Antibacterial biphenol derivative and preparation method thereof

Abstract

The invention provides an antibacterial biphenol derivative and a preparation method thereof, and belongs to the technical field of organic synthesis. The amphiphilic target compound with high antibacterial activity is obtained by carrying out structural modification on a biphenol core skeleton, introducing an amido bond to a phenolic hydroxyl site, connecting amino and guanidyl cation groups and simultaneously introducing a biphenylmethyl or n-hexyl hydrophobic side chain. The derivative disclosed by the invention has a remarkable inhibition effect on gram-positive bacteria, gram-negative bacteria and multi-drug-resistant strains. The compound can be widely applied to preparation of antibacterial drugs, medical disinfection preparations and antibacterial functional materials, and has important clinical transformation value in the fields of infectious disease treatment and medical protection.

Description

Technical Field

[0001] This invention relates to the field of organic synthesis technology, and in particular to an antibacterial biphenyl derivative and its preparation method. Background Technology

[0002] Bacterial infections continue to pose a serious challenge to global public health, significantly increasing global morbidity and mortality. The overuse and overprescription of traditional antibiotics, coupled with the natural adaptive and evolutionary capabilities of bacteria, have jointly driven the emergence of multidrug-resistant strains, weakening the efficacy of many existing treatments. A Lancet report indicates that the severe burden of antimicrobial resistance (AMR) causes approximately 4.95 million deaths globally each year, with 1.27 million of these deaths directly attributable to drug-resistant infections. This death toll exceeds the combined total of HIV / AIDS and malaria. So-called "superbugs," such as methicillin-resistant Staphylococcus aureus (MRSA), carbapenem-resistant Pseudomonas aeruginosa, vancomycin-resistant enterococci, and multidrug-resistant Acinetobacter baumannii, are now prevalent in healthcare settings and community environments, posing a serious threat to immunocompromised individuals and severely ill patients. Therefore, the World Health Organization has prioritized the development of novel treatment strategies targeting these key priority pathogens. Thus, there is an urgent need for continued exploration of innovative treatment strategies and novel chemical entities to combat these persistent infections.

[0003] Faced with this pressing challenge, antimicrobial peptides (AMPs) are increasingly being recognized as a promising alternative antimicrobial agent. As key effector molecules of the innate immune system in many organisms, AMPs are typically short-chain, cationic, amphiphilic peptides composed of 20-50 amino acids. Their mechanism of action often involves targeting the microbial cell membrane, leading to membrane disruption and cell death. This membrane-targeting characteristic, coupled with their broad-spectrum activity against bacteria, fungi, and even viruses, makes AMPs ideal candidates for overcoming traditional drug resistance mechanisms. Unlike conventional antibiotics that act on specific intracellular targets, AMPs typically exert their effects by physically disrupting membrane integrity, a mode of action less likely to induce rapid bacterial resistance. Despite their enormous potential, their clinical translation is still constrained by inherent limitations such as proteolytic instability, high production costs, systemic toxicity, and the challenges of large-scale synthesis. To overcome these limitations, researchers have begun designing antimicrobial peptide mimics, aiming to replicate the core physicochemical and biological properties of AMPs while optimizing their pharmacological properties. Among the many mimics, small-molecule amphiphiles and cationic salts have shown significant potential. By modifying structures such as linker length, introducing aromatic core structures, and regulating hydrophobic tails, researchers optimized antibacterial efficacy while reducing cytotoxicity. Notably, utilizing approved drugs or natural products as molecular scaffolds offers a strategic advantage, as it integrates known safety and bioavailability into novel designs. Small molecule mimics such as CSA-13, XF-73, and PMX-30063 have entered clinical trials, highlighting the feasibility of this strategy in developing next-generation anti-infective drugs. Summary of the Invention

[0004] The purpose of this invention is to provide an antibacterial biphenyl derivative and its preparation method, in order to solve the above-mentioned technical problems.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides an antibacterial biphenyl derivative, the structural formula of which is shown below:

[0006] A

[0007] or

[0008] B; Where n is 1, 2 or 3.

[0009] This invention provides a method for preparing the above-mentioned antibacterial biphenyl derivative, wherein when the antibacterial derivative is compound A, the method includes the following steps: Step 1) Compound 1, Compound 2 and acetonitrile are mixed and reacted in the presence of potassium carbonate to obtain Compound 3; Step 2) Compound 4, potassium carbonate, and ethyl bromoacetate are mixed in a solvent and subjected to an O-alkylation reaction to obtain intermediate 5; Step 3) Intermediate 5 is hydrolyzed under alkaline conditions to obtain compound 6. The obtained compound 6 is then acidified, filtered and dried in sequence, and then mixed with DIPEA, HATU, compound 3 and acetonitrile for amide coupling to obtain intermediate 7. Step 4) Mix intermediate 7, trifluoroacetic acid and dichloromethane, remove the protecting group to obtain compound 8, namely the antibacterial biphenyl derivative; In step 1), the structural formula of compound 1 is as follows: ; The structural formula of compound 2 is as follows: n is 1, 2, or 3; In step 2), compound 4 is magnolol, and its structural formula is [insert structural formula here]. .

[0010] Furthermore, in step 1), the molar ratio of compound 1, compound 2 and potassium carbonate is 0.5~1.5:0.5~1.5:1~2; The reaction temperature is 40~60℃, and the reaction time is 6~10h; In step 2), the O-alkylation reaction is carried out at a temperature of 60-70°C for 7-9 hours. The molar ratio of compound 4 to potassium carbonate is 1:1 to 4, and the amount of ethyl bromoacetate added is in excess relative to compound 4.

