MODULAR FLUORESCENT-LABELED SIDEROPHORE ANALOGS

Biomimetic analogues 1 of the microbial siderophore (iron carrier) fer richrome were labeled via piperazine with various fluorescent markers at a site not interfering with iron binding or receptor recognition (c ompounds 10-12). These iron carriers were built from a tetrahedral car bon symmetrically extended with three strands, each containing an amin o acid (G = glycyl, A = alanyl, L = leucyl and P = phenylalanyl) and t erminated by a hydroxamic acid, which together define an octahedral ir on-binding domain. A fourth exogenous strand provided the site for con necting various fluorescent markers via a short bifunctional linker. I ron(III) titrations, along with fluorescence spectroscopy, generated q uenching of fluorescence emission of some of the probes used. The quen ching process fits the Perrin model which reinforces the intramolecula r quenching process, postulated previously.(1) All tested compounds, r egardless of their probe size, polarity, or the linker binding them to the siderophore analogue, promote growth of Pseudomonas putida with t he same efficacy as the nonlabeled analogues 1, with the added benefit of signaling microbial activity by fluorescence emission. All G deriv atives of compounds 10-12 were found to parallel the behavior of natur al ferrichrome, whereas A derivatives mediated only a modest iron(III) uptake by P. putida. Incubation of various Pseudomonas strains with i ron(III)-loaded G derivatives resulted in the build-up of the labels' fluorescence in the culture medium to a much larger extent than from t he corresponding A derivatives. The fluorescence buildup corresponds t o iron utilization by the cells and the release of the fluorescent lab eled desferrisiderophore from the cell to the media. The fact that the microbial activity of these compounds is not altered by attachment of various fluorescent markers via a bifunctional linker proposes their application as diagnostic tools for detecting and identifying pathogen ic microorganisms.