Chemo-, Regio- and Stereospecific Synthesis of Unnatural, Fluorescent Amino Acids by Condensation of L-Lysine and 1-Vinylpyrrole-2-carbaldehydes

A new family of unnatural, optically active amino acids containing the pyrrole moiety have been synthesized by condensation of 1‐vinylpyrrole‐2‐carbaldehydes with L‐lysine under mild conditions (EtOH, room temp., 2.5–3 h, 0.5 wt.‐% of CF₃CO₂H) in up to 90 % yields. Unlike non‐vinylated analogues, 1‐vinylpyrrole‐2‐carbaldehydes react chemo‐, regio‐ and stereospecifically with an ϵ‐amino group only to afford products of exclusively (E) configuration. The amino acids synthesized containing aromatic or condensed aromatic substitutents in the pyrrole ring fluoresce in the UV/Vis region (λ_max = 350–382 nm, Stokes shifts 6150–7800 cm^–1).