Insights on the Chemical Behavior of Ethyl Cyanoformate: Dipolarophile, Cyano or Ethoxycarbonyl Source

Imidazo[1,2-a]pyridines (azaindolizines) 1a-k have been designed and easily synthesized by the [3 + 2] cycloaddition reaction between cycloimmonium salts and ethyl cyanoformate used as dipolarophile. The behavior of the latter in cycloaddition reactions has been studied using different pyridinium, (iso)quinolinium or benzimidazolium salts and demonstrated the substrate-dependent reactivity, and the observation in many cases of its reaction as a cyano or an ethoxycarbonyl donor reagent. New chemical platforms have been identified thanks to the different reactivity of ethyl cyanoformate. Final molecules were subjected to a biological evaluation on ESKAPE pathogens (five bacteria: Escherichia coli, Klebsiella pneumoniae (MDR), Acinetobacter baumannii, Pseudomonas aeruginosa, Staphylococcus aureus (MRSA) and two fungi: Cryptococcus neoformans (H99) and Candida albicans). Azaindolizines 1b and 1e displayed antifungal activity on Candida albicans and ylide 11 inhibited both fungi Candida albicans and Cryptococcus neoformans. These results open the way for the development of analogues with improved antifungal activity.