Synthesis and Acaricidal Evaluation of Some 2-Arylidene-[1,3]-Thiazolo[3,2 а]Benzimidazol-3(2H)-ones Derivatives and Their Impact on Cucumber (Cucumis sativus L) Growth Performance

 Corresponding author: Camara Tchambaga Etienne; Coulibaly Souleymane Copyright © 2025 Author(s) retain the copyright of this article. This article is published under the terms of the Creative Commons Attribution License 4.0. Synthesis and Acaricidal Evaluation of Some 2-Arylidene-[1,3]-Thiazolo[3,2 а]Benzimidazol-3(2H)-ones Derivatives and Their Impact on Cucumber (Cucumis sativus L) Growth Performance Camara Tchambaga Etienne 1, *, Coulibaly Bamoro 2, Bolou Bi Bolou Antoine 3, Coulibaly Souleymane 1, *, Ballo Daouda 1 and Fanté Bamba 1 1 Laboratory of Constitution and Reaction of Matter, School of Sciences of the Structures of Matter and Technology, Félix Houphouët-Boigny University, 22 BP 582 Abidjan 22, Côte d’Ivoire 2 Laboratory of Agro-Industrial Sciences and Technologies (STAgI), School of Agriculture, Halieutic Resources and AgroIndustry (ARHAI), University of San Pedro, San Pedro, Côte d’Ivoire 3 Laboratory of Biotechnology, Agricultural and Valorization of Biological Resources, Research Unit of Plant Pathology and Physiology, Félix Houphouët-Boigny University, Abidjan, Côte d’Ivoire. GSC Biological and Pharmaceutical Sciences, 2025, 33(03), 082-099 Publication history: Received 27 October 2025; revised on 06 December 2025; accepted on 08 December 2025 Article DOI: https://doi.org/10.30574/gscbps.2025.33.3.0486 Abstract A series of 2-(arylidene)thiazolo[3,2-a]benzimidazol-3(2H)-ones derivatives 7a-13a and 7b-13b were synthesized using an efficient and straightforward method. The reaction of 2-mercaptobenzimidazole or its derivatives 3a-c with ethyl 2-bromoacetate 4 under reflux in ethanol afforded thiazolo[3,2-a]benzimidazol-3(2H)-one 5a-c through intramolecular cyclization. These intermediates were then condensed with various aryl aldehydes 6a-g to yield the corresponding 2-arylidene derivatives. The structures of all compounds were confirmed by spectral analyses. Preliminary Acaricidal activity of these compounds was evaluate by determined Phytosanitary and agronomic parameters. The results showed that compounds 5b and 7b, exhibited promising dual functionality. These treatments not only significantly reduced pest presence, especially mites and mealybugs, but also enhanced key agronomic traits such as fruit size, weight, and yield. Keywords: Benzimidazole; Intramolecular cyclization; Thiazolo[3;2-a] benzimidazol-3(2H)-one; Acaricidal activity 1. Introduction The benzimidazole ring is a well-established heterocyclic scaffold widely used in drug design due to its broad spectrum of pharmacological properties. Several clinically approved drugs, such as thiabendazole, albendazole, mebendazole, and flubendazole, are benzimidazole-based anthelmintics. Others, including omeprazole and lansoprazole, serve as proton pump inhibitors, while astemizole functions as an antihistamine [1-3]. Structural modifications of the benzimidazole core have yielded a wide variety of bioactive compounds, with the nature and position of substituents playing a critical role in modulating their biological activities [4-5]. In recent years, the fusion of additional heterocycles to the benzimidazole core have attracted significant attention. Among these, thiazolo[3,2-a]-benzimidazoles have emerged as promising candidates with notable pharmaceutical potential. These fused systems have demonstrated activity against several disease targets, particularly well known as neoplasm inhibitors [6-8]. Additionally, derivatives of thiazolo-benzimidazoles have shown antiviral, antibacterial, anticancer, and antifungal properties [9-16]. Some compounds within this class have also been reported to act as potent non-nucleoside reverse transcriptase inhibitors (NNRTIs) against HIV-1 and to combat resistant fungal strains [8] [17]. GSC Biological and Pharmaceutical Sciences, 2025, 33(03), 082-099 83 The biological activity of such molecules is strongly influenced by their three-dimensional structure. Many