Phenanthro [9, 10d] imidazole quaternary ammonium salt derivative as well as preparation method and antibacterial application thereof

Abstract

The invention discloses a phenanthro [9, 10-d] imidazole quaternary ammonium salt derivative as well as preparation and antibacterial application thereof. According to the series of compounds, phenanthro [9, 10-d] imidazole quaternary ammonium salt derivatives which are novel in structure and good in antibacterial activity are prepared by taking phenanthro quinone as a lead compound and modifying the structure of phenanthro quinone, the structural general formula of the phenanthro [9, 10-d] imidazole quaternary ammonium salt derivatives is shown in the specification, and R is selected from H, C6-C14 alkyl or C3-C8 alkylene. The phenanthro [9, 10-d] imidazole quaternary ammonium salt derivative prepared by the invention has a relatively good antibacterial effect on gram-positive bacteria such as staphylococcus aureus S.aureus ATCC 29213 and various clinical methicillin-resistant staphylococcus aureus (MRSA), meanwhile, the water solubility is improved, the biotoxicity of a parent body is reduced, and the phenanthro [9, 10-d] imidazole quaternary ammonium salt derivative has relatively high yield and is suitable for industrial production. The compound is expected to be further developed into a clinical candidate antibacterial drug. # imgabs0 #

Description

Technical Field

[0001] The invention belongs to the technical field of phenanthrenequinone derivatives, and specifically relates to phenanthrene[9,10-d]imidazole quaternary ammonium salt derivatives, preparation methods and antibacterial applications thereof. Background Art

[0002] [9,10-d]Phenanthrenequinone is a type of quinone compound with good biological activities in the medical field, such as antibacterial, anti-tumor, anti-inflammatory, and analgesic.

[0003] Phenanthro[9,10-d]imidazole is composed of a chromophore phenanthroimidazole unit and a bipolar imidazole unit, and has a nitrogen-containing heterocyclic structure with a large conjugated rigid plane, which determines that the phenanthroimidazole building unit has good thermodynamic stability and high fluorescence quantum efficiency (A novel bipolar D-π-A type phenanthroimidazole / carbazole hybrid material for high efficiency nondoped deep-blue organic light-emitting diodes with NTSC CIEy and low efficiency roll-off[J]. Journal of Materials Chemistry C, 2017, 5: 11901-11909). Due to its unique chemical structure and properties, it has been widely used in the fields of molecular chemistry, organic optoelectronic materials, and has also played a great role in fluorescent probes.

[0004] In recent years, with the in-depth study of the properties of phenanthroimidazole derivatives, more and more researchers have paid attention to the biological activities of phenanthroimidazole derivatives. Imidazole and its derivatives are an important class of heterocycles, and the introduction of imidazole rings has been widely used in drug discovery. It is reported that various imidazole derivatives have a wide range of biological activities, such as anti-neurodegeneration, anti-inflammatory, anticonvulsant, anti-tumor, anti-tuberculosis, anti-leishmanial, anti-hyperglycemic, anti-aging, antifungal and antibacterial activities (Promisingantileishmanial activity of novel imidazole antifungal drug Luliconazoleagainst Leishmania major: in vitro and in silico studies[J].Journal of GlobalAntimicrobial Resistance,2018,14:260-265; Imidazole clubbed 1,3,4-oxadiazolederivatives as potential antifungal agents[J].Bioorganic&MedicinalChemistry,2015,23(15):4172-4180.). However, there are few reports on the antibacterial activity of phenanthroimidazoles, and their water solubility is relatively poor and they have certain biological toxicity. Summary of the invention

[0005] Purpose of the invention: In view of the above technical problems, the present invention provides a phenanthro[9,10-d]imidazolium quaternary ammonium salt derivative and its preparation method and antibacterial application. The phenanthro[9,10-d]imidazolium quaternary ammonium salt derivative has a good antibacterial effect on Gram-positive bacteria such as Staphylococcus aureus S.aureus ATCC 29213 and various clinically isolated MRSA, and solves the problems of poor water solubility and improved cytotoxicity.

