English

• Plant diseases cause severe crop yield reduction and result in significant economic losses every year.^[1] How to control them in modern agriculture is still a big challenge. Searching for novel fungicides with different structures is a promising way to overcome resistant fungi and plays a key role in preventing loss of agricultural output.^[2] The botanical fungicide is one of the plant protection alternatives, generally considered safe for the environment and health. The development botanical fungicide is important.^[3]

  Harmine, belonging to the β-carboline alkaloids class, is present in traditional uygur herb Peganum harmala L.^[4] It was reported to exhibit a diverse range of pharmacological activities such as sedative and anxiolytic, ^[5] antitumor, ^{[6, 7]} antimalarial, ^[7] antiparasitic, ^[8] anti-HIV^[9] activities. As for pest management, the extracts of Peganum harmala L. plant species containing a mixture of harmine, harmaline and norharman, as well as their derivatives, have long been proven to have insecticidal, fungicidal and plant growth regulatory properties.^[10-15] In our previous work, ^[16] we found that 9-fluorosubstituted-Harmine displayed higher fungicidal activities against Rhizoctonia solani, Verticillium dahlia, Cotton Fusarium and Alternaria solani.

  Benzimidazoles are heterocyclic aromatic compounds that consist of the benzene ring and imidazole. From the evaluation of the works of various researchers, benzimidazole derivatives have been reported to possess anticancer^[17] and antimicrobial^{[18, 19]} activities among others. For example, carbendazim (methyl benzimidazol-2-ylcarbamate) is a benzimidazolic systemic fungicide with protective and curative action.^[20] Thiabendazole, another benzimidazole compound, serves as a commonly used postharvest pesticide to control the diseases of citrus fruits caused by fungi.^[21] As benzimidazole's bioisostere, benzothiazole scaffold possesses a broad range of biological activities such as anticancer, antimicrobial and antifungal.^{[22, 23]} Mefenacet and fenthiaprop, two herbicides containing benzothiazole substituent, are widely used in the preemergence and early postemergence of transplanted rice to control the grass.^{[24, 25]}

  Accordingly, tempted by the aforementioned findings, it was thought of interest to construct some new hybrid molecules that comprise β-carboline moiety linked to benzimidazole or its bioisostere benzothiazole at position-1 of β-carboline core (Scheme 1) in order to investigate the effect of such molecular variation on the antifungal efficacy.

  Scheme 1

  

  Scheme 1.  Designed strategy of β-carboline-benzimidazole or β-carboline-benzothiazole hybrids

  下载: 全尺寸图片 幻灯片

  1.   Results and discussion

  1.1   Synthesis

  The synthetic route for the preparation of benzimidazole-β-carboline and benzothiazole-β-carboline hybrids is outlined in Scheme 2. 1-Methyl-β-carboline (1) was obtained by the condensation of L-tryptophan with acetaldehyde in dilute sulfuric acid solution and followed by aromatization, oxidation and decarboxylation in a single step through the action of Active MnO₂.^[26] The N⁹ of 1 was alkylated or benzylated by the action of sodium hydride in anhydrous N, N-dimethylformamide (DMF) followed by the addition of the appropriate alkylating and benzylating agents to afford intermediates 2a~2g.^[27] The methyl group in position-1 of compounds 2a~2g was further oxidized to its corresponding by SeO₂ in anhydrous dioxane to provide β-carboline-1-carboxal-dehydes 3a~3g in 31%~61% yield.^[28]

  Scheme 2

  

  Scheme 2.  Synthetic pathway for the benzimidazole-β-carbolines 4a~4g and benzothiazole-β-carbolines 5a~5g

  Reagents and conditions: (ⅰ) H₂SO₄, H₂O, CH₃CHO; (ⅱ) H₂SO₄, MnO₂; (ⅲ) DMF, NaH, alkyl halogenide, stirred at r.t.; (ⅳ) SeO₂, dioxane, reflux, 2 h; (ⅴ) o-phenlyenediamine, NH₄OAc, ethanol, UI; (ⅵ) 2-aminothiophenol, PTSA, DMF, 80 ℃

  下载: 全尺寸图片 幻灯片

  The reaction of compounds 3a~3g with o-phenylenedi-amine afford the required benzimidazole substituted β-carboline derivatives 4a~4g in excellent yields catalyzed by ammonium acetate in absolute ethanol under ultrasonic irradiation (UI). But this method was found ineffective for the synthesis of benzothiazole substituted β-carbolines. So preparation of the benzothiazole-β-carboline hybrids 5a~5g was accomplished through reaction of compounds 3a~3g with 2-aminothiophenol in anhydrous DMF and catalyzed by p-toluenesulfonic acid (PTSA). All of the newly synthetic compounds were characterized by ¹H NMR, ¹³C NMR and HRMS analysis

  1.2   In vitro fungicidal activities

  From the synthetic route mentioned above, we obtained two series of benzimidazole-β-carboline hybrids (4a~4g) and benzothiazole-β-carboline hybrids (5a~5g). These compounds were evaluated in a series of fungicidal tests in vitro against a range of phytopathogenic species including Fusarium oxysporum, R. solani, sunflower sclerotinia rot, rape sclerotinia rot, and Botrytis cinerea Pers. The activity results obtained as an inhibition rate are summarized in Table 1.

