Schiff bases of indoline-2,3-dione (isatin) derivatives and nalidixic acid carbohydrazide, synthesis, antitubercular activity and pharmacophoric model building.

Tuberculosis (TB) remains among the world's great public health challenges. Worldwide resurgence of TB is due to two major problems: the AIDS epidemic, which started in the mid-1980s, and the outbreak of multidrug resistant (MDR) TB. Thus, there is an urgent need for anti-TB drugs with enhanced activity against MDR strains. In recent years, Schiff bases of 1H-indole-2,3-diones are reported to exhibit anti-TB activity. On the other hand, several quinolone antibacterial agents have been examined as inhibitors of TB, as well as other mycobacterial infections. Accordingly, the current work involved design and synthesis of Schiff bases of nalidixic acid carbohydrazide and isatin derivatives (5,6a-f and 7,8a-c). Structures of the synthesized derivatives were confirmed on the bases of spectral methods of analyses. Anti-TB activity of the synthesized derivatives was investigated against four Mycobacterium strains: Mycobacterium intercellulari, Mycobacterium xenopi, Mycobacterium cheleneo and Mycobacterium smegmatis. Modest anti-TB activity was observed within the investigated compounds, however, compound 5f revealed potent anti-TB activity with MIC 0.625 microg/ml, which is 20 times greater than the reference drug isoniazid, INH, (MIC = 12.5 microg/ml). A hypothetical pharmacophore model was built using Molecular Operating Environment (MOE) program and 10 compounds structurally related to the synthesized ones with reported anti-TB activity. The Pharmacophoric model built revealed the necessity of the following pharmacophoric features for anti-TB activity: aromatic center, hydrogen bond acceptor/metal ligator center, hydrogen bond donor center and aromatic center/hydrophobic area. Theses features were consistent with the found anti-TB activity of the tested compounds.