Novel 4-Methylumbelliferone Amide Derivatives: Synthesis, Characterization and Pesticidal Activities.

A series of novel 4-methylumbelliferone amide derivatives were designed, synthesized and characterized by ¹H NMR, 13C NMR and HR-ESI-MS. The structures of compounds 4bd and 4be (compounds named by authors) were further confirmed by X-ray single crystal diffraction. The acaricidal, herbicidal and antifungal activities of the synthesized compounds were assayed for their potential use as pesticide. The results indicated that compounds 4bi, 4ac and 4bd were strong acaricidals against Tetranychus cinnabarinus, with 72h corrected mortalities of greater than 80% at 1000 mg/L. Meanwhile, compounds 4bh and 4bf exhibit the strongest inhibition against the taproot development of Digitaria sanguinalis and Chenopodium glaucum, and were even more potent than the commercial herbicide Acetochlor against D. sanguinalis. In addition, compounds 4bk, 4bh and 4bp showed the highest antifungal activity against the mycelium growth of Valsa mali, which makes them more effective than commercial fungicide Carbendazim.

1. Introduction

The coumarin scaffold is an important structure type which exists in a wide class of natural and synthetic compounds [1]. Derivatives of coumarin have broad applications in the fields of perfume, food additives, cosmetics, optical brighteners [2] and dye lasers [3]. They also exhibit many bioactivities of the following categories: anticoagulant [4], vasodilator [5], sedation and hypnosis [6], analgesic and hypothermy [7], estrogenic [8], antioxidant [9], dermal photosensitization [10], antibacterial [11], antifungal [12], moluscicidal and anthelmintic [13]. Among the various coumarins, 4-methylumbelliferone (7-hydroxy-4-methylcoumarin, hymecromone) and its derivatives have been used as fluorescent probes to detect Hg2+ in neat aqueous solutions [14], and hypochlorite in tap water and cancer cells [15], as well as to assay lipases and esterases [16]. 4-Methylumbelliferone derivatives also possess diverse biological properties, such as antipsychotic [17], antidepressant [18], anaphylaxis [19], hypoglycemic [20], antioxidant [21], anti-inflammatory [22], antitumor [23,24], antibacterial [25] and antifungal [26] properties. Even though some coumarins are toxic, 4-methylumbelliferone is a safe compound used as active ingredient in several approved drugs [27,28].

4-Methylumbelliferone and its derivatives exhibited interesting pesticidal activities as well. These compounds displayed strong inhibition to weeds Setaria viridis and Amaranthus retroflexus. The C7 hydroxyl group was considered as a potentially active site and a methyl substitution at the C4 position contributed significantly to the activity [29]. 4-Methylumbelliferone derivatives also showed strong growth inhibition against phytopathogenic fungi Alternaria alternata, Alternaria solani, Botrytis cinerea and Fusarium oxysporum, and a C4 methyl in the compounds contributed to the fungicidal activity [30]. Moreover, brominated 4-methylumbelliferone showed remarkable larvicidal and ovicidal activities against vectors Aedes aegypti and Culex quinquefasciatus [31]. 4-Methylumbelliferone esters of the chrysanthemic acid type could be metabolized by glutathione S-transferase from the mosquito Culex pipiens pipiens [32]. The Schiff base and its metal complexes of 4-methylumbelliferone derivatives showed anthelmintic to Pheretima posthuma [33].

The amide group is a common functional group in natural compounds. Many commercial pesticidal compounds have acylamino group in the molecule, for example carbamates and benzoylphenyl urea insecticides, anilide fungicides, ureas, amides and carbamates herbicides [34]. As a continuous study on the development of novel pesticides based on the coumarin scaffold [35,36], by introducing amides to 4-methylumbelliferone, a series of novel 4-methylumbelliferone amide derivatives were designed and synthesized through the principle of bioactive substructure combination. The acaricidal, herbicidal and antifungal activities of these new compounds were tested.

2. Results and Discussion

2.1. Chemistry

The synthetic route of the target compounds is illustrated in Scheme 1. Resorcinol and ethylacetoacetate occurred following a Pechmann reaction with catalyst of Con. H2SO4 to produce compound 1 [22]. Nitration of 4-methylumbelliferone can be achieved with HNO3/H2SO4 [37], HNO3/HOAc [37], Cr(NO3)3/Ac2O [38], (NH2)2CNH·HNO3/H2SO4 [39], Ce(NH4)2(NO3)6/H2O2 [40] and NO2BF4 [41]. Each method was reported to have some regioselectivity, but it is obvious that HNO3/HOAc was more safe and accessible. Thus, in the present study, compound 1 was nitrated by Conc. HNO3 in acetic acid to give the mixture of compounds 2a and 2b [37]. Nitro 4-methylumbelliferone can be reduced by SnCl2/HCl [22], Na2S2O4/NH3·H2O [42] and d-glucose/KOH [43] to give an amino product. Considering the temperature requirement, time requirements and ease of the operation, Na2S2O4/NH3·H2O was used as reductant. Thus the mixtures 2a and 2b were reduced in whole with Na2S2O4 in aqueous NH3 to obtain the mixture of compounds 3a and 3b [41]. The target compounds 4aa–4ah and 4ba–4bq were furnished by the acylazation of compounds 3a and 3b, respectively, with a series of acyl chlorides catalyzed by triethylamine [44]. The structures of all target compounds were well characterized by 1H NMR, 13C NMR and HR-ESI-MS. Additionally, to confirm the three-dimensional structural information of the target compounds, the single-crystal structures of 4bd and 4be were determined by X-ray crystallography as illustrated in Figure 1. Crystallographic data (excluding structure factors) for the structures of 4bd and 4be have been deposited with the Cambridge Crystallographic Data Centre as supplementary publication CCDC 1584028 and 1584029 (12 Union Road, Cambridge CB2 1EZ, UK; Fax: +44 1223 336033; E-mail: deposit@ccdc.cam.ac.uk). The C6 substituted target compounds were more polar than the C8 substituted compounds with the same group. Many fewer pure C6 substituted target compounds were created by column chromatography (CC). Moreover the C6 substituted target compounds 4aa–4ah were dissolved by DMSO-d6 to determine the NMR, while the C8 substituted compounds 4ba–4bq were dissolved by CDCl3 for NMR.

