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Nanao/organocatalyat SiO2/4-(2-Aminoethyl)-morpholine as a new, reusable, and efficacious catalyst for the synthesis of polyhydroquinolines derivatives and antibacterially active evaluation

BMC Chemistry volume 19, Article number: 58 (2025) Cite this article

Abstract

In this study, a new nanocomposite comprising 4-(2-Aminoethyl)-morpholine, an organic catalyst, was prepared on the surface of silica. The absence of metal in the catalyst structure contributes to its environmental friendliness. This novel nanocatalyst was used for multi-component reactions (MCRs). Having a nano size for the composite enhances the contact between the raw materials and the catalytic surface, leading to significant advancement in the reaction. The synthesized composite was identified and evaluated using FT-IR, EDX, EDX-Mapping, TGA, XRD, BET, TEM, and FE-SEM analysis. The characteristic analysis confirmed the synthesis of both nano-silica/4-(2-Aminoethyl)-morpholine catalyst and polyhydroquinoline. The composite’s catalytic properties for synthesizing some polyhydroquinoline derivatives were investigated, yielding promising and remarkable results with high 95% yields and short reaction times. The antibacterial properties of the synthesized compounds were also examined against four types of pathogenic bacteria. The highest inhibitory effect was attributed to the compound Ethyl-4-(3-hydroxyphenyl)-2,7,7-trimethyl-5-oxo-1,4,5,6,7,8-hexahydroquinoline-3-carboxylate exhibited the highest antibacterial properties.

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Introduction

Over the past decade, many studies have focused on developing sustainable practices that aim to minimize waste and adhere to the principles of green chemistry [1, 2]. Among different methods, multi-component reactions (MCRs) emerge as one of the effective strategies in green chemistry. Multi-component reactions are one of the most effective ways to increase molecular complexity and structural variety through a straightforward process. As a procedure for creating organic chemicals, this approach enables the creation of numerous chemical compounds with more structural variety [3,4,5,6,7,8,9]. Demonstrating several advantages such as synthetic convergence, simplicity, selectivity, ease of use, rapid reaction times, high economic efficiency, and the elimination of intermediate separation and purification steps [10, 11]. Producing the final product in a single step is particularly important in synthesizing pharmaceutical and organic compounds [12]. In recent years, substantial progress has been achieved in the field of multi-component reactions, with ongoing efforts directed toward further refinement and expansion of MCR methodologies.

In comparison to the traditional step-by-step preparation, these reactions are also thought to be a practical and efficient technique for the synthesis of organic compounds. They typically exhibit strong selectivity and a decrease in by-products. [13,14,15,16].

In this trajectory of enhancing MCRs, incorporating organocatalysts emerges as a promising avenue. Organocatalysts, characterized by their small organic molecule nature and potent catalytic capabilities, offer distinct advantages over traditional metal catalysts in synthesizing organic compounds [17, 18]. Notably, these advantages include the absence of metal-associated concerns during the purification process, thus mitigating environmental pollution risks, as well as their cost-effectiveness and widespread availability [19]. The enhancement of catalyst performance and adherence to green chemistry principles are achieved by immobilizing these organocatalysts on various substrates [20].

Various substrates have been explored for immobilizing organocatalysts, including cellulose [21], polymers [22], graphene oxide [23], and silica [24], among others. Among these, silica stands out as one of the most frequently utilized substrates owing to its non-toxicity, stability, potential for functionalization, and ready availability [25, 26]. Integrating silica as a substrate in the context of MCRs represents a strategic choice, aligning with the overarching objective of promoting environmentally friendly and sustainable synthetic methodologies [8].

Polyhydroquinolines, as robust organic heterocyclic compounds, represent a class of molecules synthesized through MCRs. They have garnered much interest because of their crucial function in biological and pharmacological processes. [27,28,29,30]. Notably, these compounds' one-pot, four-component synthesis has drawn much more attention due to their essential pharmacological and biological properties [31,32,33,34]. The reported activities of these compounds encompass anti-inflammatory, antimicrobial, antioxidant, anti-ulcer, anti-seizure, and calcium channel inhibitory effects, underscoring their diverse and potentially therapeutic applications [35, 36].