DNAinteracting agents, including transcription inhibitors, feature conjugated heteroaromatic frameworks with an S-shaped conformation. The 2-arylidene-substituted thiazolo[3,2-a] benzimidazole scaffold provides a rigid tricyclic core coupled with a flexible arylidene moiety, enabling multiple hydrogen-bonding interactions. This structural framework may favor binding to DNA or DNA-associated enzymes, enhancing therapeutic potential [18,19]. This study explores the synthesis and biological evaluation of 2-arylidene thiazolo[3,2-a] benzimidazole derivatives, specifically targeting their acaricidal activity and impact on cucumber agronomic performance. These hybrid molecules combine two pharmacologically significant moieties: the 2-mercaptobenzimidazole core, known for its antimicrobial and antiparasitic properties [20-22], and a chalcone-like arylidene group, recognized for disrupting pathogenic enzyme systems [23]. By merging these motifs, the designed compounds aim to achieve enhanced biological efficacy through structural synergy. 2. Materials and methods 2.1. Materials of chemistry All chemicals were purchased from Aldrich Chemical, Fischer Scientific (France), and were used without further purification unless otherwise stated. The reactions were followed by TLC on pre-coated Merck 60 F254 silica gel plates and revealed using a UV lamp (6 W, 254 nm, and/or 365 nm). The purification of the products was carried out on a Merck G60 silica gel column. Melting points (m.p., °C) were determined using a temperature gradient (40-265°C) Köfler bench. For all compounds, the Nuclear Magnetic Resonance (NMR) spectra of proton 1H and carbon 13C were recorded on a Brucker 300 advance device. Tetramethylsilane (TMS) was used as a reference for chemical displacements expressed in δ (ppm). The NMR spectra description uses the following symbols: s (singlet), d (doublet), dd (double doublet), t (triplet), q (quadruplet), m (multiplet). The mass spectra were recorded on a JEOL JMS DX300 spectrometer in ESI mode (electrospray/quadripolar ionization or ESI mass). 2.2. Materials of Biology 2.2.1. Study site The experiment was conducted on the campus of Université Félix Houphouët-Boigny in Cocody, Abidjan, located in the southern region of Côte d'Ivoire (5.3453° N, -4.0209° W), at an altitude of approximately 50 meters. The region has a hot and humid subequatorial climate (Eldin, 1971), and the soil is characterized as sandy-clay ferrallitic. 2.2.2. Plant material The plant material consisted of cucumber plants obtained from seeds of the commercial hybrid variety Tokyo F1, known for its adaptability to both open-field and protected cultivation. This variety produces cylindrical, dark green fruits, 1820 cm in length, typically maturing 45-50 days after sowing. 2.2.3. Plot Establishment Sowing was carried out on November 2, 2024. Two (2) to three (3) seeds were placed in each pot, and thinning was performed two weeks later to retain only the most vigorous seedlings for uniform growth. 2.2.4. Experimental design A completely randomized Fisher block design was implemented with two replicates. Each replicate included seven treatments, corresponding to six synthesized compounds (5a, 5b, 10a, 13a, 7b, and 9b) and one untreated control (T0). Compounds were applied at a concentration of 10 mg/L (10 ppm). Each treatment included 10 cucumber plants arranged in double rows on ridges measuring 2 meters in length and 0.7 meters in width. Plants were spaced 0.5 meters apart within and between rows. The ridges were spaced 1.5 meters apart, yielding a total plot area of 27 m². 2.2.5. Crop management Plants were watered daily and weeded regularly to control competition. Fertilization was performed during the vegetative phase using urea and an NPK compound at a rate of 6-7 g per plant. GSC Biological and Pharmaceutical Sciences, 2025, 33(03), 082-099 84 2.2.6. Extract application Each test compound (10 mg) was dissolved in 1L of distilled water, with three drops of Tween 80 added as a surfactant. After thorough mixing, the solution was left to stand for 2 hours before foliar application. Spraying was targeted at the leaves and initiated on November 25th 2024, 23 days after sowing. Applications were repeated every 15 days, for a total of three treatments. 