2-[(1,3-Dihydro-1,3-dioxo-2H-isoindol-2-yl)acetyl]-butanedioic-2-13C Acid Diethyl Ester is an intermediate in the synthesis of 5-Aminolevulinic Acid-3-13C Hydrochloride which is a naturally occurring amino acid; precursor of tetrapyrroles in the biosynthesis of chlorophyll and heme. Antineoplastic (photosensitizer).