized a series of coumarin derivatives with high fungicidal activity. Compounds such as pyrano [3,2-c]chromene-2,5-diones, pyrrole/pyrazole-substituted coumairn derivatives, furo [3,2-c]coumarins, coumarin-3-carboxamide derivatives, and fluorinated 7-hydroxycoumarin derivatives containing an oxime ether moiety were studied [13][14][15][16][17]. However, their potency to be used as agricultural fungicide still has a long way to go.
Carboxamide and sulfonamide moieties exhibit many important biological activities in the agricultural field. Carboxamide fungicides are a kind of ancient fungicides, the number of which occupies a large proportion. Bayer, BASF, Syngenta, and other companies have successively developed novel varieties of commercial amide fungicides, such as sopyrazam, fluopyram, and bixafen [18][19][20]. Sulfonamide compounds have various physiological activities and are widely used in pesticides. Amisulbrom, which features a sulfonamide group, was applied to control phytophthora and downy mildew [21]. 4-Hydroxycoumarin sulfonamides hybrids show significant antifungal activity in vitro against M. canis [22] (Figure 2). Based on these encouraging results, we considered that combining the coumarin skeleton with carboxamide and sulfonamides moieties may result in diversified coumarin hybrids with high fungicidal activity ( Figure 3). Herein, we synthesized a novel se- Based on these encouraging results, we considered that combining the coumarin skeleton with carboxamide and sulfonamides moieties may result in diversified coumarin hybrids with high fungicidal activity ( Figure 3). Herein, we synthesized a novel series of coumarin 7-carboxamide/sulfonamide derivatives, which involved the Pechmann reaction, carbamate deprotection, and amidation/sulfonamidation. In addition, we examined their fungicidal activity against six phytopathogenic fungi to further improve their fungicidal effects. ries of coumarin 7-carboxamide/sulfonamide derivatives, which involved the Pechmann reaction, carbamate deprotection, and amidation/sulfonamidation. In addition, we examined their fungicidal activity against six phytopathogenic fungi to further improve their fungicidal effects.

Synthesis
The synthesis of coumarin 7-amide/sulfonamide derivatives is depicted in Scheme 1. The reported route led to six kinds of 7-aminocoumarin derivatives and involved the Pechmann reaction and carbamate deprotection [23,24]. Five types of aroyl chloride were prepared by the reaction of thionyl chloride on the corresponding aromatic carboxylic acids in CH2Cl2 under reflux. Five kinds of phenylsulfonyl chlorides were commercially available. The target molecules 5 were synthesized by the reaction between compounds 4 and aroyl chloride in good yields in CH2Cl2 as the solvent and triethylamine as the base, as shown in Scheme 1. It is worth noting that compounds 5k-5v did not form under these reaction conditions. When THF was the solvent and NaHCO3 was the base, compounds 5k-5v were obtained in moderate yield. In the synthesis of coumarin 7-sulfonamide derivatives, pyridine was used as the base, CH2Cl2 as the solvent, and DMAP as the catalyst, and compounds 6a-6r were synthesized subsequently. We also tried to use different kinds of condensation agents to prepare amides. However, due to the poor reactivity of aromatic amines with heterocyclic carboxylic acids, the reaction was not ideal. Finally, carboxylic acid was prepared into a more reactive acyl chloride to react with the amino group. All reaction processes were monitored by thin-layer chromatography (TLC).