2.3. Synthesis methods 2.3.1. General procedure for the synthesis of 2-mercaptobenzimidazole derivatives 3a-c [24,25] To a solution of o-phenylenediamine or its derivatives 1a-c (1.0 eq, 9.25 mmol) in 15 mL of DMF, cooled in an ice bath, carbon disulfide 2 (5eq, 46.23 mmol) was added dropwise. The reaction mixture was then stirred at room temperature for 24 to 48 hours. Upon completion of the reaction, 200 mL of water was added, resulting in the formation of a precipitate. The precipitate formed was filtered, washed several times with water and dried in an oven (80°C). The crude product was purified obtained by recrystallization from an ethanol/water mixture (1/1) to afford compounds 3ac in 80 to 90% yield. 2-Mercaptobenzimidazole 3a: Beige crystals, yield = 80%, m.p. > 260 °C. 1H NMR (DMSO-d6, 300 MHz)  (ppm) 12.52 (s, 1H, NH), 7.16-7.08 (m, 4H, HAr), 3.40 (s, 1H, SH). 13C NMR (75 MHz, DMSO-d6)  (ppm) 167.23, 131.40, 125.11, 112.85, 108.60. HRMS (ESI) Calc. for C7H6N2S (M + Na+) = 173.0252 Found = 173.0354. 2-Mercapto-5-methylbenzimidazole 3b: Brown crystals, yield = 82%, m.p. > 260 °C. 1H NMR (DMSO-d6, 300 MHz)  (ppm) 12.50 (s, 1H, NH), 7.20-7.10 (m, 4H, HAr), 3.20 (s, 1H, SH), 2.35 (s, 3H, CH3). 13C NMR (75 MHz, DMSO-d6)  (ppm) 167.23, 131.80, 127.13, 114.85, 112.52, 109.60, 107.61, 20.05. HRMS (ESI) Calc. for C8H8N2S (M + Na+) = 187.0408 Found = 187.0308 2-Mercapto-5-nitrobenzimidazole 3c: Orange crystals, yield = 90%, m.p. > 260 °C. 1H NMR (DMSO-d6, 300 MHz)  (ppm) 13.50 (s, 1H, NH), 8.30-7.50 (m, 4H, HAr), 2.50 (s, 1H, SH); 13C NMR (75 MHz, DMSO-d6)  (ppm) 171.69, 142.48, 141.12, 139.81, 114.15, 112.22, 104.56. HRMS (ESI) Calc. for C7H5N3O2S (M + H+) = 196.0102 Found = 196.0208 General procedure for the synthesis of thiazolo[3,2-a]benzimidazol-3(2H)-ones 5a-c [24] To a suspension of 2-mercaptobenzimidazoles 3a-c (1.0 eq, 6.65 mmol) in 20 mL of anhydrous ethanol, ethyl bromoacetate 4 (1.2 eq, 8.0 mmol) was added dropwise. The reaction mixture was then refluxed for 2 to 3 hours. After completion, the reaction mixture was allowed to cool to room temperature, and the solvent was evaporated under reduced pressure. The crude residue was purified either by silica gel chromatography (hexane/ethyl acetate: 70/30) or by recrystallization from a dichloromethane/ethanol mixture to afford thiazolobenzimidazol-3(2H)-ones 5a-d in 75 to 90% yield. Thiazolo[3,2-a]benzimidazol-3(2H)-one 5a : white crystals, yield = 85%, m.p. 135-137 °C. 1H NMR (DMSO-d6, 300 MHz)  (ppm) 7.56-7.24 (m, 4H, HAr), 4.32 (s, 2H, CH2). 13C NMR (75 MHz, DMSO-d6)  (ppm) 169.28, 149.70, 113.47, 136.34; 34.09. Mass (m/z) = 190. M+ = 190 (100), m/z (%): 162 (42), 150 (4), 118 (72), 90 (16), 77 (7), 63 (16), 36 (19), 28 (4). 7-Methylthiazolo[3,2-a]benzimidazol-3(2H)-one 5b : Beige crystals, yield = 75%, m.p. 169-170 °C. 1H NMR (DMSO-d6, 300 MHz)  (ppm) 7.59-7.27 (m, 3H, HAr), 4.51 (s, 2H, CH2), 2.46 (s, 3H, CH3). 13C NMR (75 MHz, DMSO-d6)  (ppm) 168.65, 149.24, 112.91, 135.01, 52.94, 21.04. Mass (m/z) = 204. M+ = 204 (100), M+1 = 205 (12), m/z (%) : 175 (16), 163.19 (26), 142.88 (23), 131.97 (45), 130.97 (34), 121 (29), 90 (43), 45 (33), 41 (31). GSC Biological and Pharmaceutical Sciences, 2025, 33(03), 082-099 85 7-Nitrothiazolo[3,2-a]benzimidazol-3(2H)-one 5c et 6-Nitrothiazolo[3,2-a]benzimidazol-3(2H)-one 5c’: Light green crystals, yield = 90%, m.p. 141-143 °C. 1H NMR (DMSO-d6, 300 MHz)  (ppm) 8.54 (d, J = 2.1 Hz, 1H, HAr), 8.31 (d, J = 2.1 Hz, 1H, HAr), 8.13-8.19 (m, 2H, HAr), 7.60 (d, J = 9 Hz, 1H, HAr), 7.40 (d, J = 9 Hz, 1H, HAr), 3.99 (s, 2H, CH2), 3.97 (s, 2H, CH2). 