Novel 3-chloro-6-nitro-1H-indazole derivatives as promising antileishmanial candidates: synthesis, biological activity, and molecular modelling studies.

An efficient pathway was disclosed for the synthesis of 3-chloro-6-nitro-1H-indazole derivatives by 1,3-dipolar cycloaddition on dipolarophile compounds 2 and 3. Faced the problem of separation of two regioisomers, a click chemistry method has allowed us to obtain regioisomers of triazole-1,4 with good yields from 82 to 90% were employed. Also, the antileishmanial biological potency of the compounds was achieved using an MTT assay that reported compound 13 as a promising growth inhibitor of Leishmania major. Molecular docking demonstrated highly stable binding with the Leishmania trypanothione reductase enzyme and produced a network of hydrophobic and hydrophilic interactions. Molecular dynamics simulations were performed for TryR-13 complex to understand its structural and intermolecular affinity stability in a biological environment. The studied complex remained in good equilibrium with a structure deviation of ∼1-3 Å. MM/GBSA binding free energies illustrated the high stability of TryR-13 complex. The studied compounds are promising leads for structural optimisation to enhance the antileishmanial activity.

1-Allyl-6-nitro-1H-indazole.

The fused five- and six-membered rings in the title mol-ecule, C10H9N3O2, are essentially coplanar, the largest deviation from the mean plane being 0.012 (1) Šfor the C atom linked to the nitro group. The fused-ring system makes a dihedral angle of 11.34 (6)° with the nitro group, leading to a syn-periplanar conformation. The plane through the atoms forming the allyl group is nearly perpendicular to the indazole fused-ring system, as indicated by the dihedral angle of 73.3 (5)°. In the crystal, each mol-ecule is linked to its symmetry equivalent about the center of inversion by pairs of non-classical C-H⋯O hydrogen bonds, forming an extended tape motif parallel to the (-12-1) plane.

Crystal structure and Hirshfeld surface analysis of 5-[(5-nitro-1H-indazol-1-yl)meth-yl]-3-phenyl-4,5-di-hydro-isoxazole.

In the title compound, C17H14N4O3, the indazole unit is planar to within 0.0171 (10) Šand makes dihedral angles of 6.50 (6) and 6.79 (4)°, respectively, with the nitro and pendant phenyl groups. The conformation of the oxazole ring is best described as an envelope. In the crystal, oblique stacks along the a-axis direction are formed by π-π stacking inter-actions between the indazole unit and the pendant phenyl rings of adjacent mol-ecules. The stacks are linked into pairs through C-H⋯O hydrogen bonds. Hirshfeld surface analysis and two-dimensional fingerprint plots indicate that the most important contributions to the crystal packing are from H⋯H (36.3%), O⋯H/H⋯O (23.4%), C⋯H/H⋯C (13.4%) and N⋯H/H⋯N (11.4%) inter-actions.

Crystal structure of triethyl 2-(5-nitro-2H-indazol-2-yl)propane-1,2,3-tri-carboxyl-ate.

In the title compound, C19H23N3O8, the 5-nitro-2H-indazol-2-yl unit is almost planar, with the maximum deviation from the mean plane being 0.024 (2) Å. The fused-ring system is nearly perpendicular to the three carboxyl-ate groups, with dihedral angles of 90.0 (3), 83.8 (1) and 80.4 (1)°. The ethyl groups attached to both ends of the propane chain are each disordered over two sets of sites, with site-occupancy ratios of 0.425 (17):0.575 (17) and 0.302 (15):0.698 (15). In the crystal, mol-ecules are linked by pairs of C-H⋯N hydrogen bonds, forming inversion dimers. The dimers are further linked by C-H⋯O hydrogen bonds, forming a three-dimensional network.