[0006] Technical solution: In order to achieve the above-mentioned invention object, the technical solution adopted by the present invention is as follows:

[0007] Phenanthro[9,10-d]imidazole quaternary ammonium salt derivatives, the structural formula of which is as follows:

[0008]

[0009] Wherein, R is selected from H, C6-C14 alkyl or C3-C8 olefin.

[0010] As a preferred embodiment, R is selected from H, C6-C14 single chain alkyl or C3-C8 olefin group containing a double bond.

[0011] As a preferred embodiment, R is selected from H, C9-C11 single chain alkyl or C4-C6 olefin group containing a double bond.

[0012] As the most preferred embodiment, R is selected from the following groups a or b:

[0013]

[0014] The selection of the above groups a and b corresponds to compounds 6a and 6b in the specific embodiment of the present invention, respectively.

[0015] The present invention also provides a method for preparing the phenanthro[9,10-d]imidazole quaternary ammonium salt derivative, comprising the following steps:

[0016] Step 1: Under acidic conditions, phenanthrenequinone 1 reacts with p-nitrobenzaldehyde 2 to generate intermediate 3;

[0017] Step 2: Intermediate 3 reacts with differently substituted bromoalkane R-Br under alkaline conditions to generate intermediate 4;

[0018] Step 3, intermediate 4 generates intermediate 5 under the action of a reducing agent;

[0019] Step 4, intermediate 5 reacts with methyl iodide to obtain the target compound;

[0020]

[0021] Wherein, the R is the same as described above.

[0022] As a specific implementation scheme, in step 1, the acid in the acidic condition is ammonium acetate, the reaction molar ratio of intermediate 1, p-nitrobenzaldehyde 2 and acid is 1:1:5-1:2:10, the reaction temperature is 90-120°C, and the reaction solvent is acetic acid.

[0023] As a specific implementation scheme, in step 2, the base in the alkaline conditions is K2CO3, the reaction molar ratio of intermediate 3, bromoalkane R-Br and base is 1:3:3-1:7:7, the reaction temperature is 45-60°C, and the reaction solvent is acetone.

[0024] As a specific implementation scheme, in step three, the reducing agent is selected from stannous chloride, the reaction molar ratio of the intermediate 4 to the reducing agent is 1:10-1:15, the reaction temperature is 40-78°C, and the reaction solvent is ethyl acetate or ethanol.

[0025] As a specific implementation scheme, in step 4, the reaction molar ratio of the intermediate 5 to methyl iodide is 1:5-1:10, the reaction temperature is 35-80°C, and the reaction solvent is acetonitrile.

[0026] Finally, the present invention provides the use of the phenanthro[9,10-d]imidazole quaternary ammonium salt derivatives in the preparation of antibacterial agents. Preferably, the antibacterial agent can inhibit Staphylococcus aureus S.aureus ATCC 29213 and various clinical methicillin-resistant Staphylococcus aureus (MRSA).

[0027] The present invention designs and synthesizes phenanthro[9,10-d]imidazole quaternary ammonium salt derivatives by imitating the structure and function of antimicrobial peptides. The parent structure in the derivatives as a hydrophobic part is conducive to the compound inserting into the bacterial phospholipid bilayer membrane, and the hydrophilic cationic part is conducive to interacting with the negatively charged bacterial cell membrane. The derivatives can also bind to DNA, destroy DNA, cause DNA degradation, and cause DNA damage, thereby causing bacterial cell death. All target compounds are evaluated for antibacterial activity, and they have strong antibacterial activity against Staphylococcus aureus (S.aureus) ATCC 29213 and clinically isolated methicillin-resistant Staphylococcus aureus (MRSA). The antibacterial value is higher than that of its parent compound phenanthroquinone, equivalent to the positive control vancomycin, and the hemolytic activity is also lower than that of the parent compound phenanthroquinone. The compound of the present invention increases the water solubility of the parent compound, can significantly improve the toxicity, is not easy to produce drug resistance, and has good stability.