13C NMR (75 MHz, DMSO-d6)  (ppm) 182.8, 155.2, 153.61, 149.6, 140.80, 132.5, 120.6, 112.40, 33.7. HRMS (ESI) Calc. for C9H5N3O3S (M + H+) = 236.0052 Found = 236.0154. General procedure for the synthesis of 2-(benzylidene)thiazolo[3,2-a]benzimidazol-3(2H)-ones 7a-13a et 7b-13b [26,27] Compounds 5a-b (1 eq, 1.05 mmol) and sodium acetate (1 eq, 1.05 mmol) were dissolved in 20 mL of acetic acid. The mixture was stirred at room temperature for 30 minutes. Subsequently, benzaldehyde or its derivatives 6a-g (1.2 eq, 1.26 mmol) were added, and the reaction mixture was heated under for 4 hours. Upon cooling to room temperature, a precipitate formed, which was filtered, washed with water, and air-dried. The crude product obtained was recrystallized from ethanol to yield 2-benzylidenethiazolo[3,2-a]benzimidazol-3(2H)-ones 7a-13a and 7b-13b with yields ranging from 44 to 54%. 2-benzylidenebenzimidazo[2,1-b]thiazol-3(2H)-one 7a: Yellow crystals, yield = 67%, m.p. 212-214 °C. 1H NMR (DMSOd6, 300 MHz)  (ppm) 8.13 (s, 1H, CH=C), 7.98-7.95 (m, 1H, HAr), 7.78-7.36 (m, 8H, HAr). 13C NMR (75 MHz, DMSO-d6)  (ppm) 170.28, 145.5, 142.5, 141.5, 135.2, 132.8, 130.7, 128.5, 127.9, 123.05, 119.6, 114.1 HRMS (ESI) Calc. for C16H10N2OS (M + H+) = 278.0514 Found = 278.0255. 2-(2-chlorobenzylidene)benzimidazo[2,1-b]thiazol-3(2H)-one 8a: Yellow crystals, yield = 45%, m.p. > 260 °C. 1H NMR (DMSO-d6, 300 MHz) δ (ppm) 8.40 (s, 1H, CH=C), 8.06-7.52 (m, 4H, HAr), 7.45-7.36 (m, 4H, HAr). 13C NMR (75 MHz, DMSO-d6)  (ppm) 169.28, 145.6, 142.4, 141.4, 135.1, 132.8, 130.7, 128.5, 127.9, 123.05, 119.3, 114.5 HRMS (ESI) Calc. for C16H9ClN2OS (M + H+) = 312.0124 Found = 312.0146. 2-(4-chlorobenzylidene)benzimidazo[2,1-b]thiazol-3(2H)-one 9a: Yellow crystals, yield = 75%, m.p. = 200-201 °C. 1H NMR (DMSO-d6, 300 MHz) δ (ppm) 8.12 (s, 1H, CH=C), 8.14-7.60 (m, 4H, HAr), 7.53-7.44 (m, 4H, HAr). 13C NMR (75 MHz, DMSO-d6)  (ppm) 169.28, 145.6, 142.4, 141.4, 135.1, 132.8, 130.7, 128.5, 127.9, 123.05, 119.3, 114.5 HRMS (ESI) Calc. for C16H9ClN2OS (M + H+) = 312.0124 Found = 312.0156. 2-(2,4-dichlorobenzylidene)benzimidazo[2,1-b]thiazol-3(2H)-one 10a: Yellow crystals, yield = 70%, m.p. > 260 °C. 1H NMR (DMSO-d6, 300 MHz) δ (ppm) 8.40 (s, 1H, CH=C), 7.95-7.93 (m, 3H, HAr), 7.82-7.56 (m, 4H, HAr). 13C NMR (75 MHz, DMSO-d6)  (ppm) 171.30, 146.7, 142.2, 141.8, 136.1, 132.5, 130.9, 128.5, 127.9, 123.05, 119.6, 114.3. HRMS (ESI) Calc. for C16H8Cl2N2OS (M + H+) = 345.9734 Found = 345.888. 2-(4-methoxybenzylidene)benzimidazo[2,1-b]thiazol-3(2H)-one 11a: Orange crystals, yield = 69%, m.p. = 193-195 °C. 1H NMR (DMSO-d6, 300 MHz) δ (ppm) 8.13 (s, 1H, CH=C), 8.08-7.67 (m, 4H, HAr), 7.28-7.22 (m, 2H, HAr), 7.34-6.94 (m, 2H, HAr), 4.17 (s, 3H, OCH3). 13C NMR (75 MHz, DMSO-d6)  (ppm) 170.45, 146.6, 141.8, 140.7, 136.1, 133.5, 131.8, 128.4, 127.8, 123.15, 119.9, 114.8. HRMS (ESI) Calc. for C17H12N2O2S (M + Na+) = 331.0619 Found = 331.0517. 2-(4-dimethylaminobenzylidene)benzimidazo[2,1-b]thiazol-3(2H)-one 12a: Orange crystals, yield = 59%, m.p.= 243245 °C. 1H NMR (DMSO-d6, 300 MHz) δ (ppm) 8.11 (s, 1H, CH=C), 7.61-7.58 (m, 2H, HAr), 7.45-7.39 (m, 2H, HAr), 7.247.19 (m, 2H, HAr), 6.78-6.67 (m, 2H, HAr), 3.40 (s, 6H, N(CH3)2). 13C NMR (75 MHz, DMSO-d6)  (ppm) 169.30, 150.3 145.46, 141.8, 140.7, 136.1, 133.5, 131.8, 128.4, 127.8, 123.15, 119.9, 114.8, 41.3HRMS (ESI) Calc. for C18H15N3OS (M + Na+) = 344.0936 Found = 344.1006. 2-(thiophen-2-ylmethylene)benzimidazo[2,1-b]thiazol-3(2H)-one 13a: Yellow crystals, yield = 61%, m.p. 241-242 °C. 1H NMR (300 MHz, DMSO-d6)  (ppm) 8.25 (d, 1H, HAr), 7.88 (d, 1H, HAr), 7.75 (s, 1H, CH=C), 7.73-7.65 (m, 3H, HAr), 7.24-7.19 (m, 2H, HAr). 13C NMR (75 MHz, DMSO-d6)  (ppm) 171.93, 151.95, 142.56, 141.58, 137.92, 132.81, 130.75, 130.58, 129.14, 128.35, 123.05, 119.69, 114.18. GSC Biological and Pharmaceutical Sciences, 2025, 33(03), 082-099 86 HRMS (ESI) Calc. for C14H8N2OS2 (M + Na+) = 307.0078 Found = 307.0020. 2-benzylidene-7-methylbenzimidazo[2,1-b]thiazol-3(2H)-one 7b Brown crystals, yield = 72%, m.p 182-184 °C. 1H NMR (300 MHz, DMSO-d6)  (ppm) 8.10 (s, 1H, CH=C), 7.91-7.29 (m, 7H, HAr), 2.43 (s, 3H, CH3). 13C NMR (75 MHz, DMSO-d6)  (ppm) 172.34, 145.65, 141.53, 136.81, 132.81, 132, 70, 128.85, 128.55 127.93, 127.78, 125.88, 115.35, 115.18, 21.37. HRMS (ESI) Calc. for C17H12N2OS (M + H+) = 293.0670 Found = 293.0380. 