Synthesis and properties of mesoionic pyrimido[1,2‐b]pyridazine‐2,4‐diones and mesoionic pyridazino[2,3‐a]‐s‐triazine‐2,4‐diones: Mesoionic analogs structurally related to fervenulin

Derivatives of two new and unusual classes of heterocycles, possessing structural similarities to the broad spectrum antibiotic fervenulin, were synthesized and examined for in vitro antimicrobial activity. Only three of 17 mesoionic pyrimido[1,2‐b]pyridazine‐2,4‐diones exhibited evidence of antimicrobial activity while seven of eight mesoionic pyridazino[2,3‐a]‐s‐triazine‐2,4‐diones were active against one or more microorganisms. Susceptibility toward attack by nucleophiles of both mesoionic pyridazino[2,3‐a]‐s‐triazine‐2,4‐diones and fervenulin was observed.