Azido-Desferrioxamine Siderophores as Functional Click-Chemistry Probes Generated in Culture upon Adding a Diazo-Transfer Reagent

Abstract

This work aimed to undertake the in situ conversion of the terminal amine groups of bacterial desferrioxamine (DFO) siderophores, including desferrioxamine B (DFOB), to azide groups to enable downstream click chemistry. Initial studies trialed a precursor-directed biosynthesis (PDB) approach. Supplementing Streptomyces pilosus culture with blunt-end azido/amine non-native substrates designed to replace 1,5-diaminopentane as the native diamine substrate in the terminal amine position of DFOB did not produce azido-DFOB. Addition of the diazo-transfer reagent imidazole-1-sulfonyl azide hydrogen sulfate to spent S. pilosus medium that had been cultured in the presence of 1,4-diaminobutane, as a viable native substrate to expand the suite of native DFO-type siderophores, successfully generated the cognate suite of azido-DFO analogues. CuI-mediated or strain-promoted CuI-free click chemistry reactions between this minimally processed mixture and the appropriate alkyne-bearing biotin reagents produced the cognate suite of 1,4-disubstituted triazole-linked DFO-biotin compounds as potential molecular probes, detected as FeIII-loaded species. The amine-to-azide transformation of amine-bearing natural products in complex mixtures by the direct addition of a diazo-transfer reagent to deliver functional click chemistry reagents adds to the toolbox for chemical proteomics, chemical biology, and drug discovery.