Optimization of the synthesis of the cross-linked amino acid ornithinoalanine and nuclear magnetic resonance characterization of lysinoalanine and ornithinoalanine

Lysinoalanine (LAL) and ornithinoalanine (OAL) are unnatural amino acids th at can be formed in food submitted to thermal treatment, especially in alka line conditions. The paper presents an optimization of the synthetic proced ure for the preparation of a standard of OAL that could be very useful to s tudy the toxicological and nutritional consequences of the presence of OAL in food. In the meantime, it was possible to develop a method based on nucl ear magnetic resonance for the diastereomeric characterization of LAL and O AL without derivatization. Interest in this method is based on the known di fferences in the nephrotoxicity of the two diastereisomers of LAL.