2-(2-chlorobenzylidene)-7-methylbenzo[4,5]imidazo[2,1-b]thiazol-3(2H)-one 8b Yellow crystals, yield = 51%, m.p 235-237 °C. 1H NMR (300 MHz, DMSO-d6)  (ppm) 8.30 (s, 1H, CH=C), 7.59-7.51 (m, 3H, HAr), 7.43 (s, 1H, HAr), 7.28-7.24 (m, 2H, HAr), 7.08 (m, 1H, HAr), 2.43 (s, 3H, CH3). 13C NMR (75 MHz, DMSO-d6)  (ppm) 172.34, 144.62, 141.51, 136.41, 132.51, 132, 77, 127.88, 128.45 127.83, 126.79, 125.94, 115.32, 115.58, 21.32. HRMS (ESI) Calc. for C17H11ClN2OS (M + H+) = 327.0281 Found = 327.0510. 2-(4-chlorobenzylidene)-7-methylbenzo[4,5]imidazo[2,1-b]thiazol-3(2H)-one 9b Yellow crystals, yield = 78%, m.p 258-260 °C. 1H NMR (300 MHz, DMSO-d6)  (ppm) 8.10 (s, 1H, CH=C), 7.85-7.23 (m, 7H, HAr), 2.43 (s, 3H, CH3). 13C NMR (75 MHz, DMSO-d6)  (ppm) 172.34, 144.62, 141.51, 136.41, 132.51, 132, 77, 127.88, 128.45 127.83, 126.79, 125.94, 115.32, 115.58, 21.32. HRMS (ESI) Calc. for C17H11ClN2OS (M + H+) = 327.0281 Found = 327.0510. 2-(2,4-chlorobenzylidene)-7-methylbenzo[4,5]imidazo[2,1-b]thiazol-3(2H)-one 10b Brown crystals, yield = 73%, m.p. > 260 °C. 1H NMR (300 MHz, DMSO-d6)  (ppm) 8.30 (s, 1H, CH=C), 7.92-7.28 (m, 6H, HAr), 2.43 (s, 3H, CH3). 13C NMR (75 MHz, DMSO-d6)  (ppm) 172.14, 144.22, 141.31, 136.21, 132.31, 132, 46, 127.88, 128.45 127.83, 126.79, 125.94, 115.32, 115.58, 21.53. HRMS (ESI) Calc. for C17H10Cl2N2OS (M + Na+) = 382.9891 Found = 382.9771. 2-(4-methylbenzylidene)-7-methylbenzo[4,5]imidazo[2,1-b]thiazol-3(2H)-one 11b Yield crystals, yield = 81%, m.p 235-237 °C. 1H NMR (300 MHz, DMSO-d6)  (ppm) 8.10 (s, 1H, CH=C), 7.93-6.90 (m, 7H, HAr), 2.50 (s, 3H, CH3), 2.43 (s, 3H, CH3). 13C NMR (75 MHz, DMSO-d6)  (ppm) 170.34, 159.86, 145.91, 141.50, 138.84, 132.71, 130.20, 127.58, 125.69, 125.34, 115.12, 55.80, 21.45. HRMS (ESI) Calc. for C18H14N2O2S (M + H+) = 323.0776 Found = 323.0872. 2-(4-dimethylaminobenzylidene)-7-methylbenzo[4,5]imidazo[2,1-b]thiazol-3(2H)-one 12b Orange crystals, yield = 78%, m.p. > 260 °C. 1H NMR (300 MHz, DMSO-d6)  (ppm) 8.10 (s, 1H, CH=C), 7.82-6.67 (m, 7H, HAr), 3.30 (s, 6H, N(CH3)2), 2.43 (s, 3H, CH3). 13C NMR (75 MHz, DMSO-d6)  (ppm) 171.43, 150.35, 145.71, 140.51, 138.44, 132.71, 130.25, 127.55, 125.96, 125.43, 115.12, 41.30, 21.45. HRMS (ESI) Calc. for C19H17N3OS (M + H+) = 336.1092 Found = 336.1220. 2-(thiophen-2-ylmethylene)-7-methylbenzo[4,5]imidazo[2,1-b]thiazol-3(2H)-one 13b Beige crystals, yield = 58%, m.p. > 260 °C. 1H NMR (300 MHz, DMSO-d6)  (ppm) 8.35 (d, 1H, HAr), 7.98 (d, 1H, HAr), 7.85-7.42 (m, 3H, HAr), 7.75 (s, 1H, CH=C), 7.65 (s, 1H, HAr), 7.24-7.19 (m, 2H, HAr). 13C NMR (75 MHz, DMSO-d6)  (ppm) 171.93, 151.95, 142.56, 141.58, 137.92, 132.81, 130.75, 130.58, 129.14, 128.35, 123.05, 119.69, 114.18, 21.3. HRMS (ESI) Calc. for C15H10N2OS2 (M + Na+) = 321.0235 Found = 321.0113. GSC Biological and Pharmaceutical Sciences, 2025, 33(03), 082-099 87 2.4. Biological methods Methods for assessing extract efficacy: 2.4.1. Phytosanitary parameters Phytosanitary parameters were used to evaluate the biological activity of the synthesized compounds. These included: the presence of mite droppings, whitish flecks on the leaf surface, mite eggs and larvae, total mite count, presence of scale insects, and the number of non-target insects (excluding mites and scale insects). Well-developed cucumber leaves were sampled from three different leaf positions: the upper (Top), middle (Middle), and lower (Bottom) stages, determined from the plant apex toward the base. From each leaf stage, three mature leaves were collected per treatment group, using three plants as biological replicates. The samples were placed in Kraft paper envelopes and transported to the laboratory. Observations were conducted under a binocular magnifying glass to identify and quantify the presence of mites, mealybugs and other arthropods on the leaf surfaces. 