Biochemical characteristics of the 6-nitro regioisomer of nitroxoline and its 1,2,3,4-tetrahydroquinoline analogues

A significant amount of data about the different pharmacological activities of the established antimicrobial compound nitroxoline (8-hydroxy-5-nitroquinoline) is available in the scientific literature. On the other hand, its regioisomer 8-hydroxy-6-nitroquinoline was never characterised biochemically and the same also applies to their 1,2,3,4-tetrahydroquinoline analogues. Herein, we determined the influence of pyridine ring saturation and the position of the nitro group on various biochemical characteristics of compounds, such as metal-chelating properties, inhibition of methionine aminopeptidases (MetAPs) from Mycobacterium tuberculosis and human MetAP2, as well as antibacterial activities on Escherichia coli, Staphylococcus aureus, and Mycobacterium smegmatis. In addition, inhibition of endopeptidase and exopeptidase activities of cathepsin B was determined, together with the ability of new nitroxoline analogues to reduce intracellular collagen IV degradation. Substantially different biological activities were observed for the 6-nitro regioisomer of nitroxoline, as well as for both of their partially saturated counterparts.