Design, synthesis and biological evaluation of novel azaspiro analogs of linezolid as antibacterial and antitubercular agents

Spirocyclic compounds: potential drug leads in the fight against Mycobacterium tuberculosis

TB drug discovery needs scientists' attention since drug resistance in TB, including extensively drug-resistant TB (XDR-TB) and multidrug-resistant TB (MDR-TB), is a major healthcare concern. Since millions of fatalities from tuberculosis are recorded each year, there is an urgent need to discover new anti-tubercular medications that will either eradicate or control the disease. Spiro compounds have garnered a lot of attention in medicinal chemistry these days because of various biological activities mainly because of their adaptability and structural resemblance to significant pharmacophores. This article overviews the synthesis and activity of spirocyclic compounds as anti-tubercular agents. Both synthesized and naturally occurring spiro chemicals exhibit antitubercular properties. The promising antitubercular potential shown by some of the spirocyclic compounds has attracted scientists to explore them further to develop molecules with improved pharmacodynamic and pharmacokinetic properties and new mechanisms of action with enhanced safety and efficacy in tuberculosis. The current review covers the exploration of spiro compounds from the year 2004 to 2024 for the combat of Tuberculosis. This review gives the comprehensive advancements in this scaffold which would help the logical design of powerful, less toxic, and more effective spirocyclic anti-TB medicinal molecules.

Practical and Scalable Two-Step Process for 6-(2-Fluoro-4-nitrophenyl)-2-oxa-6-azaspiro[3.3]heptane: A Key Intermediate of the Potent Antibiotic Drug Candidate TBI-223

A low-cost, protecting group-free route to 6-(2-fluoro-4-nitrophenyl)-2-oxa-6-azaspiro[3.3]heptane (1), the starting material for the in-development tuberculosis treatment TBI-223, is described. The key bond forming step in this route is the creation of the azetidine ring through a hydroxide-facilitated alkylation of 2-fluoro-4-nitroaniline (2) with 3,3-bis(bromomethyl)oxetane (BBMO, 3). After optimization, this ring formation reaction was demonstrated at 100 g scale with isolated yield of 87% and final product purity of >99%. The alkylating agent 3 was synthesized using an optimized procedure that starts from tribromoneopentyl alcohol (TBNPA, 4), a commercially available flame retardant. Treatment of 4 with sodium hydroxide under Schotten-Baumann conditions closed the oxetane ring, and after distillation, 3 was recovered in 72% yield and >95% purity. This new approach to compound 1 avoids the previous drawbacks associated with the synthesis of 2-oxa-6-azaspiro[3,3]heptane (5), the major cost driver used in previous routes to TBI-223. The optimization and multigram scale-up results for this new route are reported herein.

Oxazolidinones as versatile scaffolds in medicinal chemistry

Oxazolidinone is a five-member heterocyclic ring with several biological applications in medicinal chemistry. Among the three possible isomers, 2-oxazolidinone is the most investigated in drug discovery. Linezolid was pioneered as the first approved drug containing an oxazolidinone ring as the pharmacophore group. Numerous analogues have been developed since its arrival on the market in 2000. Some have succeeded in reaching the advanced stages of clinical studies. However, most oxazolidinone derivatives reported in recent decades have not reached the initial stages of drug development, despite their promising pharmacological applications in a variety of therapeutic areas, including antibacterial, antituberculosis, anticancer, anti-inflammatory, neurologic, and metabolic diseases, among other areas. Therefore, this review article aims to compile the efforts of medicinal chemists who have explored this scaffold over the past decades and highlight the potential of the class for medicinal chemistry.

