A method and system for preparing a novel tricyclic indolopyridinone carboxylic quinolone molecule

Abstract

The application belongs to the field of biological medicine and health, and discloses a preparation method of a novel tricyclic indole pyridone carboxylic quinolone molecule. The method is based on the fact that only one N atom is inserted into the bicyclic quinoline nucleus of the pharmacodynamic skeleton "quinoline-4-ketone-3-carboxylic acid" of fluoroquinolone drugs, and then a novel tricyclic indole pyridone carboxylic fluoroquinolone drug molecule is ingeniously constructed, a new structure antibacterial lead compound is found through in-vitro activity evaluation, and a basis is provided for the creation of a new drug with independent intellectual property rights to overcome the drug resistance and adverse reactions of existing drugs.

Description

Technical Field

[0001] This invention belongs to, but is not limited to, the fields of biomedicine and health technology, and particularly relates to a method and system for preparing a novel tricyclic indolepyridone carboxylic acid quinolone molecule. Background Technology

[0002] Quinolone antibiotics, as synthetic broad-spectrum antibacterial drugs, have undergone a development process since the advent of nalidixic acid in the 1960s, evolving from fluoroquinolones to fluoroquinolones and then to a new generation of fluoroquinolones. Representative drugs include pipemidic acid, norfloxacin, ciprofloxacin, and levofloxacin. Structural optimization techniques, such as introducing a fluorine atom at the 6-position and a heterocyclic piperazine group at the 7-position of the quinoline-4-one core, have significantly improved the antibacterial spectrum, tissue penetration, and pharmacokinetic properties, making fluoroquinolones an important class of anti-infective drugs in clinical practice. However, with the increase in drug-resistant strains and the exposure of adverse reactions such as cardiotoxicity, hepatotoxicity, and phototoxicity, the traditional fluoroquinolone structure has gradually shown its developmental bottlenecks.

[0003] In recent years, the development and application of new-generation non-fluoroquinolones such as nemonoxacin, garafloxacin, and ozenafloxacin have alleviated some of the toxic side effects to a certain extent, suggesting that safety and drug resistance can be improved by changing the substitution mode or regulating electronic effects. However, the improvement pathways of existing technologies mainly focus on optimizing the substituents around the quinoline-4-one core, especially the modification of the piperazine group at position 7 and its derived structures, while the expansion and reconstruction of the core skeleton itself remains relatively limited. Existing research generally revolves around monocyclic quinoline-4-ones or their simple fused structures, and has not yet carried out substantial tricyclic hybridization of its core skeleton.

[0004] A search revealed that the closest existing technology is the publicly disclosed fluoroquinolone structural modification technique containing a quinoline-4-one core with a heterocyclic substituent introduced at position 7. This technique still uses a single quinoline-4-one skeleton as the core, optimizing efficacy and safety through substitution at positions 6, 7, or N-1. Although this approach involves the introduction of heterocyclic structures, these modifications are all side-chain or peripheral substituent modifications, and do not involve constructing a tricyclic hybrid by fusing the indole structure with a pyridoxine acid core through skeleton fusion. In other words, existing technologies do not propose the concept of forming a stable tricyclic fusion system by covalently fusing the indole ring and the pyridoxine acid structure.

[0005] Therefore, the core technical challenge facing existing technologies lies in how to overcome the structural limitations of the traditional quinoline-4-one monocyclic core while maintaining the antibacterial activity of quinolone drugs. This can be achieved through structural reconstruction and hybridization at the core level to obtain novel antibacterial molecules with novel skeletons, aiming to achieve new breakthroughs in drug resistance control and safety. These issues are directly related to fundamental innovation in the core structure, rather than simple substituent adjustments, and represent a key bottleneck in the current development of quinolone structures. Summary of the Invention

[0006] This invention relates to the field of antibacterial pharmaceutical chemistry, specifically to a tricyclic indole-pyridone carboxylic acid quinolone molecule and its preparation method. This invention aims to break through the traditional development path of quinoline-4-one core structure optimization, which has long relied on the 6-position fluorine atom and the 7-position heterocyclic substituent. By fusing and reconstructing the core skeleton, a novel tricyclic fused heterocyclic system is constructed, with the goal of achieving substantial structural breakthroughs in antibacterial activity, overcoming drug resistance, and improving safety.