[0028] Technical effect: The phenanthro[9,10-d]imidazole quaternary ammonium salt derivatives prepared by the present invention have good antibacterial effect on Gram-positive bacteria such as Staphylococcus aureus S.aureus ATCC 29213 and various clinical methicillin-resistant Staphylococcus aureus (MRSA), while improving water solubility, reducing the biological toxicity of the parent, and having a high yield, and are expected to be further developed into clinical candidate antibacterial drugs. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is the dynamic bactericidal curve of compound 6b.

[0030] Figure 2 It is the drug resistance induction of compound 6b.

[0031] Figure 3 The blood routine test and blood biochemical indexes of compound 6b in vivo.

[0032] Figure 4 The change of the survival rate of MRSA in the skin of infected mice with compound 6b.

[0033] Figure 5 For compound 6b 1 H-NMR spectrum.

[0034] Figure 6 For compound 6b 13 C-NMR spectrum. DETAILED DESCRIPTION

[0035] The present invention is further described in detail below through examples.

[0036] Example 1 Preparation of Intermediate Compound 3

[0037] In a round-bottom flask, a mixture of phenanthrenequinone 1 and p-nitrobenzaldehyde was dissolved in glacial acetic acid, and an appropriate amount of ammonium acetate was added. After stirring at 100°C for 1-2 hours, the reaction solution was cooled to room temperature and poured into ice water. The solid was collected by filtration and washed with ice water. The solid was vacuum dried to obtain intermediate 3.

[0038] Example 2 Preparation of Intermediate Compounds 4a and 4b

[0039] In a pear-shaped bottle, add K2CO3 to the acetone solution of intermediate 3 and 1-bromo-n-decane or 1-bromo-3-methyl-2-n-butene, reflux and stir at 50°C, and detect by thin layer chromatography (TLC) until the reaction is completed. After the reaction is completed, spin dry, extract with EtOAc, combine the organic phases, dry with anhydrous Na2SO4, concentrate, and separate by column chromatography to obtain intermediates 4a and 4b.

[0040] Example 3 Preparation of Intermediates 5a and 5b

[0041] Add an appropriate amount of stannous chloride dihydrate to the anhydrous ethanol solution of intermediates 4a and 4b in a pear-shaped bottle, react at room temperature, and detect by thin layer chromatography (TLC) until the reaction is complete. Spin dry, dissolve in a small amount of EtOAc, adjust the pH to neutral with saturated NaHCO3, filter, extract with EtOAc, combine the organic phases, dry over anhydrous Na2SO4, and concentrate to separate and obtain intermediates 5a and 5b.

[0042] Example 4 Preparation of target compounds 6a and 6b

[0043] Intermediates 5a and 5b were weighed separately into a pear-shaped bottle, and an appropriate amount of acetonitrile was added to dissolve them. Then, iodomethane was added and the mixture was refluxed at 75°C for 48 hours. The reaction was detected by thin layer chromatography (TLC) until the reaction was completed. The target compounds 6a and 6b were separated by column chromatography.

[0044] Example 5 Compound 6a

[0045] Compound 6a was synthesized by the method described in Example 4. The physicochemical properties of compound 6a are as follows:

[0046] 1) Yellow solid;

[0047] 2) The NMR spectrum of the compound ( 1 H NMR, 400 MHz; 13 C NMR, 100 MHz) characteristics:

[0048] Using DMSO-d6 as solvent, the peaks are: Yield: 36.4%, yellow solid, 1 H NMR(400MHz DMSO-d6)δ:9.12(d,J=7.6Hz,2H,-Ph),8.77(d,J=4.4Hz,1H,-Ph),8.46(d,J=7.6Hz,1H,- Ph),7.88-7.92(m,4H,-Ph),7.47-7.56(m,2H,-Ph),6.86-6.88(m,2H,-Ph),5.44(s,1H,-C H =CH2),5.30(s,2H,-CH2-),4.28(s3H,N-CH3),1.71(s,3H,-CH3),1.65(s,3H,-CH3); 13 C NMR(100MHz DMSO-d6)δ:152.9,150.8,137.8,132.2,129.1,128.4,127.9,126.4,125.1,124.7,124. 6,122.6,122.5,120.7,120.2,117.8,111.5,105.7,45.3,38.0,25.2,18.1; HRMS(ESI)C 27 H 26 IN3[MI] + calcd=392.2121; found=392.2124.