Synthesis
The synthesis of coumarin 7-amide/sulfonamide derivatives is depicted in Scheme 1. The reported route led to six kinds of 7-aminocoumarin derivatives and involved the Pechmann reaction and carbamate deprotection [23,24]. Five types of aroyl chloride were prepared by the reaction of thionyl chloride on the corresponding aromatic carboxylic acids in CH 2 Cl 2 under reflux. Five kinds of phenylsulfonyl chlorides were commercially available. The target molecules 5 were synthesized by the reaction between compounds 4 and aroyl chloride in good yields in CH 2 Cl 2 as the solvent and triethylamine as the base, as shown in Scheme 1. It is worth noting that compounds 5k-5v did not form under these reaction conditions. When THF was the solvent and NaHCO 3 was the base, compounds 5k-5v were obtained in moderate yield. In the synthesis of coumarin 7-sulfonamide derivatives, pyridine was used as the base, CH 2 Cl 2 as the solvent, and DMAP as the catalyst, and compounds 6a-6r were synthesized subsequently. We also tried to use different kinds of condensation agents to prepare amides. However, due to the poor reactivity of aromatic amines with heterocyclic carboxylic acids, the reaction was not ideal. Finally, carboxylic acid was prepared into a more reactive acyl chloride to react with the amino group. All reaction processes were monitored by thin-layer chromatography (TLC).
The structures of the target molecules listed in Tables 1 and 2 were confirmed by HRMS, 1 H NMR, and 13 C NMR. The data of target compound 5a was analyzed as a representative example. The 1 H NMR signal of 10.58 ppm was assigned to the NH of the amide group at 2.34 and 2.06 ppm, the signals corresponding to the methyl groups appeared at positions 4 and 3, respectively. In the 13 C NMR spectrum, the signal peak at 162.51 ppm confirmed that compound 5a was assigned to the carbonyl group in amide moiety, and 156.26 ppm indicated the existence of the carbonyl group in the coumarin motif. Two signals at 15.13 and 13.49 ppm were assigned to the methyl groups. In the HRMS spectrum of compound 5a, the value of the [M + H] + ion absorption signal was 284.0924, which was consistent with the calculated value (284.0917) for C 16  The structures of the target molecules listed in Tables 1 and 2 were confirmed by HRMS, 1 H NMR, and 13 C NMR. The data of target compound 5a was analyzed as a representative example. The 1 H NMR signal of 10.58 ppm was assigned to the NH of the amide group at 2.34 and 2.06 ppm, the signals corresponding to the methyl groups appeared at positions 4 and 3, respectively. In the 13 C NMR spectrum, the signal peak at 162.51 ppm confirmed that compound 5a was assigned to the carbonyl group in amide moiety, and 156.26 ppm indicated the existence of the carbonyl group in the coumarin motif. Two signals at 15.13 and 13.49 ppm were assigned to the methyl groups. In the HRMS spectrum of compound 5a, the value of the [ (iii) 45% KOH aqueous solution, 100 °C; (iv) aroyl chloride, CH2Cl2, triethylamine, rt (5a-5j); Na-HCO3, THF, rt (5k-5v); (v) substituted or unsubstituted phenylsulfonyl chloride, DMAP, CH2Cl2, pyridine, rt.
The structures of the target molecules listed in Tables 1 and 2 were confirmed by HRMS, 1 H NMR, and 13 C NMR. The data of target compound 5a was analyzed as a representative example. The 1 H NMR signal of 10.58 ppm was assigned to the NH of the amide group at 2.34 and 2.06 ppm, the signals corresponding to the methyl groups appeared at positions 4 and 3, respectively. In the 13 C NMR spectrum, the signal peak at 162.51 ppm confirmed that compound 5a was assigned to the carbonyl group in amide moiety, and 156.26 ppm indicated the existence of the carbonyl group in the coumarin motif. Two signals at 15.13 and 13.49 ppm were assigned to the methyl groups. In the HRMS spectrum of compound 5a, the value of the [ (iii) 45% KOH aqueous solution, 100 °C; (iv) aroyl chloride, CH2Cl2, triethylamine, rt (5a-5j); Na-HCO3, THF, rt (5k-5v); (v) substituted or unsubstituted phenylsulfonyl chloride, DMAP, CH2Cl2, pyridine, rt.
The structures of the target molecules listed in Tables 1 and 2 were confirmed by HRMS, 1 H NMR, and 13 C NMR. The data of target compound 5a was analyzed as a representative example. The 1 H NMR signal of 10.58 ppm was assigned to the NH of the amide group at 2.34 and 2.06 ppm, the signals corresponding to the methyl groups appeared at positions 4 and 3, respectively. In the 13 C NMR spectrum, the signal peak at 162.51 ppm confirmed that compound 5a was assigned to the carbonyl group in amide moiety, and 156.26 ppm indicated the existence of the carbonyl group in the coumarin motif. Two signals at 15.13 and 13.49 ppm were assigned to the methyl groups. In the HRMS spectrum of compound 5a, the value of the [ (iii) 45% KOH aqueous solution, 100 °C; (iv) aroyl chloride, CH2Cl2, triethylamine, rt (5a-5j); Na-HCO3, THF, rt (5k-5v); (v) substituted or unsubstituted phenylsulfonyl chloride, DMAP, CH2Cl2, pyridine, rt.