Scheme 1

Synthetic route of target compounds.

Figure 1

X-ray crystal structure of compounds 4bd (A) and 4be (B).

2.2. Acaricidal Activities

The acaricidal activities of the 25 synthesized target compounds against the phytophagous mite T. cinnabarinus were evaluated. The 72 h corrected mortalities of the mitetreated bythe compounds are listed in Table 1. The results indicate that most of the title compounds exhibited moderate to high acaricidal potency. Among them, the most attractive compounds were 4bi, 4ac and 4bd with 72 h corrected mortalities of greater than 80% at 1000 mg/L. Especially 4bi showed equal toxicity with the commercial acaricide Bifenazate. In the 6-substituted derivatives, the methacryloyl substituted compound 4ac was the most active, followed by the aroyl substituted compounds 4ae–4ah. The alkanoyl substituted compounds 4aa, 4ab and 4ad were inferior. Meanwhile, in the 8-substituted derivatives, the most active was the hydrocinnamoyl substituted compound 4bi, though its 6-position isomer 4ad and cinnyl substituted compound 4bj were much less potent. In the chain alkanoyl substituted compounds 4ba–4bc, long chains seem favorable for the activity, however the 4-chloro-butanoyl substituted compound 4bd was an exception. The smaller cyclopropyl formyl substituted compound was more active than the larger cyclohexyl formyl substituted one. The electron withdrawing groups on the aromatic ring of the amide group were favorable for the activity, but the 4-methyl benzoyl substituted compound 4bk was more active.

Table 1

Acaricidal activities of title compounds against T. cinnabarinus (%, 72 h corrected mortality).

Compd.	200 mg/L	1000 mg/L	Compd.	200 mg/L	1000 mg/L
4aa	4.2 ± 5.2	12.9 ± 5.0	4bf	18.4 ± 3.0	29.2 ± 6.3
4ab	4.5 ± 3.2	27.1 ± 6.5	4bg	40.3 ± 3.7	71.7 ± 5.4
4ac	51.9 ± 9.9	88.3 ± 4.9	4bh	54.0 ± 13.1	65.1 ± 6.6
4ad	9.1 ± 5.0	19.4 ± 2.7	4bi	87.8 ± 8.1	98.6 ± 6.1
4ae	23.0 ± 4.9	42.1 ± 10.9	4bj	26.6 ± 5.8	38.0 ± 8.0
4af	33.9 ± 2.9	56.9 ± 4.7	4bk	57.4 ± 10.9	79.8 ± 8.3
4ag	32.8 ± 5.6	52.6 ± 7.3	4bl	23.0 ± 6.3	31.7 ± 9.7
4ah	30.0 ± 3.5	53.1 ± 7.5	4bm	7.1 ± 8.6	55.0 ± 10.7
4ba	20.4 ± 9.6	30.0 ± 3.4	4bn	47.4 ± 10.3	58.8 ± 7.4
4bb	11.8 ± 7.1	29.7 ± 10.0	4bo	53.8 ± 8.0	63.4 ± 4.6
4bc	61.5 ± 2.4	69.2 ± 2.4	4bp	48.7 ± 9.5	62.6 ± 3.0
4bd	75.1 ± 7.6	83.5 ± 5.6	4bq	41.9 ± 3.0	72.6 ± 4.2
4be	65.1 ± 3.2	73.8 ± 2.3	Bifenazate	93.5 ± 5.7	100.0 ± 0.0

2.3. Herbicidal Activities

The herbicidal activities of the target compounds against the taproot and caulis development of dicotyledonous weed C. glaucum and monocotyledonous weed D. sanguinalis were screened. The inhibitory rates of the compounds an effectiveness greater than 30% at 100 mg/L to at least one organ of the weeds are displayed in Table 2. The data indicate that more compounds show stronger inhibition against D. sanguinalis than against C. glaucum. More specifically, compounds 4bh and 4bf exhibit the strongest inhibition against the taproot development of D. sanguinalis, which makes them even more potent than the commercial herbicide Acetochlor. In fact 4bh and 4bf were the most potent against the taproot development of C. glaucum. Regarding effectiveness against D. sanguinalis, the chain alkanoylsubstituted compounds 4ba–4bd (long chain compounds) seem unfavorable for the activity. Meanwhile the larger cyclohexyl formyl substituted compound was more active than the smaller cyclopropyl formyl substituted one.

Table 2

Herbicidal activities of target compounds (%, 100 mg/L).

