5-bromopyridine-2,3-diamine reacted with benzaldehyde to afford the corresponding 6-Bromo-2-phenyl-3H-imidazo[4,5-b]pyridine (1). The reaction of the latter compound (1) with a series of halogenated derivatives under conditions of phase transfer catalysis solid–liquid (CTP) allows the isolation of the expected regioisomers compounds (2–8). The alkylation reaction of (1) gives, each time, two regioisomers, N3 and N4; in the case of ethyl bromoactate, the reaction gives, at the same time, the three N1, N3 and N4 regioisomers. The structures of synthesized compounds were elucidated on the basis of different spectral data (1H NMR, 13C NMR), X-Ray diffraction and theoretical study using the DFT method, and confirmed for each compound. Hirshfeld surface analysis was used to determine the intermolecular interactions responsible for the stabilization of the molecule. Density functional theory was used to optimize the compounds, and the HOMO-LUMO energy gap was calculated, which was used to examine the inter/intra molecular charge transfer. The molecular electrostatic potential map was calculated to investigate the reactive sites that were present in the molecule. In order to determine the potential mode of interactions with DHFR active sites, the three N1, N3 and N4 regioisomers were further subjected to molecular docking study. The results confirmed that these analogs adopted numerous important interactions, with the amino acid of the enzyme being targeted. Thus, the most docking efficient molecules, 2 and 4, were tested in vitro for their antibacterial activity against Gram-positive bacteria (Bacillus cereus) and Gram-negative bacteria (Escherichia coli). Gram-positive bacteria were more sensitive to the action of these compounds compared to the Gram-negative, which were much more resistant.

In the title compound, C16H14BrN3O2, the fused-ring system is essentially planar, with the largest deviation from the mean plane being 0.0216 (15) Å for the substituted N atom of the five-membered ring, the plane of which makes dihedral angles of 28.50 (7) and 77.48 (7)° with the terminal phenyl ring and the ethoxycarbonylmethyl group mean planes, respectively. In the crystal, C—H...N hydrogen bonds link the molecules into inversion dimers. These combine with weak C—H...N contacts to stack the molecules into columns along theb-axis direction.

The title imidazo [4,5-b] pyridine derivative, C 16 H 14 BrN 3 O 2 , crystallizes with two independent molecules (1 and 2) in the asymmetric unit. In molecule 1, the pendant phenyl ring is inclined to the imidazo [4,5-b]pyridine core by 43.10 (4) while in molecule 2 the corresponding angle is 49.43 (4) . The two molecules differ primarily in the conformations of the ester substituents. In the crystal, molecules are linked via C-HÁ Á ÁN and C-HÁ Á ÁO hydrogen bonds, forming sheets parallel to the ab plane. Structure descriptionImidazo [4,5-b]pyridines are an important class of heterocyclic rings, considered as analogue of purine, widely studied owing to their broad biological activities. For example, they are known for their anticancer activity (Dash et al., 2008) and antibacterial (Capelli et al., 2006), antimitotic (Temple, 1990) and tuberculostatic (Bukowski & Janowiec, 1989) properties. In a previous study, we reported the synthesis of ethyl 2-(6-bromo-2-phenyl-1H-imidazo[4,5-b]-pyridin-1-yl)acetate (Hjouji et al., 2016). The present study is extended to the synthesis of the ethyl 2-(6-bromo-2-phenyl-3H-imidazo [4,5-b]pyridin-3-yl)acetate regioisomer, by the action of ethyl 2-bromoacetate on 6-bromo-2-phenyl-3H-imidazo [4,5-b]pyridine under the same conditions.The asymmetric unit of the title compound, contains two independent molecules (1 and 2), which differ primarily in the conformations of the ester substituents ( Figs. 1 and 2). The bicyclic imidazo [4,5-b]pyridine core of molecule 1 is planar to within 0.012 (1) Å , while that in molecule 2 is planar to within 0.020 (1) Å . In molecule 1, the pendant phenyl

In the title compound, C15H20BrN3O2, the butyl substituents are in extended conformations on opposite sides of the bicyclic core. In the crystal, oblique stacks of molecules, formed by offset π-stacking interactions between pyridine and pyrazine rings in adjacent molecules, extend along the b-axis direction. The stacks are associated through a combination of C—H...O hydrogen bonds and C—Br...π(ring) interactions.