The structures of the target molecules listed in Tables 1 and 2 were confirmed by HRMS, 1 H NMR, and 13 C NMR. The data of target compound 5a was analyzed as a representative example. The 1 H NMR signal of 10.58 ppm was assigned to the NH of the amide group at 2.34 and 2.06 ppm, the signals corresponding to the methyl groups appeared at positions 4 and 3, respectively. In the 13 C NMR spectrum, the signal peak at 162.51 ppm confirmed that compound 5a was assigned to the carbonyl group in amide moiety, and 156.26 ppm indicated the existence of the carbonyl group in the coumarin motif. Two signals at 15.13 and 13.49 ppm were assigned to the methyl groups. In the HRMS spectrum of compound 5a, the value of the [ (iii) 45% KOH aqueous solution, 100 °C; (iv) aroyl chloride, CH2Cl2, triethylamine, rt (5a-5j); Na-HCO3, THF, rt (5k-5v); (v) substituted or unsubstituted phenylsulfonyl chloride, DMAP, CH2Cl2, pyridine, rt.
The structures of the target molecules listed in Tables 1 and 2 were confirmed by HRMS, 1 H NMR, and 13 C NMR. The data of target compound 5a was analyzed as a representative example. The 1 H NMR signal of 10.58 ppm was assigned to the NH of the amide group at 2.34 and 2.06 ppm, the signals corresponding to the methyl groups appeared at positions 4 and 3, respectively. In the 13 C NMR spectrum, the signal peak at 162.51 ppm confirmed that compound 5a was assigned to the carbonyl group in amide moiety, and 156.26 ppm indicated the existence of the carbonyl group in the coumarin motif. Two signals at 15.13 and 13.49 ppm were assigned to the methyl groups. In the HRMS spectrum of compound 5a, the value of the [ The structures of the target molecules listed in Tables 1 and 2 were confirmed by HRMS, 1 H NMR, and 13 C NMR. The data of target compound 5a was analyzed as a representative example. The 1 H NMR signal of 10.58 ppm was assigned to the NH of the amide group at 2.34 and 2.06 ppm, the signals corresponding to the methyl groups appeared at positions 4 and 3, respectively. In the 13 C NMR spectrum, the signal peak at 162.51 ppm confirmed that compound 5a was assigned to the carbonyl group in amide moiety, and 156.26 ppm indicated the existence of the carbonyl group in the coumarin motif. Two signals at 15.13 and 13.49 ppm were assigned to the methyl groups. In the HRMS spectrum of compound 5a, the value of the [ The structures of the target molecules listed in Tables 1 and 2 were confirmed by HRMS, 1 H NMR, and 13 C NMR. The data of target compound 5a was analyzed as a representative example. The 1 H NMR signal of 10.58 ppm was assigned to the NH of the amide group at 2.34 and 2.06 ppm, the signals corresponding to the methyl groups appeared at positions 4 and 3, respectively. In the 13 C NMR spectrum, the signal peak at 162.51 ppm confirmed that compound 5a was assigned to the carbonyl group in amide moiety, and 156.26 ppm indicated the existence of the carbonyl group in the coumarin motif. Two signals at 15.13 and 13.49 ppm were assigned to the methyl groups. In the HRMS spectrum of compound 5a, the value of the [ The structures of the target molecules listed in Tables 1 and 2 were confirmed by HRMS, 1 H NMR, and 13 C NMR. The data of target compound 5a was analyzed as a representative example. The 1 H NMR signal of 10.58 ppm was assigned to the NH of the amide group at 2.34 and 2.06 ppm, the signals corresponding to the methyl groups appeared at positions 4 and 3, respectively. In the 13 C NMR spectrum, the signal peak at 162.51 ppm confirmed that compound 5a was assigned to the carbonyl group in amide moiety, and 156.26 ppm indicated the existence of the carbonyl group in the coumarin motif. Two signals at 15.13 and 13.49 ppm were assigned to the methyl groups. In the HRMS spectrum of compound 5a, the value of the [ The structures of the target molecules listed in Tables 1 and 2 were confirmed by HRMS, 1 H NMR, and 13 C NMR. The data of target compound 5a was analyzed as a representative example. The 1 H NMR signal of 10.58 ppm was assigned to the NH of the amide group at 2.34 and 2.06 ppm, the signals corresponding to the methyl groups appeared at positions 4 and 3, respectively. In the 13 C NMR spectrum, the signal peak at 162.51 ppm confirmed that compound 5a was assigned to the carbonyl group in amide moiety, and 156.26 ppm indicated the existence of the carbonyl group in the coumarin motif. Two signals at 15.13 and 13.49 ppm were assigned to the methyl groups. In the HRMS spectrum of compound 5a, the value of the [

