Enantioselective synthesis of Nα-Fmoc protected (2S,3R)-3-phenylpipecolic acid.: A constrained phenylalanine analogue suitably protected for solid-phase peptide synthesis

Reported herein is the first enantioselective preparation of (2S,3R)-3-phenylpipecolic acid as a conformationally constrained phenylalanine analogue bearing N-a-protection suitable for solid-phase peptide synthesis. Stereochemistries at both the 2- and 3-positions are derived inductively from a single chiral center provided by the commercially available Evans chiral auxiliary, (4S)-4-benzyl-1,3-oxazolidin-2-one. By constraining phi and x(1) torsion angles, this novel amino acid analogue can serve as a useful tool for the induction of defined geometry in phenylalanine-containing peptides.