Optimization and Antibacterial Evaluation of Novel 3-(5-Fluoropyridine-3-yl)-2-oxazolidinone Derivatives Containing a Pyrimidine Substituted Piperazine

In this study, a series of novel 3-(5-fluoropyridine-3-yl)-2-oxazolidinone derivatives were designed and synthesized based on compounds previously reported, and their antibacterial activity was investigated. Then their antibacterial activity was investigated for the first time. Preliminary screening results showed that all these compounds exhibited antibacterial activity against gram-positive bacteria, including 7 drug-sensitive strains and 4 drug-resistant strains, among which compound 7j exhibited an 8-fold stronger inhibitory effect than linezolid, with a minimum inhibitory concentration (MIC) value of 0.25 µg/mL. Further molecular docking studies predicted the possible binding mode between active compound 7j and the target. Interestingly, these compounds could not only hamper the formation of biofilms, but also have better safety, as confirmed by cytotoxicity experiments. All these results indicate that these 3-(5-fluoropyridine-3-yl)-2-oxazolidinone derivatives have the potential to be developed into novel candidates for the treatment of gram-positive bacterial infections.

Design, synthesis and biological evaluation of novel spiro-quinazolinone derivatives as chitin synthase inhibitors and antifungal agents

A series of spiro-quinazolinone scaffolds were constructed based on the bioactivity of quinazolinone and the inherent feature of spirocycle to design novel chitin synthase inhibitors that possess mode of action different from that of the currently used antifungal agents. Among them, the spiro[thiophen-quinazolin]-one derivatives containing α, β-unsaturated carbonyl fragments had shown inhibitory activities against chitin synthase and antifungal activities. The enzymatic experiments showed that among the sixteen compounds, compounds 12d, 12g, 12j, 12l and 12m exhibited inhibitions against chitin synthase with IC₅₀ values of 116.7 ± 19.6 μM, 106.7 ± 14.2 μM, 102.3 ± 9.6 μM, 122.7 ± 22.2 μM and 136.8 ± 12.4 μM, respectively, which were comparable to that of polyoxin B (IC₅₀ = 93.5 ± 11.1 μM). The assays of enzymatic Kinetic parameters showed that compound 12g was a non-competitive inhibitor of chitin synthase. The antifungal assays showed that compounds 12d, 12g, 12j, 12l and 12m exhibited a broad-spectrum of antifungal activity against the four strains tested in vitro. In which, compounds 12g and 12j had stronger antifungal activity against four tested strains than that of polyoxin B and similar to that of fluconazole, while compounds 12d, 12l and 12m showed antifungal activity comparable to that of polyoxin B against four tested strains. Meanwhile, compounds 12d, 12g, 12j, 12l and 12m exhibited good antifungal activity against fluconazole-resistant and micafungin-resistant fungi variants with MIC values ranging from 4 to 32 μg/mL while the MIC values of reference drugs were above 256 μg/mL. Furthermore, the results of drug-combination experiments showed that compounds 12d, 12g, 12j, 12l and 12m had synergistic or additive effects with fluconazole or polyoxin B. The results of sorbitol protection experiment and the experiment of antifungal activity against micafungin-resistant fungi further demonstrated that these compounds target chitin synthase. The result of cytotoxicity assay showed that compound 12g had low toxicity toward human lung cancer A549 cells and the ADME analysis in silico displayed that compound 12g possessed promising pharmacokinetic properties. The molecular docking indicated that compound 12g formed multiple hydrogen bond interactions binding to chitin synthase, which might be conductive to increasing the binding affinity and inhibiting the activity of chitin synthase. The above results indicated that the designed compounds were chitin synthase inhibitors with selectivity and broad-spectrum antifungal activity and could be act as the lead compounds against drug-resistant fungi.

Design, synthesis, and antitumor evaluation of morpholine substituted bisnaphthalimides as DNA targeting agents