Antifungal Activity of the Target Molecules
The antifungal activity of the target molecules on plant pathogens was tested by a mycelium growth rate method, and the assay results are shown in Table 3. Osthole was adopted as the positive control fungicide during the assay process. Plant pathogens were from the Department of Pathology, College of Plant Protection, Nanjing Agricultural University. The phytopathogenic fungi included Botrytis cinerea, Alternaria solani, Gibberella zeae, Rhizoctorzia solani, Cucumber anthrax, and Alternaria leaf spot. The target compounds were dissolved in DMSO to generate a stock solution. The compounds possessing good activity (inhibitory rate > 60% at 50 µg/mL) were further evaluated using different concentrations by diluting the above solution. DMSO served as the negative control. In general, most of the synthesized compounds exhibited more antifungal activity against Botrytis cinerea and Rhizoctorzia solani than against Alternaria solani, Gibberella zeae, Cucumber anthrax, and Alternaria leaf spot. Noteworthy, four compounds-6d, 6e, 6q, and 6r-showed relatively effective control against Botrytis cinerea and corresponding inhibition rates of 71.1, 68.2, 78.2, and 81.6%, respectively, which were equivalent to that of the positive control fungicide Osthole (81.1%).

Antifungal Activity of the Target Molecules
The antifungal activity of the target molecules on plant pathogens was tested by a mycelium growth rate method, and the assay results are shown in Table 3. Osthole was adopted as the positive control fungicide during the assay process. Plant pathogens were from the Department of Pathology, College of Plant Protection, Nanjing Agricultural University. The phytopathogenic fungi included Botrytis cinerea, Alternaria solani, Gibberella zeae, Rhizoctorzia solani, Cucumber anthrax, and Alternaria leaf spot. The target compounds were dissolved in DMSO to generate a stock solution. The compounds possessing good activity (inhibitory rate > 60% at 50 µg/mL) were further evaluated using different concentrations by diluting the above solution. DMSO served as the negative control. In general, most of the synthesized compounds exhibited more antifungal activity against Botrytis cinerea and Rhizoctorzia solani than against Alternaria solani, Gibberella zeae, Cucumber anthrax, and Alternaria leaf spot. Noteworthy, four compounds-6d, 6e, 6q, and 6r-showed relatively effective control against Botrytis cinerea and corresponding inhibition rates of 71.1, 68.2, 78.2, and 81.6%, respectively, which were equivalent to that of the positive control fungicide Osthole (81.1%). Table 3. Antifungal activity of synthesized compounds at 50 µg/mL.