[0011] Furthermore, in step 3), the hydrolysis is carried out by mixing compound 5 and sodium hydroxide in a methanol / water solution, and the hydrolysis temperature is 50~70℃ for 4~6h. The molar ratio of intermediate 5 to sodium hydroxide is 1:8~15; The molar ratio of compound 6, compound 3, DIPEA and HATU is 1~2:2~4:4~6:2~5, and the molar ratio of compound 6 to acetonitrile is 2~3 mmol:25~40 mL; The reaction temperature for the amide coupling is 23~35℃, and the reaction time is 6~8h.

[0012] Furthermore, in step 4), the reaction temperature for removing the protecting group is 23~35℃, and the reaction time is 4~6h; The ratio of intermediate 7, trifluoroacetic acid, and dichloromethane is 0.3~1.2 mmol: 1~3 mL: 4~7 mL.

[0013] This invention also provides a method for preparing the above-mentioned antibacterial biphenyl derivative, wherein when the antibacterial derivative is compound B, the method includes the following steps: Step S1) Compound C, tert-butyl (4-aminobutyl) carbamate, DIPEA, HATU and acetonitrile are mixed and coupled to obtain compound 9; Step S2) Compound 9 is mixed with CF3COOH and dichloromethane, and after acidic deprotection, compound 10 is obtained; Step S3) In an inert atmosphere, compound 10, N,N'-bis-Boc-1-guanidinylpyrazole, DIPEA and dichloromethane are mixed and reacted. After dilution and washing, compound 11 is obtained. Finally, compound 11, CF3COOH and dichloromethane are mixed and deprotected to obtain compound 12, which is the antibacterial biphenyl derivative. The structural formula of compound C is as follows: .

[0014] Further, in step S1), the ratio of compound C, tert-butyl (4-aminobutyl) carbamate, DIPEA and HATU is 1~2:2~4:4~6:2~5; The ratio of compound C to acetonitrile is 1-2 mmol: 15-30 mL; The coupling reaction is carried out at a temperature of 20-32°C for 6-10 hours.

[0015] Furthermore, in step S2), the acidic deprotection reaction temperature is 23~35℃, and the time is 5~7h; The ratio of compound 9 to CF3COOH is 1~2:2~6, and the ratio of compound 9 to dichloromethane is 1~2mmol:5~20mL.

[0016] Further, in step S3), the molar ratio of compound 10, N,N'-bis-Boc-1-guanidinylpyrazole and DIPEA is 1~2:2~4:2~5, the reaction temperature is 23~35℃, and the time is 10~14h.

[0017] Furthermore, in step S3), the ratio of compound 11, CF3COOH and dichloromethane is 0.3~0.8 mmol: 1~4 mL: 4~8 mL, the deprotection temperature is 23~35℃, and the time is 5~8 h.

[0018] The beneficial effects of this invention are: Clear and targeted antibacterial activity: The compounds obtained in this application have significant inhibitory effects on a variety of Gram-positive bacteria, covering common clinical pathogens and drug-resistant strains such as methicillin-sensitive / drug-resistant Staphylococcus aureus, vancomycin-sensitive / drug-resistant Enterococcus faecalis, and Bacillus subtilis. The minimum inhibitory concentration (MIC) is in the range of 16~64 μg / mL (8A~8C, 10) to 2~4 μg / mL (12). In particular, after guanidine modification, the antibacterial activity of compound 12 is significantly improved compared with the amino-functionalized derivative (10), which effectively makes up for the lack of antibacterial efficacy of natural and magnolol, and provides a new candidate direction for combating multidrug-resistant bacterial infections.

[0019] This invention optimizes the amphiphilicity and charge density of the molecule by introducing cationic groups such as amino and guanidine groups into the biphenyl core, enabling it to specifically bind to bacterial membrane anionic components (such as phosphatidylglycerol) through electrostatic interactions. The mechanism of action is clear and does not easily induce bacterial resistance. At the same time, it preserves the biocompatibility of the natural product skeleton, laying a structural foundation for subsequent safety optimization.

[0020] The synthesis process of this series of compounds is mature. They can be prepared through conventional organic synthesis reactions such as amide coupling, deprotection, and guanidineization. The reaction conditions are mild and the steps are controllable, making them suitable for large-scale production. Their selective antibacterial activity against Gram-positive bacteria can be used to develop drug formulations for treating related bacterial infections. They are especially suitable for infection scenarios where existing antibiotics have developed resistance, and have important clinical application value.

[0021] This invention achieves gradient optimization of antibacterial activity by adjusting the type of cationic groups (amino, guanidinium) and the length of alkyl linkages, providing a clear structure-activity relationship basis for further structural optimization, expansion of the antibacterial spectrum, and enhancement of efficacy, and has good potential for technological expansion. Attached Figure Description

[0022] Figure 1 This is a synthetic route diagram for the antibacterial biphenyl derivative A of the present invention; Figure 2 This is a synthetic route diagram for the antibacterial biphenyl derivative B of the present invention. Detailed Implementation

[0023] This invention provides an antibacterial biphenyl derivative, the structural formula of which is shown below:

[0024] A

[0025] or

[0026] B; Where n is 1, 2 or 3.

[0027] This invention provides a method for preparing the above-mentioned antibacterial biphenyl derivative, wherein when the antibacterial derivative is compound A, the method includes the following steps: Step 1) Compound 1, Compound 2 and acetonitrile are mixed and reacted in the presence of potassium carbonate to obtain Compound 3; Step 2) Compound 4, potassium carbonate, and ethyl bromoacetate are mixed in a solvent and subjected to an O-alkylation reaction to obtain intermediate 5; Step 3) Intermediate 5 is hydrolyzed under alkaline conditions to obtain compound 6. The obtained compound 6 is then acidified, filtered and dried in sequence, and then mixed with DIPEA, HATU, compound 3 and acetonitrile for amide coupling to obtain intermediate 7. Step 4) Mix intermediate 7, trifluoroacetic acid and dichloromethane, remove the protecting group to obtain compound 8, namely the antibacterial biphenyl derivative; In step 1), the structural formula of compound 1 is as follows: ; The structural formula of compound 2 is as follows: n is 1, 2, or 3; In step 2), compound 4 is magnolol, and its structural formula is [insert structural formula here]. .

