Vinayak S. Hegde

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.

Intramolecular Amidation: Synthesis of Novel Thiazole‐Fused Diazepinones

Abstract A new class of thiazole‐fused diazepinones has been synthesized by the application of intramolecular hydrazonolysis, wherein 2‐arylamino‐4‐coumarinyl‐5‐formyl thiazoles were treated with hydrazine hydrate in refluxing ethanol to yield the rearranged products via an interesting ring‐opening and cyclization process.

Novel Pyridazine Fused Heterocyclic System: A New Route for the Synthesis of 2‐Alkyl/Aryl[1,3,4]Thiadiazole[2′,3′:2,3] Imidazo[4,5‐d]Pyridazin‐8(7H)‐One

Abstract A series of novel imidazo[2,1‐b][1,3,4]thiadiazole fused pyridazinones have been synthesized in moderate yields by the reaction of 2‐alkyl/arylimidazo[2,1‐b] [1,3,4]thiadiazole‐6‐carbohydrazides under Vilsmeier–Haack reaction conditions. This simple methodology has utility for the synthesis of various fused heterocyclic systems.

Junjappa–Ila (JI) Heteroaromatic Annulation: A New General α‐Oxoketene Dithioacetals Mediated Inverse Method for Synthesis of Substituted Benzothiazoles

Abstract 3‐(Methylthio)‐5‐oxo‐2‐(2‐phenyl‐1,3‐thiazol‐4‐yl)‐4,5‐substituted‐pent‐2‐enenitriles 3a–j were obtained in good yields by condensation of (2‐phenyl‐1,3‐thiazol‐4‐yl)‐acetonitrile (1) with various α‐oxoketene dithioacetals 2a–j in the presence of sodium hydride. The intermediates 3a–j underwent smooth cyclization in the presence of PTSA to afford the corresponding benzothiazoles 4a–j in moderate yields.

Heterocycles derived from dimethyldithioimidocarbonates of thiadiazole and thiazole

A set of imidazolidine, benzimidazole, benzothiazole and benzoxazole derivatives of 1,3,4-thiadiazoles and thiazoles were prepared from corresponding dimethyldithioimidocarbonates by the reaction with various binucleophiles. The structures of the compounds were elucidated and they were screened for 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.

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.

Chemoselectivity of thiophene dicarboxylate towards hydrazine hydrate: Synthesis of some new bis heterocycles from thiophene monocarbohydrazide

Chemoselectivity of C5-carbethoxy function over that of C3-carbethoxy function of the thiophene dicarboxylate towards the nucleophilic attack of hydrazine hydrate has been evidenced by exclusive formation of monocarbohydrazide i.e. ethyl 2-amino-5-(hydrazinocarbonyl)-4-methylthiophene-3-carboxylate and this monocarbohydrazide was reacted separately with acetylacetone, cyanogen bromide, acetonylacetone and CS2 in ethanolic potassium hydroxide solution to furnish corresponding derivatives of 3,5-dimethylpyrazole, 5-aminooxadiazole, 2,5-dimethylpyrrole and 5-thiooxadiazole respectively. Thiophene monocarbohydrazide was converted to hydrazone derivatives by reacting with p-chlorobenzaldehyde and isatin. The monocarbohydrazide was also converted to thiosemicarbohydrazide derivatives, which was then cyclised with POCl3 to afford corresponding thiadiazole derivatives. The structures of all the newly synthesized compounds were elucidated on the basis of their spectral and analytical data and the compounds were screened for their antituberculosis, antibacterial and antifungal activities.

Synthesis of Ethyl 8‐Aryl‐8‐hydroxy‐3‐oxo‐8H[1,2,4]oxadiazolo‐[3,4‐c][1,4]thiazine‐5‐carboxylates by Ring‐Expansion Rearrangement

Abstract The title compounds were prepared by the ring–ring interconversion of ethyl 5‐nitroso‐6‐arylimidazo[2,1‐b]thiazole‐3‐carboxylates with hydrochloric acid. The effect of electron‐withdrawing substituent in the thiazole ring on the general applicability of the ring–ring interconversion has been also evaluated.