Synthesis and antibacterial activity of novel series of 2-(p-tolyloxy)-3-(5-(pyridin-4-yl)-1,3,4-oxadiazol-2-yl)quinoline

Synthesis of a Series of Novel 2-Amino-5-Substituted 1,3,4-oxadiazole and 1,3,4-thiadiazole Derivatives as Potential Anticancer, Antifungal and Antibacterial Agents

BACKGROUND

Many compounds containing a five-membered heterocyclic ring display exceptional chemical properties and versatile biological activities.

OBJECTIVE

The objective of the present study was the desire to prepare the 5-substituted 2-amino-1,3,4-oxadiazole and 2-amino-1,3,4-thiadiazole derivatives and evaluate their potential anticancer, antibacterial and antifungal activities.

METHODS

Twenty-seven derivatives were synthesized by iodine-mediated cyclization of semicarbazones or thiosemicarbazones obtained from condensation of semicarbazide or thiosemicarbazide and aldehydes. The structures were confirmed by 1H-NMR, 13C-NMR and MS spectra. The antibacterial and antifungal activities were evaluated by diffusion method and the anticancer activities were evaluated by MTT assay.

RESULTS

Twenty-seven derivatives have been synthesized in moderate to good yields. A number of derivatives exhibited potential antibacterial, antifungal and anticancer activities.

CONCLUSION

Compounds (1b, 1e and 1g) showed antibacterial activity against Streptococcus faecalis, MSSA and MRSA with MIC ranging between 4 to 64 µg/mL. Compound (2g) showed antifungal activity against Candida albicans (8 µg/mL) and Aspergillus niger (64 µg/mL). Compound (1o) exhibited high cytotoxic activity against HepG2 cell line (IC50 value 8.6 µM), which is comparable to the activity of paclitaxel, and is non-toxic on LLC-PK1 normal cell line. The structure activity relationship and molecular docking study of the synthesized compounds are also reported.

(2E)-3-(2-Chloro-7-methyl-quinolin-3-yl)-1-(6-chloro-2-methyl-4-phenyl-quinolin-3-yl)prop-2-en-1-one ethanol monosolvate

In the title ethanol solvate, C₂₉H₂₀Cl₂N₂O·C₂H₅OH, the quinolinyl residues form a dihedral angle of 46.41 (4)° with each other, and each is inclined [C_p—C—C=O and C=C—C—C_p (p = pyridyl) torsion angles = 54.8 (2) and 144.44 (19)°, respectively] with respect to the almost planar bridging prop-2-en-1-one residue [O=C—C=C torsion angle = −4.1 (3)°]. The ethanol solvent mol­ecule is disordered over two positions of equal occupancy and is located close to a centre of inversion. These mol­ecules reside in cavities defined by the organic mol­ecules, which are connected into a three-dimensional architecture by C—H⋯Cl, C—H⋯O and C—H⋯N inter­actions, as well as π–π contacts [inter-centroid distances = 3.5853 (10) and 3.8268 (11) Å], each involving pyridyl rings.

(2E)-3-(2-Chloro-8-methyl-quinolin-3-yl)-1-(2-methyl-4-phenyl-quinolin-3-yl)prop-2-en-1-one

In the title compound, C₂₉H₂₁ClN₂O, there is a twist in the bridging prop-2-en-1-one group [C=C—C=O torsion angle = 22.7 (2)°]. The quinolinyl residues form a dihedral angle of 86.92 (4)°, indicating an almost perpendicular relationship. In the crystal, supra­molecular layers in the bc plane are stabilized by C—H⋯π and π–π inter­actions [centroid–centroid distance = 3.4947 (7) Å].

(2E)-3-(6-Chloro-2-meth-oxy-quinolin-3-yl)-1-(2-methyl-4-phenyl-quinolin-3-yl)prop-2-en-1-one acetone monosolvate

In the title solvate, C29H21ClN2O2·C3H6O, a prop-2-en-1-one bridge links two quinolinyl residues; the latter are almost perpendicular [dihedral angle = 78.27 (6)°]. The dihedral angle between the quinonyl ring system and its pendant phenyl group is 59.78 (8)°. A small twist in the bridging prop-2-en-1-one group is noted [O=C-C=C torsion angle = -10.6 (3)°]. In the crystal, a three-dimensional architecture arises as a result of C-H⋯O and π-π stacking [centroid-centroid distances = 3.5504 (12)-3.6623 (12) Å].

(2E)-3-(6-Chloro-2-meth-oxy-quinolin-3-yl)-1-(2,4-di-methyl-quinolin-3-yl)prop-2-en-1-one

The mol­ecule of the title compound, C₂₄H₁₉ClN₂O₂, is bent, with the dihedral angle between the terminal quinoline ring systems being 63.30 (5)°. The quinolinyl residues are connected by an almost planar prop-2-en-1-one bridge (r.m.s. deviation = 0.022 Å), with the dihedral angles between this plane and the appended quinolinyl residues being 75.86 (7) and 38.54 (7)°. The C atom of the meth­oxy group is close to coplanar with its attached ring [deviation = 0.116 (2) Å]. In the crystal, a three-dimensional architecture is constructed by meth­yl–carbonyl C—H⋯O inter­actions and π–π inter­actions between centrosymmetrically related quinolinyl residues [centroid-to-centroid separations 3.5341 (10) and 3.8719 (9) Å].

I2-mediated oxidative C-O bond formation for the synthesis of 1,3,4-oxadiazoles from aldehydes and hydrazides

A practical and transition-metal-free oxidative cyclization of acylhydrazones into 1,3,4-oxadiazoles has been developed by employing stoichiometric molecular iodine in the presence of potassium carbonate. The conditions of this cyclization reaction also work well with crude acylhydrazone substrates obtained from the condensation of aldehydes and hydrazides. A series of symmetrical and asymmetrical 2,5-disubstituted (aryl, alkyl, and/or vinyl) 1,3,4-oxadiazoles can be conveniently generated in an efficient and scalable fashion.

3-Acetyl-2,4-dimethylquinolin-1-ium chloride

In the title salt, C₁₃H₁₄NO⁺·Cl⁻, the dihedral angle between the fused ring system (r.m.s. deviation = 0.039 Å) and the attached aldehyde group is 75.27 (16)°. In the crystal, the cation and anion are linked by an N—H⋯Cl hydrogen bond and the resulting pairs are connected into four-ion aggregates by π–π inter­actions between the C₆ and pyridinium rings [3.6450 (9) Å] of inversion-related quinolinium residues.