Compd.	C. glaucum		Compd.	D. sanguinalis		Compd.	D. sanguinalis
	Taproot	Caulis		Taproot	Caulis		Taproot	Caulis
4af	31.2 ± 9.7	-	4aa	41.6 ± 2.6	67.4 ± 4.4	4bj	10.6 ± 5.7	61.5 ± 12.4
4ah	-	40.0 ± 5.3	4ab	17.4 ± 7.4	33.6 ± 9.1	4bk	41.9 ± 8.5	54.8 ± 8.7
4bb	37.1 ± 9.6	16.8 ± 6.5	4ad	25.5 ± 4.4	53.1 ± 8.9	4bl	27.8 ± 5.2	48.5 ± 7.9
4bc	40.1 ± 8.6	15.3 ± 6.5	4ag	30.6 ± 3.6	-	4bm	44.8 ± 7.7	12.2 ± 13.0
4be	35.2 ± 3.4	-	4ba	57.1 ± 4.3	70.1 ± 5.9	4bo	64.6 ± 4.4	17.7 ± 5.1
4bf	61.1 ± 9.7	50.6 ± 4.8	4bb	66.7 ± 5.1	49.0 ± 12.8	4bp	15.5 ± 3.3	42.5 ± 12.3
4bh	76.3 ± 3.3	39.3 ± 1.9	4bc	-	45.4 ± 11.7	4bq	54.8 ± 4.3	60.9 ± 10.9
4bk	41.8 ± 6.0	-	4bd	3.4 ± 12.1	62.6 ± 10.4	Acetochlor	84.2 ± 7.0	78.1 ± 8.4
4bm	51.1 ± 7.9	-	4be	18.9 ± 6.8	40.5 ± 5.6
4bn	31.1 ± 2.2	10.9 ± 8.1	4bf	86.4 ± 10.6	71.8 ± 8.1
4bo	30.1 ± 2.6	63.0 ± 5.8	4bg	44.4 ± 11.7	-
4bq	41.8 ± 6.0	9.4 ± 10.5	4bh	96.2 ± 7.0	52.0 ± 6.4
Acetochlor	88.2 ± 2.1	78.5 ± 7.0	4bi	48.0 ± 6.7	47.7 ± 10.2

2.4. Antifungal Activities

The in vitro antifungal activities of the target compounds against the mycelium growth of the phytopathogens Colletotrichum glecosporioides, B. cinerea, F. oxysporum and V. mali were assayed. The inhibitory rates of the compounds with effectiveness greater than 30% at 100 mg/L are listed in Table 3. The data indicate that more compounds showed stronger inhibition against V. mali than against the other 3 plant disease fungi. More specifically, compounds 4bk, 4bh and 4bp exhibited the strongest inhibition against the mycelium growth of V. mali, which makes them even more potent than the commercial fungicide Carbendazim. Furthermore, the effectiveness of compounds 4be, 4bi and 4bd against B. cinerea were superior than or comparable with that of the fungicide Carbendazim, though they are all only moderately active against the fungi. The inhibition of compound 4bq against F. oxysporium was comparable with that of fungicide Carbendazim.

Table 3

Antifungal activities of target compounds (%, 100 mg/L).

Compd.	F1	Compd.	F2	Compd.	F3	Compd.	F4	Compd.	F4
4bf	45.8± 8.6	4ab	48.2± 7.4	4ac	31.8± 7.9	4ab	32.6± 1.1	4bj	39.8± 2.1
4bh	32.1±5.5	4ag	45.9± 9.0	4bh	38.4± 3.3	4ae	32.6± 8.9	4bk	88.7± 1.9
4bk	56.6± 5.0	4bd	54.6± 7.8	4bj	36.1± 4.2	4ba	47.3± 1.6	4bl	48.1± 2.2
4bl	39.3± 6.1	4be	69.4± 6.2	4bk	46.6± 1.9	4bd	36.5± 1.6	4bm	51.0± 2.5
4bq	60.8± 3.6	4bf	32.9± 9.8	4bn	48.9± 4.1	4bf	46.5± 4.0	4bn	72.7± 4.1
Carb.	88.9± 4.7	4bi	57.8± 3.8	4bp	47.9± 4.2	4bg	66.1± 5.2	4bo	34.8± 8.6
		4bl	34.5± 9.9	4bq	71.2± 4.8	4bh	84.9± 1.6	4bp	81.8± 4.2
		4bn	37.7± 6.8	Carb.	70.9± 8.4	4bi	58.4±2.7	4bq	61.1± 4.8
		Carb.	54.1± 7.1					Carb.	76.1± 3.7

F1: C. glecosporioides; F2: B. cinerea; F3: F. oxysporum; F4: V. mali; Carb.: Carbendazim.

3. Experimental Section

3.1. Chemistry

All chemicals were obtained from commercial sources and used without further purification. Analytical thin-layer chromatography (TLC) was performed with silica gel plates using silica gel 60 GF254 (Qingdao Haiyang Chemical Co., Ltd., Qingdao, China). Melting points were determined on a WRS-1B digital melting-point apparatus (Shanghai Precision Optical Instrument Co., Ltd., Shanghai, China) without further calibration. Nuclear magnetic resonance spectra (NMR) were recorded on a Bruker Avance III HD 500 MHz instrument (Bruker, Faellanden, Switzerland) in CDCl3 or DMSO-d6 (1H at 500 MHz and 13C at 126 MHz) using tetramethylsilane (TMS) as the internal standard. High-resolution mass spectra (HRMS) were carried out with an IonSpec 4.7 T FTMS instrument. Single-crystal structure was determined by a Bruker AXS D8 QUEST X-ray single crystal diffractometer.

3.1.1. Synthesis of 1

A solution of resorcinol (5.5 g, 50 mmol) and ethyl acetoacetate (6.5 g, 50 mmol) in ethanol (10 mL) was added dropwise to H2SO4 (5 mL) with stirring at 0–5 °C. After the complete addition, the reaction mixture was stirred for 4 h at room temperature. Then the reaction mixture was poured onto ice-water (100 mL) with vigorous stirring for 1h. The white precipitate which formed was collected, and washed with cold water to neutral. The product was dried and crystallized, and separated from ethanol. Yield 88%, m.p. 185–186 °C (as reported) [22].

3.1.2. Synthesis of 2a and 2b

To a solution of 1 (8.8 g, 50 mmol) in acetic acid (20 mL) kept at a temperature below 10 °C, a mixture of 65% nitric acid (5.8 g, 60 mmol) and acetic acid (20 mL) was added dropwise with stirring. After the complete addition, the reaction mixture was stirred for another 6 h at room temperature and then poured onto ice-water. The orange precipitate obtained was filtered off, washed with water to neutral, and air-dried. The solid product was washed with hot acetonitrile to give the yellow mixtures 2a and 2b (3:1) with a yield of 70% [37].

