Synthesis of 2-organylchalcogenopheno[2,3-b]pyridines from elemental chalcogen and NaBH4/PEG-400 as reducing system: antioxidant and antinociceptive properties.

An alternative method to prepare 2-organylchalcogenopheno[2,3-b]pyridines was developed by the insertion of chalcogen species (selenium, sulfur or tellurium), generated in situ, into 2-chloro-3-(organylethynyl)pyridines using the NaBH4/PEG-400 reducing system, followed by an intramolecular cyclization reaction. It was possible to obtain a series of compounds with up to 93% yields in short reaction times. Among the synthesized products, 2-organyltelluropheno[2,3-b]pyridines have not been described in the literature so far. Moreover, the compounds 3b and 3c exhibited significant antioxidant potential in different in vitro assays. Further studies demonstrated that the compound 3b exerted antinociceptive effect in acute inflammatory and non-inflammatory pain models, indicating the involvement of the central and peripheral nervous system on its pharmacological action. More specifically, our results suggest that the intrinsic antioxidant property of the compound 3b may contribute to attenuate the nociception and the inflammatory process on the local injury induced by CFA.