[0007] To address the limitations of existing quinolone drug structural innovation due to peripheral substituent modifications and insufficient core expansion, this invention provides a tricyclic indole-pyridone carboxylic acid molecular structure that fuses an indole structure with a pyridone carboxylic acid structure. This structure constructs a stable tricyclic fusion system through an intramolecular ring-closure strategy, achieving synergistic regulation of the core's electronic structure and spatial conformation while maintaining the characteristics of both the carboxylic acid functional group and the ketone carbonyl pharmacophore. This provides a new structural platform for obtaining novel antibacterial active molecules.

[0008] This invention also provides a method for preparing the aforementioned tricyclic indole-pyridone carboxylic acid molecules. The method uses halogen-substituted aniline compounds as starting materials, constructing an oxime acetamide intermediate through a condensation reaction. Under strong acid catalysis, an intramolecular electrocyclization and rearrangement reaction occurs to form an indole-dione skeleton. Subsequently, the electronic structure of the skeleton is controlled through hydrazone and decarbonylation reactions to obtain an indole ketone intermediate. Further, chloroformylation and oxidation reactions are carried out sequentially at specific sites to construct aldehyde and carboxylic acid structures. Using the carboxylic acid structure as the reaction core, through activation, condensation, enamineization, and amine substitution steps, an intramolecular ring-closing reaction is finally achieved to construct the tricyclic indole-pyridone skeleton. Hydrolysis and substitution reactions yield the target tricyclic indole-pyridone carboxylic acid quinolone molecule. This method has clear reaction steps and a controllable pathway. The key cyclization step employs an intramolecular concerted reaction mechanism, improving regioselectivity and overall yield.

[0009] Compared with existing technologies, this invention has the following advantages: First, this invention is no longer limited to modifying the substituents around the quinoline-4-one core, but instead constructs a novel tricyclic fusion system through innovative fusion at the core skeleton level, providing a new direction for the diversification of quinolone drug structures; second, the tricyclic fusion structure enhances the rigidity and conformational stability of the molecule, which is beneficial for optimizing the spatial matching relationship when binding to the target enzyme; third, the structure constructed in this invention retains the key pharmacologically active groups of carboxylic acid and ketone carbonyl while achieving readjustment of electron distribution, providing a theoretical basis for improving the antibacterial spectrum and reducing toxic side effects; in addition, the synthesis method of this invention reduces side reactions and improves the generation efficiency of key intermediates through an intramolecular cyclization strategy, and has good industrialization potential.

[0010] This invention proposes a novel tricyclic indole-pyridone carboxylic acid molecular structure and its preparation method by innovatively reconstructing the core structure of quinolone, providing a new technical path for structural breakthroughs and subsequent efficacy optimization of quinolone antibacterial drugs.

[0011] This invention, as a novel approach, attempts to insert an N-heterocyclic atom between the benzene ring of the parent quinolone and the pyridin-4-one-3-carboxylic acid, thereby expanding the quinoline ring into a novel tricyclic structure of indole-pyridone carboxylic acid for the development of quinolone-like drugs. Meanwhile, the indole heterocycle is not only an important structural backbone for many natural alkaloids but also a crucial pharmacophore in drug molecules, while the pyridone acid moiety is an essential structural unit for quinolone drug molecules. However, the tricyclic indole-pyridone acid structure formed by the hybridization of indole and pyridone acid has not yet been reported. Therefore, this invention further expands new strategies for constructing quinolone drug molecules, opening up avenues for the development of novel tricyclic antibacterial drugs.

[0012] The expected benefits and commercial value of the technical solution of this invention after transformation are as follows: Although the research and development of fluoroquinolones has undergone a regression study from "non-fluoroquinolones to fluoroquinolones to non-fluoroquinolones," and several excellent antibacterial drugs have been marketed for clinical application, the development of drug resistance and adverse reactions still cannot be overcome. The reason for this may be due to the constraints imposed by changes in the substituents of the "quinoline-4-one-3-carboxylic acid" skeleton, with little attention paid to the development of new skeletons. Based on this, inserting an N atom into the parent quinoline ring constructs a tricyclic indolepyridone carboxylic acid skeleton, which, as a novel fluoroquinolone-like molecule, will lead the development of a new antibacterial drug. Attached Figure Description

[0013] Figure 1 This is a technical roadmap for the preparation of novel tricyclic indolepyridone carboxylic acid quinolone molecules provided in the embodiments of the present invention;

[0014] Figure 2This is a flowchart of the preparation method of the novel tricyclic indolepyridone carboxylic acid quinolone molecule provided in the embodiments of the present invention. Detailed Implementation

[0015] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0016] like Figure 1 , Figure 2 As shown, this invention provides a method for preparing a novel tricyclic indole-pyridone carboxylic acid quinolone molecule. Taking 3-chloro-4-fluoro-aniline 11, a raw material for the synthesis of norfloxacin, as an example, the technical route is as follows:

[0017] Fluorochloroaniline 11 condenses with chloral hydrate to give oxime acetamide 12, which undergoes intramolecular cyclization in concentrated sulfuric acid to give indole-3,4-dione 13, which reacts with hydrazine hydrate to give hydrazone 14, followed by decarbonylation with chloroquine to indole-2-one 15. Intermediate 15 undergoes chloroformylation with reagent V to give 2-chloro-indole-3-carboxaldehyde 16, which is then oxidized to the corresponding 2-chloro-indole-3-carboxylic acid 17. Compound 17 reacts with carbonyl diimidazole to generate active imidazolium amide 18, which condenses with potassium malonic acid monoester under magnesium chloride catalysis to give ethyl 2-chloro-indole-3-formyl acetate 18. This ethyl acetate then reacts with dimethylformamide acetal to an enaminoketone ester intermediate 20, which is subsequently substituted with cyclopropylamine to form cyclopropylaminomethylene-2-chloro-indole-3-formyl acetate 21. Intramolecular cyclization then forms indolepyridone carboxylic acid ester 22, followed by hydrolysis to the corresponding carboxylic acid 23. Finally, a piperazine substitute is used to form target compound 10. Different structures of target compound 10 can be obtained by substituting different anilines for 11 and other amines for cyclopropylamine using the same synthetic method as above.

[0018] This invention provides a method for preparing a novel tricyclic indole-pyridone carboxylic acid quinolone molecule. The overall design is based on the classic quinolone core construction principles, introducing a pyridone ring onto the indole skeleton and further functionalizing the side chains to achieve diverse modifications to the molecular structure and regulation of biological activity. This technical route uses 3-chloro-4-fluoro-aniline 11, the synthetic raw material for norfloxacin, as the starting material and features readily available raw materials, clear reaction steps, and strong structural scalability.

[0019] As attached Figure 1As shown, the starting material, fluorochloroaniline 11, first undergoes a condensation reaction with chloral hydrate to generate an oxime acetamide intermediate 12. This step is completed through nucleophilic addition of an amino group to an activated carbonyl group, providing the necessary bifunctional structure for subsequent cyclization. Subsequently, under concentrated sulfuric acid conditions, intermediate 12 undergoes intramolecular cyclization and rearrangement reactions to construct an indole-3,4-dione skeleton 13. This process is essentially an acid-catalyzed intramolecular electrocyclization reaction, which determines the formation of the indole core. Intermediate 13 reacts with hydrazine hydrate to generate the corresponding hydrazone 14, which further undergoes a Huangminglong decarbonylation reaction under alkaline conditions to remove the carbonyl group, yielding a stable indole-2-one structure 15, providing a reaction site for subsequent functionalization.

[0020] Building upon this, intermediate 15 reacts with Vilsmeier's reagent to introduce a chloroformyl group, yielding 2-chloro-indole-3-carboxaldehyde 16. This step achieves selective functionalization of the indole C-3 position via an activated chloroformyl cation. The resulting aldehyde is further oxidized to the corresponding carboxylic acid 17, laying the foundation for constructing a quinolone side chain. Subsequently, carboxylic acid 17 reacts with carbonyl diimidazole to generate an active imidazolium amide intermediate 18, which then undergoes a condensation reaction with potassium malonic acid monoester under magnesium chloride catalysis, introducing a β-dicarbonyl structure to form an indole-3-formylacetic acid ester skeleton.

[0021] As attached Figure 2 As shown, subsequent reactions revolve around the construction of the quinolone core ring and the optimization of side chains. The aforementioned β-dicarbonyl intermediate reacts with dimethylformamide acetal to generate enaminoketone ester intermediate 20, which provides an active methylene group site for subsequent amine substitution reactions. Nucleophilic substitution with cyclopropylamine yields cyclopropylaminomethylene indole derivative 21, which undergoes an intramolecular cyclization reaction under appropriate conditions to construct an indole-pyridone tricyclic system, forming the target quinolone ester 22. This cyclization process is essentially a condensation and ring-closure reaction between the β-dicarbonyl group and the amine group, a key step in the formation of the tricyclic skeleton. The resulting ester compound is hydrolyzed to generate the corresponding carboxylic acid 23, which is then substituted with different piperazine compounds to introduce polar side chains, yielding the final target compound 10.

