Discovery and Evaluation of Spirofluorenes Based on Imidazolidinedione as Insecticidal Agent Leads

ABSTRACT

Eight imidazolidine‐2,4‐dione derivatives based on spirofluorenes (3–10) have been investigated; these include differences in the aliphatic chain's length and functional groups. Spiro[fluorene‐9,4'‐imidazolidine]‐2',5'‐dione 1 was alkylated with different ethyl halo ester to create ethyl 3‐(2',5'‐dioxospiro[fluorene‐9,4'‐imidazolidin]‐1'‐yl)alkanoate 3‐6. The corresponding alkanoic acids 7–10 were obtained by hydrolyzing the esters 3‐6 with potassium hydroxide in methanol and then acidifying the mixture. Spectral and elemental analysis were employed to regulate the structure and purity of materials 3–10. The findings demonstrated that each product tested exhibited variable levels of insecticidal effective against the larval instars of Spodoptera littoralis. With an LC₅₀ value of 11.68 mg/L against larvae in their second instar, compound 8 was the most effective of all. A range of biological parameters, such as adult longevity, pupal weight, the proportion of normal and deformed pupae, adult emergence, fecundity, and egg hatchability, were employed to assess the latent effects of the prepared materials under examination in an effort to further marginally expand insecticidal materials. The foundation for creating next‐generation pest management strategies that address resistance issues and encourage the use of workable chemical remedies is established by this study.

1. Introduction

In chemical and medicinal chemistry, fluorene and its analogues are a noteworthy class of molecules. A diversity of fluorene derivatives with different biological and physical appearances could be created via adding functional groups to the skeleton of fluorene, a simple hydrocarbon made up of two benzene rings and a center ring with five members. In the field of medical chemistry, fluorene derivatives exhibit a broad variety of biological properties such as antiproliferative [1], antiviral [2], antimicrobic [3], anticancer [4], anti‐inflammatory [5], antioxidant [6], neuroprotective [7], and antitubercular [8] effects. Furthermore, the flurenes are useful for the treatment of diverse illnesses such as Imirestat (aldozreductase inhibitor), Pavatrin (antispasmodic), Cicloprofen (anti‐inflammatory), Lumefantrine (antimalarial), Tilorone (antiviral), and Indecainide (antiarrhythmic) (Figure 1). Moreover, imidazolidinediones are versatile compounds with a broad spectrum of biological properties, such as insecticidal [9], anti‐apoptotic Bcl‐2 proteins [10], antidepressant [11], anticonvulsant [12], anticancer [13], antiviral [14], antidiabetic [15], anti‐inflammatory [16], anti‐HIV [17], antihypertensive [18] effects. Considering the previous information as well as our previous research [19], herein we hypothesized that the combination of the fluorene moiety with the adaptable imidazoliedione pharmacophores into a single chemical structure might be capable of insecticide effects.

FIGURE 1.

Some compounds containing fluorene moiety.

Because of their synthetic availability, remarkable isomerism, tunable efficiency through substitution, and mode of action profile that either matches or exceeds that of conventional heterocycle insecticide materials, imidazoles offer a unique chemical scaffold for bioactive heterocycle compounds used as insecticides in rural areas. Traditional heterocyclic insecticides are potential insect pest control agents because of their drawbacks, which include resistance and unfavorable environmental traits. These variations demonstrate that imidazoles are a valuable class for developing agrochemical pesticides in the future [20]. The Spodoptera littoralis (Boisduval) cotton leafworm, which also damages a variety of ornamental plants, orchard trees, and vegetable crops, is considered Egypt's worst cotton pest [21]. Indeed, it has been discovered that S. littoralis infests an additional 112 plants from 44 distinct families in a broad geographic range that includes Southern Spain, the Middle East, and both Northern and Central Africa [22]. One of the main causes behind the creation of novel insecticidal agents is the increasing struggle of traditional chemically pesticide compounds. One approach to this issue is to examine novel insecticidal chemicals with unique mechanisms of action [23, 24, 25, 26, 27]. Therefore, unlike earlier studies, our goal in this one is to develop medications that effectively manage this pest. The objectives of this effort are as follows: (i) synthesize many polyfunctional substituted imidazole agents and explain them. (ii) Analyzing S. littoralis’s vulnerability to novel substances, like pesticides. (iii) Analyzing how the evaluated target‐designed materials affect different biological parameters and biochemistry (Figure 2).

FIGURE 2.

Preparation strategy and structure optimization of insecticidal compounds.

Similarly, each target produced component's insecticidal efficiency was calculated against the most dangerous pests that endanger particular crops, such as S. littoralis. Businesses may find the insecticidal impact helpful in developing new pesticides for noctuid moths because our research is still in the early stages of insecticide discovery. These compounds were motivated by the properties of ethiprole as well as the remarkable insecticidal action of the imidazole compounds that were previously discussed. This study compares the synthesized chemicals' toxicity to S. littoralis to that of the commonly used imidazoles. The findings of the current study indicate that the tested carbamates have a potential to be applied in IPM programs of S. littoralis.