[0028] In this invention, DIPEA is N,N-diisopropylethylamine, and HATU is O-(7-azabenzotriazol-1-yl)-N,N,N',N'-tetramethylurea hexafluorophosphate.

[0029] In this invention, in step 1), the molar ratio of compound 1, compound 2 and potassium carbonate is 0.5~1.5:0.5~1.5:1~2, preferably 0.8~1.2:0.8~1.2:1~2; The reaction temperature is 40~60℃, preferably 50℃; the reaction time is preferably 6~10h. In step 2), the temperature of the O-alkylation reaction is 60~70℃, preferably 65℃, and the time is 7~9h, preferably 8h; The molar ratio of compound 4 to potassium carbonate is 1:1 to 4, preferably 1:2 to 3; the amount of ethyl bromoacetate added is in excess relative to compound 4.

[0030] In this invention, the solvent is preferably anhydrous DMF.

[0031] In this invention, in step 3), the hydrolysis is carried out by mixing compound 5 and sodium hydroxide in a methanol / water solution, the hydrolysis temperature is 50~70℃, preferably 60℃, and the time is 4~6h, preferably 5h; The molar ratio of intermediate 5 to sodium hydroxide is 1:8~15, preferably 1:10~12; The molar ratio of compound 6, compound 3, DIPEA and HATU is 1~2:2~4:4~6:2~5, preferably 1.3~1.8:2.5~3.5:5:3~4; the molar ratio of compound 6 to acetonitrile is 2~3 mmol:25~40 mL, preferably 2.3~2.8 mmol:30~36 mL; The reaction temperature for amide coupling is 23~35℃, preferably 28~32℃; the reaction time is 6~8h, preferably 7h.

[0032] In this invention, in step 4), the reaction temperature for removing the protecting group is 23~35℃, preferably 28~32℃; the reaction time is 4~6h, preferably 5h. The ratio of intermediate 7, trifluoroacetic acid, and dichloromethane is 0.3-1.2 mmol: 1-3 mL: 4-7 mL, preferably 0.5-1.0 mmol: 1.5-2.5 mL: 5-6 mL.

[0033] This invention also provides a method for preparing the above-mentioned antibacterial biphenyl derivative, wherein when the antibacterial derivative is compound B, the method includes the following steps: Step S1) Compound C, tert-butyl (4-aminobutyl) carbamate, DIPEA, HATU and acetonitrile are mixed and coupled to obtain compound 9; Step S2) Compound 9 is mixed with CF3COOH and dichloromethane, and after acidic deprotection, compound 10 is obtained; Step S3) In an inert atmosphere, compound 10, N,N'-bis-Boc-1-guanidinylpyrazole, DIPEA and dichloromethane are mixed and reacted. After dilution and washing, compound 11 is obtained. Finally, compound 11, CF3COOH and dichloromethane are mixed and deprotected to obtain compound 12, which is the antibacterial biphenyl derivative. The structural formula of compound C is as follows: .

[0034] In this invention, in step S1), the ratio of compound C, tert-butyl (4-aminobutyl) carbamate, DIPEA and HATU is 1~2:2~4:4~6:2~5, preferably 1.3~1.8:3:4.5~5.5:3~4; The ratio of compound C to acetonitrile is 1-2 mmol: 15-30 mL, preferably 1.2-1.8 mmol: 18-25 mL; The coupling reaction is carried out at a temperature of 20-32°C, preferably 25-30°C, for a time of 6-10 hours, preferably 7-9 hours.

[0035] In this invention, in step S2), the acidic deprotection reaction temperature is 23~35℃, preferably 28~32℃; the time is 5~7h, preferably 6h. The ratio of compound 9 to CF3COOH is 1~2:2~6, preferably 1.3~1.6:3~5; the ratio of compound 9 to dichloromethane is 1~2mmol:5~20mL, preferably 1.3~1.7mmol:8~15mL.

[0036] In this invention, in step S3), the molar ratio of compound 10, N,N'-bis-Boc-1-guanidinylpyrazole and DIPEA is 1~2:2~4:2~5, preferably 1.3~1.8:2.5~3.5:3~4; the reaction temperature is 23~35℃, preferably 25~32℃; and the reaction time is 10~14h, preferably 12~13h.

[0037] In this invention, in step S3), the ratio of compound 11, CF3COOH and dichloromethane is 0.3~0.8 mmol: 1~4 mL: 4~8 mL, preferably 0.4~0.6 mmol: 2~3 mL: 5~7 mL; the deprotection temperature is 23~35℃, preferably 28~32℃; and the time is 5~8 h, preferably 6~7 h.

[0038] In this invention, all chemical reagents used were of analytical grade and purchased from reputable commercial suppliers. The reaction process was tracked using silica gel GF254 thin-layer chromatography plates. Structural characterization was performed using nuclear magnetic resonance (NMR) spectroscopy. 1 H and 13 C10 NMR spectra were acquired using a Bruker Avance 500 MHz NMR spectrometer with appropriate deuterated solvents (CDCl3, DMSO-d6, or CD3OD). High-resolution mass spectrometry (HRMS) data were acquired using a Thermo Fisher Scientific DFS mass spectrometer to determine the precise molecular weight and verify the molecular formula.

