Quinoline
What Is Quinoline
Quinoline is a heterocyclic aromatic organic compound with the chemical formula C9H7N. It is a colorless hygroscopic liquid with a strong odor. Aged samples, especially if exposed to light, become yellow and later brown. Quinoline is only slightly soluble in cold water but dissolves readily in hot water and most organic solvents. Quinoline itself has few applications, but many of its derivatives are useful in diverse applications. A prominent example is quinine, an alkaloid found in plants. Over 200 biologically active quinoline and quinazoline alkaloids are identified.4-Hydroxy-2-alkylquinolines (HAQs) are involved in antibiotic resistance.
Advantages of Quinoline
Possess antimalarial
Quinoline has been found to possess antimalarial, anti-bacterial, antifungal, anthelmintic, cardiotonic, anticonvulsant, anti-inflammatory, and analgesic activity.
Numerous biological effects
Quinolines have numerous biological effects, such as antibacterial, antifungal, antituberculosis, antiprotozoal, antineoplastic, anti-viral, anti-cholesterol medications, analgesics, anti-disease alzheimer's pharmaceuticals, and more.
Used as in the production of other specialty chemicals
Quinolines are used in the manufacture of dyes and the preparation of hydroxyquinoline sulfate and niacin. It is also used as a solvent for resins and terpenes. Quinoline is mainly used as in the production of other specialty chemicals.
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Biological Activity of Quinoline
Antimalarial
Quinolines are known for their excellent antimalarial properties. Raynes et al. developed bisquinolines, 19, 20 that exhibit antimalarial activity against chloroquine-resistant and chloroquine-sensitive parasites. Derivatives of ferrochloroquine, were also found to possess antimalarial activity. In these derivatives, the carbon skeleton of chloroquine is replaced by ferrocene group. Modapa et al. reported that the synthesis of ureido-4-quinolinamides, showed antimalarial activity at MIC 0.25 mg/mL against chloroquine-sensitive Plasmodium falciparum strain. Several 7-chloroquinolinyl thioureas, have been synthesized by Mahajan et al. that possess excellent antimalarial properties. Kovi et al. synthesized a chloroquinolyl derivative, that has an excellent antimalarial activity even at very low concentrations. Acharya et al. reported the synthesis and potent antimalarial activity of certain pyridine-quinoline hybrid conjugates, against chloroquine susceptible P. falciparum strain. Shiraki et al. produced some 5-aryl-8-aminoquinolines, with good antimalarial activity and had mild hemolytic activity than tafenoquine. Singh et al. developed several antimalarial 4-anilinoquinolines, which showed good antimalarial activity against chloroquine-sensitive P. falciparum strains. Novel hybrid conjugates of N-(7-chloroquinolin-4-yl) piperazine-1-carbothioamide and 1,3,5-triazine derivatives, have been synthesized by Bhat et al. These hybrid conjugates possess considerable antimalarial activity against both wild and mutant parasites on changing the pattern of substitution. McNulty et al. developed 4-arylquinoline-2-carboxylate derivatives, which show antiprotozoal activity against the pathogenic parasite Toxoplasma gondii.
Anti-inflammatory activity
A quinoline derivative, with strong anti-inflammatory activity was synthesized by Baba et al. in adjuvant arthritis rat model. Chen et al. developed 2-(furan-2-yl)-4-phenoxy-quinoline derivatives, that inhibit the lysozyme and β-glucuronidase release. Few quinoline derivatives, have been synthesized and evaluated by Gilbert et al. for treating osteoarthritis and that are amino-acetamide inhibitors of aggrecanase-2.
Analgesic activity
4-Substituted-7-trifluoromethylquinolines have been developed by Abadi et al., and these derivatives were found to possess excellent analgesic activity with nitric oxide releasing characteristics. Gomtsyan et al. synthesized an analgesic active derivative. The activity is due to its antagonism at vanilloid receptors. Some quinoline derivatives, were synthesized by Manera et al. that show analgesic activity and are selective agonists at cannabinoid CB2 receptors.
Antibacterial
Ma et al. reported the synthesis and antibacterial evaluation of phenoxy-, phenylthio-, and benzyloxy-substituted quinolones. A few 8-substituted quinoline carboxylic acids, were synthesized by Sanchez et al. that showed antibacterial activity. Upadhayaya et al. developed 3-benzyl-6-bromo-2-methoxy quinoline derivatives, and these derivatives are active against Mycobacterium tuberculosis H37Rv strain. A few analogues of 7-chloro quinolones, were synthesized by De Souza et al., and these derivatives were found to be effective against multidrug-resistant tuberculosis. Lilienkampf et al. synthesized quinoline-based compounds containing an isoxazole unit and side chain, that was active against Mycobacterium tuberculosis. The novel hybrid conjugates of N-(7-chloroquinolin-4-yl) piperazine-1-carbothioamide and 1,3,5-triazine derivatives, 30 synthesized by Bhat et al. also showed excellent antibacterial activity against several Gram-positive and Gram-negative microorganisms.