[0049] Example 6 Compound 6b

[0050] Compound 6b was synthesized by the method described in Example 4. The physicochemical properties of compound 6b are as follows:

[0051] 1) Yellow solid;

[0052] 2) The NMR spectrum of the compound ( 1 H NMR, 400 MHz; 13 C NMR, 100 MHz) characteristics:

[0053] Using DMSO-d6 as solvent, the peaks are: Yield: 28.3%, yellow solid, 1H NMR (400MHz DMSO-d6)δ:9.12-9.14(m,2H,-Ph),8.77-8.79(m,1H,-Ph)8.55(d,J=7.6Hz,1 H,-Ph),7.88-7.95(m,4H,-Ph)7.49-7.59(m,2H,-Ph)6.86(d,J=8.8Hz,2H,-P h),6.15(s,2H,-NH2-),4.71(t,J=7.2Hz,2H,-CH2-),4.25(s,3H,N-CH3),1.8 0-1.87(m,2H,-CH2-),1.10-1.23(m,14H,-CH2-),0.81(t,J=7.2Hz,3H,-CH3); 13 C NMR(100MHz DMSO-d6)δ:152.8,150.8,132.2,129.3,129.2,128.7,128.4,127.9,127.8,126.6,124.8,124.7,124.5,122.6,1 22.2,120.8,120.3,113.6,106.0,48.3,37.9,31.2,28.6,28.58,28.5,28.4,28.0,25.1,22.0,13.9; HRMS(ESI)C 32 H 38 IN3[MI] + calcd=464.3060; found=464.3067.

[0054] Application Example 1: In vitro antibacterial activity assay

[0055] 1. Test bacteria:

[0056] Staphylococcus aureus (Staphylococcus aureus ATCC 29213); Escherichia coli (EscherichiacoliATCC 25922); clinical methicillin-resistant Staphylococcus aureus strains (MRSA 1-10).

[0057] 2. Samples and reagents:

[0058] The samples were: phenanthrenequinone, vancomycin, meropenem, and compounds 6a and 6b prepared in the examples.

[0059] 3. Test method:

[0060] According to the standards of the Clinical Laboratory Standards Institute (CLSI), a 96-well plate was used to test the in vitro antibacterial activity of phenanthrenequinone, compounds 6a and 6b of the present invention, and the clinical antibacterial drug vancomycin by serial dilution method. The drug concentration of the smallest completely clear well observed by naked eye was taken as the MIC value.

[0061] Table 1. In vitro antibacterial activity of phenanthro[9,10-d]imidazolium quaternary ammonium salt derivatives 6a and 6b of the present invention against standard strains (Gram-positive bacteria and Gram-negative bacteria) (μg / mL)

[0062]

[0063] Note: 1: phenanthrenequinone, Van: vancomycin, MEM: meropenem, Sa a :Staphylococcus aureus ATCC 29213, M1 d :Micrococcus luteus, Ss c :Streptococcus suis, Ec d :Escherichia coli ATCC 29522, Kp e :Klebsiella pneumoniae 18-227, Kp f : Klebsiella pneumoniae 18-29.

