Fluorinated Analogues of Desferrioxamine B from Precursor-Directed Biosynthesis Provide New Insight into the Capacity of DesBCD

Abstract

The siderophore desferrioxamine B (DFOB, 1) native to Streptomyces pilosus is biosynthesized by the DesABCD enzyme cluster. DesA-mediated decarboxylation of L-lysine gives 1,5-diaminopentane (DP) for processing by DesBCD. S. pilosus culture medium was supplemented with rac-1,4-diamino-2-fluorobutane (rac-FDB) to compete against DP to generate fluorinated analogues of DFOB, as agents of potential clinical interest. LC-MS/MS analysis identified fluorinated analogues of DFOB with one, two or three DP units (binary notation: 0) exchanged for one (DFOA-F1[001] (2), DFOA-F1[010] (3), DFOA-F1[100] (4)), two (DFOA-F2[011] (5), DFOA-F2[110] (6), DFOA-F2[101] (7)), or three (DFOA-F3[111] (8)) rac-FDB units (binary notation: 1). The two sets of constitutional isomers 2–4 and 5–7 arose from the position of the substrates in the N-acetyl, internal or amine-containing regions of the DFOB trimer. N-Acetylated fluorinated DFOB analogues were formed where the rac-FDB substrate was positioned in the amine region (eg, N-Ac-DFOA-F1[001] (2a)). Other analogues contained two hydroxamic acid groups and three amide bonds. Experiments using rac-FDB, R-FDB or S-FDB showed a similar species profile between rac-FDB and R-FDB. These data are consistent with the following. (i) DesB can act on rac-FDB; (ii) DesC can act directly on rac-FDB; (iii) the products of DesBC or DesC catalysis of rac-FDB can undergo a second round of DesC catalysis at the free amine; (iv) DesD catalysis of these products gives N,N-diacetylated compounds; (v) a minimum of two hydroxamic acid groups is required to form a viable DesD-substrate(s) pre-complex; (vi) one or more DesBCD-catalysed steps in DFOB biosynthesis is enantioselective. This work has provided a potential path to access fluorinated analogues of DFOB and new insight into its biosynthesis.