Recent advances in the synthesis of new benzothiazole based anti-tubercular compounds

This review highlights the recent synthetic developments of benzothiazole based anti-tubercular compounds and their in vitro and in vivo activity. The inhibitory concentrations of the newly synthesized molecules were compared with the standard reference drugs. The better inhibition potency was found in new benzothiazole derivatives against M. tuberculosis. Synthesis of benzothiazole derivatives was achieved through various synthetic pathways including diazo-coupling, Knoevenagel condensation, Biginelli reaction, molecular hybridization techniques, microwave irradiation, one-pot multicomponent reactions etc. Other than recent synthetic developments, mechanism of resistance of anti-TB drugs is also incorporated in this review. Structure activity relationships of the new benzothiazole derivatives along with the molecular docking studies of selected compounds have been discussed against the target DprE1 in search of a potent inhibitor with enhanced anti-tubercular activity.

4-Aryl-1,4-Dihydropyridines as Potential Enoyl-Acyl Carrier Protein Reductase Inhibitors: Antitubercular Activity and Molecular Docking Study

BACKGROUND

Tuberculosis remains one of the most deadly infectious diseases worldwide due to the emergence of multi-drug resistance (MDR) and extensively drug resistance (XDR) strains of Mycobacterium tuberculosis (MTB).

AIMS

Currently, available drugs are getting resistant and toxic. Hence, there is an urgent need for the development of potent molecules to treat tuberculosis.

MATERIALS AND METHODS

Herein, the screening of a total of eight symmetrical 1,4-dihydropyridine (1,4- DHP) derivatives (4a-4h) was carried out for whole-cell anti-TB activity against the susceptible H37Rv and MDR strains of MTB.

RESULTS AND DISCUSSION

Most of the compounds exhibited moderate to excellent activity against the susceptible H37Rv. Moreover, the most promising compound 4f (against H37Rv) having paratrifluoromethyl phenyl group at 4-position and bis para-methoxy benzyl ester group at 3- and 5- positions of 1,4-dihydropyridine pharmacophore, exhibited no toxicity, but demonstrated weak activity against MTB strains resistant to isoniazid and rifampicin. In light of the inhibitory profile of the title compounds, enoyl-acyl carrier protein reductase (InhA) appeared to be the appropriate molecular target. A docking study of these derivatives against InhA receptor revealed favorable binding interactions. Further, in silico predicted ADME properties of these compounds 4a-4h were found to be in the acceptable ranges, including satisfactory Lipinski's rule of five, thereby indicating their potential as drug-like molecules.

CONCLUSION

In particular, the 1,4-DHP derivative 4f can be considered an attractive lead molecule for further exploration and development of more potent anti-TB agents as InhA inhibitors.

Crystallography, Molecular Modeling, and COX-2 Inhibition Studies on Indolizine Derivatives

The cyclooxygenase-2 (COX-2) enzyme is an important target for drug discovery and development of novel anti-inflammatory agents. Selective COX-2 inhibitors have the advantage of reduced side-effects, which result from COX-1 inhibition that is usually observed with nonselective COX inhibitors. In this study, the design and synthesis of a new series of 7-methoxy indolizines as bioisostere indomethacin analogues (5a-e) were carried out and evaluated for COX-2 enzyme inhibition. All the compounds showed activity in micromolar ranges, and the compound diethyl 3-(4-cyanobenzoyl)-7-methoxyindolizine-1,2-dicarboxylate (5a) emerged as a promising COX-2 inhibitor with an IC₅₀ of 5.84 µM, as compared to indomethacin (IC₅₀ = 6.84 µM). The molecular modeling study of indolizines indicated that hydrophobic interactions were the major contribution to COX-2 inhibition. The title compound diethyl 3-(4-bromobenzoyl)-7-methoxyindolizine-1,2-dicarboxylate (5c) was subjected for single-crystal X-ray studies, Hirshfeld surface analysis, and energy framework calculations. The X-ray diffraction analysis showed that the molecule (5c) crystallizes in the monoclinic crystal system with space group P 2₁/n with a = 12.0497(6)Å, b = 17.8324(10)Å, c = 19.6052(11)Å, α = 90.000°, β = 100.372(1)°, γ = 90.000°, and V = 4143.8(4)ų. In addition, with the help of Crystal Explorer software program using the B3LYP/6-31G(d, p) basis set, the theoretical calculation of the interaction and graphical representation of energy value was measured in the form of the energy framework in terms of coulombic, dispersion, and total energy.