  Table 1

  

  Table 1.  Fungicidal activities of compounds 4a~4g and 5a~5g against five kinds of phyto-pathogenic fungi at 50 μg·mL^-1

  下载: 导出CSV

  Compd.	Inhibition ratio/%
  	F. oxysporum	R. solani	Sunflower sclerotinia rot	Rape sclerotinia rot	B. cinerea Pers
  4a	30.83	51.56	81.06	91.95	20.08
  4b	6.92	45.07	57.95	80.46	18.56
  4c	10.17	71.75	83.71	88.54	67.42
  4d	12.26	40.26	74.62	79.89	64.20
  4e	19.22	49.88	84.09	77.78	31.44
  4f	15.51	51.68	78.41	82.38	16.10
  4g	7.85	45.67	77.27	52.30	65.15
  5a	15.16	61.47	0.00	21.14	37.43
  5b	0.42	58.77	51.33	72.99	18.18
  5c	14.32	46.97	0.00	53.98	48.31
  5d	9.65	50.22	0.00	23.30	29.18
  5e	0.00	44.47	31.44	80.08	9.47
  5f	0.00	45.67	68.37	81.61	65.15
  5g	11.56	62.14	51.70	42.91	11.74
  Carbendazim	70.98	54.55	89.77	100.00	88.07
  Azoxystrobin	51.25	81.82	88.07	88.51	83.71

  As indicated at Table 1, at 50 μg·mL^-1, the target compounds presented obviously different antifungal activity against the five tested fungi. Compared with that of the commercial fungicide carbendazim, some compounds exhibited moderate inhibitory effect against R. solani, in which compounds 4c, 5a and 5g had inhibitory rates of 71.75%, 61.47%, and 62.14%, respectively, displaying better antifungal activity than that of the positive control with an inhibition rate of 54.55%. Compared with that of the positive control carbendazim and azoxystrobin, these compounds have exhibited a significant inhibitory effect against Sunflower sclerotinia rot in which compounds 4a, 4c, and 4e had inhibitory rates of 81.06%, 83.71%, and 84.09%, respectively, which displayed comparable antifungal activity than that of the positive control with an inhibition rates of 89.77% and 88.07%. However, it was not as clear as the one drawn from the Rape sclerotinia rot (RSR) data. Some of the compounds exhibited significant activities in vitro toward RSR in which the compounds 4a~4c, 4f, 5e, 5f had control efficacy rates of over 80% and most of them showed weak to moderate activity. Besides, several compounds displayed moderate activity against B. cinerea Pers. For example, compounds 4c, 4d, 4g and 5f held 67.42%, 64.20%, 65.15%, and 65.15% inhibitory rates, respectively. For F. oxysporum, all the title compounds showed weak or inactive in vitro antifungal activities with an inhibition rate lower than 20% (except for compound 4a). Of all benzimidazole-β-carboline hybrids and benzothiazole-β-carboline hybrids, compound 4c exhibited excellent fungicidal activity against most of the tested fungi with an inhibition rate over 60% (except for F. oxysporum).

  2.   Conclusions

  In continuation of our research searching for novel agricultural fungicides, in this study, fourteen novel benzimidazole-β-carbolines and benzothiazole-β-carboline hybrids were synthesized by a practical and convenient reaction route, characterized by spectroscopic data, and first assayed for their fungicidal activities in vitro. Among the antifungal evaluation of the novel hybrids compounds 4a, 4c, and 4e showed satisfactory antifungal activity against sunflower sclerotinia rot, compounds 4a~4c, 4f, 5e and 5f displayed excellent fungicidal activity against rape sclerotinia rot. Specifically, compound 4c exhibited broad-spectrum fungicidal activity against most of the tested fungi.

  3.   Experimental

  3.1   Materials and characterization

  All the reactions during synthesis were monitored by thin layer chromatography (TLC) on precoated silica gel F254 plates (Qingdao Haiyang Inc., Qingdao, China) and spots were visualized with UV light. Column chromatography was performed with silica gel (200~300 mesh). Melting points were determined in capillary tubes on an electrothermal X-5 apparatus and without correction. NMR spectra were recorded at room temperature on a Bruker Avance Ⅲ HD 400 instrument at 400 MHz for ¹H NMR and 100 MHz for ¹³C NMR (Bruker Company, Gemany). The chemical shifts were reported on the delta (δ) scale relative to the resonance of tetramethylsilane (TMS) as the internal standard. High-resolution mass spectrometries (HRMS) were measured on a Bruker UltrafleXtreme MALDI-TOF/TOF-MS and Thermo Scientific LTQ Orbitrap XL. Sonication was performed in XH-300UA ultrasonic synthesis apparatus (Beijing Xianghu Science and Technology Development Co., LTD).

  All reagents were purchased from commercial suppliers and were dried and purified when necessary. The following intermediates, 2a~2g, 3a~3e and 3g have been already described in the published procedures.^{[22, 23]}

  3.2   Chemistry

  3.2.1   Procedure for the preparation of 3f

  A solution of 2f (5 mmol) in dioxane (50 mL) was stirred for 10 min until complete dissolution. Then, SeO₂ (15 mmol) was added. The mixture was refluxed for 2 h. After completion of the reaction as indicated by TLC, the reaction mixture was further cooled to room temperature and filtered. The filtrate was concentrated under vacuum and the residue was crystallized from acetone-petroleum ether. The resulting precipitates were filtered, and dried at 50 ℃ in vacuo to give 1.67 g of the title compound as pale yellow crystals, yield 89%. m.p. 129.2~131.1 ℃; ¹H NMR (400 MHz, CDCl₃) δ 10.33 (s, 1H, CHO), 8.71 (d, J=4.8 Hz, 1H, ArH), 8.20~8.18 (m, 1H, ArH), 8.15 (d, J=8.0 Hz, 1H, ArH), 7.62 (t, J=8.0 Hz, 1H, ArH), 7.46 (d, J=8.0 Hz, 1H, ArH), 7.38 (t, J=7.6 Hz, 1H, ArH), 6.54 (s, 2H, ArCH₂); ¹³C NMR (100 MHz, CDCl₃) δ: 195.4, 146.5 (m), 144.0 (m), 142.1 (m), 141.4, 139.5 (m), 139.2, 138.8 (m), 138.2, 136.3 (m), 136.2, 132. 6, 129. 8, 121.6, 121.6, 121.4 118.8, 110.8 (m), 109. 9 (t, J=2.1 Hz), 39.6.

