A new synthesis of cystamine modified Eu3+ DOTAM-Gly-Phe-OH: a conjugation ready temperature sensitive MRI contrast agent.

Several approaches towards asymmetrically derivatized peptide-decorated cyclens that yield lanthanide metal chelators, in which three of the nitrogen atoms of cyclen share a common substituent and the fourth nitrogen atom is differentially substituted, have been evaluated. The most effective route consisted of selective monoalkylation followed by peralkylation with a second different electrophile. The unique substituent also possessed a masked sulfanyl group that was suitable for subsequent chemoselective conjugation chemistry.