Role of Microwaves in the Synthesis of Fused Five-Membered Heterocycles with Three N-Heteroatoms

The development of new strategies for the synthesis of small-sized heterocycles has remained a highly attractive but challenging proposition. An overview of the application of microwave irradiation in three nitrogen atoms containing fused five-membered heterocyclic compounds synthesis is presented, focusing on the developments in the past 5–10 years. This contribution covers the literature concerning the total synthesis of N,N,N-heterocycles. The literature data are summarized based on the type of cycles.

A series of novel 7-amino-5-oxo-2-substituted-aryl/hetero-aryl-5,8-dihydro[1,2,4]triazolo[1,5-a]pyridine-6-carbonitriles (4a-4t) was synthesized, characterized and evaluated for their binding affinity and selectivity towards hA1 , hA2A , hA2B and hA3 adenosine receptors (ARs). Compound 4a with a phenyl ring at 2-position of the triazolo moiety of the scaffold showed high affinity and selectivity for hA1 AR (Ki hA1  = 0.076 μM, hA2A  = 25.6 μM and hA3  > 100 μM). Introduction of various electron donating and withdrawing groups at different positions of the phenyl ring resulted in drastic reduction in affinity and selectivity towards all the ARs, except compound 4b with a 4-hydroxyphenyl group at 2-position. Interestingly, the replacement of the phenyl ring with a smaller heterocyclic thiophene ring (π excessive system) resulted in further improvement of affinity for hA1 AR of compound 4t (Ki hA1  = 0.051 μM, hA2A  = 9.01 μM and hA3  > 13.9 μM) while retaining the significant selectivity against all other AR subtypes similar to compound 4a. The encouraging results for compounds 4a and 4t indicate that substitution at 2-position of the scaffold with π-excessive systems other than thiophene may lead to even more potent and selective hA1 AR antagonists.

7‐Amino‐2‐aryl/hetero‐aryl‐5‐oxo‐5,8‐dihydro[1,2,4]triazolo[1,5‐a]pyridine‐6‐carbonitriles: Synthesis and adenosine receptor binding studies

Conventional treatment of any disease can be achieved by the administration of drugs of natural and synthetic origin. The drug exhibits its pharmacological action by altering cellular signaling or the biochemical events associated with the respective target proteins such as receptors or enzymes. Functional groups/pharmacophores of the drug interact with functional groups present in the receptor’s binding site, complementarily thereby producing effective binding interactions. Key interactions that occur between the drug and the receptor will decide the potency and intrinsic activity of the drug. Major interactions observed in the drug-receptor complexes are mostly of reversible type which consist of electrostatic interactions, ion-dipole and dipole-dipole interactions, hydrogen bonding, charge-transfer interactions, hydrophobic, and Van der Waals interactions. In this chapter, we have discussed the types of receptors, theories and types of drug-receptor interactions, the role of functional groups, and stereo-chemical aspects involved between the drug and the receptor. Further, we have shed light on the development of adenosine receptor antagonists through in silico interactions as a case study.

Drug-Receptor Interactions

A Facile Microwave‐Assisted Synthesis of 8,9‐Cycloalkathieno[3,2‐e][1,2,4]triazolo[1,5‐c]pyrimidin‐5(6H)‐ones (III).

A new series of fused thieno[3,2-e][1,2,4]triazolo[1,5-c]pyrimidinones was synthesized by condensation of ethyl-3-cyano-4,5,6,7-tetrahydrobenzo[b]thiophene-2-yl carbamate with aryl acid hydrazides in quantitative yields using a facile, one-pot procedure under microwave-assisted conditions.

/pdf/a-facile-microwave-assisted-synthesis-of-8-9-cycloalkathieno-2plftji0qh.pdf

A facile microwave-assisted synthesis of 8,9-cycloalkathieno[3,2-e] [1,2,4]triazolo[1,5-c]pyrimidin-5(6H)-ones

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A facile microwave-assisted synthesis of 8,9-cycloalkathieno[3,2-e] [1,2,4]triazolo[1,5-c]pyrimidin-5(6H)-ones

A Facile Microwave‐Assisted Synthesis of 8,9‐Cycloalkathieno[3,2‐e][1,2,4]triazolo[1,5‐c]pyrimidin‐5(6H)‐ones (III).