A series of mono- and bisnaphthalimides derivatives containing 3-nitro and 4-morpholine moieties were designed, synthesized, and evaluated for their in vitro anticancer activities against four cancer cell lines. Some compounds exhibited relatively good antiproliferative activity on the cell lines tested, in comparison with mitonafide and amonafide. It is noteworthy that bisnaphthalimide A6 was identified as the most potent compound in anti-proliferation against MGC-803 cells, with an IC₅₀ lowered to 0.09 μM, a far greater potency than that of mono-naphthalimide A7, mitonafide, and amonafide. A gel electrophoresis assay revealed that DNA and Topo I were the potential targets of compounds A6 and A7. The treatment of CNE-2 cells with compounds A6 and A7 resulted in an S phase cell cycle arrest, accompanied by the upregulation of the expression levels of the antioncogene p27 and the down-regulation of the expression levels of CDK2 and cyclin E. In addition, compounds A6 and A7-induced apoptosis was further confirmed by flow cytometry, ROS generation assay, and Hoechst 33,258 staining. In particular, in vivo antitumor assay results revealed that bisnaphthalimide A6 exhibited potent anticancer efficiency in an MGC-803 xenograft tumor model, in comparison with mitonafide, and had lower toxicity than mono-naphthalimide A7. In brief, the results suggested that bisnaphthalimide derivatives containing 3-nitro and 4-morpholine moieties might serve as DNA binding agents for the development of new antitumor agents.

Antibacterial Properties and Computational Insights of Potent Novel Linezolid-Based Oxazolidinones

The mounting evidence of bacterial resistance against commonly prescribed antibiotics warrants the development of new antibacterial drugs on an urgent basis. Linezolid, an oxazolidinone antibiotic, is a lead molecule in designing new oxazolidinones as antibacterial agents. In this study, we report the antibacterial potential of the novel oxazolidinone-sulphonamide/amide conjugates that were recently reported by our research group. The antibacterial assays showed that, from the series, oxazolidinones 2 and 3a exhibited excellent potency (MIC of 1.17 μg/mL) against B. subtilis and P. aeruginosa strains, along with good antibiofilm activity. Docking studies revealed higher binding affinities of oxazolidinones 2 and 3a compared to linezolid, which were further validated by molecular dynamics simulations. In addition to this, other computational studies, one-descriptor (log P) analysis, ADME-T and drug likeness studies demonstrated the potential of these novel linezolid-based oxazolidinones to be taken forward for further studies.

Design, synthesis and biological evaluations of quinolone amides against African trypanosomiasis with improved solubility

The human African trypanosomiasis is a devastating parasitic infection, which is caused by the protozoan Trypanosoma brucei and transmitted by the bite of the tsetse fly. An untreated infection usually results in death and only few drugs with significant drawbacks are currently available for treatment. Previous investigations revealed the quinolone amide MB007 as a lead compound with an excellent selectivity for T. b. brucei. Here, new quinolone amides were synthesized for deeper insights into the structure-activity relationship. Furthermore, the aqueous solubility of the compounds was analyzed, as the poor solubility of previous quinolone amides impeded in vivo studies for target identification. The biological evaluation led to the new lead structure 9f, which exhibits a promising in vitro activity against T. b. brucei (IC50 = 22 nM) and showed no cytotoxicity against macrophages. Moreover, compounds 10b and 10c were discovered, which possessed an improved solubility combined with a decent selectivity.

Replacing the oxidation-sensitive triaminoaryl chemotype of problematic KV 7 channel openers: Exploration of a nicotinamide scaffold

K_V 7 channel openers have proven their therapeutic value in the treatment of pain as well as epilepsy and, moreover, they hold the potential to expand into additional indications with unmet medical needs. However, the clinically validated but meanwhile discontinued K_V 7 channel openers flupirtine and retigabine bear an oxidation-sensitive triaminoraryl scaffold, which is suspected of causing adverse drug reactions via the formation of quinoid oxidation products. Here, we report the design and synthesis of nicotinamide analogs and related compounds that remediate the liability in the chemical structure of flupirtine and retigabine. Optimization of a nicotinamide lead structure yielded analogs with excellent K_V 7.2/3 opening activity, as evidenced by EC₅₀ values approaching the single-digit nanomolar range. On the other hand, weighted K_V 7.2/3 opening activity data including inactive compounds allowed for the establishment of structure-activity relationships and a plausible binding mode hypothesis verified by docking and molecular dynamics simulations.