[0022] Through the above-described route, this invention not only achieves the efficient construction of tricyclic indolopyridone carboxylic acid quinolone cores, but also allows for the optimization of reaction conditions to achieve good selectivity and yield in each key step. Furthermore, by replacing the starting aniline 11 or subsequent amine sources, a series of structurally diverse target compounds can be conveniently obtained, demonstrating the wide applicability and technical advantages of this method in structural modification, structure-activity relationship studies, and the development of novel antibacterial drug molecules.

[0023] Example 1

[0024] Starting with 3-chloro-4-fluoro-aniline, a condensation reaction with chloral hydrate in an aqueous system yielded an oxime acetamide intermediate. An intramolecular cyclization reaction under concentrated sulfuric acid conditions formed an indole-dione skeleton. This skeleton was then reacted with hydrazine hydrate to generate a hydrazone structure, followed by decarbonylation under alkaline conditions to obtain an indoleone intermediate. The indoleone was selectively formylated under Vilsmeier conditions, followed by oxidation to construct a carboxylic acid structure. Through activation, condensation, and amine substitution reactions, a tricyclic indole-pyridone carboxylic acid compound was formed. The resulting product had a stable structure, and the key intermediates could be isolated and characterized.

[0025] Example 2

[0026] Based on Example 1, the starting material was replaced with 3-bromo-4-fluoro-aniline, while the remaining reaction steps remained the same. The results showed that different halogen substitutions had no substantial impact on the construction of the indole skeleton and the subsequent tricyclic ring closure process, and the target product was successfully generated. This indicates that the method has good adaptability to aniline halogen substitution, demonstrating the stability of the core reaction mechanism.

[0027] Example 3

[0028] After constructing the indoleone intermediate, the formyl intermediate was converted into a carboxylic acid structure under different oxidation conditions, and then reacted with a malonic acid monoester to generate a dicarbonyl-active intermediate. Subsequently, the tricyclic skeleton was constructed through enamidation and amine substitution reactions. Experimental results showed that different oxidation pathways did not affect the formation of the final tricyclic structure, indicating that the tricyclic construction depends on a concerted reaction mechanism of functional groups rather than a single condition.

[0029] Example 4

[0030] In the tricyclic framework construction stage, cyclopropylamine was replaced with ethyl-substituted piperazine as the amine source for a nucleophilic substitution reaction, and intramolecular ring closure was completed in the same reaction system. The resulting product still retains the indole-pyridone tricyclic core structure, with only the side chain changing, demonstrating that the tricyclic formation mechanism is decoupled from the amine structure, which is beneficial for structural diversification.

[0031] Example 5

[0032] Based on Example 4, the tricyclic carboxylic acid ester intermediate was hydrolyzed, followed by terminal modification with different substituted piperazines. The results showed that the hydrolysis and amine substitution processes proceeded continuously, and the target compound exhibited good purity, indicating that the terminal functionalization step did not disrupt the stability of the formed tricyclic skeleton.

[0033] Example 6

[0034] A continuous synthesis approach was adopted, in which condensation, cyclization, functionalization, and ring-closing steps were completed sequentially in a closed reaction system, with intermediates directly entering the next reaction without separation. Experiments showed that each key intermediate maintained its reactivity under continuous transfer conditions, ultimately yielding the target tricyclic indolophytone carboxylic acid compound. This verifies that the technical scheme is not only feasible for laboratory implementation but also has the potential for process scale-up.

[0035] This invention systematically optimizes the construction pathway of tricyclic indole-pyridone carboxylic acid quinolone molecules. Through the construction of an oxime acetamide intermediate, acid-catalyzed intramolecular electrocyclization to form an indole-dione skeleton, hydrazone decarbonylation to regulate the skeleton's electronic structure, and subsequent cascade reaction design of chloroformylation-oxidation-activation-intramolecular ring closure, the efficient and controllable construction of the tricyclic fused structure is achieved. To verify the beneficial effects of this invention, a comparative experiment was conducted with the traditional stepwise condensation-addition cyclization route under the same starting material purity (≥99%) and reaction scale (10 mmol).

[0036] Experimental data show that the intramolecular cyclization yield of this invention reaches 82.4% in the indole-dione skeleton construction stage, while the yield of the existing technology for constructing a similar skeleton through exogenous condensation is 63.1%. In the tricyclic ring-closing stage, the regioselectivity of the intramolecular ring-closing reaction of this invention reaches 92.7%, with a byproduct ratio of less than 5%, while the byproduct ratio of the comparative method exceeds 18%. The overall total yield is increased from 21.5% in the existing technology to 38.9%, the number of steps is reduced by 2, and the reaction time is shortened by approximately 28%. HPLC purity testing shows that the purity of the target product can consistently reach over 98.6%, eliminating the need for large-scale column chromatography separation.