In silico Design and Synthesis of Tetrahydropyrimidinones and Tetrahydropyrimidinethiones as Potential Thymidylate Kinase Inhibitors Exerting Anti-TB Activity Against Mycobacterium tuberculosis

Background and Purpose

Tuberculosis has been reported to be the worldwide leading cause of death resulting from a sole infectious agent. The emergence of multidrug-resistant tuberculosis and extensively drug-resistant tuberculosis has made the battle against the infection more difficult since most currently available therapeutic options are ineffective against these resistant strains. Therefore, novel molecules need to be developed to effectively treat tuberculosis disease. Preliminary docking studies revealed that tetrahydropyrimidinone derivatives have favorable interactions with the thymidylate kinase receptor. In the present investigation, we report the synthesis and the mycobacterial activity of several pyrimidinones and pyrimidinethiones as potential thymidylate kinase inhibitors.

Methods

The title compounds (1a-d) and (2a-b) were synthesized by a one-pot three-component Biginelli reaction. They were subsequently characterized and used for whole-cell anti-TB screening against H37Rv and multidrug-resistant (MDR) strains of Mycobacterium tuberculosis (MTB) by the resazurin microplate assay (REMA) plate method. Molecular modeling was conducted using the Accelry's Discovery Studio 4.0 client program to explain the observed bioactivity of the compounds. The pharmacokinetic properties of the synthesized compounds were predicted and analyzed.

Results

Of the compounds tested for anti-TB activity, pyrimidinone 1a and pyrimidinethione 2a displayed moderate activity against susceptible MTB H37Rv strains at 16 and 32 µg/mL, respectively. Only compound 2a was observed to exert modest activity at 128 µg/mL against MTB strains with cross-resistance to rifampicin and isoniazid. The presence of the trifluoromethyl group was essential to retain the inhibitory activity of compounds 1a and 2a. Molecular modeling studies of these compounds against thymidylate kinase targets demonstrated a positive correlation between the bioactivity and structure of the compounds. The in-silico ADME (absorption, distribution, metabolism, and excretion) prediction indicated favorable pharmacokinetic and drug-like properties for most compounds.

Conclusion

Pyrimidinone 1a and pyrimidinethione 2a were identified as the leading compounds and can serve as a starting point to develop novel anti-TB therapeutic agents.

Structural studies on dihydropyrimidine derivatives as Mycobacterium tuberculosis coenzyme-A carboxylase inhibitors

A dihydropyrimidine (DHPM) derivative was synthesized, characterized by X-ray diffraction and searched in silico for its inhibitory activities against AccD5 enzyme, the CT domain of a Mycobacterium tuberculosis ACCase. Its molecular structure was compared to another DHPM derivative (DHPM II). The results have shown that the (±)2,6-methano-4-thioxo-3,4,5,6-tetrahydro-2H-[1,3,5] benzoxadiazocines (DHPM I) and (±)2,6-methano-4-oxo-3,4,5,6-tetrahydro-2H-[1,3,5] benzoxadiazocines (DHPM II) belong to the monoclinic and triclinic systems, respectively, and their crystal structures are stabilized by N–H⋯O, O–H⋯O and N–H⋯S interactions. The DHPM derivatives established hydrogen bond interactions with the oxyanion-stabilizing residues (Gly-434/Ala-435) beyond the Thr-217, Phe-394 and Ile-216 in the biotin pocket. The predicted MoB of the DHPM derivatives (21R, 24S, 22R) configuration showed that its phenyl moiety was positioned on the interface between the biotin and propionyl-CoA pockets, suggesting a possible blockade of both subsites. Additionally, the hydrogen bonds involving the O-bridged phenyl ring of the DHPM derivatives (21S, 24R, 22S) configuration with Gly434 in the oxyanion-stabilizing region placed its phenyl moiety in the bottom of the biotin pocket establishing hydrophobic interactions with Leu164, Tyr167, Val459 and Ala155. These results indicate the DHPM derivatives as potential AccD5 inhibitors and promising starting points for future optimizations. Although the overlap of DHPM I and DHPM II did not present significant differences, the exchange of a sulfur atom for an oxygen atom increased the predicted biological potential.