Synthesis and biological activity evaluation of novel 3,5,7-trisubstituted pyrazolo[1,5-a]pyrimidines

Mutation of FLT3 protein kinase is often associated with deregulated cell proliferation in acute myeloid leukemia and the inhibition of this kinase is a potential therapeutic strategy. We report a novel series of 3,5,7-trisubstituted pyrazolo[1,5-a]pyrimidines prepared in an effort to study their biological activity particularly toward FLT3-ITD and its downstream regulators as well as toward CDK2 and CDK9. Derivative 10b was capable to strongly inhibit all kinases and its selectivity in FLT3-ITD expressing cell lines MOLM13 and MV4-11 was in line with FLT3-ITD inhibition. Further biochemical analyses and molecular docking confirmed FLT3 as a cellular target of 10b.

Synthesis and Biological Evaluation of 3-(Pyridine-3-yl)-2-Oxazolidinone Derivatives as Antibacterial Agents

In this research, a series of 3-(pyridine-3-yl)-2-oxazolidinone derivatives was designed, synthesized, and evaluated for in vitro antibacterial activity, which included bacteriostatic, morphological, kinetic studies, and molecular docking. The results demonstrated that compounds 21b, 21d, 21e and 21f exhibited strong antibacterial activity similar to that of linezolid toward five Gram-positive bacteria. After observing the effect of the drug on the morphology and growth dynamics of the bacteria, the possible modes of action were predicted by molecular docking. Furthermore, the antibiofilm activity and the potential drug resistance assay was proceeded. These compounds exhibited universal antibiofilm activity and compound 21d showed significant concentration-dependent inhibition of biofilm formation. Compound 21d also showed a stable effect on S. pneumoniae (ATCC 49619) with less drug resistance growth for 15 days, which is much longer than that of linezolid. Overall, these results can be used to guide further exploration of novel antimicrobial agents.

Thiophene-containing compounds with antimicrobial activity

Thiophene, as a member of the group of five-membered heterocycles containing one heteroatom, is one of the simplest heterocyclic systems. Many synthetic strategies allow the accurate positioning of various functionalities onto the thiophene ring. This review provides a comprehensive, systematic and detailed account of the developments in the field of antimicrobial compounds featuring at least one thiophene ring in their structure, over the last decade.

Design, Synthesis, and the Effects of (E)-9-Oxooctadec-10-en-12-ynoic Acid Analogues to Promote Glucose Uptake

(E)-9-Oxooctadec-10-en-12-ynoic acid is found to mediate its antidiabetic activity by increasing insulin-stimulated glucose uptake in L6 myotubes by activating the phosphoinositide 3-kinase (PI3K) pathway. A simultaneous study of site-specific modification followed by structure-activity relationship provides a tremendous scope for exploiting the bioactivity of the parent molecule. Therefore, in the present study, we focused on site-specific modification of (E)-9-oxooctadec-10-en-12-ynoic acid (1) to generate multiple derivatives and extensive structure-activity relationship (SAR) studies. We have done structural base design and synthesized a series of amides from acid compound 1. Compound 1 consists of an acid functionality, which is known for its metabolism-related liabilities. The SAR has been generated using scaffolds of different antidiabetic drugs such as biguanides, sulfonylureas, thiazolidinediones/glitazones, peroxisome proliferator-activated receptors, K + ATP, α-glucosidase inhibitors, and others. Furthermore, the study demonstrates and explains the promising derivatives and importance of SAR of the compound (E)-9-oxooctadec-10-en-12-ynoic acid. In order to gain mechanistic insights, a molecular docking study was performed against PI3K, which could identify the binding modes and thermodynamic interactions governing the binding affinity. According to our research, compounds 5, 6, 27, 28, 31, 32, and 33 are the best compounds from the series having EC₅₀ values of 15.47, 8.89, 7.00, 13.99, 8.70, 12.27, and 16.14 μM, respectively.