[0037] In structural stability verification, differential scanning calorimetry (DSC) showed that the decomposition temperature of the tricyclic structure obtained in this invention was increased by approximately 12°C. In a pH 7.4 buffer system, a 48-hour stability test showed a degradation rate of only 3.8%, compared to 11.6% for the control sample. Furthermore, preliminary in vitro antibacterial activity testing (MIC method) showed that the inhibitory concentration of the target compound against Gram-positive bacteria was reduced by approximately 30%, indicating that the rigid tricyclic structure and the carboxylic acid site synergistically enhanced the conformational stability relevant to pharmacodynamics.

[0038] The experimental data above show that the present invention, through intramolecular synergistic cyclization and electronic structure optimization strategy, not only improves the regioselectivity and overall yield of key intermediates, but also significantly improves product purity, thermal stability and chemical stability, and exhibits superior effects in terms of biological activity compared to existing technologies. This verifies that the technical solution of the present invention has significant progress in terms of structure construction efficiency and performance improvement.

[0039] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions, and improvements made by those skilled in the art within the scope of the technology disclosed in the present invention, and within the spirit and principles of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a tricyclic indolepyridone carboxylic acid quinolone molecule, characterized in that, Includes the following steps: Starting with halogen-substituted aniline compounds, an oxime acetamide structure is constructed via condensation. Under strong acid conditions, the oxime acetamide undergoes an intramolecular cyclization reaction to form an indole-dione skeleton. The indole-dione skeleton is then subjected to hydrazone treatment and further decarbonylation to obtain an indole ketone structure. At specific sites on the indole ketone structure, an aldehyde structure and a carboxylic acid structure are sequentially constructed via chloroformylation and oxidation. Using the carboxylic acid structure as the reaction core, an indole-pyridone tricyclic skeleton is constructed through activation, condensation, enamineization, amine substitution, and intramolecular cyclization. The obtained tricyclic skeleton is then subjected to hydrolysis and amine substitution to obtain the target tricyclic indole-pyridone carboxylic acid quinolone molecule.

2. The preparation method according to claim 1, characterized in that, The oxime acetamide is constructed via a nucleophilic addition reaction of an aniline amino group to an activated carbonyl group, and the reaction is carried out in an aqueous system.

3. The preparation method according to claim 1, characterized in that, The formation of the indoledione skeleton depends on a synergistic mechanism of intramolecular electrocyclization and rearrangement under acid catalysis.

4. A method for preparing a tricyclic indolepyridone carboxylic acid quinolone molecule, characterized in that, Includes the following steps: Using an indole ketone structure as the core intermediate, a reactive formyl structure is constructed by selectively formylating the carbon atoms on the indole ring. This formyl structure is then converted into a carboxylic acid structure and further condensed with a compound having two carbonyl reaction sites to form an activated intermediate capable of amine substitution. Through amine substitution and intramolecular condensation, carbon-nitrogen bond construction and ring closure are simultaneously completed within the same molecule, forming an indole-pyridone tricyclic skeleton. Terminal functionalization of this tricyclic skeleton yields the target tricyclic indole-pyridone carboxylic acid quinolone molecule.

5. The preparation method according to claim 4, characterized in that, The selective formylation reaction is achieved by electrophilic substitution of specific sites on the indole ring by an activated formaldehyde chlorocation.

6. The preparation method according to claim 4, characterized in that, The amine used in the amine substitution reaction is an organic amine containing a cyclopropyl or piperazine structure.

7. A synthetic system for carrying out a method for preparing tricyclic indolepyridone carboxylic acid quinolone molecules, characterized in that, include: The reaction unit is used to complete the condensation, cyclization, and decarbonylation reactions of aniline raw materials; Functionalization units are used for the formylation, oxidation, and carboxylic acid construction of indole skeletons; The tricyclic building block is used to complete amine substitution and intramolecular cyclization reactions; The terminal modification unit is used to complete the hydrolysis reaction and amine substitution reaction to obtain the target product; The units are connected sequentially according to the reaction order to ensure that the intermediates are continuously transformed in the same synthetic pathway.

8. The synthesis system according to claim 7, characterized in that, A closed transfer structure for intermediate transfer is provided between the reaction unit and the functionalization unit.

9. The synthesis system according to claim 7, characterized in that, The tricyclic building block can complete both amine substitution and ring closure reactions in the same reaction environment.

10. The synthesis system according to claim 7, characterized in that, The terminal modification unit can achieve structural diversification of the target molecule by changing different amine sources.

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