  3.2.2   General procedure for the preparation of the target compounds 4a~4g

  In a 50 mL Pyrex flask, o-phenlyenediamine (1.5 mmol), compound 3a (1.5 mmol), NH₄OAc (2.2 mmol) and anhydrous ethanol (25 mL) were added. The mixture was irradiated by sonicator of frequency 500 Hz, and choose the reaction model as 2: 1. Sonication was continued until the compound 3a disappeared by TLC. After the reaction was completed, the solvent was evaporated to give the crude product, which was purified by column chromatography with a mixture of petroleum ether and ethyl acetate to afford the compound 4a. Products 4b~4g were prepared according to the same method of 4a.

  1-(1H-Benzo[d]imidazol-2-yl)-9-ethyl-β-carboline (4a): Yellow solid, yield 87%. m.p. 182.9~184.3 ℃; ¹H NMR (400 MHz, CDCl₃) δ 12.20 (s, 1H, NH), 8.49 (d, J=4.8 Hz, 1H, ArH), 8.16 (d, J=7.6 Hz, 1H, ArH), 8.06 (d, J=5.0 Hz, 1H, ArH), 7.85 (s, 1H, ArH), 7.67~7.62 (m, 1H, ArH), 7.60 (d, J=8.0 Hz, 1H, ArH), 7.50 (s, 1H, ArH), 7.35~7.30 (m, 1H, ArH), 7.29~7.25 (m, 2H, ArH), 5.32 (q, J=7.2 Hz, 2H, CH₂CH₃), 1.20 (t, J=7.2 Hz, 3H, CH₂CH₃); ¹³C NMR (100 MHz, CDCl₃) δ: 150.8, 142.8, 137.23, 137.19, 134.52, 134.51, 133.2, 133.1, 132.82, 132.81, 129.1, 121.4, 121.3, 120.2, 115.6, 110.8, 40.8, 14.3; HRMS calcd for C₂₀H₁₇N₄ [M+H]⁺ 313.1448, found 313.1447.

  1-(1H-Benzo[d]imidazol-2-yl)-9-n-butyl-β-carboline (4b): White solid, yield 82%. m.p. 207.4~208.8 ℃; ¹H NMR (400 MHz, CDCl₃) δ: 11.93 (s, 1H, NH), 8.48 (d, J=4.8 Hz, 1H, ArH), 8.17 (d, J=8.0 Hz, 1H, ArH), 8.07 (d, J=4.8 Hz, 1H, ArH), 7.83 (s, 1H, ArH), 7.67~7.40 (m, 3H, ArH), 7.34~7.26 (m, 3H, ArH), 5.30 (t, J=7.6 Hz, 2H, CH₂CH₂CH₂CH₃), 1.65~1.57 (m, 2H, CH₂CH₂-CH₂CH₃), 1.20~1.10 (m, 2H, CH₂CH₂CH₂CH₃), 0.75 (t, J=7.2 Hz, 3H, CH₂CH₂CH₂CH₃); ¹³C NMR (100 MHz, CDCl₃) δ 150.8, 143.0, 137.1, 134.7, 133.1, 132.5, 129.0, 121.3, 121.1, 120.1, 115. 6, 110.8, 45.8, 31.5, 20.0, 13.8; HRMS calcd for C₂₂H₂₁N₄ [M+H]⁺ 341.1761, found 341.1753.

  1-(1H-Benzo[d]imidazol-2-yl)-9-benzyl-β-carboline (4c): White solid, yield 84%. m.p. 184.2~185.7 ℃; ¹H NMR (400 MHz, CDCl₃) δ: 12.11 (s, 1H, NH), 8.24~8.17 (m, 2H, ArH), 8.04~8.01 (m, 1H, ArH), 7.84~7.41 (m, 4H, ArH), 7.36~7.32 (m, 1H, ArH), 7.28~7.27 (m, 1H, ArH), 7.26~7.24 (m, 1H, ArH), 7.08~7.03 (m, 1H, ArH), 6.98~6.94 (m, 2H, ArH), 6.57~6.54 (m, 4H, ArH, ArCH₂); ¹³C NMR (100 MHz, CDCl₃) δ: 150.3, 143.6, 138.0, 137.44, 137.43, 134.8, 133.5, 133.4, 132.8, 129.3, 128.2, 126.8, 126.2, 122.9, 121.4, 121.2, 120.5, 115.5, 111.1, 49.0. HRMS calcd for C₂₅H₁₉N₄ [M+H]⁺ 375.1604, found 375.1613.