3.1.3. Synthesis of 3a and 3b

To a suspension of 2a and 2b mixtures (11.1 g, 50 mmol) in 60 mL of concentrated aqueous ammonia, 70 mL of 15% sodium hydrosulfite was added slowly with stirring at room temperature. After the complete addition, the reaction mixture was stirred for 6 h until the color changed from bright orange to light green. The mixture was then boiled for 15 min, cooled to 5 °C, and the solid was filtered off to give the mixtures 3a and 3b (3:1) with a yield of 93% [41].

3.1.4. General Procedure for Synthesis of 4-Methylumbelliferone Amide Derivatives (4aa–4ah, 4ba–4bq)

To a suspension of 1.91 g of 6-amino-7-hydroxyl-4-methylcourmin (10 mmol) and 100 uL of triethylamine in 30 mL of dichloromethane (DCM), a solution of acyl chloride (10 mmol) in 20 mL DCM was added with stirring at 0–5 °C. The mixture was allowed to restore to room temperature and was stirred until the end of the reaction. The resulting organic mixture was washed with 30 mL of water (producing Na2SO4), then dried, filtered and concentrated in vacuo sequentially. The obtained residue was purified by silica gel column chromatography (petroleum ether–ethyl acetate = 1:1 for 4aa–4ah, petroleum ether–ethyl acetate = 4:1 for 4ba–4bq) to give the target compounds [44]. The yield, appearance, m.p., the 1H-NMR and 13C NMR spectra of Compounds 4aa–4bq as Supplementary Materials, NMR and HRMS dates of the synthesized compounds are listed below.

6-(n-Butanoylamino)-4-methylumbelliferone (4aa). Pale yellow solid; yield: 71.2%; m.p. 251.6–254.8 °C; 1H NMR δ: 11.10 (s, 1H), 9.27 (s, 1H), 8.24 (s, 1H), 6.83 (s, 1H), 6.18 (s, 1H), 2.40 (t, J = 7.0 Hz, 2H), 2.35 (s, 3H), 1.67–1.58 (m, 2H), 0.93 (t, J = 7.5 Hz, 3H); 13C NMR δ: 172.29, 160.77, 153.87, 152.55, 151.05, 124.51, 118.06, 111.81, 111.26, 102.66, 38.29, 19.09, 18.66, 14.13; HR-ESI-MS m/z: 260.0918 [M − H]− (calculated for C14H14NO4, 260.0923).

6-(Cyclohexyl-formylamino)-4-methylumbelliferone (4ab). Yellow solid; yield: 56.3%; m.p. 116.5–117.8 °C; 1H NMR δ: 11.08 (s, 1H), 9.15 (s, 1H), 8.25 (s, 1H), 6.81 (s, 1H), 6.16 (s, 1H), 2.58–2.53 (m, 1H), 2.34 (s, 3H), 1.82–1.73 (m, 3H), 1.66–1.63 (m, 1H), 1.44 (qd, J1 = 12 Hz, J2 = 2.5 Hz, 2H), 1.32–1.13 (m, 4H); 13C NMR δ: 175.37, 160.74, 153.85, 152.39, 150.96, 124.62, 117.73, 111.81, 111.26, 102.65, 44.68, 29.76, 25.66, 18.66; HR-ESI-MS m/z: 300.1232 [M − H]− (calculated for C17H18NO4, 300.1236).

6-(2-Methyl-acryloylamino)-4-methylumbelliferone (4ac). Pale yellow solid; yield: 53.4%; m.p. 289.1–291.2 °C; 1H NMR δ: 11.10 (s, 1H), 8.99 (s, 1H), 8.10 (s, 1H), 6.84 (s, 1H), 6.18 (s, 1H), 5.89 (s, 1H), 5.54 (s, 1H), 2.36 (s, 3H), 1.99 (s, 3H); 13C NMR δ: 166.80, 160.71, 153.82, 153.60, 151.73, 140.19, 123.92, 121.26, 119.45, 111.93, 111.35, 102.81, 18.98, 18.67. HR-ESI-MS m/z: 260.0926 [M + H]+ (calculated for C14H14NO4, 260.0923).

6-Hydrocinnamoylamino-4-methylumbelliferone (4ad). White solid; yield: 59.2%; m.p. 245.5–247.1 °C; 1H NMR δ: 11.10 (s, 1H),9.37 (s, 1H), 8.24 (s, 1H), 7.31–7.26 (m, 4H), 7.21–7.17 (m, 1H), 6.84 (s, 1H), 6.16 (s, 1H), 2.91 (t, J = 20.8 Hz, 2H), 2.75 (s, J = 18.75 Hz, 2H), 2.34 (s, 3H); 13C NMR δ: 171.55, 160.80, 153.86, 152.73, 151.07, 141.64, 128.78, 126.41, 124.49, 117.91, 111.68, 111.16, 102.66, 37.93, 31.41, 18.66. HR-ESI-MS m/z: 324.1235 [M + H]+ (calculated for C19H18NO4, 324.1236).

6-(4-Methyl-benzoylamino)-4-methylumbelliferone (4ae). White solid; yield: 44.7%; m.p. 286.8–288.1 °C; 1H NMR δ: 11.09 (s, 1H), 9.54 (s, 1H), 8.07 (s, 1H), 7.90 (s, 2H), 7.34 (s, 2H), 6.88 (s, 1H), 6.19 (s, 1H), 2.38 (s, 6H); 13C NMR δ: 165.72, 160.74, 154.44, 153.86, 152.05, 142.30, 129.54, 128.07, 123.94, 120.81, 111.99, 111.31, 103.01, 21.51, 18.69; HR-ESI-MS m/z: 308.0923 [M − H]−(calculated for C18H14NO4, 308.0923).