Antiviral
Several mono- and poly-substituted quinolones, synthesized by Fakhfakh et al. were found to exhibit activity against HIV-1. Ghosh et al. synthesized anilidoquinoline derivatives, which were found to possess an excellent antiviral activity against Japanese encephalitis virus. A few quinoline derivatives, possessing the behavior as HIV-1 Tat-TAR interaction inhibitors were synthesized by Chen et al. Massari et al. synthesized few desfluoroquinolones, for treating HIV infection.
Skraup synthesis method
This method is the most widely used method for the preparation of quinoline. In this method, aniline and glycerol are heated at a high temperature in the presence of sulphuric acid and mild oxidising agents like nitrobenzene or the presence of peroxides like arsenic peroxide. Ferrous sulphate (feso4) or boric acid (h3bo3) is generally added to make the reaction less violent because skraup synthesis is a highly exothermic reaction.
Mechanism of skraup synthesis method:
Step 1: In this step, glycerol undergoes a dehydration reaction in the presence of sulphuric acid to give acrolein. Step 2: In this step, the above-formed acrolein reacts with the aniline and forms an intermediate as a product of this reaction. Step 3: In this method the cyclization of the intermediate takes place. This cyclization process occurs in the presence of concentrated sulphuric acid to form 1, 2-dihydro quinoline. Step 4: In this step, the oxidation of 1,2-dihydroquinoline takes place on the reaction with nitrobenzene. On reacting with nitrobenzene, 1,2-dihydroquinoline forms the quinoline as a product.
Friedlander synthesis
In this method, ortho- amino benzaldehyde is condensed with acetaldehyde in the presence of sodium hydroxide (naoh) solution by the cyclisation process.
Doebner
Miller synthesis- primary aryl amines with free ortho positions can react with the alpha, beta-unsaturated carbonyl compound in the presence of acid to yield quinolines.
Knorr quinoline synthesis
In this reaction, the condensation of aniline takes place with the beta- ketoester at a high temperature to give an anilide intermediate. This formed anilide intermediate undergoes the cyclisation process. The concentrated sulphuric acid is added to the reaction for the dehydration process. The dehydration phenomena lead to the production of 2-hydroxyquinolines.
1.Antimicrobial activities
Amer et al. via in vitro analysis tested pyrazole- and pyridine-based quinoline hybrids for both antibacterial and antifungal activities. Antifungal analysis was conducted against Candida albicans using Ketoconazole as standard at a concentration of 100 μg/mL while antibacterial screening against two Gram-positive bacteria (Staphylococcus aureus and Bacillus subtilis), and two Gram-negative bacteria (Salmonella typhimurium and Escherichia coli) was carried out using Ciprofloxacin as standard. Some of the synthesized derivatives, displayed far broader antibacterial activity than Ciprofloxacin, while others demonstrated good to moderate antimicrobial performance against the pathogens examined. These compounds were found to have antibacterial activity against a variety of bacteria.
2.Antitubercular activities
Multidrug-resistant tuberculosis (MDR–TB) has been a significant obstacle in the fight against tuberculosis around the world. The quinoline-oxadiazole hybrids were synthesized by Shruthi et al. as a novel family of TB-specific compounds. Compound 28 with a MIC value of .5 μg/mL was reported to have the highest activity against Mtb WT H37Rv. Pharmacokinetics (PK) studies demonstrated that it is orally bioavailable having blood levels above the MIC of 2.5 μg/mL. The compounds produced were found to be metabolically stable, bioavailable, non-toxic, and exhibited good PK values, making them suitable for further research in a TB infection on an animal model.
3.Antiproliferative activity
Nitric oxide release and induction of apoptosis are some of the mechanisms nitrones and oximes use to exhibit antiproliferative properties. Activation of caspase (a group of key apoptosis mediators) occurs when reactive nitrogen species (RNS) including NO2 and N2O3 targets P53. Caspase-3 which is the most important one can activate death protease and cleave some important cellular proteins.
4.Antileishmanial activity
Macrophages play an important role in the cellular immune response and are activated as the first line of defense by host against Leishmania sp. Activation lead to increase in intracellular calcium levels and nitric oxide production which plays a role in parasite death. Upadhyay et al. discovered that imidazo-quinoline hybrids via macrophage activation exhibited antileishmanial activity, hence synthesized series of quinoline-triazole hybrids which were evaluated as possible antileishmanial agents on cutaneous leishmaniasis as adjunct to antimonial using experimental models and clinical studies. Among all the derivatives, therapeutic in vitro action was observed for compounds against intracellular amastigotes of Leishmania donovani. Using the golden hamster model, in vivo antileishmanial activity of L. donovani was investigated for these four derivatives and compound demonstrated promising leishmanicidal activity.