Despite the success in synthesizing these organic derivatives through various techniques, challenges persist across different methodologies [37, 38]. Many catalysts including diammonium phosphate modified with bismuth [39], UiO‑66‑Pyca‑Ce (III) [40], Fe3O4@SiO2@BHA-Cu(II) [41], Fe3O4@dextrin/BF3 [42], copper (II)-poly(acrylic acid)/M-MCM-41 [43], Fe3O4@DABA-PA-CuBr2 [44], Fe3O4@SiO2@(CH2)3@Gl [45], etc.

These challenges encompass harsh reaction conditions, prolonged reaction times, hazardous solvents, intricate product separation processes, reliance on costly catalysts, low product yields, and the formation of undesirable by-products [46]. Recognizing the limitations inherent in existing methodologies, the pursuit of improving multi-component reactions remains an ongoing endeavor within the scientific community [47].

This study aims to develop the application of the MCRs technique as an effective method in green chemistry. Next, it was focused on the complexity of various MCR methodologies, the reported activities and applications of polyhydroquinolines, the challenges associated with existing techniques, and the role of organocatalysts immobilized on silica in addressing these challenges. In this work, for the first time, the organic molecule 4-(2-Aminoethyl)-morpholine has been placed on the surface of silica, which has resulted in the production of a heterogeneous organocatalyst. Nitrogen groups are present in the intended composite structure. Consequently, this composite's electrons free N have been given to create a catalyst with base properties suitable for the reaction.

Then, some polyhydroquinoline derivatives were produced using this catalyst under suitable conditions. The reaction was carried out under specific conditions, including EtOH/ H2O solvent and 70 °C. Additionally, after synthesizing the polyhydroquinoline compounds, the inhibitory effect of these compounds on four strains of bacteria, namely Escherichia coli (E. coli), Salmonella typhi (S. typhi), Enterococcus faecalis (E. faecalis), and Staphylococcus aureus (S. aureus), was investigated. This paper can provide valuable insights into establishing a comprehensive foundation for future research endeavors involving multi-component reactions and sustainable synthetic approaches.

Materials and methods

All reagents and solvents were procured from Merck, Aldrich, and Fluka chemical companies. The melting point of synthetic materials was measured using the Buchi B-540 B. V. CHI apparatus. KBr tablets were utilized for FT-IR analysis with the Bruker Equinox 55 spectrometer. Proton nuclear magnetic resonance (1H NMR) and carbon-13 nuclear magnetic resonance (13C NMR) spectra were recorded in DMSO-d6 as the solvent using the Bruker DRX-400 Avance instrument. A Mira 3-XMU field emission scanning electron microscope (FE-SEM) determined the nanoparticle's size and catalyst morphology. The crystallographic properties of the sample were analyzed using an X-ray diffractometer (XRD, Philips Xpert) with Ni-filtered CuKα radiation (kCuK = 0.1542 nm), operating at 40 kV and 30 mA, within the 2θ range from 10° to 80°. Thermo gravimetric analysis (TGA) was conducted using an STA 505 instrument under an argon atmosphere. The BET surface area, pore size, and pore volume were measured using a Tristar II 3020 analyzer. Melting points were determined using a Buchi B-540 B. V. CHI apparatus. Energy Dispersive X-ray Spectroscopy (EDX) was performed using a Phenom Pro X. Compounds M4, M5, M6, M7 and M8 were checked by 1HNMR, and the 1CNMR spectra are added to the supplementary file.

The synthesis of a nano-silica/4-(2-Aminoethyl)-morpholine catalyst

For the synthesis of silicon chloride, initially, in a round-bottom flask (250 mL), nano-silica gel (8 g) and thionyl chloride (30 mL) (toxic and should be used under a fume hood and safety conditions) was refluxed for 48 h. After cooling to room temperature, the reaction mixture was filtered through a Büchner funnel. The residue was washed several times with dichloromethane, and, ultimately, the obtained silicon chloride precipitate was dried at room temperature for 24 h. In the next step of preparing nano-silica/4-(2-Aminoethyl)-morpholin, (1 g) of the precipitate from the previous step was placed in a round-bottom flask and subjected to ultrasonic waves in hexane for 10 min. Subsequently, 4-(2-Aminoethyl)-morpholin (2 mL) was added dropwise to the reaction vessel while stirring, and the mixture was allowed to reflux for 12 h. After the completion of the reaction, the reaction mixture was cooled and filtered. The obtained precipitate was washed several times with hot hexane. Finally, the nano SiO2/4-(2-Aminoethyl)-morpholin catalyst was air-dried at room temperature.