Antifungal Activity of the Target Molecules
The antifungal activity of the target molecules on plant pathogens was tested by a mycelium growth rate method, and the assay results are shown in Table 3. Osthole was adopted as the positive control fungicide during the assay process. Plant pathogens were from the Department of Pathology, College of Plant Protection, Nanjing Agricultural University. The phytopathogenic fungi included Botrytis cinerea, Alternaria solani, Gibberella zeae, Rhizoctorzia solani, Cucumber anthrax, and Alternaria leaf spot. The target compounds were dissolved in DMSO to generate a stock solution. The compounds possessing good activity (inhibitory rate > 60% at 50 µg/mL) were further evaluated using different concentrations by diluting the above solution. DMSO served as the negative control. In general, most of the synthesized compounds exhibited more antifungal activity against Botrytis cinerea and Rhizoctorzia solani than against Alternaria solani, Gibberella zeae, Cucumber anthrax, and Alternaria leaf spot. Noteworthy, four compounds-6d, 6e, 6q, and 6r-showed relatively effective control against Botrytis cinerea and corresponding inhibition rates of 71.1, 68.2, 78.2, and 81.6%, respectively, which were equivalent to that of the positive control fungicide Osthole (81.1%).

Antifungal Activity of the Target Molecules
The antifungal activity of the target molecules on plant pathogens was tested by a mycelium growth rate method, and the assay results are shown in Table 3. Osthole was adopted as the positive control fungicide during the assay process. Plant pathogens were from the Department of Pathology, College of Plant Protection, Nanjing Agricultural University. The phytopathogenic fungi included Botrytis cinerea, Alternaria solani, Gibberella zeae, Rhizoctorzia solani, Cucumber anthrax, and Alternaria leaf spot. The target compounds were dissolved in DMSO to generate a stock solution. The compounds possessing good activity (inhibitory rate >60% at 50 µg/mL) were further evaluated using different concentrations by diluting the above solution. DMSO served as the negative control. In general, most of the synthesized compounds exhibited more antifungal activity against Botrytis cinerea and Rhizoctorzia solani than against Alternaria solani, Gibberella zeae, Cucumber anthrax, and Alternaria leaf spot. Noteworthy, four compounds-6d, 6e, 6q, and 6r-showed relatively effective control against Botrytis cinerea and corresponding inhibition rates of 71.1, 68.2, 78.2, and 81.6%, respectively, which were equivalent to that of the positive control fungicide Osthole (81.1%). Table 3. Antifungal activity of synthesized compounds at 50 µg/mL.  To comprehensively study the antifungal activity of the effective molecules, we further examined the EC 50 values of these compounds together with Osthole. As shown in Table 4, four compounds (6d, 6e, 6q, and 6r) showed fair to good activity; the EC 50 values were lower than that of Osthole (30.67 µg/mL) against Botrytis cinerea. It was worth noting that compound 6r displayed much more activity than the control Osthole did.

Structure-Activity Relationships
Although the antifungal activity of most coumarin 7-amide/sulfonamide derivatives was poor, making it difficult to extract a clear structure-activity relationship summary, some preliminary conclusions can still be drawn. Firstly, most of the synthesized coumarin derivatives were relatively more active against Botrytis cinerea and Rhizoctorzia solani, but they usually lacked potency against the other tested fungi. Secondly, the overall effect on antifungal activity of the sulfonamide group seemed helpful compared with that of the carboxamide group. Thirdly, compounds 6d, 6e, 6q, and 6r exhibited significant antifungal activity against Botrytis cinerea, equivalent to that of the positive control fungicide Osthole, and 6r was identified as the most promising candidate. The results favor the introduction of CH 3 /Cl at the C-3 cite in the coumarin core. Meanwhile, para-Cl/Br substituted to the phenyl ring was helpful to improving the antifungal activity of these molecules.

Chemicals and Instruments
All chemical reagents were purchased from commercial sources used without further purification. The progress of reactions and the purity of products were monitored by TLC using silica gel GF/UV 254. The melting points of coumarin compounds were measured on an X-4 apparatus (uncorrected). 1 H-NMR and 13 C-NMR spectra were detected on a Bruker Avance 400 MHz spectrometer (Billerica, MA, USA) with TMS as an internal standard. HR-MS (ESI) spectra were operated using a Thermo Exactive spectrometer (Waltham, MA, USA).

