Synthesis and characterization of novel conformers of (E)-2-(3-nitro-H-imidazo[1,2-a]pyridin-2-ylthio)-N′-benzylideneacetohydrazide derivatives

Eighteen new N-acylhydrazones (9a-r) containing the imidazo[1,2-a]pyridine scaffold were synthesized through a seven steps reaction sequence, ending with a condensation of 2-(3-nitro-H-imidazo[1,2-a]pyridin-2-ylthio)acetohydrazide with various benzaldehyde derivatives (8a-r). All synthesized compounds were characterized by 1D NMR (H-1 and C-13 NMR) and 2D NMR (NOESY) spectroscopic analyses and high-resolution mass spectrometry (HRMS). The analysis of H-1 NMR data performed at room temperature in deuterated dimethylsulfoxide (DMSO-d(6)) revealed the presence of (E)-2-(3-nitro-H-imidazo[1,2-a]pyridin-2-ylthio)-N '-benzylideneacetohydrazide (9a-r) as a mixture of two conformers, namely, syn-periplanar E (sp E) and anti-periplanar E (ap E). For all N-acylhydrazones that were synthesized, the sp E conformer was found to be the major form except in the case of hydrazone derived from o-hydroxybenzaldehyde.

Automated summary

Eighteen new N-acylhydrazones containing the imidazo[1,2-a]pyridine scaffold were synthesized through a seven-step reaction sequence. The synthesized compounds were characterized using NMR spectroscopy and mass spectrometry. It was found that the majority of the synthesized compounds exist in the syn-periplanar E conformer.