The synthesis of polyhydroquinoline

The general method for synthesizing polyhydroquinoline derivatives involves combining nano-SiO2/4-(2-Aminoethyl)-morpholine (0.04 g) as a nanocatalyst with a mixture of dimedone (1 mmol), aromatic aldehyde (1 mmol), ethyl acetoacetate (1 mmol), and ammonium acetate (1 mmol). A round-bottom flask and a certain amount of the catalyst in H2O/EtOH (1:1) at 60 °C. The progress of the reaction was monitored using TLC (hexane–ethyl acetate, 3:1). Once the reaction was complete, the catalyst was separated from the reaction mixture through simple filtration. The reaction solvent was evaporated, and the obtained residue was recrystallized in hot ethanol.

The catalytic property of polyhydroquinoline

The synthesis of polyhydroquinoline derivatives was explored upon identifying the synthesized catalyst. As a model reaction, the interaction between 4-nitrobenzaldehyde, ethyl acetoacetate, dimedone, and ammonium acetate was chosen, and the reaction was carried out under varying conditions, including different temperatures, solvent concentrations and amounts of catalyst. (Table 1) Subsequent investigations revealed that the highest efficiency within the most suitable timeframe was achieved when the reaction was conducted at a temperature of 70 °C, using a water/ethanol solvent, and with 40 g. of the catalyst. These parameters were determined to be optimal. After identifying the synthesized catalyst, the conditions for optimizing the synthesis of polyhydroquinoline derivatives were determined. To achieve this goal, the reaction involving 4-nitrobenzaldehyde, ethyl acetoacetate, dimedone, and ammonium acetate as a model reaction was selected, and the reaction was conducted under various temperature, solvent, and catalyst quantity conditions. (Table 1).

Table 1 Optimization of various reaction conditions
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In the first stage, the reaction was performed in the presence of SiO2, SiO2/4-(2-Aminoethyl)-morpholine, and the absence of a catalyst (Table 1, entry 1–3). The objective of this stage was to examine the catalytic effect of 2-morpholinoethanamine and confirm its role in catalyst synthesis. In the second stage, the reaction was carried out in different solvents such as ethanol, ethyl acetoacetate, and water/ethanol to find the best solvent. Conducting the reaction in the water/ethanol solvent yielded the best results. Water is a green and cost-effective solvent, and using ethanol alongside it ensures the complete dissolution of organic compounds, which is an advantage of using this solvent. In the third stage, the reaction was examined at different temperatures to determine the optimal temperature. For this purpose, the model reaction was conducted at room temperature, 50 and 70 °C, with 70 °C as the optimum temperature. In the final stage, the amount of catalyst required was investigated, and the best result was obtained using 0.04 g. of the catalyst. After analyzing the results, the reaction was conducted at 70 °C in a water/ethanol solvent with 0.40 g. of the catalyst, demonstrating the highest efficiency in the most appropriate timeframe. These conditions were determined as optimal (Table 1, entry 6. The reaction was conducted at 70°C in a water/ethanol solvent with 0.40 g of catalyst, achieving the highest yield of 95% in the optimal time of 12 minutes. These conditions were identified as the optimum).

The synthesis of polyhydroquinoline derivatives

After determining the optimal conditions for synthesizing polyhydroquinoline derivatives in the presence of the silica/2-morpholine base catalyst, a variety of aldehydes were employed to synthesize different derivatives of polyhydroquinoline. The summarized results are reported in Table 2. As observed, the best efficiency and reaction time results were achieved for electron-withdrawing groups. The best yield (95%) is obtained for 0.04g of catalyst, which corresponds to the TON and TOF values, respectively 1759.2 and 117.28 min−1. [6, 7, 11].

Table 2 Different polyhydroquinoline derivatives under various conditions, including time, yield, and m.p
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The mechanism of the catalytic process with polyhydroquinoline

Considering the catalytic activity, the following mechanism is suggested for this reaction. In the base catalyst's presence, dimedone attacks the aldehyde with hydrogen elimination, forming intermediate 1. Subsequently, ammonium acetate and ethyl acetoacetate generate intermediate 2. Finally, in the presence of the catalyst, these two intermediates synthesize intermediate 3 through an increase in the Michael intermediate, ultimately leading to the formation of the desired product through intramolecular cyclization.

