Synthesis of various S-S linked symmetric bisazaheterocycles: A review

There has been an increasing interest in discovering and developing small molecules that are of pharmaceutical importance. Heterocyclic compounds are known to be the most versatile class of these types of molecules, either prepared synthetically or occurring in nature. However, in some cases, it has been reported that the activity is enhanced to a larger extent when these heterocycles are repeated in the molecule separated by a suitable spacer, i.e., a bis-heterocycle. Thus, the synthesis of new bis-heterocyclic compounds has become an eye-catchy field to explore in the recent past owing to their pharmacological, biological and industrial importance. The synthesis of bis-heterocycles is mainly achieved by joining heterocyclic nuclei together using a variety of linkers and points of linkages. These structural permutations and combinations have given an unlimited number of available bis-heterocycles. Use of S-S linkage is one such facile method of getting bis-heterocycles as they are easily obtained from the oxidation of thiols and protected thiols by using broad range of reagents and reaction conditions. Disulphide linkage being an integral part of the biological system, as disulphide bonds are found in peptides and proteins, also adds to the efficacy of these bis-heterocycles.