[0064] It can be seen from Table 1 that both compounds 6a and 6b showed strong anti-Gram-positive bacteria effects, with MIC values ​​of 0.5-4μg / mL, and also showed good anti-Gram-negative bacteria effects, with MIC values ​​of 8-64μg / mL. It is worth noting that compound 6b has the strongest anti-Gram-positive bacteria effect, with an MIC value of 0.5-4μg / mL. By measuring the hemolytic activity of phenanthro[9,10-d]imidazolium quaternary ammonium salt derivatives on sheep erythrocytes (HC 50 ) to evaluate its toxicity. The results showed that compound 6b exhibited low hemolytic toxicity to sheep erythrocytes, and its HC 50 The selectivity index (SI: HC 50 / MICs, Staphylococcus aureus) is the safe range for judging drug efficacy. The larger the SI, the better the membrane selectivity of the compound and the larger the safety range. As shown in Table 1, compound 6b not only exhibits a strong antibacterial effect, but also has good membrane selectivity and safety.

[0065] Table 2. MIC values ​​of phenanthro[9,10-d]imidazolium quaternary ammonium salt derivatives 6a and 6b of the present invention against 10 clinical strains of MRSA

[0066]

[0067] It can be concluded from Table 2 that compounds 6a and 6b prepared in the present invention exhibit strong anti-MRSA effects, with MIC values ​​of 0.5-2 μg / mL. Compound 6b has the best anti-MRSA effect, with MIC values ​​of 0.5 μg / mL for 5 clinically isolated MRSA strains, which is equivalent to the antibacterial effect of the positive control drug vancomycin. Therefore, it is expected to become a clinical antibacterial drug for methicillin-resistant Staphylococcus aureus.

[0068] Application example 2: Time sterilization kinetics experiment:

[0069] 1. Test bacteria:

[0070] Staphylococcus aureus ATCC 29213; MRSA-4 (clinical isolate).

[0071] 2. Samples and reagents:

[0072] The samples were: vancomycin and compound 6b prepared in Example.

[0073] 3. Test method:

[0074] The Time-Kill dynamic bactericidal curve of the compound against S. aureus ATCC 29213 and MRSA-4 was determined by the drop plate counting method. Overnight cultured S. aureus and MRSA-4 were diluted into 1 mL of LB medium at a ratio of 1:10000 and cultured (37°C, 200 rpm) until the concentration of the culture reached 1×10 5 CFU / mL. Immediately afterwards, different concentrations of compounds (8×MIC, 4×MIC) and vancomycin (8×MIC) were added to the bacterial solution, and cultured at 37°C, 200rpm. 100μL of bacterial solution was taken at 0, 0.5, 1, 2, 4, 6, and 8h for multiple dilution and then counted on MHB agar plates. Cultured at 37°C for 16-18h, the number of colonies was read and a dynamic bactericidal curve of the logarithm of the number of colonies and time was drawn. The bacterial solution without drug treatment was used as a blank control, and each group was repeated three times. The results are as follows Figure 1 shown.

[0075] Figure 1It shows that when the concentration of 6b is 8×MIC, it can completely kill S.aureus and MRSA-4 within 0.5-1h. The positive control drug vancomycin also showed a certain bactericidal trend, but it can only inhibit bacterial reproduction to a certain extent and cannot completely kill bacteria. At the same concentration (8×MIC), the bactericidal rate of compound 6b is higher than that of the positive control drug vancomycin. It can be seen that 6b has a strong bactericidal effect on S.aureus ATCC 29213 and MRSA-4, and the bactericidal effect is concentration-dependent.

[0076] Application Example 3: Drug Resistance Induction Experiment

[0077] 1. Test bacteria:

[0078] Staphylococcus aureus ATCC 29213.

[0079] 2. Samples and reagents:

[0080] The samples were: norfloxacin and compound 9b prepared in Example;

[0081] 3. Test method:

[0082] First, the MIC values ​​of the target compound and the positive control norfloxacin were determined, and the test method was based on Application Example 1. Single colonies of Staphylococcus aureus were placed in 1 mL of MHB liquid culture medium containing sub-inhibitory concentration (1 / 2MIC) compounds and norfloxacin, and cultured at 200 rpm and 37°C for 3-5 hours. They were then inoculated in LB solid culture medium containing sub-inhibitory concentration (1 / 2MIC) compounds and norfloxacin, and cultured in a 37°C constant temperature incubator for 24 hours. The culture was continued for 20 generations, and the MIC changes of each generation were detected.