The desired catalyst was synthesized in two stages. Initially, a mixture of thionyl chloride and nano-silica was refluxed for 48 h to produce silica chloride. In this reaction, chlorine atoms from thionyl chloride replaced the OH functional groups of silica gel. Subsequently, the nano-silica chloride was dried. In the next step, 2-morpholinoethanamine was added dropwise to the nano-silica chloride in n-hexane solvent, and the reaction was allowed to proceed under reflux conditions. The desired composite was separated by filtration and then dried at room temperature. Finally, various analyses were conducted to identify and characterize the target catalyst, including FTIR, EDX, EDX-Map, TGA, XRD, BET, TEM, and FE-SEM.

Antimicrobial evaluation

According to Gholami et al. [55], we assessed the minimum inhibitory concentrations (MIC) of various agents against several tested microorganisms, including S. aureus, E. faecalis, S. typhi, and E. coli. Each microorganism was subjected to two-fold serial dilutions of the agents and control groups using Muller-Hinton broth. Following preparation, the plates were then incubated for 24 h at 37 °C. Subsequently, the optical density was measured using a microplate reader spectrophotometer at 620 nm (Power Wave TM X52, BioTek Instruments Inc., VT, USA). MIC was determined to be the lowest concentration that inhibited the growth of microorganisms. Minimal bactericidal concentration (MBC) assays were conducted by directly plating media from each agent well onto MHB agar and incubating them overnight at 37 °C. Following incubation, colony counts were performed, and MBC were determined as the lowest concentration with no observable colony growth.

For statistical analysis, IBM SPSS software (v.21, IBM Corporation, New York, NY, USA) was utilized, employing one-way ANOVA followed by Scheffe’s post-hoc test for multiple comparisons of bacterial growth. A significance level of p < 0.05 was considered statistically significant. All experiments were conducted in triplicate (Fig. 1).

Fig. 1
figure 1

Proposed mechanism for synthesis of polyhydroquinoline in the presence of nano-SiO2/4-(2-Aminoethyl)-morpholine

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Result and discussion

The progress of catalyst construction can be examined through the analysis of FT-IR. Accordingly, in Fig. 2a, the FT-IR spectra of three compounds, SiO2-Cl (a), 4-(2-Aminoethyl)-morpholin (b), and SiO2/4-(2-Aminoethyl)-morpholin (c), are compared. In spectrum (a), the peak observed at 3390 cm−1 is related to the SiO–H stretching vibration groups [56]. Spectrum (b) corresponds to 2-morpholinoethanamine, with peaks in the 2700–2800 cm−1 region attributed to CH2 groups in the ring and chain. The peak around 3400 cm−1 is also assigned to NH2 groups [57]. As shown in Fig. 2a–c, the spectrum of the synthesized composite exhibits distinct peaks, confirming the presence of 2-morpholinoethanamine on SiO2. The peaks appearing in the 2700–2800 cm−1 region in the spectrum (C) are attributed to the CH2 groups present in 2-morpholinoethanamine, clearly evident in this spectrum. Furthermore, the observed changes in the 1000–1600 cm−1 region in the spectrum (C) are indicative of the presence of 4-(2-Aminoethyl)-morpholine in its structure.

Fig. 2
figure 2

a FTIR analysis of SiO2 a, 4-(2-Aminoethyl)-morpholine b, nano-silica/4-(2-Aminoethyl)-morpholine (c), b EDX of nano-silica/4-(2-Aminoethyl)-morpholine for detecting the amount of silica in nanocatalyst c EDX-map of nano-silica/4-(2-Aminoethyl)-morpholine

