Mesoionic Purinone Analogs. 7. In vitro Antibacterial Activity of mesoionic 1,3,4-thiadiazolo[3,2,-a]pyrimidine-5,7-diones

The discovery of in vitro antibacterial activity of mesoionic thiazolo[3,2-a]pyrimidine-5,7-diones (1) and mesoionic 1,3,4-thiadiazolo[3,2-a]pyrimidine-5,7-diones (2) has been recently reported.¹These compounds are members of a large, virtually unknown, class of mesoionic structures, termed mesoionic purinone analogs, which are isoelectronic and isosteric to the purinones: xanthine, hypoxanthine, or purin-2-one. The formulation, classification, and quantum chemical study of a large number of these heterocyclic structures have been described.^2,3 In this report, a series of alkyl- and aryl-substituted mesoionic 1.3.4- thiadiazolo[3,2-a]pyrimidine-5,7-diones (2), mesoionic xanthine analogs, was prepared and examined for antibacterial activity in order to develop structure-activity relationships leading to more active derivatives.