Synthesis and characterization of fused imidazole heterocyclic selenoesters and their application for chemical detoxification of HgCl2

Abstract

A new series of selenoester derivatives of imidazo[1,2-a]pyridine and imidazo[1,2-a]pyrimidine was synthesized under mild conditions using a simple methodology by the reaction of in situ generated sodium selenocarboxylates with 2-(chloromethyl)imidazo[1,2-a]pyridine/pyrimidine (3a–b) in water and ethanol. Excellent yields of phenyl/4-tolyl selenoesters of imidazo[1,2-a]pyridine/pyrimidine (6a–b and 6e–f) were obtained in water, whereas 4-methoxyphenyl/4-chlorophenyl/2-thienyl selenoesters of imidazo[1,2-a]pyridine/pyrimidine (6c–d and 6g–i) could only be synthesized in ethanol. Further, a series of reactions was carried out with 6e as a model compound in order to study the reaction behavior of selenoesters with mercury(II) chloride (HgCl₂). The deprotection of compound 6e by HgCl₂ was carried out in the presence of K₂CO₃ under different conditions to obtain bis(imidazo[1,2-a]pyrimidin-2-ylmethyl)selenide (8) and bis(imidazo[1,2-a]pyrimidin-2-ylmethyl) diselenide (9) along with a small amount of less soluble bis((imidazo[1,2-a]pyrimidin-2-ylmethyl)selanyl)mercury (10). The mercury–selenium complex 10 has a short shelf life and decomposes to give HgSe, which was characterized using EDX analysis. The structure of compound 9 was established with X-ray crystallography. The formation of HgSe indicates that the selenoester derivatives may prove useful in the treatment of HgCl₂ induced toxicity.