Res Chem Intermed (2015) 41:2019–2024 DOI 10.1007/s11164-013-1328-4 Synthesis and antimicrobial activity of novel mancozeb derivatives containing 1,3,4-thiadiazole Yuting Liu • Gangtao Liang • Dawei Yin Received: 11 March 2013 / Accepted: 20 June 2013 / Published online: 29 June 2013 Ó Springer Science+Business Media Dordrecht 2013 Abstract Four mancozeb derivatives containing 1,3,4-thiadiazole, 5a–5d, were successfully synthesized, then characterized by IR, 1H NMR, and 13C NMR spectroscopy and elemental analysis. Their antimicrobial activity against paddy fusarium, Botrytis cinerea, cucumber fusarium, tomato gibberella, and grape white rot was tested in vitro by use of the filter paper disk-diffusion technique. Compounds 5a–5d had moderate to excellent antimicrobial activity in comparison with mancozeb, 6. Among these compounds, 5a had the best inhibitory activity. Keywords Mancozeb
1,3,4-Thiadiazole
Synthesis
Antimicrobial activity Introduction 1,3,4-Thiadiazole compounds have been of much interest in synthetic chemistry and as pesticides because of their unique biological properties. Recently, 1,3,4-thiadiazole derivatives have been shown to have a variety of biological activity, for example as fungicides [1], plant growth regulators [2, 3], insecticides [4], herbicides [5], and anticholinergic [6] and anticonvulsant [7] compounds. Therefore, these compounds attract much attention as novel pesticides. Dithiocarbamate salts are widely used in the petroleum [8], agriculture [9], pharmaceutical [10], environmental protection [11], and rubber [12] industries. However, because resistance to Zineb has been observed, development of novel potent antimicrobial agents with superior bioavailability is Y. Liu (&)
G. Liang
D. Yin Key Laboratory of Auxiliary Chemistry and Technology for Chemical Industry Ministry of Education, Shaanxi University of Science and Technology, Xi’an 710021, Shaanxi, China e-mail: lgt_no1@163.com Y. Liu
G. Liang
D. Yin School of Chemistry and Chemical Engineering, Shaanxi University of Science and Technology, Xi’an 710021, Shaanxi, China 123 2020 Y. Liu et al. highly desirable. Herein, we describe the synthesis and antimicrobial activity of four novel mancozeb derivatives containing 1,3,4-thiadiazole (Scheme 1). Results and discussion All the reagents described in this paper were commercially available, and all solvents were freshly distilled before use. Melting points were recorded on an X-4 microscopic melting point apparatus, and are uncorrected. Elemental analysis (C, H, and N) was performed with a VarioEL III. IR spectra, as KBr pellets, were recorded on a Vector-22 instrument. 1H NMR and 13C NMR spectra were recorded on an Avance III 400 MHz instrument, with CDCl3 as solvent and SiMe4 as internal reference. Synthesis of 2-amino-1,3,4-thiadiazole derivatives A mixture of 20 mL concentrated hydrochloric acid, 0.026 mol carboxylic acid, and 0.022 mol thiosemicarbazide was heated under reflux for 5 h. After cooling to room temperature, the mixture was adjusted to pH 8 with 40 % sodium hydroxide solution. The white solid powder obtained was isolated by filtration, washed with water, and finally recrystallized from 30 % ethanol. Results from characterization of 2-amino-1,3,4-thiadiazole derivatives 3a–3d are listed in Tables 1, 2, and 3. Synthesis of mancozeb and 1,3,4-thiadiazole derivatives of mancozeb A mixture of 0.010 mol 1,2-ethanediamine or 2-amino-1,3,4-thiadiazole derivative and 0.010 mol sodium hydroxide aqueous solution was stirred, heated to 30 °C, then 0.020 mol carbon disulfide was slowly added dropwise to the mixture. The S R COOH + H2N NH HCl N NH2 R R N R NH2 (3a-3d) N MnCl2 CS2 , NaOH N S 2 (1a-1d) ZnCl2 C N S S N H C S Mn S C S C a, R = b, R = c, R = d, R = N Zn N H S N H S R y x (5a-5d) H2C NH2 H2C NH2 CS2 , NaOH H2C H2C S H N C H N C S S Na Na S MnCl2 H2C ZnCl2 H2C S H N C H N C S 6 Scheme 1 Synthetic routes to 5a–5d and 6 123 SNa (4a-4d) N S N S Mn S Zn x y H CH3 CH2CH3 CH2CH2CH3 Synthesis and antimicrobial activity 2021 Table 1 Yield, melting point, and results from elemental analysis of compounds 3a–3d Compound Molecular formula Yield (%) Melting point (°C) Elemental analysis found (calculated) (%) 3a C2H3N3S 91.6 192–194 C: 23.68 (23.75), H: 3.05 (3.00), N: 41.43 (41.56) 3b C3H5N3S 89.5 236–239 C: 31.27 (31.28), H: 4.43 (4.38), N: 36.28 (36.49) 3c C4H7N3S 90.3 205–212 C: 37.42 (37.18), H: 5.13 (5.27), N: 32.48 (32.53) 3d C5H9N3S 84.1 212–218 C: 41.81 (41.83), H: 6.30 (6.35), N: 29.31 (29.34) Table 2 Characteristic IR spectral data for compounds 3a–3d Compound IR (mmax, KBr, cm-1) 3a 3,288, 3,082 (mN–H, s); 1,618, 1,611 (mC=N, s); 1,021 (m=C–S–C=, s); 680 (m=C–S–C=, m) 3b 3,324, 3,100 (mN–H, s); 2,939 (mC–H, s); 1,618, 1,520 (mC=N, s); 1,445, 1,376 (mC–H, w); 1,022 (m=C–S–C=, s); 685 (m =C–S–C=, m) 3c 3,287, 3,104 (mN–H, s); 2,974, 2,929, 2,870 (mC–H, s); 1,678, 1,637 (mC=N, s); 1,489, 1,453, 1,368 (mC–H, w); 1,027, 823, 742, 691, 482 (m N–C–S, w) 3d 3,433 (mN–H, s); 2,987, 2,927, 2,760 (mC–H, s); 1,639, 1,527 (mC=N, s); 1,498, 1,451, 1,407(mC–H, w); 1,027, 820, 740, 687, 587(mN–C–S, w) Table 3 Characteristic 1H NMR and 13 C NMR data for compounds 3a–3d Compound 1 3a 6.96 (s, 2H, –NH2); 9.16 (s, 1H, N=C–H) 152.0; 161.7 3b 2.64 (s, 3H, –CH3); 6.96 (s, 2H, –NH2) 19.5; 142.7; 161.5 3c 1.25 (t, 3H, –CH3); 3.07 (q, 2H, –CH2–); 6.96 (s, 2H, –NH2) 13.4; 24.3; 161.6; 168.5 3d 0.91 (t, 3H, –CH3); 1.67 (m, 2H, –CH2–); 2.86 (t, 2H, –CH2–); 6.97 (s, 2H, –NH2) 13.7; 23.8; 30.7; 161.6; 168.9 H NMR (CDCl3, TMS, ppm) 13 C NMR (CDCl3, TMS, ppm) reaction was monitored until completion then cooled to room temperature. Manganous chloride (0.01 mol) aqueous solution was slowly added dropwise, the mixture was stirred for 0.5 h, then 0.01 mol zinc chloride aqueous solution was slowly added dropwise, followed by stirring for 1.5 h. Mancozeb was obtained as a gray solid powder after filtration and drying. Results from characterization of mancozeb, 6, and 1,3,4-thiadiazole derivatives of mancozeb, 5a–5d, are listed in Tables 4, 5, and 6. Antimicrobial activity of 1,3,4-thiadiazole derivatives of mancozeb Antimicrobial activity was determined by use of the filter paper disk method [13]. Paddy fusarium, Botrytis cinerea, cucumber fusarium, tomato gibberella, and grape white rot were selected for the test. 123 2022 Y. Liu et al. Table 4 Yield and results from elemental analysis of compounds 5a–5d and 6 Compound Molecular formula Yield (%) Elemental analysis found (calculated) (%) 6 C4H6MnN2S2Zn 96.5 C: 18.79(18.02), H: 2.19(2.27), N: 10.56(10.51) 5a C6H4MnN6S6Zn 84.9 C: 15.29(15.24), H: 0.78(0.85), N: 17.72(17.77) 5b C8H8MnN6S6Zn 85.2 C: 19.09(19.18), H: 1.55(1.61), N: 16.83(16.78) 5c C10H12MnN6S6Zn 82.1 C: 22.74(22.71), H: 2.31(2.29), N: 15.80(15.89) 5d C12H16MnN6S6Zn 79.4 C: 25.81(25.88), H: 2.88(2.90), N: 15.12(15.09) Table 5 Characteristic IR spectral data for compounds 5a–5d and 6 Compound IR (mmax, KBr, cm-1) 6 3,425 (mN–H); 1,609 (mC=N); 1,442 (mN–C); 1,125 (mC=S); 1,075 (mC–S–C); 956 (mC–S); 550 (mS–X) 5a 3,410 (mN–H); 1,615 (mC=N); 1,442 (mN–C); 1,128 (mC=S); 1,007 (mC–S–C); 920 (mC–S); 529 (mS–X) 5b 3,411 (mN–H); 1,618 (mC=N); 1,431 (mN–C); 1,233 (mC=S); 1,075 (mC–S–C); 865 (mC–S); 658 (mS–X) 5c 3,443 (mN–H); 1,622 (mC=N); 1,429 (mN–C); 1,230 (mC=S); 1,013 (mC–S–C); 930 (mC–S); 576 (mS–X) 5d 3,421 (mN–H); 1,625 (mC=N); 1,433 (mN–C); 1,119 (mC=S); 1,078 (mC–S–C); 944 (mC–S); 530 (mS–X) Table 6 Characteristic 1H NMR and 13 C NMR data for compounds 5a–5d and 6 Compound 1 13 6 2.00(t, 1H, –NH–), 2.93(d, 2H, –CH2–) 47.6; 200.5 5a 4.00 (s, 1H, –NH–); 9.16 (s, 1H, N=C–H) 152.0; 152.9; 196.1 5b 2.65 (s, 3H, –CH3); 4.05 (s, 1H, –NH–) 19.5; 142.9; 152.5;198.1 5c 1.25 (t, 3H, –CH3); 3.07 (q, 2H, –CH2–); 3.98(s, 1H, – NH–) 13.2; 24.4; 152.4; 168.5; 196.0 5d 0.91 (t, 3H, –CH3); 1.68 (m, 2H, –CH2–); 2.86 (t, 2H, –CH2–); 4.01 (s, 1H, –NH–) 13.9; 23.9; 30.7; 152.5; 167.3; 196.5 H NMR (CDCl3, TMS, ppm) C NMR (CDCl3, TMS, ppm) The samples (1,3,4-thiadiazole derivatives of mancozeb 5a–5d) were separately dissolved in an appropriate solvent at a concentration of 10 mg/mL. Compound 6 was used as the standard. Cultures of known inoculum size (106 cells/mL) of the tested strains were spread on nutrient agar plates. Sterile filter paper disks 6 mm in diameter was placed on the plates and the 0.5 ml of 10 mg/mL solutions of the mancozeb derivatives were applied to the filter disks. The plates were incubated for three days at 28 °C. Antimicrobial activity was evaluated by measuring the diameter of the zone of inhibition; the results are summarized in Table 7. Investigation of the antimicrobial screening data revealed that all the novel mancozeb derivatives 5a–5d had moderate to excellent antimicrobial activity 123 Synthesis and antimicrobial activity 2023 Table 7 Antimicrobial activity of mancozeb derivatives 5a–5d and 6 Compound (10 mg/ mL) Zone of Inhibition (mm) Paddy fusarium Botrytis cinerea 5a 19.6 14.5 5b 13.8 23.6 5c 14.3 5d 6 Cucumber fusarium Tomato gibberella Grape white rot 8.1 20.2 14.3 7.8 12.7 15.4 14.3 15.1 12.4 13.5 12.5 7.8 13.6 8.9 11.4 14.2 25.6 7.6 8.1 8.0 The results in the table are average values from three experiments; the diameter of the filter paper was 6 mm against the five strains tested. Compound 5b had the best inhibitory activity against Botrytis cinerea, besides the standard 6; its zone of inhibition reached 23.6 mm. Compounds 5c and 5d had better inhibitory activity than standard 6 against cucumber fusarium; their zones of inhibition were 15.1 mm and 13.6 mm, respectively. All these novel mancozeb derivatives had stronger inhibitory activity than the standard 6 against grape white rot. Among these mancozeb derivatives, compound 5a had the most broad spectrum and strongest inhibitory activity. From the discussion above we can propose a speculative mechanism of the antimicrobial activity of these novel mancozeb derivatives. Mancozeb had a relatively strong inhibitory antimicrobial effect and mancozeb containing the 1,3,4thiadiazole group had stronger antimicrobial activity than mancozeb because the 1,3,4-thiadiazole group is a fat-soluble functional group. Different 1,3,4-thiadiazolecontaining derivatives of mancozeb had different antimicrobial activity against the five strains tested. Because of less steric hindrance, compound 5a had high activity against paddy fusarium, tomato gibberella, and grape white rot. Conclusion Novel mancozeb derivatives containing the 1,3,4-thiadiazole group were synthesized in good yield. 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