2.4.2. Agronomic parameters Data collection on agronomic parameters began at fruit harvest. The parameters assessed included fruit size, median diameter, number of healthy and damaged fruits, fruit mass, average fruit weight, and overall yield. At each harvest, ten fruits were randomly selected per treatment group for measurement. Fruit length and median diameter were measured using an electronic caliper. The number of healthy and damaged fruits was recorded for each treatment, and their respective masses were determined using a Roberval balance. The average fruit weight for each treatment was calculated using the following formula: The average yield for each plot was calculated per unit area using the expression below: 2.5. Statistical analysis Phytosanitary parameters such as the presence of mite droppings, whitish flecks, mite eggs and larvae, and scale insects were subjected to the Chi-square test of independence in XLSTAT (Version 2016). Quantitative variables, including the number of mites, the number of other insects, and agronomic parameters, were subjected to an analysis of variance (ANOVA) following a normality test to ensure statistical validity. When significant differences between means were detected, Fisher's Least Significant Difference (LSD) test was applied at the 5% significance level to group treatments with statistically similar effects. 3. Results and discussion 3.1. Chemistry The synthetic strategy began with the preparation of 2-mercaptobenzimidazole and its derivatives 5-nitro-2mercaptobenzimidazole and 5-methyl-2-mercaptobenzimidazole 3a-c from ortho-phenylenediamine and its substituted analogues (1a-c). These intermediates were obtained in good yields (80% to 90%) using standard cyclization conditions. Subsequently, the reaction of these mercaptobenzimidazole derivatives (3a–c) with ethyl 2-bromoacetate (4) under reflux conditions in ethanol resulted in the formation of thiazolo[3,2-a]benzimidazol-3(2H)-ones (5a, 5b, and 5c′). The cyclization proceeded smoothly, affording the tricyclic products as the main compounds in this step. In the final stage, compounds 5a and 5b were subjected to a condensation reaction with various aromatic aldehydes (6), yielding a series of 2-(benzylidene)thiazolo[3,2-a]benzimidazol-3(2H)-one derivatives (7a–13a and 7b–13b). These reactions were generally efficient, leading to the targeted arylidene derivatives in moderate to excellent yields. The overall synthetic route is illustrated in Figure 1. GSC Biological and Pharmaceutical Sciences, 2025, 33(03), 082-099 88 Figure 1 Synthesis of 2-benzylidenebenzo[4,5]imidazo[2,1-b]thiazol-3(2H)-ones 7a-13a and 7b-13b The synthesis of compounds 3a-c was carried out using the Van Allan method, as modified by Sorba et al. [19]. This approach involves the condensation of ortho-phenylenediamine or its derivatives 1a-c with carbon disulfide (CS2) 2 in N,N-dimethylformamide (DMF) at room temperature over 24 hours. The resulting precipitate formed was filtered, washed with water, and recrystallized to yield the corresponding 2 mercaptobenzimidazoles 3a-c. The physico-chemical properties of these thiol compounds were consistent with literature reports. Building on the methodology reported by Siomenan et al. [17], the 2-mercaptobenzimidazoles (3a–c) were then reacted with ethyl 2-bromoacetate (4) under reflux in ethanol to afford the desired thiazolo[3,2-a]benzimidazol-3(2H)-ones (5a, 5b, 5c, and 5c′). Compounds 5a and 5b were purified by silica gel chromatography, yielding 85% and 75%, respectively. Compounds 5c and 5c′, formed as a mixture of isomers, were isolated by recrystallization with a combined yield of 90 %. The structures of compounds 5a and 5b were confirmed by 1H and 13C NMR spectroscopy. In the 1H NMR spectra, the disappearance of signals corresponding to the the pyrrolic (NH) and the thiol group (SH) protons present in the precursors 3a and 3b indicated successful cyclization. Instead, singlets at 4.32 ppm (5a) and 4.51 ppm (5b) were observed, corresponding to the two methylene (CH2) protons. These findings were supported by corresponding signals in the 13C NMR spectra. In the case of compounds 5c and 5c', the 1H NMR spectra reveals the presence of two isomers. Ten protons signals were observed, including two singlets on their 1H NMR spectrum. One at 3.99 ppm and another 3.97 ppm, each integrating for two protons, consistent with methylene protons (CH2). Additionally, six aromatic protons appeared between 8.54 