Patent ID: 8410263

Claim:
In a process for synthesizing a purified sample of a compound of Formula 1: wherein: M is Gd 3+ or Lu 3+ ; each X is independently selected from the group consisting of OH − , AcO − , Cl − , Br − , I − , F − , H 2 PO 4 − , ClO − , ClO 2 − , ClO 3 − , ClO 4 − , HCO 3 − , HSO 4 − , NO 3 − , N 3 − , CN − , SCN − , and OCN − ; R 4 and R 7 are C 3 H 6 OH; R 5 and R 6 are C 2 H 5 ; R 3 and R 8 are CH 3 ; R 1 and R 2 are H; and each x is independently selected from the group consisting of 1, 2, 3, 4, 5, and 6; the improvement comprises synthesizing a purified sample of a compound of Formula 1 wherein each x is 3 in at least about 98.4% of compounds of Formula 1 in the purified sample; the process comprising the steps of: i. pegylating a compound of Formula 6 comprising reacting a compound of Formula 7 with an o-dihydroxybenzene of Formula 6: in tetrahydrofuran to provide a compound of Formula 5 having the structure: