Method for preparing S-Bz-MAG3 as a precursor of contrast media

A method for preparing S-Bz-MAG3 as a precursor of contrast media, comprising steps of:

• taking thioglycolic acid and benzoyl chloride and stirring for 2 hours at room temperature for performing a thiol protection reaction and producing a first product;
• using concentrated hydrochloric acid to adjust pH value of said first product until pH=1, then filtering said first product;
• flushing said first product using water and drying said first product;
• taking N,N′-dicyclohexylcarbodiimide and N-hydroxysuccinimide to react with said first product for converting to a second product, wherein said second product includes a byproduct dicyclohexylurea;
• flushing and filtering said second product using ethyl acetate for eliminating said dicyclohexylurea;
• taking said second product and triglycine to perform an amide bonding reaction and producing a reaction product;
• using acetone to recrystallize said reaction product for forming a crystal product;
• filtering said crystal product;
• and
• using a flushing agent having an alkyl structure to flush the crystal product and producing a final product.