6-(3-Fluoro-benzoylamino)-4-methylumbelliferone (4af). Yellow solid; yield: 49.2%; m.p. 228.8–229.5 °C; 1H NMR δ: 11.00 (s, 1H), 9.77 (s, 1H), 7.98 (s, 1H), 7.85 (d, J = 7.8 Hz, 1H), 7.80 (d, J = 9.9 Hz, 1H), 7.60 (qd, J1 = 6.0 Hz, J2 = 2.0 Hz, 1H), 7.46 (td, J1 = 8.5 Hz, J2 = 2.0 Hz, 1H), 6.88 (s, 1H), 6.20 (s, 1H), 2.38 (s, 3H); 13C NMR δ: 164.66, 162.49, 160.71, 155.04, 153.84, 152.45, 137.09, 131.17, 124.31, 123.39, 121.96, 119.12, 114.99, 112.06, 111.37, 103.12, 18.70; HR-ESI-MS m/z: 314.0828 [M + H]+ (calculated for C17H13FNO4, 314.0829).

6-(Furyl-2-formylamino)-4-methylumbelliferone (4ag). White solid; yield: 43.4%; m.p. 298.5–299.7 °C; 1H NMR δ: 11.23 (s, 1H), 9.27 (s, 1H), 8.21 (s, 1H), 7.95 (s, 1H), 7.31 (s, 1H), 6.88 (s, 1H), 6.72 (s, 1H), 6.20 (s, 1H), 2.37 (s, 3H); 13C NMR δ: 160.68, 156.49, 153.78, 153.25, 151.78, 147.75, 146.35, 123.39, 118.94, 115.48, 112.90, 112.05, 111.46, 102.81, 18.63; HR-ESI-MS m/z: 284.0563 [M − H]− (calculated for C15H10NO5, 284.0559).

6-(Thienyl-2-formylamino)-4-methylumbelliferone (4ah). White solid; yield: 53.4%; m.p. 253.2–254.8 °C; 1H NMR δ: 10.99 (s, 1H), 9.68 (s, 1H), 8.01 (d, J = 3.5 Hz, 1H), 7.93 (s, 1H), 7.86 (d, J = 4.9 Hz, 1H), 7.22 (t, J = 4.5 Hz, 1H), 6.87 (s, 1H), 6.19 (s, 1H), 2.37 (s, 3H); 13C NMR δ: 160.66, 160.64, 154.88, 153.77, 152.33, 139.91, 132.27, 129.77, 128.62, 123.20, 121.86, 112.05, 111.33, 103.08, 18.63; HR-ESI-MS m/z: 300.0328 [M − H]− (calculated for C15H10NO4S, 300.0331).

8-(n-Butanoylamino)-4-methylumbelliferone (4ba). Pale yellow solid; yield: 17.2%; m.p. 141.1–143.4 °C; 1H NMR δ: 10.72(s, 1H), 8.09(s, 1H), 7.36 (d, J = 9.0 Hz, 1H), 6.96 (d, J = 9.0 Hz, 1H), 6.13 (s, 1H), 2.57 (t, J = 7.5 Hz, 2H), 2.42 (s, 3H), 1.86–1.79 (m, 2H), 1.06 (t, J = 7.5 Hz, 3H); 13C NMR δ: 173.58, 158.83, 152.67, 151.43, 144.56, 121.20, 115.38, 113.00, 111.56, 110.03, 37.86, 18.23, 17.95, 12.56; HR-ESI-MS m/z: 260.0921 [M − H]− (calculated for C14H14NO4, 260.0923).

8-(i-Butanoylamino)-4-methylumbelliferone (4bb). White solid; yield: 46.8%; m.p.121.5–122.6 °C; 1H NMR δ: 10.83 (s, 1H), 8.18 (s, 1H), 7.36 (d, J = 8.9 Hz, 1H), 6.95 (d, J = 8.9 Hz, 1H), 6.13 (s, 1H), 2.85–2.81 (m, 1H), 2.42 (s, 3H), 1.34 (d, J = 6.9 Hz, 6H); 13C NMR δ: 178.65, 159.85, 153.70, 152.46, 145.69, 122.18, 116.37, 114.00, 112.56, 111.02, 36.27, 19.73, 18.96; HR-ESI-MS m/z: 262.1081 [M + H]+ (calculated for C14H16NO4, 262.1079).

8-(Lauroylamino)-4-methylumbelliferone (4bc). White solid; yield: 25.2%; m.p. 149.2–151.8 °C; 1H NMR δ: 10.75 (s, 1H), 8.11 (s, 1H), 7.36 (d, J = 8.2 Hz, 1H), 6.96 (d, J = 9.4 Hz, 1H), 6.14 (s, 1H), 2.58 (t, J = 5.0 Hz, 2H), 2.42 (s, 3H), 1.78 (m, 2H), 1.41–1.26 (m, 16H), 0.88 (t, J = 5.0 Hz, 3H); 13C NMR δ: 174.87, 159.94, 153.76, 152.47, 145.58, 122.21, 116.44, 114.08, 112.58, 111.04, 37.09, 31.92, 29.60, 29.44, 29.34, 29.28, 29.10, 25.75, 22.70, 18.99, 14.13; HR-ESI-MS m/z: 396.2146 [M + Na]+ (calculated for C22H31NNaO4, 396.2151).

8-(4-Chloro-butanoylamino)-4-methylumbelliferone (4bd). White solid; yield: 55.7%; m.p. 155.2–156.8 °C; 1H NMR δ: 10.41 (s, 1H), 8.30 (s, 1H), 7.36 (d, J = 8.8 Hz, 1H), 6.96 (d, J = 8.8 Hz, 1H), 6.13 (s, 1H), 3.68 (t, J = 6.1 Hz, 2H), 2.82 (t, J = 7.1 Hz, 2H), 2.41 (s, 3H), 2.28–2.22 (m, 2H); 13C NMR δ: 173.45, 159.90, 153.71, 152.50, 145.73, 122.43, 116.41, 113.90, 112.70, 111.15, 43.92, 33.60, 27.97, 18.96; HR-ESI-MS m/z: 294.0541, 296.0497 [M − H]− (calculated for C14H13ClNO4, 294.0533, 296.0504).