  1-(1H-Benzo[d]imidazol-2-yl)-9-(4-fluorobenzyl)-β-carboline (4d): Slightly yellow solid, yield 79%. m.p. 171.6~172.7 ℃; ¹H NMR (400 MHz, CDCl₃) δ: 11.80 (s, 1H, NH), 8.34~8.30 (m, 1H, ArH), 8.20 (d, J=7.6 Hz, 1H, ArH), 8.07 (d, J=5.2 Hz, 1H, ArH), 7.97~7.40 (m, 4H, ArH), 7.38~7.34 (m, 1H, ArH), 7.31~7.26 (m, 2H, ArH), 6.68~6.63 (m, 2H, ArH), 6.59~6.54 (m, 4H, ArH, ArCH₂); ¹³C NMR (100 MHz, CDCl₃) δ: 161.7 (d, J=243.5 Hz), 150.3, 143.5, 137.69, 137.66, 134. 7, 133.8 (d, J=3.1 Hz), 133.4, 132.9, 129.4, 127.8 (d, J=8 Hz), 121.5, 121.3, 120. 7, 115.6, 115.1 (d, J=21.2 Hz), 111.0, 48.5; HRMS calcd for C₂₅H₁₈FN₄ [M+H]⁺ 393.1510, found 393.1502.

  1-(1H-benzo[d]imidazol-2-yl)-9-(3-chlorobenzyl)-β-carboline (4e): Slightly yellow solid, yield 85%. m.p. 164.7~165.4 ℃; ¹H NMR (400 MHz, DMSO-d₆) δ: 13.02 (s, 1H, NH), 8.62 (d, J=5.2 Hz, 1H, ArH), 8.43 (d, J=5.2 Hz, 1H, ArH), 7.86 (d, J=8.4 Hz, 1H, ArH), 7.75 (d, J=7.2 Hz, 1H, ArH), 7.71~7.67 (m, 1H, ArH), 7.55 (d, J=7.2 Hz, 1H, ArH), 7.40 (t, J=7.6 Hz, 1H, ArH), 7.32~7.24 (m, 2H, ArH), 7.08 (d, J=8.0 Hz, 1H, ArH), 7.00 (t, J=8.0 Hz, 1H, ArH), 6.57 (s, 3H, ArH, ArCH₂), 6.46 (d, J=7.6 Hz, 1H, ArH); ¹³C NMR (100 MHz, DMSO-d₆) δ: 150.7, 143.8, 143.0, 141.2, 138.8, 134.7, 134.4, 134.2, 133.3, 132.1, 130.6, 129.8, 127.3, 126.3, 124.8, 123.7, 122.4, 122.3, 121.18, 121.16, 119.7, 116.4, 112.3, 111.7, 48.0; HRMS calcd for C₂₅H₁₈ClN₄ [M+H]⁺409.1215, found 409.1220.

  1-(1H-Benzo[d]imidazol-2-yl)-9-((perfluorophenyl)-methyl)-β-carboline (4f): White solid, yield 83%. m.p. 201.5~203.3 ℃; ¹H NMR (400 MHz, CDCl₃) δ: 12.15 (s, 1H, NH), 8.55 (d, J=5.2 Hz, 1H, ArH), 8.14 (d, J=7.6 Hz, 1H, ArH), 8.06 (d, J=5.2 Hz, 1H, ArH), 7.83 (s, 1H, ArH), 7.64~7.59 (m, 1H, ArH), 7.56 (d, J=8.0 Hz, 1H, ArH), 7.48 (s, 1H, ArH), 7.36~7.31 (m, 1H, ArH), 7.30~7.25 (m, 2H, ArH), 7.19 (s, 2H, ArCH₂); ¹³C NMR (100 MHz, CDCl₃) δ: 151.3, 146.5 (m), 144.0 (m), 142.1, 141.7 (m), 139.2 (m), 138.6 (m), 138.1, 136.1 (m), 135.4, 133.5, 132.9, 129.5, 123.9 (m), 122.4 (m), 121.8, 121.5, 121.1, 120.0 (m), 115.6, 111.4 (m), 110.3 (t, J=2.3 Hz), 38.8; HRMS calcd for C₂₅H₁₄F₅N₄ [M+H]⁺ 465.1133, found 465.1142.

  1-(1H-Benzo[d]imidazol-2-yl)-9-(3-phenylpropyl)-β-carboline (4g): White solid, yield 81%. m.p. 157.2~158.1 ℃; ¹H NMR (400 MHz, CDCl₃) δ: 11.99 (s, 1H, NH), 8.42 (dd, J=4.8, 1.6 Hz, 1H, ArH), 8.14 (d, J=7.6 Hz, 1H, ArH), 8.02~8.00 (m, 1H, ArH), 7.80~7.55 (m, 3H, ArH), 7.46 (d, J=8.4 Hz, 1H, ArH), 7.33~7.28 (m, 3H, ArH), 7.17~7.07 (m, 3H, ArH), 6.93 (d, J=7.2 Hz, 2H, ArH), 5.30 (t, J=7.6 Hz, 2H, ArCH₂CH₂CH₂), 2.49 (t, J=7.6 Hz, 2H, ArCH₂CH₂CH₂), 2.00~1.92 (m, 2H, ArCH₂CH₂CH₂); ¹³C NMR (100 MHz, CDCl₃) δ: 150.7, 142.9, 141.4, 137.2, 134.6, 133.1, 132.6, 129.0, 128.2, 128.1, 125.8, 123.0, 121.4, 121.0, 120.2, 115.6, 110.7, 45.6, 32.9, 31.1; HRMS calcd for C₂₇H₂₃N₄ [M+H]⁺403.1917, found 403.1919.