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To confirm the connection of 4-(2-Aminoethyl)-morpholin to the silica surface, elemental analysis (EDX) was conducted. Figure 2b illustrates the elemental analysis of the synthesized composite. The presence of C, N, Si, and O is evident as observed. The weight percentage of each element is respectively equal to %36.8, %21.67, %37.41, and %4.09. EDX analysis is also employed to examine the distribution of 4-(2-Aminoethyl)-morpholin on the silica surface. As depicted in Fig. 2c, the distribution of 4-(2-Aminoethyl)-morpholin on the silica surface appears uniform. The combined figure clearly showed the presence of Si, O, and C on the catalyst’s surface, confirming the successful synthesis of polyhydroquinoline. The thermal stability of the synthesized catalyst was investigated, and the results of the TGA analysis are presented in Fig. 3a. According to this analysis, two decomposition stages occurred. The first decomposition in the region of 100 °C is attributed to moisture removal. The second decomposition in the 100–225 region involves removing organic groups on the composite surface. The weight loss of the catalyst by 38% indicates the amount of organic material in the composite. Figure 3b shows the XRD analysis of nano-silica/4-(2-Aminoethyl)-morpholin. The broader peak at 2θ = 23° suggests the presence of an amorphous phase of silica (SiO2) [58]. Amorphous materials do not exhibit a regular crystalline structure, resulting in a broad peak in the XRD pattern. Other available peaks at around 14°, 18°, 27°, 29°, and 59° suggest the presence of crystalline phases in addition to the amorphous silica, which approves the presence of morpholine in the nano-silica/4-(2-Aminoethyl)-morpholine structure. The XRD peaks are aligned with the polycrystalline morpholine phase, according to JCPDS Card No. 00–033–1524 (Quality: Blank) [59]. The International Centre for Diffraction Data (ICDD) database (COD-2016) lists 16 JCPDS card numbers for morpholine. Unfortunately, these JCPDS card numbers do not provide information on the growth plane direction (h k l). Moreover, by using the Scherrer equation, the peak at 23° suggests a particle size of approximately 3.4 nm for the crystalline phase(s) present in the catalyst.

Fig. 3
figure 3

a TGA of nano-silica/4-(2-Aminoethyl)-morpholine, b XRD nano-silica/4-(2-Aminoethyl)-morpholine, BET of nano-silica/4-(2-Aminoethyl)-morpholine including, c Langmuir-plot, d BET-Plot, e t-Plot, f) BJH-Plot, j Adsorption/desorption isotherm diagram

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The catalyst's average particle size, which ranged from 12 to 30 nm, is depicted in Fig. 4 as nanospheres with a pseudo-spherical shape. TEM observations, which reveal nanoparticles, were used to analyze the intrinsic structure (Fig. 4).

Fig. 4
figure 4

TEM of nano-silica/4-(2-Aminoethyl)-morpholine

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A BET analysis was performed to assess the catalyst's porosity. According to the data in Fig. 3c–j, The BET analysis indicates that the catalyst has a specific surface area of 19.13 m2/g, suggesting a moderate surface area available for catalytic reactions. The total pore volume of 0.052382 cm3/g and the mean pore diameter of 10.953 nm imply the presence of pores within the catalyst structure, which could facilitate reactant diffusion and enhance catalytic activity. The Langmuir analysis yields a specific surface area of 20.316 m2/g, slightly higher than that obtained from the BET analysis. This discrepancy may arise from differences in the assumptions and models used in the two methods. The Langmuir analysis suggests the presence of a monolayer of adsorbate on the catalyst surface. The t-plot analysis provides a specific surface area of 14.612 m2/g, lower than the BET and Langmuir analyses. This result suggests the presence of micropores or non-specific adsorption sites on the catalyst surface, which may contribute to its overall surface area. The catalyst nano-silica/4-(2-Aminoethyl)-morpholine exhibits a moderate specific surface area and pore volume, indicating its potential suitability for synthesizing polyhydroquinolines derivatives. Pores within the catalyst structure could enhance reactant diffusion and catalytic activity. FE-SEM analysis was employed to examine the morphology. Figure 5a displays the FE-SEM analysis of the synthesized composit before and after reuse (Figures a(A) and a (B), respectively). As observed in the figure, both exhibit spherical and uniform characteristics. This analysis also studied particle size, revealing that for SiO2/4-(2-Aminoethyl)-morpholin, the particle size is less than 50 nm. As anticipated, there was minimal alteration in the catalytic characteristics, and the catalyst can be reused several times.

Fig. 5
figure 5

a FE-SEM nano-silica/4-(2-Aminoethyl)-morpholin b FT-IR analysis of nano-silica/4-(2-Aminoethyl)-morpholin before (a) and after (b) reuse. C XRD and d EDX analysis of nano-silica/4-(2-Aminoethyl)-morpholin after reuse

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Centrifugation was used to isolate nano-GO/3-aminopyridine from the reaction media, followed by a hot ethanol wash and overnight drying at 60 °C to assess the catalyst’s reusability. In later model reaction rounds, the dry catalyst was employed. The used catalyst was subjected to FT-IR, XRD, and EDX analyses and then compared to the original catalyst analyses. The findings are displayed in Figs. 5b–d, respectively. A comparison of the washed catalyst with the original FT-IR, XRD, and EDX catalyst is shown in Figures. The covalent bond formed between 4-(2-Aminoethyl)-morpholine and the silica surface prevents the organic compound from being separated.