2. Materials and Methods

2.1. Insecticidal Activities

S. littoralis larvae, initially captured from pesticide‐free cotton fields in Shandaweel, Sohag Governorate, Egypt (26°33′38″N 31°41′30″E), were established as a laboratory colony at the Cotton Leafworm Research Department, Plant Protection Institute, Agricultural Research Centre [28]. In this case, ethiprole was bought from Shandong Leeder Crop Science, LTD. in China. Using the widely used leaf dip bioassay methodology, the insecticidal bioactivity of every chemical that were produced was evaluated [29, 30, 31]. 100 milliliters of distilled water were mixed with 0.10 grams of products suspended in five milliliters of dimethylformamide to create components stocks for 103 parts per million [32]. The stocks were stored in a refrigerator until they were needed. The concentrations obligatory for killing 50% (LC₅₀) of S. littoralis larvae were strongminded based on the outcomes of the target compounds' testing [33, 34, 35]. Five distinct dosages of imidazole derivatives (200, 100, 50, 25, 12.5, 6.25) were used, together with 0.1% tween 80 as a surfactant [36]. The second and fourth larvae, where were roughly the equivalent size and contained in glass jars weighing five pounds apiece, were immersed in the concentration under investigation for 10 s before being suckled castor bean leaf (Ricinus communis) discs, which had a diameter of nine centimeters [37]. 10 larvae were used for each action, which was replicated three times. We have verified that the castor bean leaves utilized in this work, which were gathered from the Shandaweil research station geographic region, Suhag governorate, Egypt, comply with all appropriate institutional, national, and intercontinental norms and legislation [38]. All experimental procedures were conducted in accordance with institutional, national, and international ethical and biosafety guidelines.

2.2. Statistical Analysis

Bioassay assays were conducted using recently molted larvae of the second and fourth instars of S. littoralis to assess the insecticidal bioeffectiveness of new imidazole scaffolds at different dosages. Larval mortality, on the other hand, was measured using Abbott's method [39]. Furthermore, the statistical Finney approach was employed to regulate the LC₂₅ and LC₅₀ values of the imidazolidinedione materials under examination [40]. As a result, the Sun equation was used to get the toxicity index [41].

2.3. Biological Studies

The Costat program determined the likelihood level of comparison for the differences between parameter averages (p < 0.05) using Duncan's check, and SPSS 13.0 software was used to examine all biological characteristics [42, 43]. In their fourth instar, larvae were fed caster bean leaves that had been soaked in LC₂₅ of each herbicide that was being tested. Every medicine under examination was tried on 15 larvae. Using the leaf‐dip technique, the effects of the estimated produced imidazole derivative compounds 5, 6, 7, and 8 at their LC₂₅ values were evaluated on live, fourth‐instar larvae of the S. littoralis laboratory strain. These characteristics included: fecundity (number of eggs per female), fertility (% of egg hatchability), pupal weight, the proportion of normal and malformed pupae, and larval and pupal duration, as well as adult longevity (from emergence to death for both male and female) [44, 45]. To determine the fecundity, the crystal and lachance methodology and the subsequent estimation were employed. Fecundity is calculated as the number of eggs from regarded females separated by the number of eggs from unconsidered female's X 100.

2.4. Experimental

2.4.1. Synthesis of Ethyl 3‐(2',5'‐dioxospiro[fluoren‐9,4'‐imidazolidin]‐1'‐yl)alkanoate (3‐6)

For approximately 14 h, a solution containing 10 mmol of the spiro[fluorene‐9,4'‐imidazolidin]‐2',5'‐dione 1 (1.25 grams, 10 mmole), 5.50 mmole of a suitable ester, BrCH₂COOCH₂CH₃ (0.92 grams), BrCH₂CH₂COOCH₂CH₃ (1.00 gram), BrCH₂CH₂CH₂COOCH₂CH₃ (1.10 grams), BrCH₂CH₂CH₂COOCH₂CH₃ (1.23 grams), and anhydrous K₂CO₃ (2.00 grams, 16 mmoles) in dimethylformamid (50 milliliter) was left to stir at 25°C. Following the reaction's completion (as shown by TLC), the reaction solution was diluted with 200 mL of cold H₂O, and the precipitation that resulted allowed to filter, repeatedly washing with H₂O, and dried. The matching products 3‐6 were obtained by crystallizing the crude product from ethanol [46, 47].