8-(Cyclopropyl-formylamino)-4-methylumbelliferone (4be). Yellow solid; yield: 31.2%; m.p. 162.5–163.7 °C; 1H NMR δ: 10.82 (s, 1H), 8.40 (s, 1H), 7.34 (d, J = 8.9 Hz, 1H), 6.94 (d, J = 8.8 Hz, 1H), 6.13 (s, 1H), 2.41 (s, 3H), 1.90–1.86 (m, 1H), 1.22–1.16 (m, 2H), 1.04–1.00 (m, 2H); 13C NMR δ: 175.23, 160.08, 153.79, 152.50, 145.46, 121.97, 116.38, 114.34, 112.53, 110.94, 18.95, 15.60, 9.48; HR-ESI-MS m/z: 260.0921 [M + H]+ (calculated for C14H14NO4, 260.0923).

8-(Cyclohexyl-formylamino)-4-methylumbelliferone (4bf). Yellow solid; yield: 14.1%; m.p. 156.3–158.4 °C; 1H NMR δ: 10.87 (s, 1H), 8.12 (s, 1H), 7.3 (d, J = 9.0 Hz, 1H), 6.93 (d, J = 9.0 Hz, 1H), 6.11 (s, 1H), 2.51 (tt, J1 = 11.5 Hz, J2 = 3.5 Hz, 1H), 2.40 (s 3H), 2.01 (d, J = 13.5 Hz, 2H), 1.86 (dt, J1 = 13.5 Hz, J2 = 3.0 Hz, 2H), 1.58 (qd, J1 = 12.0 Hz, J2 = 3.0 Hz, 2H), 1.38–1.24 (m, 4H); 13C NMR δ: 177.70, 159.90, 153.73, 152.46, 145.67, 122.13, 116.37, 114.06, 112.54, 111.00, 45.83, 29.74, 25.44, 18.97; HR-ESI-MS m/z: 302.1384 [M + H]+ (calculated for C17H20NO4, 302.1392).

8-(2-Methyl-acryloylamino)-4-methylumbelliferone (4bg). White solid; yield: 20.8%; m.p. 289.1–291.2 °C; 1H NMR δ: 10.75 (s, 1H), 8.44 (s, 1H), 7.35 (d, J = 9.0 Hz, 1H), 6.96 (d, J = 8.5 Hz, 1H), 6.12 (d, J = 7.0 Hz, 2H), 5.66 (d, J = 1.0 Hz, 1H), 2.41(s, 3H), 2.17(s, 3H); 13C NMR δ: 168.62, 159.57, 153.57, 152.58, 145.90, 138.06, 124.06, 122.41, 116.38, 113.78, 112.62, 111.12, 18.93, 18.59; HR-ESI-MS m/z: 260.0927 [M + H]+ (calculated for C14H14NO4, 260.0923).

8-(Phenylacetylamino)-4-methylumbelliferone (4bh). White solid; yield: 39.2%; m.p. 219.2–220.9 °C; 1H NMR δ: 10.59 (s, 1H), 8.19 (s, 1H), 7.49–7.37 (m, 5H), 7.33 (d, J = 8.9 Hz, 1H), 6.93 (d, J = 8.8 Hz, 1H), 6.09 (s, 1H), 3.91 (s, 2H), 2.38 (s, 3H); 13C NMR δ: 172.56, 159.44, 153.35, 152.29, 145.75, 133.11, 129.52, 129.48, 128.21, 122.34, 116.24, 113.80, 112.57, 111.16, 43.74, 18.89;HR-ESI-MS m/z: 310.1084 [M + H]+ (calculated for C18H16NO4, 310.1079).

8-(Hydrocinnamoylamino)-4-methylumbelliferone (4bi). White solid; yield: 15.7%; m.p. 237.5–239.0 °C; 1H NMR δ: 10.16 (s, 1H),8.17 (s, 1H), 7.35 (d, J = 8.8 Hz, 1H), 7.32–7.27 (m, 2H), 7.25–7.17 (m, 3H), 6.95 (d, J = 8.8 Hz, 1H), 6.11 (s, 1H), 3.10 (t, J = 7.4 Hz, 2H), 2.91 (t, J = 7.4 Hz, 2H), 2.40 (s, 3H); 13C NMR δ: 172.94, 159.32, 152.98, 151.62, 144.63, 138.71, 127.68, 127.50, 127.30, 127.22, 125.54, 121.25, 115.48, 109.88, 37.36, 30.52, 17.91; HR-ESI-MS m/z: 322.1077 [M − H]− (calculated for C19H16NO4, 322.1079).

8-(Cinnamoylamino)-4-methylumbelliferone (4bj). Yellow solid; yield: 41.2%; m.p. 152.3–155.3 °C; 1H NMR δ: 11.25 (s, 1H), 8.42 (s, 1H), 7.86 (d, J = 15.4 Hz, 1H), 7.61 (s, 2H), 7.49–7.35 (m, 4H), 7.00–6.99 (m, 1H), 6.87 (d, J = 15.3 Hz, 1H), 6.16 (s, 1H), 2.44 (s, 3H); 13C NMR δ: 166.43, 160.20, 153.98, 152.80, 145.70, 145.43, 134.02, 130.82, 129.09, 128.46, 122.38, 118.27, 116.57, 114.25, 112.57, 110.94, 19.01; HR-ESI-MS m/z: 344.0901 [M + Na]+ (calculated for C19H15NNaO4, 344.0899).

