N,N'-Trimethylenediphthalimide-d6 is an intermediate used in the synthesis of Spermidine-d6 Trihydrochloride (S680407), which is a labeled Trihydrochloride derivatibe of Spermidine (S680400); a biogenic polyamine formed from putrescine and a precursor of Spermine (S680510). Spermidine is also essential for both normal and neoplastic tissue growth.