Chemistry
3.2.1. General Procedure for the Synthesis of the Intermediates 4 7-Aminocoumarins were synthesized through procedures reported in [16,25].

General Procedure for the Synthesis of the Intermediates 5a-5j
Compound 4 (2.5 mmol) was dissolved in dichloromethane (20.0 mL), and then triethylamine (20.0 mmol) was added to the solution and cooled to 0 • C. To the mixture, 5.0 mmol of aroyl chloride in 20 mL of dichloromethane solution was slowly added and stirred at room temperature for 2 h. After the reaction was completed, the reaction mixture was washed with water (100 mL × 3), and the organic phase was dried over with Na 2 SO 4 and concentrated under reduced pressure. The crude product was purified by column chromatography using dichloromethane/methanol (V dichloromethane /V methanol = 98:2→95:5) as the eluent to give compounds 5a-5j. Compound 4 (2.5 mmol) was dissolved in tetrahydrofuran (20.0 mL), and then sodium bicarbonate (10.0 mmol) was added to the solution and cooled to 0 • C. To the mixture, 5.0 mmol of aroyl chloride in 20 mL of tetrahydrofuran solution was slowly added and stirred at room temperature for 2 h. After the reaction was completed, the reaction mixture was washed with water (100 mL × 3), and the organic phase was dried over with Na 2 SO 4 and concentrated under reduced pressure. The crude product was purified by column chromatography using dichloromethane/methanol (V dichloromethane /V methanol = 98:2→95:5) as the eluent to obtain compounds 5k-5t.

Antifungal Bioassay
The antifungal activity of the target compounds against Botrytis cinerea, Alternaria solani, Gibberella zeae, Rhizoctorzia solani, Cucumber anthrax, and Alternaria leaf spot was assessed by the mycelium growth rate method according to the literature [26]. The tested compounds (10 mg) were dissolved in 2 mL of DMSO to make a solution of 5 mg/mL. The solution (0.1 mL) was taken and added to 50 mL of sterilized PDA medium to make a drug-containing medium with a concentration of 50 µg/mL. The medium was poured into 3 sterile petri dishes with an average diameter of 9 cm. The medium with the same amount of DMSO (0.1 mL) added was used as a control. Osthole was taken as the positive control at the same concentration. The preserved strains could be used after being activated twice continuously in a fresh sterile PDA medium. A puncher (inner diameter of 0.5 cm) was used to make a bacterial cake at the edge of the colony. The bacterial cake was inserted into the center of the medium plate with an inoculation needle and cultured in an incubator at 25 • C. The diameters of the colonies on the medium for solvent control were measured when they grew to 2/3 of the diameter of the plate. The diameters of each colony were measured twice with the cross method, and the average value was calculated. Each concentration and two controls were repeated three times, and the data were averaged. According to the preliminary screening results of in vitro activity, compounds with an inhibition rate greater than 60% at a concentration of 50 µg/mL were further tested for their EC 50 values. The concentration gradients of 50, 25, 12.5, 6.25, and 3.125 µg/mL were set, and the EC 50 values of the selected compounds against the tested plant pathogenic fungi were determined by the mycelial growth rate method. The data are listed in Tables 3 and 4, respectively.

Conclusions
In summary, two series of coumarin 7-carboxamide/sulfonamide derivatives were designed and efficiently synthesized. All target compounds were confirmed by 1 H NMR, 13 C NMR, and HRMS spectra. Biological assays indicated that the synthesized coumarin derivatives the antifungal activity displayed against Botrytis cinerea and Rhizoctorzia solani was generally better than that against Alternaria solani, Gibberella zeae, Cucumber anthrax, and Alternaria leaf spot. In particular, compounds 6d, 6e, 6q, and 6r possessed effective antifungal activity against Botrytis cinerea (EC 50 = 27.34, 27.76, 27.78, and 20.52 µg/mL), which was better than that of Osthole (33.67 µg/mL). Among them, compound 6r was the most promising candidates for further study. Further investigations to modify the coumarin derivatives are well underway, aiming to improve their levels of antifungal activity.