Mesoionic purinone analogs IV: Synthesis and in vitro antibacterial properties of mesoionic thiazolo[3,2‐a]pyrimidin‐5,7‐diones and mesoionic 1,3,4‐thiadiazolo[3,2‐a]pyrimidin‐5,7‐diones

Derivatives of two members of a new and unusual class of heterocycles, termed mesoionic purinone analogs, were synthesized and examined for in vitro antibacterial activity. Mesoionic thiazolo[3,2‐a]pyrimidin‐5,7‐diones and mesoionic 1,3,4‐thiadiazolo[3,2‐a]pyrimidin‐5,7‐diones, which are isoconjugate with xanthine, were found to exhibit antibacterial activity against both Gram‐negative and Gram‐positive organisms. Several mesoionic 1,3,4‐thiadiazolo[3,2‐a]pyrimidin‐5,7‐diones possess significant levels of activity against Proteus vulgaris and Staphylococcus aureus.