Recent advances on anticancer and antimicrobial activities of directly-fluorinated five-membered heterocycles and their benzo-fused systems

Due to the importance of the fluorinated heterocycles as main components of marketed drugs where 20% of the anticancer and antibiotic drugs contain fluorine atoms, this review describes the reported five-membered heterocycles and their benzo-fused systems having directly connected fluorine atom(s). The in vivo and in vitro anticancer and antimicrobial activities of these fluorinated heterocycles are well reported. Some fluorinated heterocycles were found to be lead structures for drug design developments where their activities were almost equal to or exceeded the potency of the reference drugs. In most cases, the fluorine-containing heterocycles showed promising safety index via their reduced cytotoxicity in non-cancerous cell lines. SAR study assigned that fluorinated heterocycles having various electron-donating or electron-withdrawing substituents significantly affected the anticancer and antimicrobial activities.

A Comprehensive Review of the Diverse Spectrum Activity of 1,2,3-Triazole-linked Isatin Hybrids

Heterocyclic compounds containing 1,2,3-triazole and isatin as core structures have emerged as promising drug candidates due to their diverse biological activities such as anti-cancer, antifungal, antimicrobial, antitumor, anti-epileptic, antiviral, and more. The presence of 1,2,3-triazoles and isatin heterocycles in these hybrids, both individually known for their medicinal significance, has increasingly piqued the interest of drug discovery researchers, as they seek to delve deeper into their extensive pharmacological potential for enhancing therapeutic efficacy. Moreover, these hybrid compounds are synthetically accessible using readily available materials. Therefore, there is a pressing need to provide a comprehensive overview of the existing knowledge in this field, offering valuable insights to readers and paving the way for the discovery of novel 1,2,3-triazole-linked isatin hybrids with therapeutic potential.

Emerging impact of triazoles as anti-tubercular agent

Tuberculosis, a disease of poverty is a communicable infection with a reasonably high mortality rate worldwide. 10 Million new cases of TB were reported with approx 1.4 million deaths in the year 2019. Due to the growing number of drug-sensitive and drug-resistant tuberculosis cases, there is a vital need to develop new and effective candidates useful to combat this deadly disease. Despite tremendous efforts to identify a mechanism-based novel antitubercular agent, only a few have entered into clinical trials in the last six decades. In recent years, triazoles have been well explored as the most valuable scaffolds in drug discovery and development. Triazole framework possesses favorable properties like hydrogen bonding, moderate dipole moment, enhanced water solubility, and also the ability to bind effectively with biomolecular targets of M. tuberculosis and therefore this scaffold displayed excellent potency against TB. This review is an endeavor to summarize an up-to-date innovation of triazole-appended hybrids during the last 10 years having potential in vitro and in vivo antitubercular activity with structure activity relationship analysis. This review may help medicinal chemists to explore the triazole scaffolds for the rational design of potent drug candidates having better efficacy, improved selectivity and minimal toxicity so that these hybrid NCEs can effectively be explored as potential lead to fight against M. tuberculosis.

Therapeutic Outcomes of Isatin and Its Derivatives against Multiple Diseases: Recent Developments in Drug Discovery

Isatin (1H indole 2, 3-dione) is a heterocyclic, endogenous lead molecule recognized in humans and different plants. The isatin nucleus and its derivatives are owed the attention of researchers due to their diverse pharmacological activities such as anticancer, anti-TB, antifungal, antimicrobial, antioxidant, anti-inflammatory, anticonvulsant, anti-HIV, and so on. Many research chemists take advantage of the gentle structure of isatins, such as NH at position 1 and carbonyl functions at positions 2 and 3, for designing biologically active analogues via different approaches. Literature surveys based on reported preclinical, clinical, and patented details confirm the multitarget profile of isatin analogues and thus their importance in the field of medicinal chemistry as a potent chemotherapeutic agent. This review represents the recent development of isatin analogues possessing potential pharmacological action in the years 2016–2020. The structure–activity relationship is also discussed to provide a pharmacophoric pattern that may contribute in the future to the design and synthesis of potent and less toxic therapeutics.