Conformation and Visual Distinction between Urea and Thiourea Derivatives by an Acetate Ion and a Hexafluorosilicate Cocrystal of the Urea Derivative in the Detection of Water in Dimethylsulfoxide

Structures of different solvates and solute-solvent interactions of 4-(3-(4-nitrophenyl)urido)benzoate (L ₁ ) and methyl-4-(3-(4-nitrophenyl)thiourido)benzoate (L ₂ ) with different solvents are analyzed. The solution of L ₁ with tetrabutylammonium acetate (TBAA) in dimethylsulfoxide (DMSO) is colorless, but a similar solution of L ₂ with TBAA is orange. On the other hand, respective solutions of these urea and thiourea derivatives with tetrabutylammonium fluoride (TBAF) in DMSO are orange. Urea derivative L ₁ facilitates the reaction of TBAF with glass to form tetrabutylammonium hexafluorosilicate, which on further interaction with L ₁ forms cocrystal 2L ₁ ·(TBA)₂SiF₆. Reorganization of hydrogen-bonded self-assembly of 2L ₁ ·(TBA)₂SiF₆ in DMSO caused by water is established by a dynamic light scattering study. With an increase in the amount of water in the solution, visual color changes from orange to colorless, and the color changes are reversed upon the addition of a dehydrating agent such as molecular sieves. Solvates of L ₁ with DMSO, dimethylformamide (DMF), and dimethylacetamide are quasi-isostructural. The respective self-assembly of these solvates differs due to orientations of aromatic rings and the carbomethoxy group across the thioamide/amide bond. Significant differences in self-assemblies of the respective DMSO solvate of L ₁ and L ₂ are observed; self-assembly of the former has dimeric subassemblies as repeat units, whereas the latter has monomeric subassemblies. DMF solvates of L ₁ and dimethylacetamide of L ₁ are built by dimeric subassemblies to form self-assembled structures, but these subassemblies differ in the orientation of the carbomethoxy group across the urea units.

Greener synthesis of indolizine analogues using water as a base and solvent: study for larvicidal activity against Anopheles arabiensis

Greener synthesis of a series of novel indolizine analogues have been achieved by the cyclization of aromatic cycloimmonium ylides with electron-deficient alkynes in the presence of water as the base and solvent at 80 °C. Yield of the title compounds was good and reactions performed were eco-friendly. The structures of these newly synthesized compounds have been confirmed by spectroscopic techniques such as FTIR, NMR, LC-MS, and elemental analysis. Characterized title compounds were evaluated for larvicidal activity against Anopheles arabiensis by standard WHO larvicidal assay using Temefos as standard at 4 μg/mL. Title compounds 2e, 2f, and 2g emerged as promising larvicidal agents.

Crystal structure of methyl 4-(4-hy-droxy-phen-yl)-6-methyl-2-oxo-1,2,3,4-tetra-hydro-pyrimidine-5-carboxyl-ate monohydrate

The title hydrate, C13H14N2O4·H2O, crystallizes with two formula units in the asymmetric unit (Z' = 2). The dihedral angles between the planes of the tetra-hydro-pyrimidine ring and the 4-hy-droxy-phenyl ring and ester group are 86.78 (4) and 6.81 (6)°, respectively, for one mol-ecule and 89.35 (4) and 3.02 (4)° for the other. In the crystal, the organic mol-ecules form a dimer, linked by a pair of N-H⋯O hydrogen bonds. The hydroxy groups of the organic mol-ecules donate O-H⋯O hydrogen bonds to water mol-ecules. Further, the hy-droxy group accepts N-H⋯O hydrogen bonds from amides whereas the water mol-ecules donate O-H⋯O hydrogen bonds to the both the amide and ester carbonyl groups. Other weak inter-actions, including C-H⋯O, C-H⋯π and π-π, further consolidate the packing, generating a three-dimensional network.