[0039] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0040] Example 1

[0041] Compound 1 (5.00 mmol), compound 2 (n = 1, 5 mmol) and potassium carbonate (6.00 mmol) were mixed in acetonitrile and stirred at 50 °C for 8 h. Then, the mixture was sequentially evaporated, diluted with water, and extracted with ethyl acetate to obtain compound 3, denoted as compound 3A. Compound 4 (5.63 mmol) and potassium carbonate (14.08 mmol) were mixed in anhydrous DMF (8 mL), and excess ethyl bromoacetate (16.89 mmol) was added. The mixture was stirred at 65 °C for 8 h. After standard post-treatment and rapid chromatography purification, intermediate 5 (1.93 g, 78%) was obtained. Intermediate 5 (3.42 mmol) and sodium hydroxide (34.20 mmol) were dissolved in 50 mL of methanol-water mixed solvent and reacted at 60 °C for 5 h. After removing methanol, the solution was acidified to pH 3 with hydrochloric acid, filtered and dried to obtain compound 6 (1.11 g, 85%). Compound 6 (2.61 mmol) was dissolved in 30 mL of dry acetonitrile, and HATU (5.22 mmol) and DIPEA (7.83 mmol) were added sequentially. The mixture was stirred at 30 °C for 10 min to generate an active ester. Then, compound 3A (5.22 mmol) was added and stirred for 7 h. The reaction solution was concentrated, acidified, extracted with ethyl acetate, and then purified by column chromatography to obtain intermediate 7A. Intermediate 7A (1.00 mmol) was dissolved in 5 mL of dichloromethane, and 2 mL of trifluoroacetic acid was added. The mixture was reacted at 30 °C for 5 h. The mixture was then concentrated, and the residue was ground with diethyl ether and filtered to obtain the purified product compound 8A.

[0042] Compound 3A: tert-butyl(3-(([1,1'-biphenyl]-4-ylmethyl)amino)propyl)carbamate, white solid, yield 43%; 1 H NMR (500MHz, CDCl3) δ7.50 (td, J=8.4, 1.7Hz, 4H), 7.36 (t, J=7.6Hz, 4H), 7.32–7.23 (m, 1H), 3 .78 (s, 2H), 3.17 (q, J=6.1Hz, 2H), 2.70 (t, J=6.5Hz, 2H), 1.67 (t, J=6.5Hz, 2H), 1.37 (s, 9H).

[0043] Compound 7A: Di-tert-butyl(((2,2'-((3',5-diallyl-[1,1'-biphenyl]-2,4'-diyl)bis(oxy)bis(acetyl)bis([1,1'-biphenyl]-4-ylmethyl)azaldiyl))bis(propane-3,1-diyl))dicarbamate, colorless oil, yield 62%; 1 ¹H NMR (500 MHz, DMSO-d6) δ 7.71–7.56 (methyl, 8H), 7.45 (doublet, J = 6.5, 4.1, 2.2 Hz, 4H), 7.38–7.25 (methyl, 7H), 7.13–7.02 (methyl, 2H), 6.93 (quadripolar, J = 4.1, 3.5 Hz, 1H), 6.89–6.74 (methyl, 2H), 6.09–5.89 (methyl, 2H), 5.14–4.52 (methyl, 12H), 3.43–3.24 (methyl, 8H), 3.01–2.85 (methyl, 4H), 1.75 (quadripolar, J = 7.2 Hz, 4H), 1.34 (doublet, J = 10.5, 3.3 Hz, 18H); 13 C NMR (125MHz, CDCl3) δ167.57, 167.42, 164.59, 159.68, 155.67, 155.54, 154.79, 153.25, 139.90, 139.69, 139.23, 138.96, 138.04, 136.97, 136.90, 132.15, 130.68, 130.58, 130.38, 130.30, 129.6 0, 128.92, 128.05, 127.98, 127.75, 127.46, 127.35, 127.01, 126.71, 126.67, 126.58, 115.52, 77.57, 77.47, 66.42, 65.92, 49.19, 47.13, 47.12, 43.65, 38.66, 38.24, 37.30, 34.07, 28.20, 27.41.

[0044] Compound 8A: 2,2'-((3',5-Diallyl-[1,1'-biphenyl]-2,4'-diyl)bis(oxy)bis(N-([1,1'-biphenyl]-4-ylmethyl)-N-(3-aminopropyl)acetamide), white solid, 82% yield; 1H NMR (500MHz, DMSO-d6) δ8.22 (d, J=67.0Hz, 6H), 7.64 (tdd, J=17.1, 12.4, 5.9Hz, 8H), 7.51–7.23 (m, 12H), 7.14–6.95 ( m, 3H), 6.88–6.78 (m, 1H), 5.99 (m, 2H), 5.14–4.53 (m, 12H), 3.42–3.30 (m, 8H), 2.93–2.69 (m, 4H), 2.03–1.76 (m, 4H); 13 C NMR (125MHz, DMSO-d6) δ168.62, 168.04, 153.69, 140.36, 140.13, 139.77, 139.45, 139.40, 138.54 ,138.47, 137.50, 137.40, 136.70, 132.77, 130.83, 129.43, 129.41, 128.59, 128.51, 128.25, 127. 97, 127.86, 127.82, 127.54, 127.49, 127.20, 127.15, 127.09, 127.07, 116.06, 113.15, 111.75, 66.72, 66.39, 49.62, 47.66, 43.83, 43.37, 39.13, 39.10, 36.99, 36.66, 34.58, 34.45, 26.58, 25.63.

[0045] HRMS (ESI) C 54 H 59 N4O4[M+1] + Calculated value = 827.4531; Measured value = 827.4536.

[0046] Example 2

[0047] Unlike Example 1, in this example, n is 2 in the structure of compound 2, and the resulting compound 8 is denoted as compound 8B.

[0048] Compound 3B: tert-butyl(4-(([1,1'-biphenyl]-4-ylmethyl)amino)butyl)carbamate, white solid, yield 55%; 1H NMR (500MHz, CDCl3) δ7.49 (dd, J=7.6, 4.6Hz, 4H), 7.36 (t, J=7.3Hz, 4H), 7.26 (d, J=7.3Hz, 1H), 4. 80 (s, 1H), 3.79 (s, 2H), 3.09-3.00 (m, 2H), 2.64 (t, J=7.0Hz, 2H), 1.63-1.45 (m, 4H), 1.36 (s, 9H).

