Directing the chemoenzymatic assembly of desferrioxamine B as a single product using N-tert-butoxycarbonyl-protected...

Desferrioxamine B (DFOB, 1) is a clinical hydroxamic acid siderophore used as a chelator to treat acute and secondary iron overload disease, with further applications in metal-based radiopharmaceuticals, medicinal chemistry, and chemical biology. Its current production method uses whole-organism fermentation which results in the co-production of other hydroxamic acid analogues, and the need to purify complex mixtures to produce clinical grade 1. Here, we have exploited the elastic properties of the Salinispora tropica CNB-440 recombinant NRPS-independent siderophore (NIS) synthetase DesD (StDesD) responsible for the late-stage biosynthesis of 1, in combination with N-Boc protected substrates, to direct the production of 1 as a single product. Mixtures of StDesD and native amine-bearing substrates followed either a C-to-N or N-to-C directionality to assemble appreciable quantities of 1 alongside higher order homo- and/or hetero-oligomeric products. Substituting the native amine substrates for the N-Boc protected counterparts generated N-Boc protected desferrioxamine B (N-Boc 1) as the sole enzyme-mediated product in exceptional yields exceeding 80%, which following an in situ deprotection procedure furnished 1.