and 7.40 ppm, three from each isomer. The absence of NH and SH signals further confirmed the formation of cyclized products 5c and 5c′. The proposed reaction mechanism involves nucleophilic substitution (SN2) of the halogen-bearing carbon by the sulfur atom’s lone pair, followed by elimination of hydrobromic acid (HBr). Protonation of the carbonyl oxygen, due to the acidic nature of the medium facilitates nucleophilic attack by the nitrogen atom on the ester’s electrophilic carbon. This leads to intramolecular cyclization and subsequent elimination of ethanol (Figure 2). GSC Biological and Pharmaceutical Sciences, 2025, 33(03), 082-099 89 Figure 2 Mechanism for obtaining compounds 5 In contrast, compound 5b exhibits an electron-donating effect. The formation of compound 5c' can be attributed to the electron-withdrawing nature of the nitro group (NO2), which promotes tautomerization. This effect facilitates the migration of the proton from the pyrrolic nitrogen (N-H) to the imine nitrogen (C=N), by a tautomeric effect, resulting in an equilibrium between two tautomeric forms (Figure 3). In contrast the methyl group in compound 5b, exhibits an electron-donating which reduces the acidity of the pyrrolic proton and inhibits its migration. As a result, tautomerization is suppressed, and only a single cyclized product is formed. Figure 3 Migration of the proton from the pyrrolic nitrogen to the second nitrogen atom These two isomeric forms of compound 5c/5c′ could not be separated using standard techniques. Efforts are ongoing to achieve separation through selective crystallization or high-performance liquid chromatography (HPLC). Following this, compounds 5a and 5b were then condensed with various aromatic aldehydes, following the procedure reported by Om Prakash et al. [20]. The reactions between compounds 5 and aldehydes 6 yielded a series of 2- (benzylidene)thiazolo[3,2-a]benzimidazol-3(2H)-ones (7a-13a and 7b-13b) which were isolated in yields ranging from 45% to 81% after purification by recrystallization or silica gel chromatography. The reaction mechanism of compounds 7a-13a and 7b-13b proceeds via a base-catalyzed aldol condensation mechanism followed by crotonization. Initially, the acetate ion abstracts an α-proton adjacent to the carbonyl group, generating a carbanion. This reactive intermediate subsequently attacks the carbonyl carbon of the aromatic aldehyde to form a β-hydroxy intermediate. The final step involves dehydration of this intermediate, leading to the formation of the conjugated arylidene product (Figure 4). GSC Biological and Pharmaceutical Sciences, 2025, 33(03), 082-099 90 Figure 4 Mechanism for obtaining compounds 7a-13a and 7b-13b All synthesized compounds 7a-13a and 7b-13b were fully characterized by 1H NMR, 13C NMR and HRMS. The 1H NMR spectra confirmed the successful formation of the target structures. Specifically, the disappearance of the singlets signals at 4.32 ppm and 4.51 ppm, corresponding to the two methylene protons (CH2) present in precursors 5a and 5b, indicates successful condensation. In their place, a new singlet appears around 8.4 ppm, attributed to the vinylic protons (-CH=) of the newly formed arylidene moiety. This downfield shift is consistent with the deshielding effect caused by conjugation with the adjacent carbonyl group, a result of extended π-electron delocalization. Additionally, the ¹H NMR spectra of compounds 7a–13a and 7b–13b show an increased number of aromatic proton signals, reflecting the introduction of substituted aryl rings through the condensation with aromatic aldehydes. 