[0083] Figure 2 The results showed that after culturing Staphylococcus aureus for 20 generations, the MIC value of compound 6b did not change, indicating that 6b is not easy to develop drug resistance against Staphylococcus aureus. In contrast, the positive control drug norfloxacin showed an MIC value increase from 1μg / mL to 128μg / mL at the 15th generation, indicating that norfloxacin can induce bacterial resistance. Application Example 4: In vivo safety evaluation of compounds and in vivo anti-MRSA infection activity experiments

[0084] 1. Reagents:

[0085] Compound 6b prepared in Example, 0.9% NaCl.

[0086] 2. Test animals

[0087] Healthy SPF-grade KM female mice aged 4-6 weeks, weighing 17-24 g, were purchased from the Experimental Animal Center of Zhengzhou University.

[0088] 3. Test methods

[0089] In vivo acute toxicity experiments are the basis for safety evaluation of compounds on mice. Thirty healthy female KM mice aged 4-6 weeks were selected, and each group was divided into 5 mice: a blank group (injected with 0.9% NaCl), and a drug-treated group (2.5 mg / kg, 5 mg / kg, 10 mg / kg, 20 mg / kg, and 40 mg / kg). The mice were then depilated on their backs, anesthetized 24 hours later, and injected with 60 μL of compound 9b of different concentrations and 0.9% NaCl solution. After 24 hours, the mice were observed to see if they died and if they showed abnormalities such as redness, swelling, hardening, and ulcers. The mice in the maximum dose group that did not cause adverse reactions were killed, and blood was collected from the eyeballs. The skin and tissues at the drug-treated site of the mice were aseptically separated and dissected. Blood routine and blood biochemical indicators were tested to evaluate the differences compared with the blank group. The results are as follows Figure 3 shown.

[0090] The results showed that after 24 hours of subcutaneous administration of different concentrations of the compound, the mice were in good mental state and no abnormalities were observed. The survival rate of mice at different concentrations was 100%, but when the compound was 40 and 20 mg / kg, the mouse skin had slight redness and swelling. The compound was 10, 5 and 2.5 mg / kg, and the skin was in good condition, no different from the blank group. We killed the mice at the maximum dose (10 mg / kg) that did not cause adverse reactions, and took their blood dilutions and serum for blood routine blood biochemical index detection. Figure 2 The results showed that the blood biochemistry and blood routine indexes (creatinine, albumin, urea, white blood cells, red blood cells, hematocrit, hemoglobin, mean corpuscular volume, platelet count) of mice treated with 6b (10 mg / kg) were all within the normal range, almost the same as those of the blank control group, indicating that compound 6b has a certain in vivo safety when the concentration is ≤10 mg / kg.

[0091] A mouse skin abscess infection model was constructed to evaluate the antibacterial effect of the compound in vivo. Thirty KM mice were selected and divided into a blank group (injected with 0.9% NaCl), a control group (injected with MRSA-4 bacterial solution), a high-dose group (injected with MRSA-4 bacterial solution and high-dose compound 6b), a low-dose group (injected with MRSA-4 bacterial solution and low-dose compound 6b), and a positive control group (injected with MRSA-4 bacterial solution and vancomycin). The back of the mice was depilated. After 24 hours, the mice were anesthetized and MRSA-4 (60 μL, 6×10 8CFU / mL) bacterial solution was subcutaneously injected into the back. 2 hours later, 60 μL of different concentrations of compound, vancomycin, and 0.9% NaCl were injected into the infected part of the skin. 24 hours after medication, the mice were killed by dislocation, and the skin of the infected part of the drug-treated mice was dissected and counted by drop plate counting method to evaluate the antibacterial effect of the compound in vivo. The results are shown in Figure 4 shown.