[0049] Compound 7B: di-tert-butyl(((2,2'-((3',5-diallyl-[1,1'-biphenyl]-2,4'-diyl)bis(oxy)bis(acetyl)bis([1,1'-biphenyl]-4-ylmethyl)azaldiyl))bis(butane-4,1-diyl))dicarbamate, colorless oil, 78% yield.

[0050] 1 H NMR (500MHz, DMSO-d6) δ 7.69–7.54 (m, 8H), 7.45 (td, J = 7.7, 2.8 Hz, 4H), 7.37–7.25 (m, 7H), 7.12–7.01 (m, 2H), 6.94 (ddd, J = 8.4, 5.3, 2.6 Hz, 1H), 6.86–6.75 (m, 2H), 5.98 (ddddd, J = 27.4, 17.2, 10.2, 7.0, 3.4 Hz, 2H), 5.13–4.52 (m, 12H), 3.41 (d, J = 6.7 Hz, 1H), 3.35–3.16 (m, 8H), 2.96–2.81(m, 4H), 1.64–1.42 (m, 4H), 1.37–1.34 (m, 18H), 1.25–1.14 (m, 4H); 13C NMR (125MHz, DMSO-d6) δ167.91, 165.11, 156.11, 153.70, 140.36, 140.20, 139.44, 139.36 ,138.47,137.51,137.46,137.41,137.35,136.99,132.76,131.16,130.84,130.14,129.3 8, 128.54, 128.44, 128.26, 127.87, 127.81, 127.46, 127.15, 127.10, 127.03, 115.98, 113.22, 87.86, 77.83, 47.69, 46.52, 39.13, 38.70, 34.47, 29.64, 28.71, 28.03, 26.92, 23.92.

[0051] Compound 8B: 2,2'-((3',5-Diallyl-[1,1'-biphenyl]-2,4'-diyl)bis(oxy)bis(N-([1,1'-biphenyl]-4-ylmethyl)-N-(4-aminobutyl)acetamide), white solid, yield 76%; 1 H NMR (500MHz, DMSO-d6) δ7.98 (d, J=26.4Hz, 6H), 7.73–7.56 (m, 8H), 7.50–7.24 (m, 12H), 7.14–6.78 (m , 4H), 6.11–5.85 (m, 2H), 5.16–4.52 (m, 12H), 3.23 (s, 4H), 2.76 (d, J=24.4Hz, 4H), 1.76–1.41 (m, 8H); 13 C NMR (125MHz, DMSO-d6) δ168.09, 153.66, 140.35, 140.14, 139.73, 139.39, 138.51, 13 8.46, 137.45, 131.10, 130.83, 129.41, 128.55, 128.47, 128.26, 127.96, 127.87, 127. 82, 127.51, 127.46, 127.20, 127.15, 127.06, 116.06, 116.01, 113.16, 111.78, 79.76, 79.49, 49.42, 47.60, 45.91, 39.14, 38.92, 38.83, 34.52, 25.29, 24.80, 24.74, 24.29.

[0052] HRMS (ESI) C 56 H 63 N4O4[M+1] + Calculated value = 855.4844; Measured value = 855.4850.

[0053] Example 3

[0054] Unlike Example 1, in this example, n is 3 in the structure of compound 2, and the resulting compound 8 is denoted as compound 8C.

[0055] Compound 3C: tert-butyl(5-(([1,1'-biphenyl]-4-ylmethyl)amino)pentyl)carbamate, white solid, yield 49%; 1H NMR (500MHz, CDCl3) δ7.50 (td, J=8.4, 1.7Hz, 4H), 7.39-7.31 (m, 4H), 7.26 (t, J=7.4Hz, 1H), 4.51 (s, 1H), 3.77 (s, 2H), 3.03 (q, J =6.7Hz, 2H), 2.59 (t, J=7.2Hz, 2H), 1.50 (p, J=7.4Hz, 2H), 1.42 (q, J=7.2Hz, 2H), 1.36 (s, 9H), 1.29 (qd, J=7.4, 6.4, 4.0Hz, 2H).

[0056] Compound 7C: di-tert-butyl(((2,2'-((3',5-diallyl-[1,1'-biphenyl]-2,4'-diyl)bis(oxy)bis(acetyl)bis([1,1'-biphenyl]-4-ylmethyl)azadiylidene)bis(pentane-5,1-diyl)dicarbamate, colorless oil, yield 56%; 1 H NMR (500MHz, DMSO-d6) δ 7.71–7.53 (m, 8H), 7.45 (dd, J = 9.6, 5.6 Hz, 4H), 7.38–7.24 (m, 7H), 7.14–7.00 (m, 2H), 6.94 (dt, J = 8.1, 5.3 Hz, 1H), 6.87–6.77 (m, 2H), 6.09–5.87 (m, 2H), 5.12–4.49 (m, 12H), 3.41 (d, J = 6.7Hz, 1H), 3.35–3.16 (m, 7H), 2.99–2.83 (m, 4H), 1.35 (d, J = 4.2 Hz, 30H).

[0057] 13 C NMR (125MHz, DMSO-d6) δ167.92, 165.10, 156.16, 156.10, 155.27, 153.71, 140.36, 140.19, 139.73, 139.41, 139.3 5, 138.48, 138.43, 137.43, 137.36, 132.80, 132.69, 131.04, 130.83, 130.11, 129.38, 128.59, 128.50, 128.41, 12 8.23, 127.93, 127.81, 127.74, 127.47, 127.41, 127.15, 127.11, 127.03, 115.98, 113.13, 111.90, 111.74, 77.91, 77.85, 66.47, 49.52, 47.66, 46.21, 39.13, 38.70, 34.49, 34.39, 28.70, 27.36, 27.19, 27.10, 25.65, 25.55, 24.63.