2.4.2. Ethyl 2‐(2',5'‐dioxospiro[fluorene‐9,4'‐imidazolidin]‐1'‐yl)acetate (3)

Yield 90%; m.p. 196°C (reported 196°C [47]); IR ν_max (cm⁻¹): 3395 (HN‐), 3064 (CHarom.), 2958, 2873 (CHaliph.), 1770, 1732 (C═O); ¹H‐NMR (DMSO‐d₆ ) δ: 9.03 (s, 1H, HN‐), 7.92 (d, J = 8 Hz, 2H, CHarom.), 7.57‐7.49 (m, 4H, CHarom.), 7.43‐7.39 (t, J = 8 Hz, 2H, CHarom), 4.35 (s, 2H, NCH2), 4.25‐4.19 (q, J = 6.8 Hz, 2H, OCH₂), 1.28‐1.24 (t, J = 7 Hz, 3H, Me) (see Figure S1); ¹³C‐NMR (DMSO‐d₆ ) δ: 171.61, 167.91, 156.53, 142.89, 141.22, 130.51, 128.84, 124.25, 121.26, 71.68, 61.97, 40.27, 14.47 ppm (see Figure S2); Dept‐135 (DMSO‐d₆ ): δ 61.97 and 40.27 (2 CH₂, exchangeable) (see Figure S3); Elemental analysis, analysis calculated for C₁₉H₁₆N₂O₄ (336.34): C, 67.84, H, 4.78, N, 8.32%. Found: C, 67.98, H, 4.61, N, 8.49.

2.4.3. Ethyl 3‐(2ʹ,5ʹ‐dioxospiro[fluorene‐9,4ʹ‐imidazolidine]‐1ʹ‐yl)propanoate (4)

Yield 88%; m.p. 181°C (reported 178‐180°C [47]); IR ν_max (cm⁻¹): 3173 (HN‐), 3095 (CHarom.), 2966, 2859 (CHaliph.), 1774, 1713 (C═O); ¹H‐NMR (DMSO‐d₆ ) δ: 8.90 (s, 1H, HN‐), 7.91 (d, J = 7.8 Hz, 2H, CHarom.), 7.53‐7.46 (m, 4H, CHarom.), 7.39‐7.36 (t, J = 8 Hz, 2H, CHarom), 4.11‐4.05 (q, J = 6.8 Hz, 2H, OCH₂), 3.80‐3.76 (t, J = 8 Hz, 2H, NCH₂), 2.71‐2.68 (t, J = 8 Hz, 2H, CH₂), 1.21‐1.18 (t, J = 7 Hz, 3H, Me) (see Figure S4); ¹³C‐NMR (DMSO‐d₆ ) δ: 172.68, 171.07, 156.94, 143.10, 141.20, 130.38, 128.88, 128.75, 124.19, 121.19, 71.32, 60.72, 35.34, 32.71, 14.43. ppm (see Figure S5); Dept‐135 (DMSO‐d₆ ): δ 60.72, 35.34 and 32.71 (3 CH₂, exchangeable) (see Figure S6); Elemental analysis, analysis calculated for C₂₀H₁₈N₂O₄ (350.37): C, 68.56, H, 5.18, N, 8.00%. Found: C, 68.72, H, 5.01, N, 8.15.

2.4.4. Ethyl 4‐(2ʹ,5ʹ‐dioxospiro[fluorene‐9,4ʹ‐imidazolidine]‐1ʹ‐yl)butanoate (5)

Yield 89%; m.p. 153°C (reported 145‐150°C [47]); IR ν_max (cm⁻¹): 3331 (NH), 3050 (CHarom.), 2960, 2857 (CHaliph.), 1779, 1707 (C═O); ¹H‐NMR (DMSO‐d₆ ) δ: 8.95 (s, 1H, HN), 7.92 (d, J = 8 Hz, 2H, CHarom.), 7.54‐7.48 (m, 4H, CHarom.), 7.40‐7.37 (t, J = 7.6 Hz, 2H, CHarom), 4.11‐4.06 (q, J = 8 Hz, 2H, OCH₂), 3.60‐3.56 (t, J = 8 Hz, 2H, NCH₂), 2.42‐2.38 (t, J = 8 Hz, 2H, CH₂), 1.93‐1.86 (m, 2H, CH₂), 1.21‐1.17 (t, J = 8 Hz, 3H, Me) (see Figure S7); ¹³C‐NMR (DMSO‐d₆ ) δ: 173.07, 172.72, 157.36, 143.13, 141.20, 130.40, 128.84, 124.09, 121.27, 71.41, 60.37, 38.36, 31.18, 23.53, 14.56 ppm (see Figure S8); Dept‐135 (DMSO‐d₆ ): δ 60.37, 38.36, 31.18 and 25.53 (4CH₂, exchangeable) (see Figure S9); Elemental analysis, analysis calculated for C₂₁H₂₀N₂O₄ (364.40): C, 69.21, H, 5.52, N, 7.68%. Found: C, 69.42, H, 5.33, N, 7.80.

