The invention relates to the compounds (2R,4R), (2S,4R)-2-methylthiazolidine-2,4-dicarboxylic acid and (2RS,4R)-2-methylthiazolidine-2,4-dicarboxylic acid and salts of said compounds, the use thereof for the prophylaxis and/or treatment of neurodegenerative diseases, methods for the prophylaxis and/or treatment of neurodegenerative diseases, and pharmaceutical compositions containing said compounds together with physiologically compatible carriers, auxiliary agents, and/or solvents.