Isatin Hybrids and Their Pharmacological Investigations

Hybridization is an important strategy to design molecules that can be effectively used to treat fatal diseases known to mankind. Molecular hybrids and their pharmacological investigations aided in discovering several potent isatin (Indole 2, 3 dione) derivatives with anti-HIV, antimalarial, antitubercular, antibacterial, and anticancer activities. Indole-2,3-dione and their derivatives have diverse pharmacological properties and have a prominent role in the discovery of new drugs. To understand the various approaches for designing new molecules based on isatin nucleus analysis of various pharmacophore hybrids, spacers/linkers between pharmacophores and isatin for hybridization and their biological activities are important. This review discusses the progress in developing isatin hybrids as biologically effective agents and their crucial aspects of design and structure-activity relationships.

Triazole-containing hybrids with anti-Mycobacterium tuberculosis potential - Part I: 1,2,3-Triazole

Tuberculosis regimens currently applied in clinical practice require months of multidrug therapy, which imposes a major challenge of patient compliance and drug resistance development. Moreover, because of the increasing emergence of hard-to-treat tuberculosis, this disease continues to be a significant threat to the human population. 1,2,3-triazole as a privileged structure has been widely used as an effective template for drug discovery, and 1,2,3-triazole-containing hybrids that can simultaneously act on dual or multiple targets in Mycobacterium tuberculosis have the potential to circumvent drug resistance, enhance efficacy, reduce side effects and improve pharmacokinetic as well as pharmacodynamic profiles. Thus, 1,2,3-triazole-containing hybrids are useful scaffolds for the development of antitubercular agents. This review aims to highlight recent advances of 1,2,3-triazole-containing hybrids with potential activity against various forms of M. tuberculosis, covering articles published between 2015 and 2020. The structure-activity relationship and the mechanism of action are also discussed to facilitate further rational design of more effective drug candidates.

Synthesis of Bioactive Complex Small Molecule-Ciprofloxacin Conjugates and Evaluation of Their Antibacterial Activity

Conjugates between pharmaceuticals and small molecules enable access to a vast chemical space required for the discovery of new lead molecules with modified therapeutic potential. However, the dearth of specific chemical reactions that are capable of functionalizing drugs and bioactive natural products presents a formidable challenge for preparing their conjugates. Here, we report a support-free CuI-nanoparticle-catalyzed strategy for conjugating electron-deficient and electron-rich terminal alkynes with a ciprofloxacin methyl ester. Our conjugation technique exploits the late-stage functionalization of bioactive natural products such as tocopherol, vasicinone, amino acids, and pharmaceuticals such as aspirin and paracetamol to provide conjugates in excellent yields under mild and green conditions. This protocol also enabled the synthesis of (hetero)arene-ciprofloxacin 1,4-disubstituted 1,2,3-triazoles in good yields and high regioselectivities. These synthesized ciprofloxacin conjugates were evaluated in vitro for their antibacterial activity against a panel of relevant bacteria. A significant number of conjugates showed comparable activity against Gram-positive and Gram-negative bacteria. Moreover, some conjugates exhibited less toxicity than ciprofloxacin against two mammalian cell lines, suggesting the utility for the future investigation of these compounds for in vivo efficacy and pharmacokinetic studies.

Polymorphism of 3-(5-phenyl-1,3,4-oxadiazol-2-yl)- and 3-[5-(pyridin-4-yl)-1,3,4-oxadiazol-2-yl]-2H-chromen-2-ones

