Synthesis of 3-Substituted Bicyclic Imidazo[1,2-d][1,2,4]thiadiazoles and Tricyclic Benzo[4,5]imidazo[1,2-d][1,2,4]thiadiazoles

Synthesis of novel series of 3,5-disubstituted imidazo[1,2-d] [1,2,4]thiadiazoles involving SNAr and Suzuki–Miyaura cross-coupling reactions

The first access to 3,5-disubstituted imidazo[1,2-d][1,2,4]thiadiazole derivatives is reported. The series were generated from 2-mercaptoimidazole, which afforded the key intermediate bearing two functional positions. The S_NAr reactivity toward tosyl release at the C-3 position was investigated and a regioselective electrophilic iodination in C-5 position was performed to allow a novel C–C bond using Suzuki–Miyaura reaction. Palladium-catalyzed cross-coupling conditions were optimized. A representative library of various boronic acids was employed to establish the scope and limitations of the method. To complete this methodological study, the influence of the nature of the C-3 imidazo[1,2-d][1,2,4]thiadiazole substitutions on the arylation in C-5 was investigated.

A convenient design of 3,5-disubstituted imidazo[1,2-d][1,2,4]thiadiazoles is reported from 2-mercaptoimidazole, which afforded a versatile platform that was then used to access a variety of original heterocycles.

Copper-Catalyzed Aerobic Oxidative [3+2] Annulation for the Synthesis of 5-Amino/Imino-Substituted 1,2,4-Thiadiazoles through C-N/N-S Bond Formation

A copper-catalyzed aerobic oxidative annulation reaction of 2-aminopyridine/amidine with isothiocyanate has been reported. This strategy involving C-N/N-S bond formations provides various 5-amino/imino-substituted 1,2,4-thiadiazole derivatives under a Cu/O₂ catalytic system. This method has demonstrated high reactivity, mild reaction conditions, and a broad substrate scope. Furthermore, the synthetic utilities of the approach are demonstrated by further modifications.

Synthesis of [1,3,4]Thiadiazolo[3',2':1,2]imidazo[4,5-c]quinolines including Pictet-Spengler Reaction and Exploration of Their C-2 Reactivity through SNAr

This work reports the design of [1,3,4]thiadiazolo[3',2':1,2]imidazo[4,5-c]quinolines using a Pictet-Spengler reaction. The scope of the reaction was achieved from 6-(2-aminophenyl)imidazo[2,1-b][1,3,4]thiadiazole derivatives and available aldehydes. A wide range of aldehydes were employed to examine the scope of the cyclization. In parallel, a mechanism investigation was realized and showed a hydride transfer which led to a dismutation of the intermediate species. To complete this methodological study, a "sequential" oxidation/S_NAr procedure was performed to achieve C-2 nucleophilic substitution using several amine types.

Hybrid molecules containing benzo[4,5]imidazo[1,2-d][1,2,4]thiadiazole and α-bromoacryloyl moieties as potent apoptosis inducers on human myeloid leukaemia cells

The synthesis and biological activity of a series of hybrids 1-5 prepared combining a benzo[4,5]imidazo[1,2-d][1,2,4]thiadiazole and different benzoheterocyclic alpha-bromoacryloyl amides have been described and their structure-activity relationships discussed. All these hetero-bifunctional compounds were highly cytotoxic against the human myeloid leukaemia cell lines HL-60 and U937 (IC(50) 0.24-1.72microM), significantly superior to that of both alkylating units alone. In human myeloid leukaemia HL-60 cells we observed that these compounds suppress survival and proliferation by triggering morphological changes and internucleosomal DNA fragmentation characteristic of apoptotic cell death. The apoptosis induced by these compounds is mediated by caspase-3 activation and is also associated to an early release of cytochrome c from the mitochondria.