  3.2.3   General procedure for the preparation of the target compounds 5a~5g

  A mixture of compound 3a (1.5 mmol), 2-aminothio-phenol (1.5 mmol), PTSA (20 mol%) and anhydrous DMF (10 mL) was heated at 80 ℃ for 4 h. After completion of the reaction as monitored by TLC, the reaction tube was then cooled to room temperature and the mixture was poured into H₂O (100 mL) and extracted with ethyl acetate (15 mL×3). The organic phase was washed with water and brine, then dried over anhydrous Na₂SO₄, filtered and evaporated. The residue obtained was purified by silica column chromatography with a mixture of petroleum ether and ethyl acetate to give compound 5a. Compounds 5b~5g were synthesized using a procedure similar to that used for compound 5a.

  1-(Benzo[d]thiazol-2-yl)-9-ethyl-β-carboline    (5a): Slightly yellow solid, yield 87%. m.p. 122.3~122.9 ℃; ¹H NMR (400 MHz, CDCl₃) δ: 8.56 (d, J=5.2 Hz, 1H, ArH), 8.18 (d, J=8.0 Hz, 1H, ArH), 8.12 (d, J=8.0 Hz, 1H, ArH), 8.09 (d, J=4.8 Hz, 1H, ArH), 8.01 (d, J=8.0 Hz, 1H, ArH), 7.67~7.63 (m, 1H, ArH), 7.59 (d, J=8.4 Hz, 1H, ArH), 7.55~7.50 (m, 1H, ArH), 7.42~7.43 (m, 1H, ArH), 7.36~7.32 (m, 1H, ArH), 5.04 (q, J=7.2 Hz, 2H, CH₂CH₃), 1.30 (t, J=7.2 Hz, 3H, CH₂CH₃); ¹³C NMR (100 MHz, CDCl₃) δ: 169.7, 154.0, 142.7, 138.0, 136.2, 135.6, 133.9, 132.7, 129.0, 126.0, 125.5, 123.5, 121.7, 121.4, 121.3, 120.3, 116.0, 110.6, 41.2, 14.6; HRMS calcd for C₂₀H₁₆N₃S [M+H]⁺ 330.1059, found 330.1063.

  1-(Benzo[d]thiazol-2-yl)-9-n-butyl-β-carboline    (5b): Yellow solid, yield 88%. m.p. 104.1~104.6 ℃; ¹H NMR (400 MHz, CDCl₃) δ: 8.57 (d, J=4.8 Hz, 1H, ArH), 8.18 (d, J=8.0 Hz, 1H, ArH), 8.11 (d, J=8.4 Hz, 1H, ArH), 8.10 (d, J=5.2 Hz, 1H, ArH), 8.01 (d, J=8.0 Hz, 1H, ArH), 7.67~7.62 (m, 1H, ArH), 7.57 (d, J=8.4 Hz, 1H, ArH), 7.55~7.51 (m, 1H, ArH), 7.47~7.43 (m, 1H, ArH), 7.36~7.32 (m, 1H, ArH), 5.02 (t, J=7.6 Hz, 2H, CH₂CH₂CH₂CH₃), 1.69~1.61 (m, 2H, CH₂CH₂CH₂CH₃), 1.20~1.01 (m, 2H, CH₂CH₂CH₂CH₃), 0.75 (t, J=7.6 Hz, 3H, CH₂CH₂CH₂CH₃); ¹³C NMR (100 MHz, CDCl₃) δ: 169.7, 154.0, 143.0, 137.9, 136.2, 135.6, 134.0, 132.5, 129.0, 126.0, 125.5, 123.4, 121.7, 121.4, 121.1, 120.2, 116.0, 110.7, 46.0, 31.6, 20.0, 13.8; HRMS calcd for C₂₂H₂₀N₃S [M+H]⁺ 358.1372, found 358.1377.

  1-(Benzo[d]thiazol-2-yl)-9-benzyl-β-carboline    (5c): White solid, yield 91%. m.p. 165.0~165.9 ℃; ¹H NMR (400 MHz, CDCl₃) δ: 8.58 (d, J=4.8 Hz, 1H, ArH), 8.21 (d, J=8.0 Hz, 1H, ArH), 8.12 (d, J=5.2 Hz, 1H, ArH), 7.94~7.90 (m, 1H, ArH), 7.84~7.80 (m, 1H, ArH), 7.62~7.57 (m, 1H, ArH), 7.51 (d, J=8.4 Hz, 2H, ArH), 7.48~7.43 (m, 1H, ArH), 7.42~7.39 (m, 1H, ArH), 7.38~7.33 (m, 1H, ArH), 7.12~7.03 (m, 3H, ArH), 6.77 (d, J=7.2 Hz, 2H, ArH), 6.28 (s, 2H, ArCH₂); ¹³C NMR (100 MHz, CDCl₃) δ: 153.8, 143.6, 138.5, 138.0, 136.2, 134.6, 132.8, 130.9, 129.2, 128.8, 128.3, 126.8, 126.0, 125.9, 125.5, 123.4, 121.6, 121.4, 121.3, 120.7, 116.0, 111.1, 49.9; HRMS calcd for C₂₅H₁₈N₃S [M+H]⁺392.1216, found 392.1220.

  1-(Benzo[d]thiazol-2-yl)-9-(4-fluorobenzyl)-β-carboline (5d): Slightly brown crystals, yield 94%. m.p. 182.8~183.6 ℃; ¹H NMR (400 MHz, CDCl₃) δ: 8.58 (d, J=4.8 Hz, 1H, ArH), 8.21 (d, J=8.0 Hz, 1H, ArH), 8.12 (d, J=5.2 Hz, 1H, ArH), 7.96~7.92 (m, 1H, ArH), 7.83~7.80 (m, 1H, ArH), 7.63~7.58 (m, 1H, ArH), 7.51~7.41 (m, 3H, ArH), 7.40~7.34 (m, 1H, ArH), 6.76 (s, 2H, ArH), 6.75 (s, 2H, ArH), 6.24 (s, 2H, ArCH₂); ¹³C NMR (100 MHz, , CDCl₃) δ: 161.8 (d, J=243.6 Hz), 153.8, 143.5, 138.6, 136.1, 136.0, 134.4, 133.8 (d, J=3.1 Hz), 132.8, 129.4, 127.7 (d, J=8 Hz), 126.1, 125.6, 123.3, 121.7, 121.5, 121.4, 120.8, 116.1, 115.2 (d, J=21.3 Hz), 111.0, 49.3; HRMS calcd for C₂₅H₁₇FN₃S [M+H]⁺ 410.1122, found 410.1126.

