A short asymmetric synthesis of N-α-fmoc-N-δ-boc-α-methyl-D-ornithine

The title compound was synthesized in six steps from N-Cbz-L-alanine through asymmetric alkylation of a cis-2-phenyl-4-methyl-5-oxazolidinone with tert-butyl 4-iodobutyrate. The cis-2-phenyl-4-methyl-5-oxazolidinone was obtained via a new BF3•Et2O mediated condensation with benzaldehyde dimethyl acetal and N-Cbz-L-alanine. The δ-carboxylate was converted to the δ-N-Boc derivative 5 through a Curtius rearrangement. Hydrogenation yielded N-δ-Bod-α-methyl-D-ornithine6, which was protected as the α-N-Fmoc derivative for incorporation into solid phase peptide synthesis.