Synthesis of gadolinium (±)-10-(1-hydroxypropan-2-yl)-1,4,7,10-tetraazacyclododecane-1,4,7-triyltriacetate via tribenzyl 1,4,7,10-tetraazacyclododecane-1,4,7-tricarboxylate

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Abstract
The synthesis of monogadolinium 10-(1-hydroxypropan-2-yl)-1,4,7,10-tetraazacyclododecane-1,4,7-triyltriacetate 12 has been achieved through a multistep sequence. The key step in the synthesis was the reaction of the previously unknown tribenzyl 1,4,7,10-tetraazacyclododecane-1,4,7-tricarboxylate 6 with ethyl 2-(trifluoromethylsulphonyloxy)propionate 4 to give 7. Reduction of 7 with LiBH4/9-OMe-BBN, followed by hydrogenolysis of the protecting groups (Z groups) yielded 2(1,4, 7,10-tetraazacyclododec-1-yl)propanol 10. The monosubstituted macrocycle 10 was alkylated with bromoacetic acid and then complexed with gadolinium oxide to yield the title compound.