Facile synthesis and antimycobacterial activity of isoniazid, pyrazinamide and ciprofloxacin derivatives

Abstract

Several rationally designed isoniazid (INH), pyrazinamide (PZA) and ciprofloxacin (CPF) derivatives were conveniently synthesized and evaluated in vitro against H37Rv Mycobacterium tuberculosis (M. tb) strain. CPF derivative 16 displayed a modest activity (MIC = 16 µg/ml) and was docked into the M. tb DNA gyrase. Isoniazid-pyrazinoic acid (INH-POA) hybrid 21a showed the highest potency in our study (MIC = 2 µg/ml). It also retained its high activity against the other tested M. tb drug-sensitive strain (DS) V4207 (MIC = 4 µg/ml) and demonstrated negligible cytotoxicity against Vero cells (IC₅₀ ≥ 64 µg/ml). Four tested drug-resistant (DR) M. tb strains were refractory to 21a, similar to INH, whilst being sensitive to CPF. Compound 21a was also inactive against two non-tuberculous mycobacterial (NTM) strains, suggesting its selective activity against M. tb. The noteworthy activity of 21a against DS strains and its low cytotoxicity highlight its potential to treat DS M. tb.

Keywords: ciprofloxacin; hybrid molecules; indoleamides; isoniazid; pyrazinamide; tuberculosis.

Figure 1.

Structures of INH, isonicotinyl-NAD complex, POA, PZA, and ciprofloxacin.

Figure 2.

2D representation of the putative binding interactions of ciprofloxacin (A) and compound 16 (B) with DNA

Figure 3.

Close-up view of the DNA gyrase active site (retrieved from PDB ID: 5BTC) in complex with CPF (magenta) and compound 16 (light brown, docked in silico in the active site), showing their overlay and different alignment. Green circled is the chelation/hydrogen-bonding network, designating the water/magnesium ion bridge (red/yellow spheres) coordinating the keto-acid in CPF. The putative binding profile of CPF also shows an increased support of the hydrogen-bond interactions by Ser90 and Asp94.

Scheme 1.

Synthetic pathway for compounds 10a,b. Reagents and conditions: (a) MeoH, conc. H₂SO₄, reflux, 16 h, 98%; (b) NaOH (1.1 equiv.), THF, MeoH, rt, 24h, 70%; (c) EDC.HCl, HOBt, 1-adamantanecarboxyclic acid or 9, DIPEA, DMF, 50 °C, 18h, 30-87%; (d) EDC.HCl, DMAP, 9, THF, DCM, rt, 72 h, 45%.

Scheme 2.

Synthetic pathway for compounds 13a,b. Reagents and conditions: (a) CDI, NH₂NH₂H₂O, DMF, rt, 12-16 h, 78%; (b) EDC.HCl, HOBt, 1-adamantylamine or 12, DIPEA, DMF, 50 °C, 18 h, 50-76%.

Scheme 3.

Synthetic pathway for compound 16. Reagents and conditions: (a) Di-tert-butyl dicarbonate, 2.0 M aqueous NaOH, dioxane, H₂O, rt, 48 h, 99%; (b) EDC.HCl, HOBt, 1-adamantylamine, DIPEA, DMF, 50 °C, 18 h; (c) TFA, DCM, rt, 12 h 40% (over two steps).

Scheme 4.

Synthetic pathway for compounds 18, 20 and 21a,b. Reagents and conditions: EDC.HCl, HOBt, INH, DIPEA, DMF, 50 °C, 18 h, 64%; (b) CDl, NH₂NH₂H₂O, DMF, rt, 16 h, 74%; (c) EDC.HCl, HOBt, POA, DIPEA, DMF, 50 °C, 18 h, 32%; (d) EDC.HCl, DMAP, POA, THF, DCM, rt, 72 h, 70%; (e) EDC.HCl, DMAP, INH, THF, DCM, rt, 72 h, 66%; (f) EDC.HCl, HOBt, benzohydrazide, DIPEA, DMF, 50 °C, 18 h, 41%.