This study of 3-(5-phenyl-1,3,4-oxadiazol-2-yl)-2H-chromen-2-one, C₁₇H₁₀N₂O₃, 1, and 3-[5-(pyridin-4-yl)-1,3,4-oxadiazol-2-yl]-2H-chromen-2-one, C₁₆H₉N₃O₃, 2, was performed on the assumption of the potential anticancer activity of the compounds. Three polymorphic structures for 1 and two polymorphic structures for 2 have been studied thoroughly. The strongest intermolecular interaction is stacking of the `head-to-head' type in all the studied crystals. The polymorphic structures of 1 differ with respect to the intermolecular interactions between stacked columns. Two of the polymorphs have a columnar or double columnar type of crystal organization, while the third polymorphic structure can be classified as columnar-layered. The difference between the two structures of 2 is less pronounced. Both crystals can be considered as having very similar arrangements of neighbouring columns. The formation of polymorphic modifications is caused by a subtle balance of very weak intermolecular interactions and packing differences can be identified only using an analysis based on a study of the pairwise interaction energies.

Design, synthesis and antibacterial activity evaluation of moxifloxacin-amide-1,2,3-triazole-isatin hybrids

In this work, a series of novel moxifloxacin-amide-1,2,3-triazole-isatin hybrids 7a-l were designed and synthesized. The in vitro antibacterial activity against a panel of clinically important Gram-positive and Gram-negative bacteria including drug-resistant pathogens was also evaluated. All hybrids showed considerable activity against the tested pathogens with MIC values of ≤0.03 to 128 μg/mL, and some of them such as hybrids 7e, 7g and 7j were comparable to or better than the parent moxifloxacin (MIC: ≤0.03-8 μg/mL). Moreover, hybrids 7e, 7g and 7j also demonstrated low cytotoxicity towards CHO cells. However, the in vivo pharmacokinetic profiles of these three hybrids were generally far inferior to the parent moxifloxacin. The structure-activity relationship and structure-cytotoxicity relationship were also studied and discussed which may help with the identification of new chemical entities as potent antibacterial agents.

Design, synthesis and antimicrobial evaluation of propylene-tethered ciprofloxacin-isatin hybrids

Twelve novel propylene-tethered ciprofloxacin-isatin hybrids 3a-f and 4a-f were designed, synthesized and characterized by MS, HRMS, ¹H NMR and ¹³C NMR. All hybrids were evaluated for their in vitro antimicrobial activities against representative Gram-positive, Gram-negative and mycobacterial pathogens, cytotoxicity in VERO cell line as well as metabolic stability and in vivo pharmacokinetic (PK) properties. The preliminary results indicated that all mono-isatin-ciprofloxacin hybrids exhibited excellent antibacterial activities with MIC ranging from ≤0.03 to 0.5 μg/mL against most of the tested strains. In particular, ciprofloxacin-isatin hybrid 3d was highly potent against all tested Gram-positive and Gram-negative strains including clinically important drug-resistant pathogens, which was comparable to or more potent than the parent ciprofloxacin and reference levofloxacin. Whereas, conjugate 3b (MIC: 0.10 and 0.5 μg/mL) was 4- and 8-fold more active than ciprofloxacin (MIC: 0.78 μg/mL) and rifampicin (MIC: 0.39 μg/mL) against MTB H₃₇Rv, and 4->256 times more potent than the three references ciprofloxacin (MIC: 2.0 μg/mL), rifampicin (MIC: 32 μg/mL) and isoniazid (>128 μg/mL) against MDR-TB. Both hybrid 3b and 3d with low cytotoxicity (CC₅₀: 64 and 256 μg/mL) also showed acceptable metabolic stability and in vivo PK properties, could act as leads for further optimization.

Design, synthesis and in vitro anti-mycobacterial activities of homonuclear and heteronuclear bis-isatin derivatives

A series of novel homonuclear and heteronuclear bis-isatin derivatives tethered through ethylene were designed, synthesized and evaluated for their in vitro anti-mycobacterial activities against MTB H37Rv and MDR-TB. All hybrids exhibited potential anti-mycobacterial activities against MTB H37Rv and MDR-TB with MIC ranging from 16 to 256 μg/mL. In particular, the heteronuclear bis-isatin 4i (MIC: 25 and 16 μg/mL) was most active against MTB H37Rv and MDR-TB strains, and could act as a lead for further optimization.