  1-(Benzo[d]thiazol-2-yl)-9-(3-chlorobenzyl)-β-carboline (5e): White solid, yield 87%. m.p. 176.6~177.2 ℃; ¹H NMR (400 MHz, CDCl₃) δ: 8.57 (d, J=5.2 Hz, 1H, ArH), 8.19 (d, J=7.6 Hz, 1H, ArH), 8.10 (d, J=5.2 Hz, 1H, ArH), 7.92 (d, J=7.6 Hz, 1H, ArH), 7.75 (d, J=7.6 Hz, 1H, ArH), 7.61~7.56 (m, 1H, ArH), 7.47~7.33 (m, 4H, ArH), 7.10 (d, J=8.4 Hz, 1H, ArH), 7.01 (t, J=8.0 Hz, 1H, ArH), 6.85 (s, 1H, ArH), 6.68 (d, J=7.6 Hz, 1H, ArH), 6.22 (s, 2H, ArCH₂); ¹³C NMR (100 MHz, CDCl₃) δ: 169.3, 153.7, 143.3, 140.3, 138.7, 136.1, 136.0, 134.5, 134.2, 132.8, 129.6, 129.4, 127.1, 126.3, 126.0, 125.6, 124.2, 123.3, 121.7, 121.5, 121.3, 120.9, 116.1, 110.9, 49.6; HRMS calcd for C₂₅H₁₇ClN₃S [M+H]⁺ 426.0826, found 426.0829.

  1-(Benzo[d]thiazol-2-yl)-9-((perfluorophenyl)methyl)-β-carboline (5f): White solid, yield 92%. m.p. 185.3~185.7 ℃; ¹H NMR (400 MHz, CDCl₃) δ: 8.60 (d, J=4.8 Hz, 1H, ArH), 8.14 (d, J=8.0 Hz, 1H, ArH), 8.07 (d, J=4.8 Hz, 1H, ArH), 7.98 (d, J=8.0 Hz, 2H, ArH), 7.63~7.59 (m, 1H, ArH), 7.51 (d, J=8.4 Hz, 1H, ArH), 7.49~7.40 (m, 2H, ArH), 7.37~7.32 (m, 1H, ArH), 6.89 (s, 2H, ArCH₂); ¹³C NMR (100 MHz, CDCl₃) δ: 171.3, 153.8, 146.4 (m), 143.9 (m), 142.1, 141.7 (m), 139.2 (m), 138.9, 138.7 (m), 136.1, 135.9, 134.7, 132.9, 129.4, 126.0, 125.7, 123.3, 121.8, 121.7, 121.5, 121.2, 116.2, 111.2 (m), 110.2 (t, J=2.2 Hz), 39.4; HRMS calcd for C₂₅H₁₃F₅N₃S [M+H]⁺ 482.0745, found 482.0749.

  1-(Benzo[d]thiazol-2-yl)-9-(3-phenylpropyl)-β-carboline (5g): Slightly yellow solid, yield 89%. m.p. 139.1~140.3 ℃; ¹H NMR (400 MHz, CDCl₃) δ: 8.56 (d, J=4.8 Hz, 1H, ArH), 8.16 (d, J=8.0 Hz, 1H, ArH), 8.12 (d, J=8.0 Hz, 1H, ArH), 8.09 (d, J=5.2 Hz, 1H, ArH), 8.02 (d, J=8.0 Hz, 1H, ArH), 7.63~7.58 (m, 1H, ArH), 7.55~7.51 (m, 1H, ArH), 7.48~7.44 (m, 1H, ArH), 7.43 (d, J=8.4 Hz, 1H, ArH), 7.32 (t, J=7.6 Hz, 1H, ArH), 7.17~7.12 (m, 2H, ArH), 7.11~7.06 (m, 1H, ArH), 6.94 (d, J=6.8 Hz, 2H, ArH), 5.07 (t, J=7.6 Hz, 2H, ArCH₂CH₂CH₂), 2.47 (t, J=7.6 Hz, 2H, ArCH₂CH₂CH₂), 2.03~1.95 (m, 2H, ArCH₂CH₂CH₂); ¹³C NMR (100 MHz, CDCl₃) δ: 169.8, 154.0, 142.8, 141.0, 138.0, 136.2, 135.6, 133.9, 132.6, 129.0, 128.3, 128.0, 126.1, 125.9, 125.6, 123.5, 121.8, 121.4, 121.1, 120.3, 116.1, 110.6, 45.7, 32.9, 30.9; HRMS calcd for C₂₇H₂₂N₃S [M+H]⁺ 420.1529, found 420.1533.

