Reaction Steps
[Re(CO)3][(19S,23S)-2-((1-(carboxymethyl)-1H-imidazol-2-yl)methyl)-13,21-dioxo-2,14,20,22-tetraazapentacosane-1,19,23,25-tetracarboxylic acid] (221). A solution of (19S,23S)-tetra-tert-butyl 2-((1-(2-tert-butoxy-2-oxoethyl)-1H-imidazol-2-yl)methyl)-13,21-dioxo-2,14,20,22-tetraazapentacosane-1,19,23,25-tetracarboxylate (18.8 mg, 0.019 mmol) in TFA (1.0 mL)/DCM (1.0 mL) was stirred at room temperature for overnight. The solvent was evaporated to give 19S,23S)-2-((1-(carboxymethyl)-1H-imidazol-2-yl)methyl)-13,21-dioxo-2,14,20,22-tetraazapentacosane-1,19,23,25-tetracarboxylic acid as a colorless oil. To a solution of the above deprotected product in water (1.0 mL) that was adjusted to pH=9 by 2 N NaOH was added Re(CO)3(H2O)OTf (0.50 mL, 0.10 mL/mmol). The reaction mixtures were stirred at room temperature for overnight and purified by HPLC to afford the title compound (4.0 mg, 19%) as a white solid. 1H NMR (400 MHz, DMSO-d6) 7.70 (t, J=5.6 Hz, 1H), 7.33 (s, 1H), 7.13 (s, 2H), 6.29 (d, J=8.4 Hz, 1H), 6.26 (d, J=8.4 Hz, 1H), 4.96 (d, J=4.8 Hz, 2H), 4.56 (d, J=16.4 Hz, 1H), 4.12 (d, J=16.8 Hz, 1H), 4.07-3.90 (m, 2H), 3.70 (d, J=17.2 Hz, 1H), 3.40 (d, J=17.2 Hz, 1H), 2.98-2.94 (m, 4H), 2.21 (q, J=7.73, 2H), 1.99 (t, J=7.6 Hz, 2H), 1.70-1.22 (m, 24H); MS (ESI), 485.2 (M/2+H)+.