8-(4-Methyl-benzoylamino)-4-methylumbelliferone (4bk). Yellow solid; yield: 16.8%; m.p. 183.8–185.6 °C; 1H NMR δ: 10.93 (s, 1H), 8.78 (s, 1H), 7.89 (d, J = 8.2 Hz, 2H), 7.37 (d, J = 8.9 Hz, 1H), 7.32 (d, J = 8.2 Hz, 2H), 6.98 (d, J = 8.8 Hz, 1H), 6.12 (s, 1H), 2.44 (s, 3H), 2.41 (s, 3H); 13C NMR δ: 167.85, 159.72, 153.64, 152.68, 146.07, 144.08, 129.84, 129.35, 127.78, 122.35, 116.44, 114.12, 112.69, 111.13, 21.67, 18.97; HR-ESI-MS m/z: 332.0899 [M + Na]+ (calculated for C18H15NNaO4, 332.0899).

8-(4-Methoxyl-benzoylamino)-4-methylumbelliferone (4bl). White solid; yield: 43.4%; m.p. 151.2–154.2 °C; 1H NMR δ: 11.08 (s, 1H), 8.69 (s, 1H), 7.98 (d, J = 8.9 Hz, 2H), 7.39 (d, J = 8.9 Hz, 1H), 7.03 (d, J = 9.0, 2H), 7.01 (d, J = 8.5 Hz, 1H), 6.15 (s, 1H), 3.90 (s, 3H), 2.44 (s, 3H); 13C NMR δ: 167.34, 163.61, 159.74, 153.70, 152.57, 145.95, 129.81, 124.26, 122.21, 116.46, 114.45, 114.21, 112.66, 111.10, 55.63, 29.72; HR-ESI-MS m/z: 326.1036 [M + H]+ (calculated for C18H16NO5, 326.1028).

8-(3-Fluoro-benzoylamino)-4-methylumbelliferone (4bm). White solid; yield: 26.8%; m.p. 261.7–263.2 °C; 1H NMR δ: 10.52 (s, 1H), 8.79 (s, 1H), 7.77 (dq, J1 = 7.8 Hz, J2 = 0.5 Hz, 1H), 7.72 (dt, J1 = 8.8 Hz, J2 = 2.5 Hz, 1H), 7.56–7.52 (m, 1H), 7.42 (d, J = 8.9 Hz, 1H), 7.34 (td, J1 = 8.6, J2 = 3.3 Hz, 1H), 7.02 (d, J = 8.9 Hz, 1H), 6.16 (s, 1H), 2.44 (s, 3H); 13C NMR δ: 166.61, 162.94 (J = 249.48 Hz), 159.61, 153.66, 152.65, 146.15, 134.47 (J = 7.56 Hz), 130.97 (J = 8.82 Hz), 123.00 (J = 2.52 Hz), 122.77, 120.31 (J = 21.42 Hz), 116.57, 115.42 (J = 23.94 Hz), 113.78, 112.84, 111.28, 18.99; HR-ESI-MS m/z: 312.0676 [M − H]− (calculated for C17H11FNO4, 312.0672).

8-(3-Bromo-benzoylamino)-4-methylumbelliferone (4bn). White solid; yield: 40.7%; m.p. 237.2–239.3 °C; 1H NMR δ: 10.44 (s, 1H), 8.78 (s, 1H), 8.17 (s, 1H), 7.90 (d, J = 7.5 Hz, 1H), 7.76 (d, J = 7.8 Hz, 1H), 7.49–7.37 (m, 2H), 7.03 (d, J = 8.8 Hz, 1H), 6.16 (s, 1H), 2.44 (s, 3H); 13C NMR δ: 166.51, 159.62, 153.66, 152.65, 146.16, 136.14, 134.20, 131.27, 130.63, 125.83, 123.45, 122.81, 116.60, 113.78, 112.86, 111.30, 19.00; HR-ESI-MS m/z: 374.0025, 376.0016 [M + H]+ (calculated for C17H13BrNO4, 374.0028, 376.0007).

8-(Furyl-2-formylamino)-4-methylumbelliferone (4bo). White solid; yield: 23.4%; m.p. 280.1–281.5 °C; 1H NMR δ: 10.77 (s, 1H), 8.96 (s, 1H), 7.67 (s, 1H), 7.40 (d, J = 9.0 Hz, 1H), 7.37 (d, J = 3.5 Hz, 1H), 7.00 (d, J = 9.0 Hz, 1H), 6.63 (s, 1H), 6.16 (s, 1H), 2.43 (s, 3H); 13C NMR δ: 159.61, 157.82, 153.45, 152.34, 146.17, 145.99, 145.94, 122.43, 117.76, 116.40, 113.57, 113.05, 112.77, 111.30, 18.92;HR-ESI-MS m/z: 284.0564 [M − H]− (calculated for C15H10NO5, 284.0559).

8-(Thienyl-2-formylamino)-4-methylumbelliferone (4bp). White solid; yield: 29.2%; m.p. 244.6–246.2 °C; 1H NMR δ: 10.67 (s, 1H), 8.66 (s, 1H), 7.86 (d, J = 3.8 Hz, 1H), 7.68 (d, J = 4.9 Hz, 1H), 7.40 (d, J = 8.9 Hz, 1H), 7.20 (t, J = 4.5 Hz, 1H), 7.01 (d, J = 8.9 Hz, 1H), 6.15 (s, 1H), 2.43 (s, 3H); 13C NMR δ: 162.21, 159.60, 153.63, 152.36, 145.84, 136.42, 133.09, 130.56, 128.44, 122.42, 116.47, 113.81, 112.75, 111.20, 18.97; HR-ESI-MS m/z: 302.0491 [M + H]+ (calculated for C15H12NO4S, 302.0487).