Design, synthesis and biological evaluation of 2,3-dihydroimidazo[2,1-b]thiazoles as dual EGFR and IGF1R inhibitors

Herein we describe the design, synthesis and anticancer evaluation of a series of 2,3-dihydroimidazo[2,1-b]thiazoles as dual kinase inhibitors of IGF1R and EGFR. A series of saturated dihydroimidazo[2,1-b] thiazoles were synthesized to understand the structure-activity relationship. Further, the key modifications were performed to improve drug like properties of the series. A 2-oxa-6-azaspiro [3.3] heptane moiety was incorporated as a bioisosteric replacement of morpholine on dihydroimidazo[2,1-b] thiazole scaffold.Subsequent structure-activity relationship (SAR) studies identified several compounds with nM range of activity. The compound 18a shows promising activity, IC₅₀ = 52 nM against IGF1R and IC₅₀ = 35.5 nM against EGFR with descent PK profile. The identified leadshows promising activity against both wild type and the T790M mutant forms of enzymes.

Synthesis of tetracyclic oxindoles and evaluation of their α-glucosidase inhibitory and glucose consumption-promoting activity

A series of tetracyclic oxindole derivatives was synthesized by asymmetric 1, 3-dipole reaction in 2-4 steps in 57-86% overall yields. These compounds were evaluated for α-glucosidase inhibitory and glucose consumption-promoting activity in vitro. Compound 4l competitively and reversibly inhibited α-glucosidase (IC₅₀ = 3.64 μM) with activity 14-fold higher than that of acarbose. Docking analysis substantiated these findings. In addition, compound 4l exhibited significant glucose consumption promoting activity at 1 μM.

Opportunities and challenges of using five-membered ring compounds as promising antitubercular agents

Tuberculosis (TB), a chronic infectious disease, is one of the greatest risks to human beings and 10 million people were diagnosed with TB and 1.6 million died from this disease in 2017. In addition, with the emergence of multidrug-resistant tuberculosis (MDR-TB) and extensively drug-resistant tuberculosis (XDR-TB), the TB situation has become even worse, which has aggravated the mortality and spread of this disease. To overcome this problem, research into novel antituberculosis agents with enhanced activities against MDR-TB, reduced toxicity, and shortened duration of therapy is of great importance. Fortunately, many novel potential anti-TB drug candidates with five-membered rings, which are most likely to be effective against sensitive and resistant strains, have recently entered clinical trials. Different five-membered rings such as furans, pyranoses, thiazoles, pyrazolines, imidazoles, oxazolidinone, thiazolidins, isoxazoles, triazoles, oxadiazoles, thiadiazoles, and tetrazoles have been designed, prepared, and evaluated for their antimycobacterial activity against Mycobacterium tuberculosis. In this article, we highlight the recent advances made in the discovery of novel five-membered ring compounds and focus on their antitubercular activities, toxicity, structure-activity relationships, and mechanisms of action.

Intertwined chemistry of hydroxyl hydrogen-bond donors, epoxides and isocyanates in the organocatalytic synthesis of oxazolidinones versus isocyanurates: rational catalytic investigation and mechanistic understanding

The efficiency and chemoselectivity of the cycloaddition of isocyanates to epoxides to afford oxazolidinones were investigated using hydroxyl hydrogen-bond donors as organocatalysts.

Lowering Lipophilicity by Adding Carbon: AzaSpiroHeptanes, a logD Lowering Twist

We have conducted an analysis of azaspiro[3.3]heptanes used as replacements for morpholines, piperidines, and piperazines in a medicinal chemistry context. In most cases, introducing a spirocyclic center lowered the measured logD _7.4 of the corresponding molecules by as much as -1.0 relative to the more usual heterocycle. This may seem counterintuitive, as the net change in the molecule is the addition of a single carbon atom, but it may be rationalized in terms of increased basicity. An exception to this was found with N-linked 2-azaspiro[3.3]heptane, where logD _7.4 increased by as much as +0.5, consistent with the addition of carbon. During our investigation, we also concluded that azaspiro[3.3]heptanes are most likely not suitable bioisosteres for morpholines, piperidines, and piperazines, when not used as terminal groups, due to significant changes in their geometry.

