A unified approach to mesityl amino acids based on Sharpless dihydroxylation

Enantioselective syntheses of two mesityl (2,4,6-trimethylphenyl) amino acids are described. Starting from ethyl 3-mesityl-2-propenoate both enantiomeric dihydroxy esters 5 were prepared in excellent yield and enantiomeric purity (>99% ee) by Sharpless dihydroxylation. Each diol was converted into ethyl 3-azido-2-hydroxy-3-mesitylpropanoate 3 which is the common intermediate. Compound (2S,3S)-3 was transformed into Fmoc-d-mesitylglycine d-1 and Fmoc-l-mesitylalanine l-2 through two four-step-sequences.