Reusability of the catalyst

The recyclability of the catalyst was investigated, and the results are presented in Fig. 6. For this purpose, the catalyst used in the model reaction was separated and washed with hot ethanol. After drying, it was reused in the model reaction. This process was repeated 7 times. The efficiency and reaction time showed no significant changes, indicating an acceptable reusability of the catalyst. After examination, the FT-IR spectrum of the catalyst before and after reuse was also compared, showing minimal changes in these two spectra (Fig. 5b).

Fig. 6
figure 6

The recyclability of the catalyst of nano-silica/4-(2-Aminoethyl)-morpholine

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Comparison of the catalyst's performance with literature

To confirm the acceptable performance of the composite in synthesizing polyhydroquinoline derivatives, the efficiency and reaction time obtained with this catalyst were compared with previous studies (Table 3). The results indicated that the efficiency and reaction time achieved in this work were acceptable compared to other studies. Using an organocatalyst with strong catalytic properties contributed to forming products with high efficiency under mild conditions. Additionally, the synthesis of the catalyst from alumina waste, coupled with its economic feasibility, further highlights the advantages of this work.

Table 3 Comparison of catalytic activity of Nano-SiO2/4-(2-Aminoethyl)-morpholine with other catalysts
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Antibacterial activity

The investigation examined the in vitro antimicrobial effectiveness of polyhydroxyquinolines AY-α and M1–8 against four bacterial strains: Escherichia coli (E. coli), Salmonella typhimurium (S. typhi), Enterococcus faecalis (E. faecalis), and Staphylococcus aureus (S. aureus). The study used a microdilution method to determine the minimum inhibitory concentration (MIC). Figure 7 presents the viability percentages of the tested microorganisms exposed to these polyhydroxyquinoline derivatives, revealing a dose-dependent hindrance of bacterial growth. MIC values for the polyhydroxyquinolines against bacterial strains are outlined in Table 4. The significant antibacterial activity of compound M8 is particularly noteworthy, with MIC values ranging from 32.25 to 1000 μg/mL across all strains. Compound M8 demonstrated potent antibacterial activity against all microorganisms, with a MIC value of 31.25 μg/mL, indicating effective antibacterial action. This underscores the notable influence of the ethoxy substituent on antimicrobial efficacy, with compound M8, incorporating such a substituent, emerging as the most active among tested compounds. Furthermore, the optimal lipophilicity of M8 suggests its potential as an antimicrobial agent. However, the study's focus is confined to these nine compounds, necessitating further investigations, including additional experiments to evaluate their safety and efficacy in both in vitro and in vivo environments.

Fig. 7
figure 7

Antimicrobial effects of compounds against four different bacterial pathogens

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Table 4 The MIC values of all tested compounds
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To investigate the structure–activity relationship (SAR), the impact of substituents at the positions of polyhydroxyquinolines was assessed. Compound M8, featuring an ethoxy substituent, demonstrated superior activity compared to other compounds with phenoxy substituents at the same position. M8 exhibited a high Log P value, indicative of enhanced permeability, while chlorinated compounds followed in priority. The study underscores the significance of structural modifications in polyhydroxyquinolines for enhancing antibacterial efficacy. Various functional groups were attached to the terminal pharmacophore to enhance the polarity and assimilate the lipophilicity of morpholine derivatives. Among different functional groups, ethoxy substitution has shown an excellent hydrophobic nature of the synthesized compounds. Thus, a balance between lipophilicity and hydrophilicity of ethoxy derivatives directly impacted the enhancement of the log P values of the compounds. The MIC data of the synthesized compounds demonstrated that ethoxy derivatives are the most potent among all functional groups. However, M8 showed better antimicrobial activity than the standard and was highly active against four different bacterial strains. Several resistance assays corroborated the data obtained in the experimental study; ethoxy derivatives may have a unique mechanism of action with no cross-resistance with standard drugs. Interestingly, the ethoxy substitution was significantly active against Staphylococcus aureus, Mycobacterium tuberculosis, Candida albicans, Mucor sp., Aspergillus sp., and Fusarium. Implications of the results showed that ethoxy substitution has the potential to be used in developing entirely new therapeutic agents. Functional groups are attached to the morpholine ring to modulate the lipophilic nature of synthesized candidate compounds [65,66,67,68,69,70]. Ethoxy substitution is found to be ideal, as it generally enhances lipophilicity with some extent of polarity attributed to the − O − substituent. Compounds M8 showed the most promising activity compared to the standard treated as a positive control using the microdilution broth method. Previous studies showed the effect of an ethoxy substituent unit on mycobactericidal and fungicidal activity, which was determined using a viability assay on human granulometric leukemia cells with the reference drug. Out of 10 newly synthesized compounds and their intermediates, two compounds and a standard were tested in vitro against B. subtilis, E. coli, C. albicans, Cladosporium, and A. niger by using the microdilution broth method. All the compounds were found to show good to moderate antimicrobial activities. Further research is essential to fully explore and appreciate the remarkable antibacterial properties of this compound. By delving into its mechanisms and effects in greater detail, we can unlock its true potential and harness the benefits it offers in our fight against bacterial infections.

