Synthesis of β-Hydroxytyrosine, A Component of Burkholdines.

The preparation of four stereoisomers of β-hydroxytyrosine containing burkholdines is described. Enantio-pure syn β-hydroxytyrosine was synthesized using Sharpless aminohydroxylation. To obtain anti β-hydroxytyrosine, the cinnamate derivative was oxidized to give the optical active diol derivative by the AD-mix and subsequently, the a-hydroxy group was converted to amine. Deprotection of the acid-sensitive β-hydroxytyrosine derivatives was successively accomplished by brief immersion in 4N HCl/dioxane. All prepared stereoisomers of β-hydroxytyrosine were available for solid and solution phase peptide synthesis and amino acid analysis.