Heteroring Annulated Benzimidazolinone Condensed Azepinone Derivatives: A New Class of Highly Potent Antioxidants

A new class of benzimidazolinone condensed azepinone derivatives annulated on its face “d” with pyrazole, isoxazole, pyrimidine, benzodiazepine, and benzothiazepine nucleus in 3–8, respectively, have been evaluated for their antioxidant activity by DPPH method. Results indicate these to belong to a novel class of highly potent antioxidant agents. 1. Introduction Azepinone template has emerged as a potent privileged structural fragment in synthesis, due to its broad pharmacological spectrum and its affinity to various biotargets [1]. On account of this feature, the combination of its nucleus with other heterocycles which have a proven record of biological potential has been a promising approach to the “drug like molecule build-up” in medicinal chemistry. Recent synthetic endeavours directed towards the development of biologically important materials have stressed the need to identify certain building block set in synthesis and to explore their potential to provide access to the library of compounds of medicinal utility. We envisioned that this concept could be applied in our synthetic work by utilizing the potential of a novel building block developed from the benzimidazolinone condensed analogue of azepinone 2 which could be realized in two simple steps from benzimidazolinone nucleus involving first its reaction with succinic anhydride followed by its cyclocondensation with acid. We utilized the inherent potential of this building block in heteroannulation of its face “d” with such heterocyclic scaffolds as pyrazole, isoxazole [1–3], pyrimidine [4], benzodiazepine [5], and benzothiazepine [6] which had the previous history of being highly biologically active in the literature. The synthesis of the heterocyclic materials 3–8 shown in Scheme 1, each having a benzimidazolinone pharmacophore fused on to one side of the azepinone framework and a wide range of biologically active heterocyclic scaffolds on to its other side, was conceived in the present work on this anticipation that their presence together, in the same molecular framework, could bring a favorable impact on to overall antioxidant activity in resulting materials. Scheme 1 As per to this expectations, compounds 1–8 responded fairly well in showing a remarkably high level of antioxidant activity. 2. Results and Discussion Results emanated from antioxidant studies of few selected compounds have been presented in Table 1. Perusal of results realized that the compounds analysed have exhibited moderate to good activity when compared with standard ascorbic acid. It has been observed that amongst the