2.4.5. Ethyl 6‐(2ʹ,5ʹ‐dioxospiro[fluorene‐9,4ʹ‐imidazolidine]‐1ʹ‐yl)hexanoate (6)

Yield 87%; m.p. 105‐107°C (reported 104‐106°C [47]); IR ν_max (cm⁻¹): 3176 (NH), 3017 (CHarom.), 2940, 2863 (CHaliph.), 1770, 1703 (C═O); ¹H‐NMR (DMSO‐d₆ ) δ: 8.93 (s, 1H, NH), 7.93 (d, J = 8 Hz, 2H, CHarom.), 7.54‐7.50 (t, J = 8 Hz, 2H, CHarom), 7.45‐7.36 (m, 4H, CHarom.), 4.10‐4.05 (q, J = 8 Hz, 2H, OCH₂), 3.54‐3.51 (t, J = 7 Hz, 2H, NCH₂), 2.34‐2.1.58 (m, 4H, 2CH2), 1.38‐1.32 (m, 2H, CH₂), 1.21‐1.17 (t, J = 8 Hz, 3H, Me) (see Figure S10); ¹³C‐NMR (DMSO‐d₆ ) δ: 173.29, 172.96, 157.42, 143.15, 141.20, 130.38, 128.85, 123.99, 121.28, 71.39, 60.17, 38.76, 33.80, 27.71, 26.02, 24.50, 14.60. ppm (see Figure S11); Dept‐135 (DMSO‐d₆ ): δ 60.17, 38.76, 33.80, 27.71, 26.02 and 24.50 (6CH₂, exchangeable) (see Figure S12); Elemental analysis, Analysis Calculated. For C₂₃H₂₄N₂O₄ (378.42): C, 70.38, H, 6.17, N, 7.15%. Found: C, 70.45, H, 6.06, N, 7.29.

2.4.6. Synthesis of 3‐(2',5'‐dioxospiro[fluorene‐9,4'‐imidazolidin]‐1'‐yl)alkanoic Acids (7‐10)

For 15 h, a solution containing 80 mL of 1 N sodium hydroxide and 5 mmol of a suitable ester 3‐6 was agitated at room temperature. After filtering off the reaction media, the filtrate was allowing to cool for 0°C. After that, diluted HCl was used to acidify the reaction mixture. To produce target product 7–10, the precipitate was filtered, repeatedly cleaned with H₂O, dried, and recrystallization from ethyl alcohol.

2.4.7. 2‐(2ʹ,5ʹ‐Dioxospiro[fluorene‐9,4ʹ‐imidazolidine]‐1ʹ‐yl)acetic Acid (7)

Yield 95%; m.p. 217°C (reported 212‐215°C [47]); IR ν_max (cm⁻¹): 3370 (HO‐), 3258 (HN‐), 3027 (CHarom,), 2961, 2864 (CHaliph.),1775, 1705 (C═O); ¹H‐NMR (DMSO‐d₆ ) δ: 13.06 (br s, 1H, OH), 8.92 (s, 1H, NH), 7.91‐7.90 (d, J = 6 Hz, 2H, CHarom.), 7.53‐7.49 (m, 4H, CHarom), 7.41‐7.37 (m, 2H, CHarom.), 4.24 (s, 2H, CH₂) (see Figure S13); ¹³C‐NMR (DMSO‐d₆ ) δ: 172.70, 169.04, 156.73, 143.06, 141.24, 130.42, 128.78, 124.29, 121.18, 71.70, 40.32 ppm (see Figure S14); Dept‐135 (DMSO‐d₆ ): δ 40.32 (CH₂, exchangeable) (see Figure S15); Elemental analysis calculated for C₁₇H₁₂N₂O₄ (308.29): C, 66.22, H, 3.92, N, 9.08%. Found: C, 66.48, H, 3.72, N, 9.22.

2.4.8. 3‐(2ʹ,5ʹ‐Dioxospiro[fluorene‐9,4ʹ‐imidazolidine]‐1ʹ‐yl)propanoic Acid (8)

