Photochemical Generation and Characterization of Alanine Imine: A Key Intermediate in Prebiotic Amino Acid Formation

Simple imino acids have received sparse consideration as reactive intermediates in the formation of amino acids under prebiotic or astrochemical conditions. Under cryogenic matrix isolation conditions 2-azidopropionic acid decomposes after UV irradiation to dinitrogen and 2-iminopropionic acid, namely alanine imine, which is the proposed key intermediate in biologically relevant alanine transaminase reactions. Three conformers of alanine imine were spectroscopically characterized by FT-IR and UV/Vis spectroscopy in solid argon at 3.5 K. One high-energy conformer can be selectively prepared by the near-IR induced excitation of an OH-overtone vibration. In the dark this conformer undergoes H-tunneling CO-bond rotamerization. In aqueous solution 2-azidopropionic acid decomposes to glyoxylic and pyruvic acid after hydrolysis of the intermediately formed imine intermediates as identified by 1H NMR spectroscopy. Under more acidic conditions and prolonged irradiation the intermediary formed imino acids are reduced to their glycine and alanine amino acid equivalents, respectively.