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Er et al. Chemistry Central Journal (2018) 12:121 https://doi.org/10.1186/s13065-018-0485-3 Chemistry Central Journal RESEARCH ARTICLE Open Access An integrated approach towards the development of novel antifungal agents containing thiadiazole: synthesis and a combined similarity search, homology modelling, molecular dynamics and molecular docking study Mustafa Er1*, Abdulati Miftah Abounakhla1, Hakan Tahtaci1, Ali Hasin Bawah1, Süleyman Selim Çınaroğlu2, Abdurrahman Onaran3 and Abdulilah Ece4* Abstract Background: This study aims to synthesise and characterise novel compounds containing 2-amino-1,3,4-thiadiazole and their acyl derivatives and to investigate antifungal activities. Similarity search, molecular dynamics and molecular docking were also studied to fnd out a potential target and enlighten the inhibition mechanism. Results: As a frst step, 2-amino-1,3,4-thiadiazole derivatives (compounds 3 and 4) were synthesised with high yields (81 and 84%). The target compounds (6a–n and 7a–n) were then synthesised with moderate to high yields (56–87%) by reacting 3 and 4 with various acyl chloride derivatives (5a–n). The synthesized compounds were characterized using the IR, 1H-NMR, 13C-NMR, Mass, X-ray (compound 7n) and elemental analysis techniques. Later, the in vitro anti- fungal activities of the synthesised compounds were determined. The inhibition zones exhibited by the compounds against the tested fungi, their minimum fungicidal activities, minimum inhibitory concentration and the lethal dose values (LD50) were determined. The compounds exhibited moderate to high levels of activity against all tested pathogens. Finally, in silico modelling was used to enlighten inhibition mechanism using ligand and structure-based methods. As an initial step, similarity search was carried out and the resulting proteins that belong to Homo sapiens were used as reference in sequence similarity search to fnd the corresponding amino acid sequences in target organ- isms. Homology modelling was used to construct the protein structure. The stabilised protein structure obtained from molecular dynamics simulation was used in molecular docking. Conclusion: The overall results presented here might be a good starting point for the identifcation of novel and more active compounds as antifungal agents. Keywords: 2-Amino-1,3,4-thiadiazole, Acylation, Antifungal, Homology modelling, Molecular dynamics, Molecular docking *Correspondence: [email protected]; [email protected] 1 Department of Chemistry, Faculty of Science, Karabuk University, 78050 Karabuk, Turkey 4 Department of Pharmaceutical Chemistry, Faculty of Pharmacy, Biruni University, 34010 Istanbul, Turkey Full list of author information is available at the end of the article © The Author(s) 2018. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/ publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Er et al. Chemistry Central Journal (2018) 12:121 Page 2 of 21 Background compounds, especially those containing nitrogen and sul- Due to widespread of infectious diseases killing mil- phur atoms, have a variety of biological activities [1–3]. lions of people, the need for new active, safer and more Tiadiazole is a fve-membered heterocyclic ring sys- potential antimicrobial agents has increased dramati- tem which contains two nitrogen and one sulphur atom cally. Accordingly, researchers focus on synthesising with the molecular formula of C2H2N2S. 1,3,4-Tiadia- novel compounds and their derivatives having diferent zole and its derivatives have become the focus of atten- physiochemical properties which promises high activi- tion in drug, agriculture and material chemistry due to ties with no or fewer side efects. Heterocyclic com- their high activity in 2′ and 5′ positions in substitution pounds are widespread in nature and are used in many reactions [4, 5]. felds. It has been known for many years that heterocyclic Te two-electron donor nitrogen system (–N=C–S) and hydrogen-binding domain allow for great structural Scheme 1 Synthetic route for the synthesis of the target compounds (6a–n, 7a–n) Er et al. Chemistry Central Journal (2018) 12:121 Page 3 of 21 stability and is known to be the component responsible Computer Aided Drug Design helps to design novel for biological activity [6, 7]. and active compounds which also have fewer side efects. 1,3,4-Tiadiazole and its derivatives have an important In that respect, in silico molecular modelling has been place among compounds with hetero rings containing playing an increasingly important role in the develop- nitrogen and sulphur atoms and have been extensively ment and synthesis of new drug substances and in under- used in pharmaceutics due to their biological activity standing the basis of drug-target protein interactions such as antifungal, antibacterial, antioxidant, anti-infam- [21–23]. matory, anticonvulsant, antituberculosis, and antiprolif- In the light of the literature survey, the purpose of this erative activities [8–20]. study is to synthesise a number of compounds with dif- Te drug design begins with the synthesis of a com- ferent substituted groups containing 1,3,4-thiadiazoles pound that exhibits a promising biological profle (lead ring and their acyl derivatives, to investigate their anti- compound), then the activity profle is optimised and fungal activities and fnally to discuss the inhibition fnally ends with chemical synthesis of this fnal com- mechanism by means of computational tools. pound (drug candidate). Scheme 2 The formation mechanism for the target compounds (6a–n and 7a–n) Er et al. Chemistry Central Journal (2018) 12:121 Page 4 of 21 Results and discussion and 4. All the synthesised 28 compounds (6a–n and 7a– Chemistry n) were obtained in moderate to good yields (56–87%). In the frst part of the study, the thiadiazole compounds Te synthetic route employed to synthesise these com- (3 and 4) were synthesised from the reaction of the com- pounds is given in Scheme 1 and the formation mecha- pounds 1 or 2 (purchased) with the thiosemicarbazide in nism is shown in Scheme 2. trifuoroacetic acid (TFA) at 60 °C. Te compounds 3 and As can be seen from the reaction mechanism in 4 were obtained as specifed in the literature [24, 25]. Scheme 2, the main reaction proceeds through a typical Te acyl derivatives of thiadiazole, which are the target nucleophilic acyl substitution reaction. compounds of the study, were obtained from the reac- Te structure of the compounds obtained were eluci- 1 13 tions of acyl derivatives (5a–n) with the compounds 3 dated using the FT-IR, H NMR, C NMR, elemental Table 1 Inhibition zones of compounds against plant pathogens Compounds Mean zone of inhibition (mm)a Fusarium oxysporum f. sp. lycopersici Monilia fructigena Alternaria solani Doses (µg/ml) Doses (µg/ml) Doses (µg/ml) 500 1000 500 1000 500 1000 C 0 0.00 0 0.00 0 0.00 − ± ± ± 3 10.12 0.91 12.35 0.52 14.16 0.80 18.19 0.86 12.45 0.49 14.81 0.56 ± ± ± ± ± ± 4 14.67 0.93 17.81 1.02 11.19 0.59 14.25 0.54 9.35 0.33 13.18 1.25 ± ± ± ± ± ± 6a 13.19 0.67 17.08 0.72 13.40 0.23 15.88 0.41 10.76 0.29 13.31 0.84 ± ± ± ± ± ± 6b 10.92 0.22 15.68 0.97 16.87 0.32 20.08 0.40 10.40 0.42 14.61 0.37 ± ± ± ± ± ± 6c 13.83 0.30 17.82 0.09 16.31 1.36 18.34 0.34 10.70 0.83 14.73 0.94 ± ± ± ± ± ± 6d 11.27 0.53 15.33 0.36 14.44 3.38 18.09 1.67 9.18 0.59 11.73 0.34 ± ± ± ± ± ± 6e 11.11 0.61 15.14 1.02 12.20 0.74 17.17 1.20 14.27 3.18 17.15 1.68 ± ± ± ± ± ± 6f 13.95 0.58 17.30 0.73 14.45 0.60 18.65 0.51 9.74 0.63 15.21 1.15 ± ± ± ± ± ± 6g 15.51 0.28 18.53 0.39 16.08 0.19 18.30 0.16 13.44 1.00 16.92 0.12 ± ± ± ± ± ± 6h 15.25 0.30 19.14 0.40 11.59 0.58 15.13 1.68 9.57 0.30 11.94 0.35 ± ± ± ± ± ± 6i 10.33 1.29 13.88 1.08 12.37 3.66 17.40 1.21 9.96 0.33 12.56 0.34 ± ± ± ± ± ± 6j 13.31 0.87 18.80 0.74 15.28 0.85 17.93 0.50 11.37 1.38 15.27 1.29 ± ± ± ± ± ± 6k 12.47 0.78 16.67 0.94 19.95 1.49 20.52 1.24 11.16 0.20 15.19 0.90 ± ± ± ± ± ± 6l 13.25 1.59 17.52 0.45 11.44 0.31 15.84 0.39 7.31 0.03 10.73 0.08 ± ± ± ± ± ± 6m 13.69 1.28 18.69 1.28 11.37 1.22 16.59 1.15 11.10 0.36 14.61 0.56 ± ± ± ± ± ± 6n 14.36 0.44 17.76 0.16 12.71 0.52 18.23 0.58 12.05 0.29 15.96 0.16 ± ± ± ± ± ± 7a 13.48 1.07 18.51 1.71 14.31 0.33 17.99 0.29 11.29 0.25 14.01 1.11 ± ± ± ± ± ± 7b 13.40 1.39 17.98 0.58 16.83 1.89 20.04 0.95 10.67 0.48 13.73 0.89 ± ± ± ± ± ± 7c 15.71 1.25 19.51 0.78 15.34 0.27 17.64 0.38 10.18 0.59 14.10 1.64 ± ± ± ± ± ± 7d 11.39 0.04 14.80 0.45 14.95 0.32 17.72 0.23 10.69 0.64 12.57 0.63 ± ± ± ± ± ± 7e 13.48 0.30 17.33 0.52 10.73 0.51 16.83 0.36 10.90 0.32 16.24 0.26 ± ± ± ± ± ± 7f 13.31 0.31 16.56 0.61 12.42 1.43 16.54 0.79 8.02 0.60 10.88 0.37 ± ± ± ± ± ± 7g 12.22 0.29 15.91 0.63 11.90 0.71 21.23 0.97 12.19 0.52 15.88 1.13 ± ± ± ± ± ± 7h 14.68 0.94 18.13 0.46 11.65 0.89 17.34 0.78 7.72 0.44 10.87 0.44 ± ± ± ± ± ± 7i 12.57 0.41 15.81 0.51 14.84 0.23 17.67 0.11 9.04 0.46 11.01 0.55 ± ± ± ± ± ± 7j 11.19 0.95 16.40 0.55 11.77 0.86 20.16 1.81 9.94 0.26 15.38 0.05 ± ± ± ± ± ± 7k 11.97 1.30 15.90 1.00 12.61 2.09 16.66 0.94 8.92 1.22 11.38 0.49 ± ± ± ± ± ± 7l 13.55 0.37 16.38 0.31 9.36 0.92 17.36 0.24 9.90 0.21 12.71 0.79 ± ± ± ± ± ± 7m 13.59 1.88 16.82 0.14 10.17 1.15 16.06 1.46 6.86 0.63 11.54 0.41 ± ± ± ± ± ± 7n 13.65 0.69 17.54 0.52 17.31 1.02 18.74 0.31 12.50 0.45 18.19 0.84 ± ± ± ± ± ± C 25.00 1.32 25.00 0.98 25.00 0.53 + ± ± ± Inhibition zone (IZ) standard deviation (SD); C , positive control (Thiram); C , negative control (DMSO) ± + − a Mean of three assays Er et al.