  3.3   Bioassays

  The antifungal activity of the synthesized compounds was performed according to previously reported procedures.^{[29, 30]} The fungicidal activities of the target compounds against R. solani, F. oxysporum, B. cinerea Pers., Sunflower sclerotinia rot and Rape sclerotinia rot were evaluated using a mycelium growth rate test. Carbendazim and Azoxystrobin standard purchased from J & K Scientific Ltd., were used as positive controls for comparison. The relative inhibition ratio (%) was calculated using the following equation:

  The relative inhibition ratio (%)=(colony diameter of control-colony diameter of treated)/(colony diameter of control mycelial disk diameter)×100%.

  Supporting Information ¹H NMR, ¹³C NMR spectra of all the target compounds associated with this article can be found, in the online version, at http://sioc-journal.cn.

• 1. [1]

     Qiu, D.-W.; Dong, Y.-J.; Zhang, Y.; Li, S.-P.; Shi, F.-C. Mol Plant Microbe Interact. 2017, 30, 355. doi: 10.1094/MPMI-11-16-0231-CR

  2. [2]

     Xu, W.-M.; He, J.; He, M.; Han, F.-F.; Chen, X.-H.; Pan, Z.-X.; Wang, J.; Tong, M.-G. Molecules 2011, 16, 9129. doi: 10.3390/molecules16119129

  3. [3]

     Pavela, R.; Vrchotová, N. Ind. Crops Prod. 2013, 43, 33. doi: 10.1016/j.indcrop.2012.06.044

  4. [4]

     Meester, C. D. Mutat. Res. 1995, 339, 139. doi: 10.1016/0165-1110(95)90008-X

  5. [5]

     Michael, C.; Robert, W. W.; Fil, G.; James, M. C.; Steven, A. B.; Kenner, C. R.; Jacqueline, N. C.; Steven, M. P.; Phil, S. J. Med. Chem. 1982, 25, 1081. doi: 10.1021/jm00351a015

  6. [6]

     Bournine, L.; Bensalem, S.; Fatmi, S.; Bedjou, F.; Mathieu, V.; Iguer-Ouada, M.; Kiss, R.; Duez, P. Eur. J. Integr. Med. 2017, 9, 91. doi: 10.1016/j.eujim.2016.10.002

  7. [7]

     Asgarpanah, J.; Ramezanloo, F. Afr. J. Pharm. Pharmacol. 2012, 6, 1573.

  8. [8]

     Srivastava, S. K.; Agarwal, A.; Chauhan, P. M. S.; Agarwal, S. K.; Bhaduri, A. P.; Singh, S. N.; Fatima, N.; Chatterjee, R. K. Bioorg. Med. Chem. 1999, 7, 1223. https://www.sciencedirect.com/science/article/pii/S0968089699000504

  9. [9]

     Wang, Y.-H.; Tang, J.-G.; Wang, R.-R.; Yang, L.-M.; Dong, Z.-J.; Du, L.; Shen, X.; Liu, J.-K.; Zheng, Y.-T. Biochem. Biophys. Res. Commun. 2007, 355, 1091. doi: 10.1016/j.bbrc.2007.02.081

  10. [10]

      Zhang, Z.-J.; Zhang, J.-J.; Jiang, Z.-Y.; Zhong, G.-H. Molecules 2017, 22, 1811. doi: 10.3390/molecules22111811

  11. [11]

      Nenaah, G. J. Stored Prod. Res. 2011, 47, 255. doi: 10.1016/j.jspr.2011.04.004

  12. [12]

      Abbasipour, H.; Mahmoudvand, M.; Rastegar, F.; Basij, M. Bull. Insectol. 2010, 63, 259. doi: 10.1673/031.011.16501.full

  13. [13]

      Song, H.-J.; Liu, Y.-X.; Liu, Y.-X.; Wang, Q.-M. J. Agric. Food Chem. 2014, 62, 1010. doi: 10.1021/jf404840x

  14. [14]

      Huang, Y.-Q.; Liu, Y.-X.; Liu, Y.-X.; Song, H.-J.; Wang, Q.-M. Bioorg. Med. Chem. 2016, 24, 462. https://www.sciencedirect.com/science/article/pii/S0960894X14010166

  15. [15]

      Li, Z.-B.; Chen, S.-H.; Zhu, S.-W.; Luo, J.-J.; Zhang, Y.-M.; Weng, Q.-F. Molecules 2015, 20, 13941. doi: 10.3390/molecules200813941

  16. [16]

      霍新玉, 郭亮, 韦玥婷, 张洁, 韩小强, 农药, 2018, 57, 3. http://www.cqvip.com/QK/92314X/201801/674387776.htmlHuo, X.-Y.; Guo, L.; Wei, Y.-T.; Zhang, J.; Han, X.-Q. Agrochemicals 2018, 57, 3 (in Chinese). http://www.cqvip.com/QK/92314X/201801/674387776.html

  17. [17]

      Patil, S. A.; Patil, S. A.; Patil, R. Chem. Biol. Drug Des. 2017, 89, 639. doi: 10.1111/cbdd.2017.89.issue-4

  18. [18]

      El-Gohary, N. S.; Shaaban, M. I. Eur. J. Med. Chem. 2017, 131, 255. doi: 10.1016/j.ejmech.2017.03.018

  19. [19]

      Alasmary, F. A. S.; Snelling, A. M.; Zain, M. E.; Alafeefy, A. M.; Awaad, A. S.; Karodia, N. Molecules 2015, 20, 15206. doi: 10.3390/molecules200815206

  20. [20]

      Gray, L. E.; Ostby, J.; Linder, R.; Goldman, J.; Rehnberg, G.; Cooper, R. Fundam. Appl. Toxicol. 1990, 15, 281. doi: 10.1016/0272-0590(90)90055-O

  21. [21]

