Ravi S. Lamani

Synthesis and antimicrobial studies of novel methylene bridged benzisoxazolyl imidazo[2,1-b][1,3,4]thiadiazole derivatives.

Novel methylene bridged benzisoxazolyl imidazo[2,1-b][1,3,4]thiadiazoles (3a-f) were synthesized from benzisoxazolyl-3-acetic acid and thiosemicarbazide. Reaction of 3 with bromine in glacial acetic acid in the presence of anhydrous sodium acetate yielded the corresponding 5-bromo derivatives (4a-f). While compound 3 furnished the 5-nitroso derivatives (5a-f) on refluxing with sodium nitrite solution. Thiocyanato derivatives (6a-f) were obtained by treating the imidazothiadiazole 3 with bromine and potassium thiocyanate in glacial acetic acid at room temperature. The structures of the newly synthesized compounds were confirmed by IR, NMR, mass and elemental analysis. All the compounds were screened for their antibacterial and antifungal activities. Some of the compounds displayed very good antibacterial and antifungal activity.

Mannich bases and novel benzothiazole derivatives of imidazo[2,1-b][1,3,4]thiadiazoles and their biological evaluation

A series of 2,6-disubstituted imidazo[2,1-b][1,3,4]thiadiazoles, their new Mannich bases and novel benzothiazole derivatives were synthesized. The structures of all the synthesized compounds were established by analytical and spectral data. All the compounds were screened for their antitubercular activity against Mycobacterium tuberculosis H37Rv using the BACTEC 460 radiometric system and antibacterial activity against E. coli and B. cirrhosis, antifungal activity against A. niger and P. worthmanni. Among the tested compounds Mannich bases 3e, 3f and 4 g and 5-carbaldehyde derivative 6d have shown excellent inhibition (99, 99, 97 and 95%, respectively) against M. tuberculosis. Mannich bases in general have also shown impressive antifungal activity.

Synthesis and antimicrobial activities of some ethyl 2-arylthio-6-arylimidazo[2,1-b]thiazole-3-carboxylates and their sulfones

A series of new 2-arylthio-3-ethoxycarbonyl-6-arylimidazo[2,1-b]thiazoles (4a–4h) and 2-arenesulfonyl-3-ethoxycarbonyl-6-arylimidazo[2,1-b]thiazoles (5a–5h) have been prepared and characterized by analytical and spectral methods. The title compounds 4a–4h and 5a–5h were obtained by the reaction of 2-amino-4-ethoxycarbonyl-5-arylthiothiazoles (2a and 2b)/2-amino-4-ethoxycarbonyl-5-arenesulphonyl-thiazoles (3a and 3b) with various phenacyl bromides in anhydrous ethanol. These newly synthesized compounds (4a–4h and 5a–5h) were screened for their antibacterial activity against Gram-negative bacterium Escherichia coli, Gram-positive bacterium Staphylococcus aureus, and antifungal properties against Aspergillus niger and Candida albicans.

Synthesis and Crystal Structure of 2-(4-Fluorobenzyl)-6-Phenylimidazo[2,1-b][1,3,4]Thiadiazole-5-Carbaldehyde

The crystal and molecular structure of 2-(4-fluoro-benzyl)-6-phenyl-imidazo[2,1-b][1,3,4]thiadiazole-5-carbaldehyde is described. The compound crystallizes in the monoclinic space group P21/n with a = 7.419(3)Å, b = 8.287(3)Å, c = 25.734(10)Å, β = 91.686(8)°, V = 1,581.6(10)Å3, z = 4. The crystal structure is stabilized by intermolecular C-H…N, C-H…O, and C-H…F interactions.

Synthesis and antimicrobial activitiy of novel barbituric acid and thiohydantoin derivatives of imidazo [2, 1-b][1,3,4] thiadiazoles.

A series 5-[6-aryl-2-(4-methoxybenzyl)imidazo[2,l-b][l,3,4]thiadiazol-5-yI-methylene]-pyrimidine-2,4,6-triones (4a-f) and 5-[6-aryl-2-(4-methoxybenzyl)imidazo[2,l-b][l,3,4] thiadiazol-5-yl]methylene-2-thioxoimidazolidin-4-one (5a-f) were synthesized from 5-formyl derivatives of 2-(4-methoxybenzyl)-6-arylimidazo[2,l-b][l,3,4]thiadiazole (3a-f) by the knoevenagel condensation with barbituric acid & thiohydantoin. The required 5-formyl derivatives were prepared by the Vilsmeier Haack reaction of the corresponding 2,6-disubstituted imidazo[2,l-b][l,3,4]thiadiazoles (2a-f). The structures of ail the newly synthesized compounds were established by analytical and spectral data. The synthesized compounds were screened for their antibacterial and antifungal activities.

