Synthesis and antimycobacterial activity of imidazo[1,2-b][1,2,4,5]tetrazines

Tuberculosis (TB) has recently become the leading killer among infectious diseases. Multidrug and extensively drug-resistant Mycobacterium tuberculosis strains urge the need to develop anti-TB drugs with a novel mechanism of action. We describe synthesis of 22 novel imidazo[1,2-b][1,2,4,5]tetrazine derivatives with different substituents at C(3) and C(6) positions, and their antimycobacterial activity in vitro. 8 compounds show activity as potential serine/threonine protein kinase (STPK) inhibitors in M. smegmatis aphVIII+ test-system, which is characteristic for this class. 3 compounds out of 5 most active STPK inhibitors have a prominent minimal inhibitory concentration on M. tuberculosis H37Rv of 1 μg/ml. We were able to obtain M. smegmatis mc2 155 mutants resistant to 4 compounds and show that they do not have cross resistance with other drugs, but have a common mechanism of resistance among these 4 imidazo[1,2-b][1,2,4,5]tetrazines. Compound 3h seems the most promising, combining a predicted STPK inhibitor activity, the lowest MIC on M. tuberculosis and a low frequency of drug resistant mutants' emergence.