Mono‐ and Tetraalkyne Modified Ligands and Their Eu3+ Complexes – Utilizing “Click” Chemistry to Expand the Scope of Conjugation Chemistry
The Cu+-catalyzed Huisgen [3+2] cycloaddition has been used to elaborate analogues of a candidate PARACEST MRI contrast agent, which is a complex of Eu3+ with DOTAM–Gly–Phe–OH. Analogues possessing either one L-tyrosine in place of an L-phenylalanine, or with all four phenylalanine units replaced, were transformed into Tyr(O-propargyl) substrates for “click” chemistry. Conjugation of the Eu3+–DOTAM derivatives with a spectrum of azides, including simple hydrophilic, hydrophobic, and aromatic groups, propyl glucoside, and a nucleoside were successful. The magnetic resonance properties of the resultant conjugates were examined, and their chemical exchange saturation transfer (CEST) properties are reported.