8-(Naphthyl-1-formylamino)-4-methylumbelliferone (4bq). White solid; yield: 41.2%; m.p. 208.5–210.9 °C; 1H NMR δ: 10.69 (s, 1H), 8.63 (s, 1H), 8.44 (d, J = 8.4 Hz, 1H), 8.07 (d, J = 8.3 Hz, 1H), 7.94 (t, J = 7.3 Hz, 2H), 7.66 (t, J = 7.0 Hz, 1H), 7.59 (q, J = 7.5 Hz, 2H), 7.45 (d, J = 8.9 Hz, 1H), 7.08 (d, J = 8.9 Hz, 1H), 6.15 (s, 1H), 2.45 (s, 3H); 13C NMR δ: 170.31, 159.70, 153.60, 152.68, 146.12, 133.87, 132.64, 131.46, 130.06, 128.72, 128.02, 126.97, 126.61, 124.92, 124.80, 122.71, 116.61, 114.32, 112.89, 111.30, 19.00; HR-ESI-MS m/z: 346.1079 [M + H]+ (calculated for C21H16NO4, 346.1079).

3.2. Procedures for ActivityEvaluation

3.2.1. Acaricidal Activity

The acaricidal activities of the title compounds against the phytophagous mite T. cinnabarinus were evaluated by the microimmersion bioassay method [45]. Each title compound was dissolved by acetone (for 4ba–4bq) or DMSO/H2O (1:1, for 4aa–4ah) to give a 10 g/L stock solution. Then 0.1 and 0.5 mL of the stock solution were diluted separately to 5 mL by an appropriate amount of acetone (DMSO/H2O) and 0.1% Tween 80 in order to achieve the 0.2 g/L and 1 g/L, respectively, of test compound in acetone (DMSO/H2O)-0.1% Tween 80 (3:7). Ten test mites were sucked into the terminal pipette tip by a sucking trap, then 150 μL of the compound solution was sucked in to immerse the mites for 15 seconds. After the exposure, the mites were carefully removed onto a piece of filter paper in order to air dry the body surface. At the same time, the petiole of a fresh peanut leaf was wrapped around a ball of absorbent cotton, which was then wetted and sealed with a piece of silver paper. The hydrated leaf was dipped into the same compound solution for 5 s and taken out to air dry, as with the mites. Then the treated mites and peanut leaf were sealed in one well of a six pore plate with a piece of rice paper. Finally the mites were reared in an illumination incubator set at 28 ± 1 °C and 50–55% relative humidity in alternating 12 h of light and 12 h of dark for 72 h. Acetone (DMSO/H2O)-0.1% Tween 80 (3:7) was used as a blank control, and Bifenazate was used as a positive control. Each treatment was conducted in four replicates. The dead mites were recorded every 24 h under a stereoscope and the corrected mortalities of T. cinnabarinus treated by the compounds were calculated.

3.2.2. Herbicidal Activity

The herbicidal activities of the synthesized compounds against the taproot and caulis development of the dicotyledonous weed C. album and the monocotyledonous weed D. sanguinalis were determined in vitro [38]. A suspension of 5 g agar powder in 1 L distilled water was heated to melt, and then cooled to 40–50 °C. Each title compound was dissolved by acetone to give a stock solution of 10 g/L, and 0.1 or 0.5 mL of the stock solution was added to 50 mL of the melting agar at 45 °C to achieve the required concentrations. Then, 5 mL of the agar-containing compound was added to a beaker (10 mL) and cooled, and uniform germinating seeds were placed on the surface of the agar mass. The beaker was sealed by a piece of plastic wrap with several small holes on it, and then the cultivations were carried out in an illumination incubator set at 28 ± 1 °C and 50–55% relative humidity in alternating 12 h of light and 12 h of dark for 3 days. Acetone was used as a blank control, and Acetochlor was used as a positive control. Each treatment was conducted in three replicates. After 3 days of cultivation, the taproot and caulis lengths were measured, and the growth inhibitory rate related to the untreated control was determined.

3.2.3. Antifungal Activity

The antifungal activities of the title compounds against B. cinerea, C. gloeosporioides, A. brassicae and G. gramini were tested in vitro using the mycelium growth rate test [46]. The test compound was dissolved in acetone to form a series of proper concentration solutions. Then 1 mL of the solution was added to 100 mL melting potato dextrose agar (PDA) at 45 °C, and the mixture was shaken up to obtain the required concentration of the poisoned medium. 5 mL of the poisoned medium was poured into a 6 cm petri dish and cooled to room temperature to get a solid plate. After that, a 4 mm activated mycelium disk was inoculated on the PDA plate and incubated in the dark at 28 °C for 48 h. The mycelium elongation radius (mm) of the fungus settlements was measured and the growth inhibition rate related to the untreated control was calculated. Acetone was used as a blank control, and Carbendazim was used as a positive control. Each treatment was repeated for 3 times.

4. Conclusions

Twenty-five 4-methylumbelliferone amide derivatives were synthesized and their acaricidal, herbicidal and antifungal activities were evaluated. Compounds 4bi [8-(hydrocinnamoylamino)], 4ac [6-(2-methyl-acryloylamino)] and 4bd [8-(4-chloro-butanoylamino)] were strongly acaricidal against T. cinnabarinus, with 72 h corrected mortalities of greater than 80% at 1000 mg/L. Compounds 4bh [8-(phenylacetylamino)] and 4bf [8-(cyclohexyl-formylamino)] exhibited the strongest inhibition against the taproot development of D. sanguinalis and C. glaucum, and were more potent than the commercial herbicide Acetochlor to D. sanguinalis. Moreover, compounds 4bk [8-(4-methyl-benzoylamino)], 4bh [8-(phenylacetylamino)] and 4bp [8-(thienyl-2-formylamino)] showed the highest antifungal activities against the mycelium growth of V. mali, and were more effective than the commercial fungicide Carbendazim.

Compd.	R	Compd.	R	Compd.	R
4aa	-CH2CH2CH3	4ba	-CH2CH2CH3	4bi
4ab		4bb	-CH(CH3)CH3	4bj
4ac		4bc	-CH2(CH2)9CH3	4bk
4ad		4bd	-CH2CH2CH2Cl	4bl
4ae		4be		4bm
4af		4bf		4bn
4ag		4bg		4bo
4ah		4bh		4bp
				4bq