Ethyl 7-amino-3-(3-methyl-5-oxo-1-phenyl-2-pyrazolin-4-yl)-5-aryl-5H-thiazolo[3,2-a]pyrimidine-6-carboxylate
was hydrolyzed with an ethanolic sodium hydroxide and the sodium salt thus formed underwent cyclization
with acetic anhydride to afford 2-methyl-7-(3-methyl-5-oxo-1-phenyl-2-pyrazolin-4-yl)-5-arylthiazolo[3,2-a]-
pyrimido[4,5-d]oxazin-4(5H)-one. This compound was transformed to related heterocyclic systems via its reaction
with various reagents. The biological activity of the prepared compounds was tested against Gram positive and
Gram negative bacteria as well as yeast-like and filamentous fungi. They revealed in some cases excellent biocidal
properties.