Yield 86%; m.p. 186°C(reported 185°C [47]); IR ν_max (cm⁻¹): 3345 (HO‐), 3300 (HN‐), 3041 (CHarom.), 2970, 2863 (CHaliph.), 1770, 1700 (C═O); ¹H‐NMR (DMSO‐d₆ ) δ: 11.38 (br s, 1H, OH), 8.80 (s, 1H, NH), 7.90‐7.89 (d, J = 6 Hz, 2H, CHarom.), 7.52‐7.47 (m, 4H, CHarom), 7.39‐7.35 (t, J = 7.6 Hz, 2H, CHarom.), 3.81‐3.77 (t, J = 8 Hz, 2H, NCH₂), 2.68‐2.65 (t, J = 7 Hz, 2H, CH₂) (see Figure S16); ¹³C‐NMR (DMSO‐d₆ ) δ: 172.72, 172.53, 157.06, 143.22, 141.23, 130.31, 128.73, 124.24, 121.10, 71.38, 35.43, 32.57 ppm (see Figure S17); Dept‐135 (DMSO‐d₆ ): δ 35.43 and 32.57 (2CH₂, exchangeable) (see Figure S18); Elemental analysis Anal. Calcd. For C₁₈H₁₄N₂O₄ (322.32): C, 67.06, H, 4.30, N, 8.69%. Found: C, 67.22, H, 4.19, N, 8.76.

2.4.9. 4‐(2ʹ,5ʹ‐Dioxospiro[fluorene‐9,4ʹ‐imidazolidine]‐1ʹ‐yl)butanoic Acid (9)

Yield 91%; m.p. 183°C (reported 183°C [47]); IR ν_max (cm⁻¹): 3341 (HO‐), 3150 (HN), 3081 (CHarom.), 2952, 2891 (CHaliph.), 1766, 1696 (C═O); ¹H‐NMR (DMSOd₆ ) δ: 11.96 (br s, 1H, HO‐), 8.80 (s, 1H, HN‐), 7.91‐7.89 (d, J = 8 Hz, 2H, CHarom.), 7.53‐7.44 (m, 4H, CHarom), 7.40‐7.36 (t, J = 8 Hz, 2H, CHarom.), 3.60‐3.57 (t, J = 7 Hz, 2H, NCH₂), 2.34‐2.31 (t, J = 7 Hz, 2H, CH₂), 1.91‐1.87 (t, J = 7 Hz, 2H, CH₂) (see Figure S19); ¹³C‐NMR (DMSO‐d₆ ) δ: 174.08, 173.02, 157.39, 143.24, 141.23, 130.33, 128.79, 124.00, 121.17, 71.49, 38.61, 31.44, 23.64 ppm(see Figure S20); Dept‐135 (DMSO‐d₆ ): δ 38.61, 31.44 and 23.64 (3CH₂, exchangeable) (see Figure S21); Elemental analysis, Analysis Calculated For C₁₉H₁₆N₂O₄ (336.34): C, 67.85, H, 4.79, N, 8.33%. Found: C, 68.07, H, 4.43, N, 8.20.

2.4.10. 6‐(2ʹ,5ʹ‐Dioxospiro[fluorene‐9,4ʹ‐imidazolidine]‐1ʹ‐yl)hexanoic Acid (10)

Yield 95%; m.p. 147‐148°C (reported 145‐147°C [47]); IR ν_max (cm⁻¹): 3393 (OH), 3192 (HN‐), 3058 (CHarom.) 2952, 2877 (CHarom.), 1775, 1707 (C═O); ¹H‐NMR (DMSO‐d₆ ) δ: 11.87 (br s, 1H, OH), 8.80 (s, 1H, NH), 7.91‐7.89 (d, J = 8 Hz, 2H, CHarom.), 7.53‐7.49 (t, J = 8 Hz, 2H, CHarom.), 7.43‐7.37 (m, 4H, CHarom), 3.56‐3.52 (t, J = 8 Hz, 2H, NCH₂), 2.27‐2.27 (t, J = 8 Hz, 2H, CH₂), 1.68‐1.57(m, 4H, 2CH₂), 1.40‐1.34 (m, 2H, CH₂) (see Figure S22); ¹³C‐NMR (DMSO‐d₆ ) δ: 174.69, 172.95, 157.45, 143.26, 141.23, 130.31, 128.82, 123.92, 121.18, 71.49, 38.85, 34.00, 27.72, 26.16, 24.55 ppm (see Figure S23); Dept‐135 (DMSO‐d₆ ): δ 38.85, 34.00, 27.72, 26.16 and 24.55 (5CH2, exchangeable) (see Figure S24); Elemental analysis Anal. Calcd. For C₂₁H₂₀N₂O₄ (378.42): C, 69.83, H, 5.86, N, 7.40%. Found: C, 70.03, H, 5.55, N, 7.62.