5.α-glucosidase inhibitory activity
Urease, beta-glucuronidase, thymidine phosphorylase, and α-amylase are all inhibited by nitrogen-containing heterocyclic moieties. Taha et al. developed quinoline-Schiff base hybrids as a potent family of in vitro α-glucosidase (an enzyme that hydrolyzes polysaccharides and disaccharides, the main cause of diabetes mellitus) inhibitors. All derivatives inhibited α-glucosidase activity in vitro at doses ranging from 6.20 to 48.50 µM with acarbose as the reference drug. Derivatives with two OH groups, and a fluoro group, were the most effective in the series.
Two Important Derivatives of Quinoline
Quinoline yellow
Quinoline yellow is a quinoline derivative. It's used to add colour to stuff. Quinoline yellow is a beta-diketone and aromatic ketone that belongs to the quinoline family. Quinoline has the molecular formula c18h11no2. Quinoline's chemical name is quinophthalone. Quinoline has a molecular weight of 273.3 g/mol.
Amino quinoline
Amino quinoline is a derivative of quinoline. The amino group takes the place of the hydrogen in the eighth spot. As a consequence, it's also known as quinoline's eight amino derivative. Amino quinoline has a structure that is identical to 8-hydroxyquinoline.
From Molecules to Medicine: The Remarkable Pharmacological Odyssey of Quinoline and Its Derivatives
Quinoline, a heterocyclic system composed of two fused six-membered aromatic rings (benzene and pyridine), has received considerable attention in medicinal chemistry due to its diverse and distinct biopharmaceutical activities. Quinoline derivatives belong to the nitrogen-containing heterocyclic compounds and have been extensively studied for their broad range of pharmacological responses, such as anti-cancer, anti-malarial, antibacterial, antifungal-antiprozoal, anthelmintic, local anesthetic, antiasthmatic, antipsychotic, antiglaucoma, and cardiotonic activities. The presence of quinoline alkaloids in various plant species has further amplified their significance in medicinal chemistry.
The unique chemical structure of quinoline and the ability to modify its substituents have enabled researchers to design novel and potent quinoline-based drugs. The versatility of quinoline in exhibiting a multitude of pharmacological responses has captured the attention of medicinal chemists to explore its vast potential in various therapeutic applications. Ongoing investigations into the pharmacological effects of quinoline derivatives will lead to the discovery of innovative and effective therapies for various diseases.
In medicinal chemistry, understanding the structure-activity relationship (SAR) is critical for designing and developing new drugs with improved pharmacological activity. SAR studies involve evaluating the relationship between the chemical structure of a molecule and its pharmacological activity. Researchers have conducted numerous SAR studies of quinoline derivatives to identify the specific structural features that are responsible for their diverse pharmacological effects.
For instance, SAR studies of quinoline-based antimalarial drugs have highlighted the importance of a basic nitrogen atom in the quinoline ring for antimalarial activity. The presence of a halogen atom in the molecule can also significantly enhance its activity against malaria. Similarly, in the case of quinoline-based anticancer drugs, SAR studies have demonstrated that the presence of a hydroxyl or methoxy group at position 7 on the quinoline ring can improve the compound’s antitumor activity. The introduction of a substituent at position 4 on the quinoline ring can also enhance the compound’s potency against cancer cells.
In the case of quinoline-based antibacterial drugs, SAR studies have identified the importance of the substitution pattern around the quinoline ring for antibacterial activity. The introduction of a fluorine atom at position 6 on the quinoline ring can significantly enhance the compound’s antibacterial activity.
Overall, SAR studies have provided valuable insights into the molecular mechanisms underlying the pharmacological activity of quinoline derivatives. By identifying the specific structural features responsible for a compound’s pharmacological activity, researchers can design and develop new drugs with improved efficacy and reduced side effects1
Quinoline is an exceptional organic compound that belongs to the class of nitrogen-containing heterocyclic substances. Its distinct molecular structure is characterized by the fusion of two aromatic rings, namely a benzene ring and a pyridine ring. This bicyclic compound is also referred to as benzo[b]pyridine and is considered as an analogue of naphthalene (1-azanapthalene). Its molecular weight is 129.16, and it has a log P value of 2.04, which indicates its lipophilicity. Quinoline is a weak tertiary base.31 Due to its unique structure, quinoline exhibits both electrophilic and nucleophilic substitution reactions, allowing for various modifications of its substituent groups.
Quinoline exhibits a remarkable ability to form salts with acids and display analogous chemical reactions to those observed in pyridine and benzene, showcasing its versatility as a heterocyclic compound.
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