Constituents of Microbial Iron Chelators. Alternate Syntheses of δ-N-Hydroxy-L-ornithine Derivatives and Applications to the Synthesis of Rhodotorulic Acid

Article abstract of DOI:10.1021/jo00187a023

δ-N-Hydroxy-L-ornithine derivatives, the key constituents of several microbial iron chelators, have been prepared from protected forms of L-glutamic acid.Reduction of α-tert-butyl N-Boc-glutamate (3) provided α-tert-butyl L-N-Boc-δ-hydroxynorvaline (4).Direct treatment of 4 with Cbz-O-benzylhydroxylamine (5) or trOC-O-benzylhydroxylamine (6) gave the protected δ-N-hydroxyornithine derivatives 7 and 8, respectively. δ-N-Deprotection followed by acetylation provided α-tert-butyl-L-N-Boc-δ-N-acetyl-δ-N-benzyloxyornithine (9).Appropriate α-amino and α-carboxyl deprotections of 8 and 9 provided derivatives of δ-N-hydroxy-L-ornithine suitable for the synthesis of rhodotorulic acid (24) by two routes.The first route employed conventional peptide synthesis methods.The second synthesis or rhodotorulic acid involved the direct dimerization of Leuch's anhydrides 25 and 26 derived from the δ-N-acetyl- and δ-N-trOC-δ-N-benzyloxyornithines 11 and 16.