Novel quinoline-piperazine hybrids: the design, synthesis and evaluation of antibacterial and antituberculosis properties.

A communicable disease such as tuberculosis (TB), which takes ∼10 million lives worldwide every year, is one of the major concerns for future generations. The intake of multiple antibiotics is increasing because of the emergence of multiple drug-resistant TB (MDR-TB) to pathogens which do not respond to the first-line TB drugs. Even though numerous drugs are available on the market, there is a huge need for MDR-TB drugs. Herein, our emphasis was to synthesise a series of 2,4,6-substituted quinoline conjugated piperazine coupled sulfonamides, as well as amides, and to study and evaluate their in vitro antibacterial activity against both susceptible and resistant pathogens of Gram-positive and Gram-negative bacteria. Furthermore, their antituberculosis activity was assessed against non-virulent, virulent and MDR pathogens. Few compounds displayed inhibitory activity against bacterial growth, but two compounds displayed significant inhibitory activity against all the TB strains (lowest MIC of 10g is 0.07 µM and 11e is 1.1 µM), which are more effective than other 1st line and 2nd line TB drugs. These two compounds are less cytotoxic, and could be developed as antibiotics or MDR-TB drugs by improving their hydrophilicity.

A multi-targeting pre-clinical candidate against drug-resistant tuberculosis.

FNDR-20081 [4-{4-[5-(4-Isopropyl-phenyl)- [1,2,4]oxadiazol-3-ylmethyl]-piperazin-1-yl}-7-pyridin-3-yl-quinoline] is a novel, first in class anti-tubercular pre-clinical candidate against sensitive and drug-resistant Mycobacterium tuberculosis (Mtb). In-vitro combination studies of FNDR-20081 with first- and second-line drugs exhibited no antagonism, suggesting its compatibility for developing new combination-regimens. FNDR-20081, which is non-toxic with no CYP3A4 liability, demonstrated exposure-dependent killing of replicating-Mtb, as well as the non-replicating-Mtb, and efficacy in a mouse model of infection. Whole genome sequencing (WGS) of FNDR-20081 resistant mutants revealed the identification of pleotropic targets: marR (Rv0678), a regulator of MmpL5, a transporter/efflux pump mechanism for drug resistance; and Rv3683, a putative metalloprotease potentially involved in peptidoglycan biosynthesis. In summary, FNDR-20081 is a promising first in class compound with the potential to form a new combination regimen for MDR-TB treatment.

Synthesis, antituberculosis studies and biological evaluation of new quinoline derivatives carrying 1,2,4-oxadiazole moiety.

Tuberculosis is the infectious disease caused by mycobacterium tuberculosis (Mtb), responsible for the utmost number of deaths annually across the world. Herein, twenty-one new substituted 1,2,4-oxadiazol-3-ylmethyl-piperazin-1-yl-quinoline derivatives were designed and synthesized through multistep synthesis followed by in vitro evaluation of their antitubercular potential against Mtb WT H37Rv. The compound QD-18 was found to be promising with MIC value of 0.5 µg/ml and QD-19 to QD-21 were also remarkable with MIC value of 0.25 µg/ml. Additionally, we have carried out experiments to confirm the metabolic stability, cytotoxicity and pharmacokinetics of these compounds along with kill kinetics of QD-18. These compounds were found to be orally bioavailable and highly effective. Altogether, these results indicate that QD-18, QD-19, QD-20 and QD-21 are promising lead compounds for the development of a novel chemical class of antitubercular drugs.

New quinoline derivatives: synthesis and investigation of antibacterial and antituberculosis properties.

Four new series of quinoline derivatives were synthesized starting from 2-trifluoromethyl aniline through multi-step reactions. In the reaction sequence, substituted aniline was cyclized to 4-hydroxy quinoline 1, which was then transformed to 4-chloro-2,8-bis(trifluoromethyl)quinoline 2. The key scaffold 4-hydrazinyl-2,8-bis(trifluoromethyl)quinoline 3, obtained from the compound 2, was successfully converted to target quinoline derivatives, viz. hydrazones 4a-t, ureas 5a-e, thioureas 6a-c and pyrazoles 7a-d, in good yields. The newly synthesized title compounds were evaluated for their in vitro antibacterial activity against Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa and Klebsiella pneumoniae (recultured) and antituberculosis activity against Mycobacterium tuberculosis H(37)Rv and MDR-TB. Preliminary results indicated that most of the hydrazone derivatives demonstrated very good antibacterial and antituberculosis activities while other derivatives showed moderate activity.

Design and synthesis of some new quinoline-3-carbohydrazone derivatives as potential antimycobacterial agents.

A series of 26 new quinoline derivatives carrying active pharmacophores has been synthesized and evaluated for their in vitro antituberculosis activity against Mycobacterium tuberculosis H37Rv (MTB), Mycobacterium smegmatis (MC(2)), and Mycobacterium fortuitum following the broth micro dilution assay method. Compounds 13e, 13i, 13k, 14a, 14c, 14i, and 14k exhibited significant minimum inhibition concentrations, when compared with first line drugs isoniazid (INH) and rifampicin (RIF) and could be ideally suited for further modifications to obtain more efficacious compounds in the fight against multi-drug resistant tuberculosis.

New 1,3-oxazolo[4,5-c]quinoline derivatives: synthesis and evaluation of antibacterial and antituberculosis properties.

A new class of fused oxazoloquinoline derivatives was synthesized starting from 2-bromo-1-phenylethanones 1a-b through multi-step reactions. The newly synthesized compounds were evaluated for their in vitro antibacterial against Escherichia coli (ATTC-25922), Staphylococcus aureus (ATTC-25923), Pseudomonas aeruginosa (ATCC-27853) and Klebsiella pneumoniae (recultured) and antituberculosis activity against Mycobacterium tuberculosis H37Rv (ATCC 27294). Preliminary results indicated that most of the compounds demonstrated very good antibacterial and antituberculosis activities which are comparable with the first line drugs. Compounds 6a, 6c, 6g, 6j, 6k and 6n emerged as the lead antitubercular agents with MIC, 1 microg/mL and 99% bacterial inhibition while eight compounds, viz., 5a, 15k, 6a, 6c, 6g, 6j, 6k and 6n were found to be more potent than INH (MIC: 1.5 microg/mL) with MIC 1 microg/mL.

Synthesis and antimicrobial activities of novel quinoline derivatives carrying 1,2,4-triazole moiety.

A new class of quinoline derivatives containing 1,2,4-triazole moiety were synthesized from derivatives of 4-hydroxy-8-(trifluoromethyl)quinoline-3-carbohydrazide 4 through multi-step reactions. The compound 4, on treatment with substituted Isothiocyanates yielded quinoline-thiosemicarbazides 5a-c, which were conveniently cyclized to (5-mercapto-4H-triazol-3-yl)-quinolin-4-ols 6a-c in basic medium. These intermediates were then transformed to their respective chloro derivatives 7a-c by treatment with phosphorus oxychloride, which on further reaction with different biologically active rare amines yielded the target compounds 8a-g, 9a-h and 10a-h in good yield. The ultimate step, involving nucleophilic substitution reaction was achieved by microwave-induced technique, which has reduced the reaction time drastically as well as improved the yield when compared to conventional heating. The newly synthesized final compounds were evaluated for their in vitro antibacterial and antifungal activities against four strains each. Preliminary results indicated that most of the compounds demonstrated very good antimicrobial activity, comparable to the first line standard drugs. The most effective compounds have exhibited activity at MIC of 6.25 microg/mL.