[0058] Compound 8C: 2,2'-((3',5-Diallyl-[1,1'-biphenyl]-2,4'-diyl)bis(oxy)bis(N-([1,1'-biphenyl]-4-ylmethyl)-N-(5-aminopentyl)acetamide), white solid, 87% yield; 1 H NMR (500MHz, CDCl3) δ7.88 (s, 6H), 7.61–7.27 (m, 16H), 7.24–6.63 (m, 8H), 5.15–4.26 (m, 12H), 3.49–3.26 (m, 6H), 2.97 (s, 6H), 1.92–1.09 (m, 12H); 13C NMR (125MHz, DMSO-d6) δ167.95, 155.29, 155.23, 153.72, 140.36, 140.19, 139.72, 139.42, 138 .52, 137.51, 137.46, 136.94, 132.80, 132.70, 131.08, 130.83, 130.08, 129.40, 128.56, 128.47 , 127.91, 127.83, 127.48, 127.43, 127.17, 127.06, 116.03, 115.99, 67.01, 66.61, 49.60, 47.66, 46.37, 39.13, 39.01, 38.87, 34.52, 27.91, 27.82, 27.08, 27.02, 26.72, 23.67, 23.61, 23.55; HRMS (ESI) C 58 H 67 N4O4[M+1] + Calculated value = 883.5157; Measured value = 883.5166.

[0059] Example 4

[0060] Compound C (2.56 mmol) was dissolved in 40 mL of dry acetonitrile, and HATU (5.63 mmol) and DIPEA (7.68 mmol) were added sequentially. The mixture was stirred at 30 °C for 10 min to generate an active ester. Then, tert-butyl (4-aminobutyl) carbamate (5.63 mmol) was added and stirred for 7 h. The reaction solution was concentrated, acidified, extracted with ethyl acetate, and then purified by column chromatography to obtain compound 9.

[0061] Compound 9: di-tert-butyl(((2,2'-([1,1'-biphenyl]-4,4'-diylbis(oxy))bis(acetyl))bis(hexylazodimethyl))bis(butane-4,1-diyl))dicarbamate, the product is a white solid, yield 72%.

[0062] 1 H NMR (500MHz, CDCl3) δ7.45 (d, J=8.7, 2.1Hz, 4H), 7.05–6.90 (m, 4H), 4.71 (s, 4H), 3.42–3.26 (m, 8H), 3.13 (dq, J =19.3, 6.5Hz, 4H), 1.68–1.48 (m, 12H), 1.43 (d, J=4.4Hz, 18H), 1.33–1.25 (m, 12H), 0.88 (d, J=17.2, 6.6Hz, 6H); 13C NMR (125MHz, CDCl3) δ167.53, 167.45, 157.29, 156.04, 156.02, 134.14, 127.88, 127.85, 114.93, 79.34, 79.05, 67.75, 67.48, 4 7.47, 47.00, 45.92, 45.50, 40.10, 39.96, 31.56, 31.51, 28.99, 28.42, 27.67, 27.42, 27.37, 26.62, 24.68, 22.57, 14.00, 13.98.

[0063] Example 5

[0064] Compound 9 (1.78 mmol) was dissolved in 10 mL of dichloromethane, and 5 mL of trifluoroacetic acid was added. The mixture was reacted at 30 °C for 5 h. The mixture was then concentrated, and the residue was ground with diethyl ether and filtered to obtain the purified product compound 10.

[0065] Compound 10: 2,2'-([1,1'-biphenyl]-4,4'-dimethylbis(oxy))bis(N-(4-aminobutyl)-N-hexylacetamide), white solid, 86% yield; 1 H NMR (500MHz, CDCl3) δ7.53–7.46 (m, 4H), 7.07–6.96 (m, 4H), 4.83 (s, 4H), 3.48–3.36 (m, 8H), 3.0 2–2.93 (m, 4H), 1.76–1.55 (m, 12H), 1.33 (dt, J=25.9, 4.2Hz, 12H), 0.90 (dt, J=12.0, 6.3Hz, 6H); 13 C NMR (125MHz, CDCl3) δ172.91, 172.64, 161.36, 161.32, 137.92, 131.26, 118.74, 118.66, 70.44, 70.23, 50.27, 49 .62, 48.72, 43.04, 42.93, 35.30, 35.24, 32.38, 30.96, 30.24, 30.13, 29.37, 28.47, 28.35, 27.98, 26.22, 16.90; HRMS (ESI) C 36 H 59 N4O4[M+H] + Calculated value = 611.4531; Measured value = 611.4539.

[0066] Example 6

[0067] In a nitrogen atmosphere, compound 10 (1.20 mmol) obtained in Example 5, N,N'-bis-Boc-1-guanidinylpyrazole (2.40 mmol), DIPEA (3.00 mmol) and dichloromethane were mixed and stirred at 25 °C for 12 h. After the reaction was completed, the reaction mixture was diluted with ethyl acetate and washed sequentially with 10% potassium bisulfate, saturated sodium bicarbonate and brine. After drying and concentrating the organic layer, compound 11 (0.7 g, yield 53%) was purified by column chromatography.

[0068] Compound 11: 2,2'-([1,1'-biphenyl]-4,4'-dimethylbis(oxy))bis(N-(4,4'-bisBoc-guanidinylbutyl)-N-hexylacetamide); 1 H NMR (500MHz, CDCl3) δ7.45 (qd, J=5.9, 3.2Hz, 4H), 7.04–6.94 (m, 4H), 4.71 (s, 4H), 3.52–3.22 (m, 12H), 1.72–1.54 (m, 12H), 1.50 (d, J=9.4Hz, 36H), 1.33–1.26 (m, 12H), 0.93–0.85 (m, 6H); 13 C NMR (125MHz, CDCl3) δ171.14, 167.54, 167.51, 163.61, 163.58, 157.28, 156.25, 156.16, 153.38, 1 53.29, 148.76, 134.17, 127.90, 127.87, 114.91, 114.89, 114.69, 83.27, 83.07, 79.37, 79.23, 67. 76, 67.51, 60.38, 47.47, 46.95, 45.94, 45.48, 40.54, 40.21, 31.56, 31.52, 31.44, 31.22, 29.01, 28.30, 28.06, 27.98, 27.39, 26.62, 26.57, 26.51, 26.22, 24.84, 22.57, 21.03, 14.19, 14.00, 13.97.

