Thirty-one aminocoumarin antibiotics derived from mutasynthesis experiments were investigated for their biological activities. Their inhibitory activity towards E. coli DNA gyrase was determined in two different in vitro assays: an ATPase assay and a DNA supercoiling assay. The assays gave a similar rank order of the activities of tested compounds, although the absolute IC50 values obtained in each were different. To confirm that the compounds also acted as gyrase inhibitors in vivo, reporter gene assays were carried out in E. coli using gyrA and sulA promoter fusions with the luxCDABE operon. A strong induction of both promoters was observed for those compounds that showed gyrase inhibitory activity in the biochemical assays. Compounds carrying structurally very different analogs of the prenylated benzoyl moiety (Ring A) of clorobiocin showed high activity both in the biochemical and in the reporter gene assays, indicating that the structure of this moiety can be varied considerably without losing affinity for bacterial gyrase. The experimentally determined IC50 values were compared to binding energies calculated in silico, which indicated that a shift of the pyrrole carboxylic acid moiety from the O-3’’ to the O-2’'-position of the deoxysugar moiety has a significant impact on the binding mode of the compounds. The aminocoumarin compounds were also investigated for their minimal inhibitory concentrations against different bacterial pathogens. Several compounds showed high activities against staphylococci, including a methicillin-resistant Staphylococcus aureus strain. However, they showed only poor activities against Gram-negative strains.

Anderle C, Stieger M, Burrell M, Reinelt S, Maxwell A, Page M, Heide L.

Pharmazeutische Biologie, Pharmazeutisches Institut, Universität Tübingen, Auf der Morgenstelle 8, D-72076 Tübingen, Germany; Basilea Pharmaceutica AG, Grenzacherstr. 487, CH-4005 Basel, Switzerland; Department of Biological Chemistry, John Innes Centre, Colney, Norwich, NR4 7UH, United Kingdom.