M1

M2

M3

M4

M5

M6

M7

M8

M9

Conclusion

This article introduced a nano-heterogeneous organocatalyst using a small molecule with strong catalytic properties and metal removal from the catalyst structure. Using the synthesized catalyst, various derivatives of polyhydroquinoline were efficiently synthesized with high yields and within a short timeframe. The antibacterial effects of these compounds were investigated, revealing that compound M8 exhibited the highest antibacterial properties. As the concentration increased, the antibacterial activity level also increased, which was consistent with our research findings. The results indicated that the polyhydroquinoline derivatives demonstrated promising effects against pathogenic bacteria. This work highlights several significant aspects, including the elimination of metal-induced pollutants, the development of a catalyst capable of being reused for up to 7 cycles, conducting a model reaction under gentle conditions, achieving high product efficiency, constructing a cost-effective and economically viable catalyst, and facilitating the easy separation and purification of the product.

Availability of data and materials

All data generated or analyzed during this study are included in this published Article.

Abbreviations

FT-IR:

Fourier transform infrared

EDX:

Dispersive X-ray spectroscopy

TGA:

Thermo gravimetric analysis

XRD:

X-ray diffraction

EDX:

Energy-dispersive X-ray

FE-SEM:

Field emission scanning electron microscope

TEM:

Transmission electron microscopy

NMR:

Nuclear magnetic resonance

TLC:

Thin layer chromatography

EtOH:

Ethanol

SiCl:

Silica chloride

MCRs:

Multi-component reactions

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Acknowledgements

Financial assistance from the shiraz university of medical sciences by way of Grant Number 28484 is gratefully acknowledged.

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Authors and Affiliations

  1. Biotechnology Research Center, Shiraz University of Medical Sciences, Shiraz, Iran

    Leila Amiri-Zirtol, Ahmad Gholami & Seyedeh Narjes Abootalebi

  2. School of Chemical, Petroleum and Gas Engineering, Iran University of Science and Technology (IUST), Tehran, Iran

    Zahra Karimi

  3. School of Engineering, Edith Cowan University, 270 Joondalup Drive, Joondalup, Perth, WA, 6027, Australia

    Javad Farahbakhsh

  4. Department of Pharmaceutical Biotechnology, School of Pharmacy, Shiraz University of Medical Sciences, Shiraz, Iran

    Ahmad Gholami

  5. Division of Intensive Care Unit, Department of Pediatrics, School of Medicine, Shiraz University of Medical Sciences, Shiraz, Iran

    Seyedeh Narjes Abootalebi

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Contributions

LAZ designed and performed the research, analyzed the data, ZK performed the assay and conducted the optimization. JF purification of compounds, interpreted the results, and prepared the manuscript. AGh interpreted the results, and prepared the manuscript. SNA interpreted the results, and prepared the manuscript. All authors read and approved the final manuscript.

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Correspondence to Ahmad Gholami or Seyedeh Narjes Abootalebi.

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Amiri-Zirtol, L., Karimi, Z., Farahbakhsh, J. et al. Nanao/organocatalyat SiO2/4-(2-Aminoethyl)-morpholine as a new, reusable, and efficacious catalyst for the synthesis of polyhydroquinolines derivatives and antibacterially active evaluation. BMC Chemistry 19, 58 (2025). https://doiorg.publicaciones.saludcastillayleon.es/10.1186/s13065-025-01403-7

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BMC Chemistry

ISSN: 2661-801X

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