[0069] Example 7

[0070] Compound 11 (0.5 mmol) obtained in Example 6 was dissolved in 6 mL of dichloromethane, and TFA (2 mL) was added dropwise at room temperature. After stirring until the conversion was confirmed by thin-layer chromatography, the mixture was concentrated under reduced pressure, washed with anhydrous diethyl ether, and filtered to obtain compound 12 with a separation yield of 42%.

[0071] Compound 12: 2,2'-([1,1'-biphenyl]-4,4'-dimethylbis(oxy))bis(N-(4-guanidinobutyl)-N-hexylacetamide) isolated, yield 42%; 1 H NMR (500MHz, methanol) δ7.54–7.48 (m, 4H), 7.01 (td, J=8.9, 1.1Hz, 4H), 4.83 (s, 4H), 3.48–3.35 (m, 8H), 3.26–3.16 (m, 4H), 1.76–1.53 (m, 12H), 1.32 (dd, J=25.4, 3.8Hz, 12H), 0.93–0.86 (m, 6H); 13 C NMR (125 MHz, methoxyethane) δ 168.97, 168.67, 157.40, 157.25, 157.20, 133.95, 127.31, 114.78, 114.73, 66.41, 66.29, 47.02, 46.50, 45.71, 44.89, 40.80, 40.73, 31.37, 31.30, 28.44, 27.06, 26.31, 26.21, 25.86, 25.72, 25.63, 24.26, 22.29, 12.97; HRMS (ESI) C 38 H 63 N8O4[M+H] + Calculated value = 695.4967; Measured value = 695.4972.

[0072] In vitro antibacterial test

[0073] The in vitro antimicrobial activity of the synthetic compounds was evaluated using the Clinical and Laboratory Standards Institute (CLSI) broth microdilution method, which determined the minimum inhibitory concentration (MIC). Briefly, each compound was serially diluted twofold in tryptone soy broth (TSB) in 96-well plates. Each well was then inoculated with a standardized bacterial suspension to achieve a final inoculation density of approximately 1 × 10⁻⁶. 6 CFU / mL. After static incubation at 37°C for 24 hours, the MIC value was recorded as the lowest concentration at which no visible turbidity was observed. All measurements were performed in triplicate to ensure reproducibility.

[0074] Table 1 shows the in vitro antibacterial activities of compounds 8A-8C, compounds 10 and 12, as well as vancomycin and colistin.

[0075] Table 1. In vitro antibacterial activity data of compounds 8A-8C, compounds 10 and 12, as well as vancomycin and colistin.

[0076] Staphylococcus aureus 25923: Staphylococcus aureus ATCC25923, erythromycin-sensitive strain; Staphylococcus aureus 43300: Staphylococcus aureus ATCC43300, methicillin-resistant strain; Enterococcus faecalis 29212: Enterococcus faecalis ATCC29212, vancomycin-sensitive strain; Enterococcus faecalis 51299: Enterococcus faecalis ATCC51299, vancomycin-resistant strain; Bacillus subtilis 9372: Bacillus subtilis ATCC9372, penicillin-sensitive strain; Acinetobacter baumannii 19606: Acinetobacter baumannii ATCC19606, standard strain; Escherichia coli 25922: Escherichia coli ATCC25922, penicillin-sensitive strain; Pseudomonas aeruginosa 27853: Pseudomonas aeruginosa ATCC27853, penicillin-sensitive strain. Van = vancomycin, Cos = colistin. All antimicrobial tests were performed in three independent replicates.

[0077] Compounds 8A-8C, with magnolol as their core, integrate a biphenyl fragment and two terminal cationic amino groups. These derivatives exhibit only moderate activity, primarily against Gram-positive strains, with MIC values ​​of 16-64 µg / mL. Their potency against Gram-negative strains is significantly weaker (MIC ≥ 128 µg / mL). The results indicate that the antibacterial spectrum is minimally dependent on the length of the alkyl chain linker (n = 1-3). For example, with the same biphenyl fragment, compounds 8A (n = 1), 8B (n = 2), and 8C (n = 3) showed comparable potency against all tested strains. Notably, compound 8B exhibited the best antibacterial spectrum, showing moderate activity against a variety of Gram-positive strains, including Staphylococcus aureus, Enterococcus faecalis, and Bacillus subtilis, with corresponding MIC values ​​of 16, 16, and 32 μg / mL, respectively. This limited antibacterial spectrum and overall weak efficacy suggest that although the introduction of cationic groups enhances antibacterial activity compared to unmodified magnolol, the weakly basic primary amino group may not provide sufficient cationic charge density at physiological pH, thus failing to generate strong electrostatic attraction with anionic bacterial membranes and limiting the antibacterial effect.

[0078] As shown in Table 1, derivative 12 containing a guanidinium group exhibited significantly superior antibacterial activity compared to its amino-functionalized counterpart, 10. This significant difference supports the hypothesis that the primary amino group may be unable to generate strong electrostatic attraction with the negatively charged bacterial membrane due to insufficient cationic charge density, while the guanidinium group, with its delocalized positive charge and higher pKa value, promotes more effective initial binding.