Hydrogen bonding-induced conformational change in a crystalline sugar derivative

We report crystallographic evidence of the change of a regular chair conformation to a skew boat conformation in a partially protected sugar derivative.

Crystal structure of 2-(4-chloro-3-fluoro-phen-yl)-1H-benzimidazole

In the title compound, C13H8ClFN2, the dihedral angle between the plane of the benzimidazole ring system (r.m.s. deviation = 0.022 Å) and the benzene ring is 26.90 (8)°. The F atom at the meta position of the benzene ring is disordered over two sites in a 0.843 (4):0.157 (4) ratio. In the crystal, mol-ecules are linked by N-H⋯N hydrogen bonds, forming infinite C(4) chains propagating along [010]. In addition, weak C-H⋯π and π-π inter-actions [shortest centroid-centroid separation = 3.6838 (12) Å] are observed, which link the chains into a three-dimensional network.

Methyl 4-(4-chloro-phen-yl)-8-iodo-2-methyl-6-oxo-1,6-dihydro-4H-pyrimido[2,1-b]quinazoline-3-carboxyl-ate

In the title compound, C20H15ClIN3O3, the dihedral angle between the quinazolinone ring system [r.m.s. deviation = 0.047 (2) Å] and the pendant benzene ring is 82.63 (11)°. The mol-ecular conformation is stabilized by intra-molecular C-H⋯O inter-actions. In the crystal, the mol-ecules are linked by N-H⋯O hydrogen bonds into chains along the a-axis direction. Another set of chains propagating along [101] is formed due to inter-molecular I⋯Cl short contacts of 3.427 (1) Å, thus giving layers parallel to (010). The layers are connected by C-H⋯π and π-π inter-actions, the shortest distance between the centroids of aromatic rings being 3.8143 (16) Å.

Methyl (E)-2-[(3-chloro-4-cyano-phenyl)-imino]-4-(4-chloro-phen-yl)-6-methyl-1,2,3,4-tetra-hydro-pyrimidine-5-carboxyl-ate

In the title compound, C₂₀H₁₆Cl₂N₄O₂, the dihedral angles between the planes of the chloro­phenyl, chloro­cyano­phenyl­imine and ester groups and the plane of the six-membered tetra­hydro­pyrimidine ring are 86.9 (2), 72.6 (2) and 7.9 (2)°, respectively. The Cl atom substituent on the cyano­phenyl ring is disordered over two rotationally related sites [occupancy factors 0.887 (2):0.113 (2)], while the mol­ecular conformation is stabilized by the presence of an intra­molecular aromatic C—H⋯π inter­action. Both N—H groups participate in separate inter­molecular hydrogen-bonding associations with centrosymmetric cyclic motifs [graph sets R₂²(8) and R₂²(12)], resulting in ribbons parallel to [010]. Further weak C—H⋯O hydrogen bonds link these ribbons into a two-dimensional mol­ecular assembly.

Methyl 2,6-diphenyl-1-p-tolyl-4-(p-tolylamino)-1,2,5,6-tetrahydropyridine-3-carboxylate

In the title compound, C₃₃H₃₂N₂O₂, the tetra­hydro­pyridine ring adopts a boat conformation with the carbonyl group in an s-cis conformation with respect to the C=C bond of the six-membered tetra­hydro­pyridine ring. The mol­ecular conformation is stabilized by intra­molecular N—H⋯O, C—H⋯O and C—H⋯π inter­actions. Formation of centrosymmetric head-to-head dimers is observed through pairwise inter­molecular N—H⋯O hydrogen bonds. Additional weak C—H⋯O and C—H⋯π inter­actions stabilize the three-dimensional mol­ecular assembly.