Dimethyldithioimidocarbonates-Mediated Heterocyclizations: Synthesis of Imidazolidines and Benzheterocycles as Potent Antitubercular Agents

A new series of thiadiazolylimidazolidines, thiadiazolylbenzimidazoles, thiadiazolylbenzoxazoles, and thiadiazolylbenzothiazoles were synthesized by heterocyclization reactions of dimethyldithioimidocarbonate of properly substituted thiadiazoles with various binucleophiles. The structures of all the newly synthesized compounds were elucidated and they were screened for antitubercular activity against Mycobacterium tuberculosis H 37 Rv using the BACTEC 460 radiometric system, where few compounds have shown more than 90% inhibition at MIC of < 6.25 μ g/mL in the preliminary screening level. They were also screened for their antibacterial activity against Escherichia coli and Bacillus cirrhosis, and antifungal activity against Aspergillus niger and Penicillium worthmanni. Some of the compounds have shown promising in vitro antibacterial and antifungal activities.

Synthesis and antimicrobial activity of novel sulfides and sulfones of methylene-bridged benzisoxazolylimidazo[2,1-b][1,3,4]thiadiazoles

GRAPHICAL ABSTRACT Abstract Novel classes of 3-(6-Aryl-5-phenylsulfanylimidazo[2,1-b][1,3,4]thiadiazol-2-yl-methyl)-benzo[d]isoxazoles (2a–f) and 3-(5-Benzenesulfonyl-6-arylimidazo[2,1-b][1,3,4] thiadiazol-2-yl-methyl)-benzo[d]isoxazoles (3a–f) have been synthesized. The sulfide derivatives (2a–f) were obtained by the nucleophilic substitution of bromo derivatives (1a–f) with thiophenols, and sulfone derivatives (3a–f) were obtained by the oxidation of 2a–f. All the newly synthesized compounds were characterized by elemental analysis, infrared, nuclear magnetic resonance, and mass spectroscopic data. Furthermore, these novel sulfide and sulfone derivatives were screened for their antibacterial and antifungal activities against various microorganisms.

3-{[6-(4-Chloro-phen-yl)imidazo[2,1-b][1,3,4]thia-diazol-2-yl]meth-yl}-1,2-benzoxazole.

In the title compound, C18H11ClN4OS, the benzisoxazole and imidazothiadiazole rings are inclined at an angle of 23.81 (7)° with respect to each other. The imidazothiadiazole and chlorophenyl rings make a dihedral angle of 27.34 (3)°. In the crystal, intermolecular C—H⋯N interactions generate a chain along the c axis and C—H⋯O interactions form centrosymmetric dimers resulting in an R 2 2(26) graph-set motif. Moreover, the C—H⋯N and S⋯N [3.206 (4) Å] interactions links the molecules into R(7) ring motifs. The packing is further stabilized by π–π stacking interactions between the thiadiazole rings with a shortest centroid–centroid distance of 3.497 (3) Å. In addition, C—H⋯π interactions are observed in the crystal structure

6-(4-Bromo­phen­yl)-2-(4-fluoro­benz­yl)imidazo[2,1-b][1,3,4]thia­diazole

In the title compound, C17H11BrFN3S, the imidazothiadiazole and bromophenyl rings are individually almost planar, with maximum deviations of 0.0215 (4) and 0.0044 (4) Å, respectively, and are inclined at an angle of 27.34 (3)° with respect to each other. The dihedral angle between the mean planes of the fluorobenzyl and imidazothiadiazole rings is 79.54 (3)°. The crystal structure is stabilized by intermolecular C—H⋯N interactions resulting in chains of molecules along the b axis.

Synthesis and Crystal Structure Analysis of 2-(Fluorobenzyl)-6-(4-Nitrophenyl) Imidazo[2,1-b][1,3,4]Thiadiazole

Preparation of 2-(4-fluorobexzyl)-6-(4-nitrophenyl)imidazo[2,1-b][1,3,4]thiadiazole is described and its crystal structure is discussed. The compound crystallizes in the monoclinic space group C2/c with a = 39.941(6) Å, b = 5.698(2) Å, c = 13.272(5) Å β = 90.880°, V = 3020(2) Å3, z = 8. The crystal structure is stabilized by weak intermolecular C-H…N,C-H…O,C-H…S, and C-H…F interactions.