3. Results and Discussion

3.1. Synthesis

We synthesized here a series of spiro‐fluorene ethyl 3‐(2',5'‐dioxospiro[fluorene‐9,4'‐imidazolidin]‐1'‐yl)alkanoate (3‐6) and 3‐(2',5'‐dioxospiro[fluorene‐9,4'‐imidazolidin]‐1'‐yl)alkanoic acid compounds (7‐10) to study their insecticidal activities. The starting material spiro[fluorene‐9,4'‐imidazolidine]‐2',5'‐dione 1 was designed from three‐component reaction between 9‐fluorenone, KCN and anhydrous Baker's ammonia in 60% ethanol solution, by the Bucherer–Bergs reaction [46]. Ethyl 3‐(2',5'‐dioxospiro[fluorene‐9,4'‐imidazolidin]‐1'‐yl)alkanoate (3‐6) were designed according to the synthetizing passageway showed in Scheme 1, elaborated based on the previous method [47]. alkylation of spiro[fluorene‐9,4'‐imidazolidine]‐2',5'‐dione 1 utilization anhydrous potassium carbonate as basic catalyst in DMF using BrCH₂CO₂CH₂CH₃, ethyl BrCH₂CH₂CO₂CH₂CH₃, BrCH₂CH₂CH₂CO₂CH₂CH₃ and BrCH₂CH₂CH₂CH₂CO₂CH₂CH₃ as alkylating agents, respectively. While hydrolysis of compounds 3‐6 using potassium hydroxide in methanol followed by acidification with diluted hydrochloric acid afforded 3‐(2',5'‐dioxospiro[fluorene‐9,4'‐imidazolidin]‐1'‐yl)alkanoic acids 7‐10, respectively (Scheme 1). Spectral and elements analyses were used to regulate the structure and pureness of compounds 3‐10.

SCHEME 1.

2',5'‐dioxospiro[fluorene‐9,4'‐imidazolidin derivatives 3‐10.

The formation of the products 3‐10 were established via FT‐IR, ¹H‐NMR, ¹³C‐NMR and elementals technique. For example, the IR spectra of material 4 displayed stretching beak at 3174 cm⁻¹ due to HN‐ moiety and absorption band at 3095 cm⁻¹ characteristics of aromatic C─H bonds, while absorption bands characteristic of aliphatic C─H bonds appears at 2966 and 2859 cm⁻¹, beside two stretching bands at 1774 and 1713 cm⁻¹ characteristics of C═O bonds. Its ¹H‐NMR spectrum displayed the occurrence of singlet signal at δ 8.90 ppm distinguishing of NH proton. Beside, three signals at 7.91, 7.50, and 7.37 ppm distinguishing the aromatic protons. While, the ethyl ester protons appear as a triplet integrated signal for CH₃ group at δ 1.21 ppm and a quartet signal at δ 4.09 ppm characteristic of CH₂ moiety. Furthermore, two triplet signals with coupling constant 8 Hz at δ 3.78 and 2.70 ppm, characteristic of N‐CH₂ and CH₂C═O protons, respectively. Its ¹³C‐NMR displayed two signals at δ 14.4 ppm (upward in DEPT) to Me carbon and 60.72 ppm (downward in DEPT) characteristic of the ethyl ester carbons Me and CH₂, respectively. Besides, two signals at δ 35.34 (downward in DEPT) and 32.71 (downward in DEPT) ppm characteristic the carbons of NCH₂ CH₂ moiety, respectively. While the spiro carbon appeared at δ 71.32 ppm and disappeared in DEPT. Furthermore, the aromatic and carbonyl carbons had performed at δ 172.68, 171.07, 156.94, 143.10, 141.20, 130.38, 128.88, 128.75, 124.19, and 121.19.

3.2. Toxicological Activity

The newly created binary and fused imidazole derivatives' in vitro insecticidal efficacy against S. littoralis larvae in their second and fourth instars was evaluated. The LC₅₀ values of the examined compounds demonstrated a significant degree of toxicity after 72 h of feeding on castor leaves treated with the confirmed products using the leaf‐dip bioassay, as seen in Table 1 and Figure 3. Based on LC₅₀ values ranging from 11.68 to 63.31 mg/L and a reference LC₅₀ value of 2.94 mg/L for ethiprole, the insecticidal compounds under investigation demonstrated wide ranges of toxicological effectiveness against the second larvae instar, from high to low. On the other hand, the LC₅₀ values of target materials 3‐10 against second instar were 42.10, 48.92, 35.60, 13.11, 39.63, 11.68, 63.31, and 50.13 mg/L. In addition to the toxicity index for compounds 3‐10, and ethiprole were 0.069, 0.060, 0.082, 0.224, 0.074, 0.251, 0.046, 0.058, and 1%, respectively.

TABLE 1.

