Synthesis and Biological Evaluation of New Fused Isoxazolo[4,5-d] Pyridazine Derivatives

Three new heterocyclic ring systems, isoxazolo[4,5-d]-1,2,4-triazolopyridazines 12-15, tetrazolo-[4,3-b]pyridazine 18 and isoxazolo[4,5-d]pyridazino[2,3-c]2H-triazines 16,17 along with isoxazolo[4,5-d]pyridazines 2, 5-10 have been synthesized. Preliminary screening of these tricyclic heterocycles revealed that some of them possess significant antibacterial and antifungal activity.