Design, syntheses, and anti-tuberculosis activities of conjugates of piperazino-1,3-benzothiazin-4-ones (pBTZs) with 2,7-dimethylimidazo [1,2-a]pyridine-3-carboxylic acids and 7-phenylacetyl cephalosporins

Recent developments of imidazo[1,2-a]pyridine analogues as antituberculosis agents

Over the past 2000 years, tuberculosis (TB) has killed more people than any other infectious disease. In 2021, TB claimed 1.6 million lives worldwide, making it the second leading cause of death from an infectious disease after COVID-19. Unfortunately, TB drug discovery research was neglected in the last few decades of the twentieth century. Recently, the World Health Organization has taken the initiative to develop new TB drugs. Imidazopyridine, an important fused bicyclic 5,6 heterocycle has been recognized as a "drug prejudice" scaffold for its wide range of applications in medicinal chemistry. A few examples of imidazo[1,2-a]pyridine exhibit significant activity against multidrug-resistant TB (MDR-TB) and extensively drug-resistant TB (XDR-TB). Here, we critically review anti-TB compounds of the imidazo[1,2-a]pyridine class by discussing their development based on the structure-activity relationship, mode-of-action, and various scaffold hopping strategies over the last decade, which is identified as a renaissance era of TB drug discovery research.

Bioevaluation of quinoline-4-carbonyl derivatives of piperazinyl-benzothiazinones as promising antimycobacterial agents

The quinoline moiety remains a privileged antitubercular (anti-TB) pharmacophore, whereas 8-nitrobenzothiazinones are emerging potent antimycobacterial agents with two investigational candidates in the clinical pipeline. Herein, we report the synthesis and bioevaluation of 30 piperazinyl-benzothiazinone-based quinoline hybrids as prospective anti-TB agents. Preliminary evaluation revealed 24/30 compounds exhibiting substantial activity (minimum inhibitory concentration [MIC] = 0.06-1 µg/ml) against Mycobacterium tuberculosis (Mtb) H37Rv. Cytotoxicity analysis against Vero cells found these to be devoid of any significant toxicity, with the majority displaying a selectivity index of >80. Furthermore, potent nontoxic compounds, when screened against clinical isolates of drug-resistant Mtb strains, demonstrated equipotent inhibition with MIC values of 0.03-0.25 µg/ml. A time-kill study identified a lead compound exhibiting concentration-dependent bactericidal activity, with 10× MIC completely eliminating Mtb bacilli within 7 days. Along with acceptable aqueous solubility and microsomal stability, the optimum active compounds of the series manifested all desirable traits of a promising antimycobacterial candidate.

Synthesis and evaluation of triazole congeners of nitro-benzothiazinones potentially active against drug resistant Mycobacterium tuberculosis demonstrating bactericidal efficacy

With growing concerns regarding target residue mutation hovering over established anti-TB pharmacophores, it is imperative to have reserve chemotypes at our disposal to curb unrestrained spread of tuberculosis. In this context, we herein present the synthesis and bio-evaluation of a library of new nitrobenzothiazinone (BTZ) congeners comprising 2-mercapto/amino-benzothiazinone tethered 1,2,3-triazole hybrids as antitubercular agents. In preliminary screening, 10 out of 37 compounds displayed substantial in vitro potency against Mtb H37Rv (MIC 0.5-8 μg mL^-1). Structural optimization of the initial hit 5o (MIC 0.5 μg mL^-1) led to identification of linker variants 9a, 9b, 9c, and 9d exhibiting potent anti-TB activity (MIC 0.03-0.12 μg mL^-1). When tested against Vero cells to determine their selectivity index (SI), these compounds displayed no appreciable cytotoxicity (SI >80). Further studies on activity against drug resistant (DR) Mtb indicated these compounds to be equally potent (MIC 0.03-0.25 μg mL^-1). The in silico covalent docking study suggested a similar polar interaction to that of PBTZ169 with an additional and contrasting side chain interaction at the active site of Mtb DprE1 target protein. Further, the time kill kinetic study found compounds 9a and 9d to be demonstrating bactericidal efficacy, completely eliminating bacilli in 7 days at 10× MIC. The most promising compound 9d, considering its potent anti-TB activity (MIC 0.06 μg mL^-1 against drug susceptible Mtb and MIC 0.06-0.25 μg mL^-1 against DR Mtb) along with a broad therapeutic index (SI >640) demonstrating a comparable concentration dependent bactericidal efficacy to that of RIF, holds a significant edge to be translated into a potent anti-Mtb agent.

8-cyanobenzothiazinone analogs with potent antitubercular activity

8-Nitrobenzothiazinones (BTZs) exemplified by macozinone are a new class of antitubercular agents with exceptionally potent activity. The aryl nitro group has been considered indispensable for activity since this is bioactivated within mycobacteria by the flavoenzyme DprE1 to a reactive nitroso metabolite that covalently labels Cys387. However, the aryl nitro group is a potential liability with regards to safety, stability, and resistance. In this paper, we introduced a nitrile as a bioisosteric replacement of the nitro group, which we hypothesize can maintain a similar covalent mechanism of inhibition, but mitigate against the aforementioned concerns. 8-cyanobenzothiazinone 1d displayed potent antitubercular activity with an MIC of 130 nM and had an improved volume of distribution in mice that increased the intrinsic half-life by twofold compared to macozinone. Analysis of the C-2 substituent of 1d revealed similar structure-activity relationships as observed for macozinone. Overall, the results confirm the 8-nitro group of benzothiazinones can be successfully replaced with a nitrile to retain useful activity and favorable pharmacokinetic properties.

An appraisal of anti-mycobacterial activity with structure-activity relationship of piperazine and its analogues: A review

Piperazine, is privileged six membered nitrogen containing heterocyclic ring also known as 1,4-Diazacyclohexane. Consequently, piperazine is a versatile medicinally important scaffold and is an essential core in numerous marketed drugs with diverse pharmacological activities. In recent years several potent molecules containing piperazine as an essential subunit of the structural frame have been reported, especially against Mycobacterium tuberculosis (MTB). Remarkably, a good number of these reported molecules also displayed potential activity against multidrug-resistant (MDR), and extremely drug-resistant (XDR) strains of MTB. In this review, we have made a concerted effort to retrace anti-mycobacterial compounds for the past five decades (1971-2019) specifically where piperazine has been used as a vital building block. This review will benefit medicinal chemists as it elaborates on the design, rationale and structure-activity relationship (SAR) of the reported potent piperazine based anti-TB molecules, which in turn will assist them in addressing the gaps, exploiting the reported strategies and developing safer, selective, and cost-effective anti-mycobacterial agents.

Synthesis and Biological Activity of 2-Amino- and 2-aryl (Heteryl) Substituted 1,3-Benzothiazin-4-ones

Tuberculosis (TB) takes the second place among the reasons for mortality from infectious diseases. For this reason, the problem of tuberculosis treatment requires urgent attention all over the world. Some 2-amino substituted 1,3-benzothiazin-4-ones (2-amino-1,3-BTZs) represent a promising new class of antitubercular agents. Other 1,3-benzothiazin-4-one derivatives, mostly 2-aryl and 2- (pyridin-2-yl) ones, are attractive due to their ability to suppress oxidative stress-induced cardiomyocyte apoptosis. This review covers the synthetic approaches to 2-amino- and 2-aryl(heteryl) substituted 1,3-benzothiazin-4-ones (1,3-BTZs). A brief overview of structure-activity relationships is presented.

Insights of synthetic analogues of anti-leprosy agents

Today, the emergence of the phenomenon of drug or multidrug-resistance for community-associated diseases represents a major concern in the world. In these contexts, the chronic infectious disease, leprosy, grounded by a slow-growing bacterium called Mycobacterium leprae or Mycobacterium lepromatosis is a leadingcause of severe disfiguring skin sores and nerve damage in the arms, legs, and skin areas around the body. Even, over 200,000 new leprosy cases are being accounted every year along with the relapsed leprosy cases. Nonetheless, this has been considered a curable disease with a higher dose of multidrug therapy (MDT) for a long period of time. The prolonged action of a high dose of combination drugs administration may cause an adverse reaction that can significantly affect patient compliance, particularly the outbreak of multidrug-resistance in the infected person. To overcome these shortfalls or prevent the resistance-associated problems, researchers are diligently involved in the structural modifications of the clinically used anti-leprosy drugs or the allied compounds for the structure-antimycobacterial activity relationship study. This review article described the detailed synthesis and biological assays of different anti-leprosy compounds reported by several research groups.

Quinolone-isoniazid hybrids: synthesis and preliminary in vitro cytotoxicity and anti-tuberculosis evaluation

Herein, we propose novel quinolones incorporating an INH moiety as potential drug templates against TB. The quinolone-based compounds bearing an INH moiety attached via a hydrazide-hydrazone bond were synthesised and evaluated against Mycobacterium tuberculosis H37Rv (MTB). The compounds were also evaluated for cytotoxicity against HeLa cell lines. These compounds showed significant activity (MIC₉₀) against MTB in the range of 0.2-8 μM without any cytotoxic effects. Compounds 10 (MIC₉₀; 0.9 μM), 11 (MIC₉₀; 0.2 μM), 12 (MIC₉₀; 0.8 μM) and compound 15 (MIC₉₀; 0.8 μM), the most active compounds in this series, demonstrate activities on par with INH and superior to those reported for the fluoroquinolones. The SAR analysis suggests that the nature of substituents at positions -1 and -3 of the quinolone nucleus influences anti-MTB activity. Aqueous solubility evaluation and in vitro metabolic stability of compound 12 highlights favourable drug-like properties for this compound class.