After 72 h of treatment, the insecticidal agent of products 3‐10, and ethiprole, as a reference insecticide, was applied to S. littoralis.

second instar larvae					fourth instar larvae
Comp.	LC50 (mg/L)	Slope	χ2	Toxic ratio a	LC50 (mg/L)	slope	χ2	Toxic ratio
3	42.10	0.612 ± 0.265	0.189	0.069	82.34	0.582 ± 0.244	0.118	0.172
4	48.92	0.667 ± 0.244	0.128	0.060	89.36	0.736 ± 0.246	0.112	0.159
5	35.60	0.610 ± 0.271	0.489	0.082	44.21	0.514 ± 0.243	0.569	0.398
6	13.11	0.466 ± 0.259	0.198	0.224	27.50	0.581 ± 0.244	0.102	0.516
7	39.63	0.632 ± 0.241	0.358	0.074	69.46	0.736 ± 0.245	0.442	0.204
8	11.68	0.456 ± 0.247	0.361	0.251	23.15	0.517 ± 0.246	0.532	0.613
9	63.31	0.610 ± 0.245	0.098	0.046	120.9	0.747 ± 0.245	0.089	0.117
10	50.13	0.644 ± 0.249	0.498	0.058	110.3	0.727 ± 0.240	0.126	0.128
Ethiprole	2.942	0.362 ± 0.276	0.316	1	14.20	0.495 ± 0.248	0.122	1

^a Notes: The toxicity ratio is strongminded via subtracting the baseline (ethiprole) poisonousness LC₅₀ value from the compound's LC₅₀ value.

FIGURE 3.

Imidazoles derivatives 3‐10, and the reference insecticide's toxicological action against S. littoralis's second and fourth.

Larvae in their fourth instar had LC₅₀ values of 82.34, 89.36, 44.21, 27.50, 69.46, 23.15, 120.9, 110.3, and 14.20 mg/L for 3‐10, and ethiprole, respectively, following a 72‐h exposure. They were 0.172, 0.159, 0.398, 0.516, 0.204, 0.613, 0.117, 0.128, and 1% in the same context. Consequently, produced product 8's insecticidal bioactivity was almost the same as reference ethiprole when applied to S. littoralis insects in their second larval instar. Binary and fused imidazole materials are more effective against S. littoralis than other known spiro nitrogenous heterocyclic scaffolds, according to this paper [48]. This idea can be explained in a number of ways. (i) Spiro constitutions have a restricted capacity to attack the active site of the receptor target protein and their conjuration is stiff in 3D. (ii) In contrast, the conformation of fused imidazole scaffolds is less restricted and more planar, which facilitates the interaction of the functional groups with the biological target.

3.3. Biological Activity

Although the novelty molted fourth‐instar larvae were let to feed on caster leaves treated with LC₂₅ of the most clearly detrimental target imidazole derivatives 5, 6, 7, and 8 for 72 h and untreated leaves till pupation, the biological properties of S. littoralis were nevertheless examined. The basic biological tests' verified data are displayed in Tables 2 and 3.

TABLE 2.

Effectiveness of the extremely poisonous synthetic imidazole derivatives 5, 6, 7, and 8 on several biological features as strongminded via the LC₂₅ values obtained from the leaf‐dip technique in lab‐grown S. littoralis.

Treatments	Larval duration (days)	Pupal duration (days)	Pupal weight (mg)	Normal pupae (%)	Deformed pupae (%)	Adult emergence (%)
8	24.6a ± 0.26	10.3e ± 0.13	260.1e ± 1.1	54.2e ± 0.26	19.3a ± 0.30	62.9e ± 0.25
7	19.5b ± 0.29	12.4d ± 0.18	269.1d ± 0.5	61.5d ± 0.25	18.5b ± 0.20	76.6d ± 0.25
6	17.9c ± 0.26	13.1c ± 0.11	274.2c ±0.5	72.6c ± 0.23	14.5c ± 0.40	84.5c ± 1.52
5	13.9d ± 0.28	15.4b ± 0.21	289.1b ± 0.5	86.5b ± 0.32	10.7d ± 0.20	87.5b ± 0.85
control	11.5e ± 0.45	16.1a ± 0.21	302.5a ± 1.0	95.5a ± 0.12	6.65e ± 0.20	99.6a ± 0.70
LCD 0.05	1.21	0.50	2.12	1.01	0.98	1.91

TABLE 3.

Effectiveness of the extremely assessed synthetic imidazoles at their LC₂₅ values on some biological parameters against S. littoralis larvae.

Treatments	No. of eggs/female	Fecundity (%)	Egg hatchability (%)
8	840.6e ± 4.6	31.4e± 0.25	49.2e ± 0.22
7	928.4d ± 8.3	39.5d ± 0.25	55.6d ± 0.11
6	2015.4c ± 10.9	59.5c ± 0.27	69.5c ± 0.36
5	2320.4b ± 7.1	68.4b ± 0.25	88.6b ± 0.52
Control	2870.5a ± 10.0	100a	98.3a ± 0.33
LCD 0.05	22.12	0.97	1.17