[0079] As shown in the above embodiments, this invention provides an antibacterial biphenyl derivative and its preparation method. By introducing cationic groups such as amino and guanidine groups into the magnolol core, this invention optimizes the amphiphilicity and charge density of the molecule, enabling it to specifically bind to bacterial membrane anionic components (such as phosphatidylglycerol) through electrostatic interactions. The mechanism of action is clear and does not easily induce bacterial resistance. Simultaneously, it retains the biocompatibility of the natural product skeleton, laying a structural foundation for subsequent safety optimization. The synthetic process of this series of compounds is mature, and they can be prepared through conventional organic synthesis reactions such as amide coupling, deprotection, and guanidineization. The reaction conditions are mild, the steps are controllable, and it is suitable for large-scale production. This invention achieves gradient optimization of antibacterial activity by adjusting the type of cationic group (amino, guanidine) and the length of the alkyl linking chain, providing a clear structure-activity relationship basis for further structural optimization, expanding the antibacterial spectrum, and improving efficacy, and has good potential for technological expansion.

[0080] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. An antibacterial biphenyl derivative, characterized in that, The structural formula is as follows: A or B； Where n is 1, 2 or 3.

2. The method for preparing the antibacterial biphenyl derivative according to claim 1, characterized in that, When the antibacterial derivative is compound A, the following steps are included: Step 1) Compound 1, Compound 2 and acetonitrile are mixed and reacted in the presence of potassium carbonate to obtain Compound 3; Step 2) Compound 4, potassium carbonate, and ethyl bromoacetate are mixed in a solvent and subjected to an O-alkylation reaction to obtain intermediate 5; Step 3) Intermediate 5 is hydrolyzed under alkaline conditions to obtain compound 6. The obtained compound 6 is then acidified, filtered and dried in sequence, and then mixed with DIPEA, HATU, compound 3 and acetonitrile for amide coupling to obtain intermediate 7. Step 4) Mix intermediate 7, trifluoroacetic acid and dichloromethane, remove the protecting group to obtain compound 8, namely the antibacterial biphenyl derivative; In step 1), the structural formula of compound 1 is as follows: ; The structural formula of compound 2 is as follows: n is 1, 2, or 3; In step 2), compound 4 is magnolol, and its structural formula is [insert structural formula here]. .

3. The method for preparing an antibacterial biphenyl derivative according to claim 2, characterized in that, In step 1), the molar ratio of compound 1, compound 2 and potassium carbonate is 0.5~1.5:0.5~1.5:1~2; The reaction temperature is 40~60℃, and the reaction time is 6~10h; In step 2), the O-alkylation reaction is carried out at a temperature of 60-70°C for 7-9 hours. The molar ratio of compound 4 to potassium carbonate is 1:1 to 4, and the amount of ethyl bromoacetate added is in excess relative to compound 4.

4. The method for preparing an antibacterial biphenyl derivative according to claim 2, characterized in that, In step 3), the hydrolysis is carried out by mixing compound 5 and sodium hydroxide in a methanol / water solution, and the hydrolysis temperature is 50~70℃ for 4~6h. The molar ratio of intermediate 5 to sodium hydroxide is 1:8~15; The molar ratio of compound 6, compound 3, DIPEA and HATU is 1~2:2~4:4~6:2~5, and the molar ratio of compound 6 to acetonitrile is 2~3 mmol:25~40 mL; The reaction temperature for the amide coupling is 23~35℃, and the reaction time is 6~8h.

5. The method for preparing an antibacterial biphenyl derivative according to claim 2, characterized in that, In step 4), the reaction temperature for removing the protecting group is 23~35℃, and the reaction time is 4~6h; The ratio of intermediate 7, trifluoroacetic acid, and dichloromethane is 0.3~1.2 mmol: 1~3 mL: 4~7 mL.

6. The method for preparing the antibacterial biphenyl derivative according to claim 1, characterized in that, When the antibacterial derivative is compound B, the following steps are included: Step S1) Compound C, tert-butyl (4-aminobutyl) carbamate, DIPEA, HATU and acetonitrile are mixed and coupled to obtain compound 9; Step S2) Compound 9 is mixed with CF3COOH and dichloromethane, and after acidic deprotection, compound 10 is obtained; Step S3) In an inert atmosphere, compound 10, N,N'-bis-Boc-1-guanidinylpyrazole, DIPEA and dichloromethane are mixed and reacted. After dilution and washing, compound 11 is obtained. Finally, compound 11, CF3COOH and dichloromethane are mixed and deprotected to obtain compound 12, which is the antibacterial biphenyl derivative. The structural formula of compound C is as follows: .

7. The method for preparing the antibacterial biphenyl derivative according to claim 6, characterized in that, In step S1), the ratio of compound C, tert-butyl (4-aminobutyl) carbamate, DIPEA and HATU is 1~2:2~4:4~6:2~5. The ratio of compound C to acetonitrile is 1-2 mmol: 15-30 mL; The coupling reaction is carried out at a temperature of 20-32°C for 6-10 hours.

8. The method for preparing the antibacterial biphenyl derivative according to claim 6 or 7, characterized in that, In step S2), the acidic deprotection reaction temperature is 23~35℃ and the time is 5~7h; The ratio of compound 9 to CF3COOH is 1~2:2~6, and the ratio of compound 9 to dichloromethane is 1~2mmol:5~20mL.

9. The method for preparing the antibacterial biphenyl derivative according to claim 8, characterized in that, In step S3), the molar ratio of compound 10, N,N'-bis-Boc-1-guanidinylpyrazole and DIPEA is 1~2:2~4:2~5, the reaction temperature is 23~35℃, and the reaction time is 10~14h.

10. The method for preparing the antibacterial biphenyl derivative according to claim 6 or 9, characterized in that, In step S3), the ratio of compound 11, CF3COOH and dichloromethane is 0.3~0.8 mmol: 1~4 mL: 4~8 mL, the deprotection temperature is 23~35℃, and the time is 5~8 h.

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