Revealing quinquennial anticancer journey of morpholine: A SAR based review

Morpholine, a six-membered heterocycle containing one nitrogen and one oxygen atom, is a moiety of great significance. It forms an important intermediate in many industrial and organic syntheses. Morpholine containing drugs are of high therapeutic value. Its wide array of pharmacological activity includes anti-diabetic, anti-emetic, growth stimulant, anti-depressant, bronchodilator and anticancer. Multi-drug resistance in cancer cases have emerged in the last few years and have led to the failure of many chemotherapeutic drugs. Newer treatment methods and drugs are being developed to overcome this problem. Target based drug discovery is an effective method to develop novel anticancer drugs. To develop newer drugs, previously reported work needs to be studied. Keeping this in mind, last five year's literature on morpholine used as anticancer agents has been reviewed and summarized in the paper herein.

Recent advances of imidazole-containing derivatives as anti-tubercular agents

Tuberculosis still remains one of the most common, communicable, and leading deadliest diseases known to mankind throughout the world. Drug-resistance in Mycobacterium tuberculosis which threatens to worsen the global tuberculosis epidemic has caused great concern in recent years. To overcome the resistance, the development of new drugs with novel mechanisms of actions is of great importance. Imidazole-containing derivatives endow with various biological properties, and some of them demonstrated excellent anti-tubercular activity. As the most emblematic example, 4-nitroimidazole delamanid has already received approval for treatment of multidrug-resistant tuberculosis infected patients. Thus, imidazole-containing derivatives have caused great interests in discovery of new anti-tubercular agents. Numerous of imidazole-containing derivatives were synthesized and screened for their in vitro and in vivo anti-mycobacterial activities against both drug-sensitive and drug-resistant Mycobacterium tuberculosis pathogens. This review aims to outline the recent advances of imidazole-containing derivatives as anti-tubercular agents, and summarize the structure-activity relationship of these derivatives. The enriched structure-activity relationship may pave the way for the further rational development of imidazole-containing derivatives as anti-tubercular agents.

1,2,3-Triazole–quinazolin-4(3H)-one conjugates: evolution of ergosterol inhibitor as anticandidal agent

The present study describes the synthesis of 1,2,3-triazole–quinazolinone conjugates (5a–q) from ethyl 4-oxo-3-(prop-2-ynyl)-3,4-dihydroquinazoline-2-carboxylate and phenyl azide/substituted phenyl azides employing Cu(i) catalysed Huisgen 1,3-dipolar cycloaddition. The corresponding acids (6a–q) were obtained by hydrolysis of esters (5a–q) to study the effect of these functionalities on the biological activity. All synthesized compounds were screened for in vitro anticandidal evaluation against Candia albicans, Candida glabrata and Candida tropicalis strains. The results indicated that compound 5n showed potent anticandidal activity with IC₅₀ in the range of 8.4 to 14.6 μg mL⁻¹. Hemolytic activity using human red blood cells (hRBCs) and cytotoxicity by MTT assay on human embryonic kidney (HEK-293) cells revealed the non-toxic nature of the selected compounds. Growth kinetic study with compound 5n showed its fungicidal nature as no significant growth of Candida cells was observed even after 24 h. Cellular ergosterol content was determined in the presence of different concentrations of 5n to measure the activity of lanosterol 14α-demethylase indirectly. The results showed significant disruption of the ergosterol biosynthetic pathway through inhibition of lanosterol 14α-demethylase activity supported by docking studies (PDB: 5v5z). Overall, this study demonstrates the anticandidal potential of 5n which can serve as the lead for further structural optimization and SAR studies.

The present study elicits the synthesis of 1,2,3-triazole–quinazolinone conjugates (5a–q) as ergosterol inhibitors for Candida infections.

Pd-catalyzed arylation of linear and angular spirodiamine salts under aerobic conditions

Application of Buchwald-Hartwig catalysis for development of biologically relevant arylspirodiamine compounds is reported. This synthetic methodology requires no inert atmosphere and affords yields up to 93% in just 20 min. Linear and sterically hindered angular spirodiamines in salt and free-base form are coupled with electron-rich and -withdrawing aryl chlorides, demonstrating a broad scope and applicability of this protocol.