All of the imidazole derivatives that were studied produced a satisfactory increase in the lifespan of the larvae and pupae when compared to the untreated larvae (11.5 days). This was demonstrated by compounds 8 at 24.6 days, 7 at 19.5 days, 6 at 17.9 days, and 5 at 13.9 days; the difference between these compounds and the control group was statistically significant (Table 2). In contrast, target compounds 8, 7, 6, and 5 resulted in pupal lengths of 10.3, 12.4, 13.1, and 15.4 days, respectively. This was much shorter than the normal larvae's lifespan of 16.1 days. Furthermore, the pupal weight reductions generated by the most effective imidazole scaffolds under investigation varied significantly. The newly synthesized compounds 7, 6, and 5 (269.1, 274.2, and 289.1 mg, respectively) were arranged in descending order in Table 2, with molecule 8 (260.1 mg) being the most active and outperforming the untreated larvae (302.5 mg) (Figure 4). In terms of the latent effects of the most powerful toxic novel imidazole, LC₂₅, on S. littorals larvae in their fourth instar, component 8 was the most dynamic, according to the data validated in Table 2.

FIGURE 4.

Normal larvae, pupae, and adult (A); deformed larvae, pupae, adult (B).

Compared to the untreated larvae (95.5%, 5.65%, and 99.6%, respectively), Compound 8 recorded 54.2%, 19.3%, and 62.9% of normal pupae, malformed pupae, and adult emergence, respectively. Compounds 7 (61.5%, 18.7%, and 76.6%), 6 (72.6%, 14.5%, and 84.5%), and 5 (86.5%, 10.7, and 87.5%) are also displayed. We discovered that the offspring generation of the parent fourth instar larvae exposed to 8, 7, 6, and 5 had experienced an abnormally significant decrease in both egg hatchability (fertility) and the mean number of eggs produced by adult females (fecundity) due to the newly synthesized imidazole derivatives. The information shown in Table 3 (number of eggs per female, fecundity percentage, and egg hatchability percentage) served as the basis for this conclusion. The final operative insecticide significantly decreased fertility compared to the untreated group, which produced 2870.5 eggs/female, 100.0% fecundity, and 98.3% fertility. Following this were 8 (840.6 eggs/female, 31.4% fecundity, and 49.2% fertility), 7 (928.4 eggs/female, 39.5% fecundity, and 55.6% fertility), 6 (2015.4 eggs/female, 59.5% fecundity, and 69.5% fertility), and 5 (2320.4 eggs/female, 68.4% fecundity, and 88.6% fertility).

4. Conclusion

Agricultural pests have caused large losses in agricultural output, putting global food security at jeopardy. Synthetic insecticides continue to be the main control method. However, given the rapid emergence of pest resistance and the more stringent regulations limiting the use of pesticides, the development of efficient insecticides with novel structures is particularly important. To ascertain the insecticidal poisonousness, biochemical activity, and latent impact of novel materials against one of the most damaging and destructive pests, more research has been done [49, 50, 51, 52]. The length of the aliphatic chain and the functional groups of eight imidazolidine‐2,4‐dione derivatives based on spirofluorenes (3–10) have been investigated. Fluorene‐9,4'‐imidazolidine Spiro[Ethyl 3‐(2',5'‐dioxospiro[fluorene‐9,4'‐imidazolidin]‐1'‐yl)alkanoate 3‐6 was produced by alkylating ‐2',5'‐dione 1 with ethyl halo esters. The corresponding alkanoic acids 7–10 were obtained by hydrolyzing the esters 3‐6 with potassium hydroxide in methanol and then acidifying the mixture. Additional research on the latent impact, and insecticidal toxicity of imidazole derivatives against one of the most dangerous and destructive pests. According to the data, all of the compounds used in the experiments had varying degrees of insecticidal effects on S. littoralis larvae in both instars. Compound 8 was the most poisonous of them all, having LC₅₀ values S. littoralis larvae of 11.68 and 23.15 mg/L, respectively. As a result, the most potent imidazole derivatives' insecticidal properties were reduced by 8, 7, 6, and 5, respectively. In an attempt to further marginally improve insecticidally materials, the latent effects of the synthesized compounds under investigation were evaluated on a quantity of biological parameters.

Author Contributions

Mohamed A. Gad was responsible for the formal analysis, data collection. Sameera N. Al‐Ghamdi: creation of the original draft and funding acquisition. Antar A. Abdelhamid: editing, and review writing. Nujud H. Alqahtani: synthesis all newly discovered compounds and formal analysis. Review & editing are some of the things that Fatemah M. Asiri possesses. Amal A. Alageel: length of data, resources, formal analysis. Ohoud J. Alotaibi and Ibtesam Y. Mashnoy: creative draught writing, and review writing editing.

Conflicts of Interest

The authors declare no conflict of interest.

Supporting information

Supporting File 1: cbdv71327‐sup‐0001‐SuppMat.docx

Data Availability Statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.