      Feng, J.-Y.; Hu, Y.-X.; Grant, E.; Lu, X.-N. Food Chem. 2018, 239, 816. doi: 10.1016/j.foodchem.2017.07.014

  22. [22]

      Zhao, S.-Z.; Zhao, L.-Y.; Zhang, X.-Q.; Liu, C.-C.; Hao, C.-Z.; Xie, H.-L.; Sun, B.; Zhao, D.-M.; Cheng, M.-S. Eur. J. Med. Chem. 2016, 123, 514. doi: 10.1016/j.ejmech.2016.07.067

  23. [23]

      Chugunova, E.; Boga, C.; Sazykin, I.; Cino, S.; Micheletti, G.; Mazzanti, A.; Sazykina, M.; Burilov, A.; Khmelevtsova, L.; Kostina, N. Eur. J. Med. Chem. 2015, 93, 349. doi: 10.1016/j.ejmech.2015.02.023

  24. [24]

      Tomlin, C. E. The Pesticide Manual, 11th ed., The British Crop Protection Council, Surrey, 1997, p. 463.

  25. [25]

      Smith, A. E. J. Agric. Food Chem. 1985, 33, 483. doi: 10.1021/jf00063a038

  26. [26]

      Guo, L.; Fan, W.-X.; Chen, W.; Ma, Q.; Cao, R.-H. J. Chin. Pharm. Sci. 2015, 24, 801.

  27. [27]

      (a) Guo, L.; Fan, W.-X.; Chen, X.-M.; Ma, Q.; Cao, R.-H. Chin. J. Org. Chem. 2013, 33, 332 (in Chinese).
      (郭亮, 范文玺, 陈雪梅, 马芹, 曹日晖, 有机化学, 2013, 33, 332.)
      (b) Guo, L.; Xie, J.-W.; Fan, W.-X.; Chen, W.; Dai, B.; Ma, Q. Chin. J. Org. Chem. 2017, 37, 1741 (in Chinese).
      (郭亮, 谢建伟, 范文玺, 陈伟, 代斌, 马芹, 有机化学, 2017, 37, 1741.)

  28. [28]

      Chen, W.; Zhang, G.-X.; Guo, L.; Fan, W.-X.; Ma, Q.; Zhang, X.-D.; Du, R.-L.; Cao, R.-H. Eur. J. Med. Chem. 2016, 124, 249. doi: 10.1016/j.ejmech.2016.08.050

  29. [29]

      袁小勇, 张鹭, 韩小强, 周子原, 杜士杰, 万川, 杨冬燕, 覃兆海, 有机化学, 2014, 34, 170. http://www.cqvip.com/QK/93463X/201401/48446310.htmlYuan, X.-Y.; Zhang, L.; Han, X.-Q.; Zhou, Z.-Y.; Du, S.-J.; Wan, C.; Yang, D.-Y.; Qin, Z.-H. Chin. J. Org. Chem. 2014, 34, 170 (in Chinese). http://www.cqvip.com/QK/93463X/201401/48446310.html

  30. [30]

      农药室内生物测定试验准则杀菌剂第2部分: 抑制病原真菌菌丝生长试验平皿法: NY/T1156.2-2006.中国农业出版社, 北京, 2006.Pesticides Guidelines for Laboratory Bioactivity Tests: Part 2: Petri Plate Test for Determining Fungicide Inhibition of Mycelial Growth: NY/T1156.2-2006, China Agriculture Press, Beijing, 2006 (in Chinese).

• 

  Scheme 1  Designed strategy of β-carboline-benzimidazole or β-carboline-benzothiazole hybrids

  下载: 全尺寸图片 幻灯片
  

  Scheme 2  Synthetic pathway for the benzimidazole-β-carbolines 4a~4g and benzothiazole-β-carbolines 5a~5g

  Reagents and conditions: (ⅰ) H₂SO₄, H₂O, CH₃CHO; (ⅱ) H₂SO₄, MnO₂; (ⅲ) DMF, NaH, alkyl halogenide, stirred at r.t.; (ⅳ) SeO₂, dioxane, reflux, 2 h; (ⅴ) o-phenlyenediamine, NH₄OAc, ethanol, UI; (ⅵ) 2-aminothiophenol, PTSA, DMF, 80 ℃

  下载: 全尺寸图片 幻灯片

  Table 1.  Fungicidal activities of compounds 4a~4g and 5a~5g against five kinds of phyto-pathogenic fungi at 50 μg·mL^-1

  Compd.	Inhibition ratio/%
  	F. oxysporum	R. solani	Sunflower sclerotinia rot	Rape sclerotinia rot	B. cinerea Pers
  4a	30.83	51.56	81.06	91.95	20.08
  4b	6.92	45.07	57.95	80.46	18.56
  4c	10.17	71.75	83.71	88.54	67.42
  4d	12.26	40.26	74.62	79.89	64.20
  4e	19.22	49.88	84.09	77.78	31.44
  4f	15.51	51.68	78.41	82.38	16.10
  4g	7.85	45.67	77.27	52.30	65.15
  5a	15.16	61.47	0.00	21.14	37.43
  5b	0.42	58.77	51.33	72.99	18.18
  5c	14.32	46.97	0.00	53.98	48.31
  5d	9.65	50.22	0.00	23.30	29.18
  5e	0.00	44.47	31.44	80.08	9.47
  5f	0.00	45.67	68.37	81.61	65.15
  5g	11.56	62.14	51.70	42.91	11.74
  Carbendazim	70.98	54.55	89.77	100.00	88.07
  Azoxystrobin	51.25	81.82	88.07	88.51	83.71

  下载: 导出CSV
•