Syntheses of four unusual amino acids, constituents of cyclomarin A

The stereoselective syntheses of four unusual amino acids, constituents of cyclomarin A, are described. The protected N-methylhydroxyleucine 2 was synthesized using Evans’ asymmetric azide-transfer reaction. The unusual amino acid 3 was prepared via diastereoselective methylation of the l-aspartic acid derived lactone 13. The stereoselective formation of threo-β-methoxyphenylalanine 4 was performed via aldol reaction using Schöllkopfʹs chiral glycine enolate. The synthesis of N-reverse prenylated tryptophane 5 was achieved by the AQN ligand-promoted Sharpless regioreversed asymmetric aminohydroxylation protocol.