| CPC C07F 5/003 (2013.01) | 21 Claims |
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1. A process for the manufacturing of a dimeric complex of formula 5
 comprising the following steps:
a) admixing a salt of formula 1B
 wherein X is bromide, and y is 1;
with a basic aqueous solution and an organic solvent immiscible with the basic aqueous solution, to provide a heterogenous mixture comprising the salt of formula 1B, wherein the organic solvent is methyl tert-butyl ether (MTBE);
b) converting the salt of formula 1B comprised in the heterogenous mixture of step a), to provide a heterogenous mixture comprising DO3A tri-tert-butyl ester of formula 1A
 c) collecting the organic solvent from the heterogenous mixture of step b), to obtain an organic solution comprising DO3A tri-tert-butyl ester 1A;
d) preparing a solution comprising a compound of formula 2
 in an organic solvent;
e) admixing the solutions of steps c) and d) to obtain a solution comprising a compound of formula 3
 f) without isolating the compound from the solution of step e), removing the tert-butyl protecting groups from the compound of formula 3 to obtain a solution comprising a free ligand of formula 4
 g) without isolating the free ligand of formula 4, adding gadolinium metal ions to the solution of step f) to obtain a solution comprising the dimeric complex of formula 5; and
h) isolating the dimeric complex of formula 5,
wherein the solvent in all the steps following the obtaining of the compound of formula 3 is an aqueous solvent.
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