3.2. Biology 3.2.1. Phytosanitary parameters Presence of mite droppings on leaves The Chi-square (2) test of independence shows that the treatments had no statistically significant effect on the presence of mite droppings on cucumber leaves (p = 0.074 > 0.05), suggesting no association between treatment and this parameter (Table 1). However, notable differences were observed among individual treatments. Specifically, compound 5b resulted in 0% mite droppings, distinguishing it from all other treatments. In contrast, the highest incidence of droppings (41.67%) was recorded in treatment 7b. Table 2 Percentages of mite droppings on leaves Percentages / Line (Trts / Presence of droppings) Test of independence between rows and columns (2): compounds No Yes Total 2 (Observed value) 11.507 5a 91.667 8.333 100.000 2(Critical value) 12.592 5b 100.000 0.000 100.000 DDL 6 10a 91.667 8.333 100.000 p-value 0.074 13a 91.667 8.333 100.000  0.05 7b 58.333 41.667 100.000 9b 91.667 8.333 100.000 To 83.333 16.667 100.000 Total 86.9047619 13.0952381 100 GSC Biological and Pharmaceutical Sciences, 2025, 33(03), 082-099 97 Table 12 Summary of agronomic parameters Modality Mites Other insects Yield 1 Yield 2 Healthy fruits (no) Tainted fruit Healthy fruit mass Average weight (kg) Average yield (kg) Final assessment 5b 0.000 0.000 A A Medium 0.000 Medium A Medium (A–B–C) Ideal & clean 7b 0.360 0.000 A A Very good 0.000 Very good A High (A) Highly efficient 5a 0.334 0.583 A A–B Excellent 0.500 Very good A–B High (A) Very good but at risk 9b 0.837 0.000 A A– B–C Very good 0.500 Very good A good (A–B) Productive, but very infected 10a 0.000 0.000 A– B A–B Low 0.000 Low A–B Low (B–C) Clean, but not profitable 13a 0.000 0.000 B– C C Low 0.000 Low B Low (C) Discard T0 0.415 0.250 C B–C Low 1.000 Low A–B Low (A–C) Control — very low GSC Biological and Pharmaceutical Sciences, 2025, 33(03), 082-099 98 4. Conclusion In this study, we successfully synthesized a series of novel 2-(arylidene)thiazolo[3,2-a]benzimidazol-3(2H)-one derivatives and six of them were evaluated for their acaricidal effects alongside with their impact on the agronomic performance of cucumber (Cucumis sativus L.). The compounds were obtained through an efficient three-step synthetic route, and their structures were confirmed by spectral analysis (¹H NMR, ¹³C NMR, and HRMS. Notably, the formation of isomeric products in the case of nitro-substituted intermediates (5c/5c′) underscores the influence of electronic effects on tautomeric equilibrium and product distribution. These findings can highlight the synthetic versatility of the thiazolo[3,2-a]benzimidazole scaffold. Biological evaluations revealed that several of the synthesized molecules, particularly compounds 5b and 7b, exhibited promising dual functionality. These treatments not only significantly reduced pest presence, especially mites and mealybugs, but also enhanced key agronomic traits such as fruit size, weight, and yield. Compound 5b, in particular, stood out as the most effective treatment across nearly all parameters, highlighting its potential as an integrated pest management agent with plant growth-promoting effects. In contrast, compound 13a consistently performed poorly in both phytosanitary and agronomic assessments, emphasizing the importance of structural variations in determining biological efficacy. The control treatment (T0) performed poorly across most parameters. Overall, the study demonstrates the potential of hybrid benzimidazole-based scaffolds as environmentally safer alternatives to conventional pesticides, with added agronomic benefits. Further studies, including field trials and environmental toxicity assessments, are recommended to confirm the broader applicability and safety of these compounds in sustainable agriculture. Compliance with ethical standards Acknowledgments We wish to thank the CEISAM laboratory (Chimie Et Interdisciplinarité, Synthèse, Analyse, Modélisation) of the University of Nantes (France) and the laboratory LG2A (Laboratoire de Glycochimie et des Agroressources d’Amiens) of Jules Verne Picardie University for providing the material and facilities for the spectroscopic analyses. Disclosure of conflict of interest The authors declare that there are no conflicts of interest regarding the publication of this article. References [1] Bera, T., and Belsare, D. (1992). Synthesis, antineoplastic and anthelmintic activities of n-alkyoxycarbonyl-n'-(4benzyloxy-2-nitrophenyl)thioureas as prodrugs of(6-benzyloxy-1h-benzi mida-zol-2-yl)carbamic acid ester. 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