The LR-EIMS of the I N i -phthaloyl ( I S i )-amino acids showed the molecular ion peak [M] SP +- sp . Method B (conventional heating method) A mixture of the appropriate ( I S i )-amino acid (0.10 g) and phthalic anhydride (1.3 eq) in the presence of lemon juice (1-2 drops, 0.1 mL) was heated at 130-135 °C in an oil bath for 15-20 min, as indicated by TLC in EtOAc or EtOH. We found that ( I S i )-amino acids do not undergo racemization in the protection reactions. General procedure for synthesis of (S)-N-phthaloyl amino acids (3a-f) Method A (microwave mediated reaction) A mixture of phthalic anhydride (1.1 eq) and the appropriate ( I S i )-amino acid (0.10 g) in a small amount of lemon juice (1-2 drops, 0.1 mL) was irradiated for 5-12 min in a closed flask, the time being signified by TLC in EtOAc or EtOH. [Extracted from the article]