[0092] The results showed that: To further investigate the in vivo therapeutic effect of 6b, we determined the bacterial survival rate in the skin tissue of infected mice. Figure 4 As shown, the number of MRSA bacteria in the mouse skin was significantly reduced after treatment with vancomycin (2.5 mg / kg) and 6b (2.5 and 5 mg / kg) compared with the control group. Compared with the model, the bacterial survival rate of the infected area of ​​the mouse skin after treatment with compound 6b (5 mg / kg) was 0.01%. In addition, the bacterial survival rates of the infected skin of mice treated with 6b (2.5 mg / kg) and vancomycin were 0.59% and 8.34%, respectively. It can be seen that the antibacterial effect of high doses is more obvious, and both the low-dose and high-dose 6b groups showed more effective in vivo antibacterial effects than vancomycin. These research results show that phenanthro[9,10-d]imidazole quaternary ammonium salt derivatives provide a reference for the development of new antibacterial agents for the treatment of MRSA infections.

Claims

1. Phenanthro[9,10-d]imidazole quaternary ammonium salt derivatives, the structural formula of which is as follows: in, R is selected from H, C6-C14 alkyl or C3-C8 olefin.

2. The phenanthro[9,10-d]imidazolium quaternary ammonium salt derivative according to claim 1, characterized in that: The R is selected from H, a C6-C14 single chain alkyl group or a C3-C8 olefin group containing a double bond.

3. The phenanthro[9,10-d]imidazolium quaternary ammonium salt derivative according to claim 1, characterized in that: The R is selected from H, C9-C11 single chain alkyl or C4-C6 olefin group containing one double bond.

4. The phenanthro[9,10-d]imidazolium quaternary ammonium salt derivative according to claim 1, characterized in that: The R is selected from the following groups a or b:

5. The method for preparing the phenanthro[9,10-d]imidazolium quaternary ammonium salt derivative according to any one of claims 1 to 4, characterized in that: The steps include: Step 1: Under acidic conditions, phenanthrenequinone 1 reacts with p-nitrobenzaldehyde 2 to generate intermediate 3; Step 2: Intermediate 3 reacts with differently substituted bromoalkane R-Br under alkaline conditions to generate intermediate 4; Step 3, intermediate 4 generates intermediate 5 under the action of a reducing agent; Step 4, intermediate 5 reacts with methyl iodide to obtain the target compound; Wherein, the R is the same as that described in any one of claims 1-4.

6. The method for preparing the phenanthro[9,10-d]imidazolium quaternary ammonium salt derivative according to claim 5, characterized in that: In step 1, the acid in the acidic condition is ammonium acetate, the reaction molar ratio of the intermediate 1, p-nitrobenzaldehyde 2 and the acid is 1:1:5-1:2:10, the reaction temperature is 90-120° C., and the reaction solvent is acetic acid.

7. The method for preparing the phenanthro[9,10-d]imidazolium quaternary ammonium salt derivative according to claim 5, characterized in that: In step 2, the base in the alkaline conditions is K2CO3, the reaction molar ratio of the intermediate 3, the bromoalkane R-Br and the base is 1:3:3-1:7:7, the reaction temperature is 45-60°C, and the reaction solvent is acetone.

8. The method for preparing the phenanthro[9,10-d]imidazolium quaternary ammonium salt derivative according to claim 5, characterized in that: In step 3, the reducing agent is selected from stannous chloride, the reaction molar ratio of the intermediate 4 to the reducing agent is 1:10-1:15, the reaction temperature is 40-78° C., and the reaction solvent is ethyl acetate or ethanol.

9. The method for preparing the phenanthro[9,10-d]imidazolium quaternary ammonium salt derivative according to claim 5, characterized in that: In step 4, the reaction molar ratio of the intermediate 5 to methyl iodide is 1:5-1:10, the reaction temperature is 35-80° C., and the reaction solvent is acetonitrile.

10. Use of the phenanthro[9,10-d]imidazolium quaternary ammonium salt derivatives according to any one of claims 1 to 4 in the preparation of antibacterial agents.

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