Synthesis of heterobactins A and B and Nocardia heterobactin
摘要:
The synthesis of the Rhodococcus erythropolis siderophores heterobactins A and B, and the structurally related Nocardia heterobactin, is described. Two approaches for the assembly of these asymmetric ligand donor chelators are explored. In the first approach, a scheme predicated on the biosynthesis of the Para coccus denitrificans siderophore, parabactin, is employed. In this approach, the central donor synthon is added last. In the second scheme, the central donor and the terminal 2,3-dihydroxybenzoyl fragment are first fixed to the ligand's D-ornithine backbone. This is followed by condensation with the cyclic ornithine hydroxamate glycine segment. The schemes offer a flexible approach to other heterobactins. Job's plots suggest that heterobactin A and Nocardia heterobactin form 1:1 ligand/metal complexes, while heterobactin B forms a 3:2 ligand/metal complex. (C) 2011 Elsevier Ltd. All rights reserved.
The first total synthesis of exochelin MN is described along with rationally designed analogues. The required L-threo-beta-hydroxyamino acidcomponents were constructed using either Sharpless asymmetric aminohydroxylation reactions or an aldol reaction of imidazolidinone 19. A newconcise procedure for the preparation of the constituent six-membered cyclic hydroxamate was developed. In addition, a
The synthesis of Gobichelin-A, a naturally occurring mixed-ligand siderophore isolated from Streptomyces sp. NRRL F-4415, is described. The target molecule was planned to be synthesized by a convergent process involving the combination of two halves, Gob-A 1st half and Gob-A 2nd half, at the prefinal stage of the synthetic route. By adopting this method, fully protected Gobichelin-A was synthesized