Azido-mono-amide-DOTA-tris(t-Bu ester) → (14S,18S)-tri-tert-butyl 1-(1-(2-(bis(2-(tert-butoxy)-2-oxoethyl)amino)-2-oxoethyl)-1H-imidazol-2-yl)-8,16-dioxo-2-(4-((1-(3-(2-(4,7,10-tris(2-(tert-butoxy)-2-oxoethyl)-1,4,7,10-tetraazacyclododecan-1-yl)acetamido)propyl)-1H-1,2,3-triazol-4-yl)methoxy)benzyl)-2,9,15,17-tetraazaicosane-14,18,20-tricarboxylate

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To a solution of (14S,18S)-tri-tert-butyl 1-(1-(2-(bis(2-(tert-butoxy)-2-oxoethyl)amino)-2-oxoethyl)-1H-imidazol-2-yl)-8,16-dioxo-2-(4-(prop-2-yn-1-yloxy)benzyl)-2,9,15,17-tetraazaicosane-14,18,20-tricarboxylate (145 mg, 0.13 mmol), tri-tert-butyl 2,2′,2″-(10-(2-((3-azidopropyl)amino)-2-oxoethyl)-1,4,7,10-tetraazacyclododecane-1,4,7-triyl)triacetate (59 mg, 0.090 mmol) in THF (5.0 mL) and water (1.0 mL) was added copper powder (6.4 mg) and 1 N CuSO4 (0.01 mL). The mixture was stirred at room temperature for overnight under nitrogen, diluted with EtOAc, washed with an aqueous saturated solution of EDTA. The solvent was evaporated under reduce pressure to afford a residue, which was purified by Biotage SP4 to afford ((14S,18S)-tri-tert-butyl 1-(1-(2-(bis(2-(tert-butoxy)-2-oxoethyl)amino)-2-oxoethyl)-1H-imidazol-2-yl)-8,16-dioxo-2-(4-((1-(3-(2-(4,7,10-tris(2-(tert-butoxy)-2-oxoethyl)-1,4,7,10-tetraazacyclododecan-1-yl)acetamido)propyl)-1H-1,2,3-triazol-4-yl)methoxy)benzyl)-2,9,15,17-tetraazaicosane-14,18,20-tricarboxylate (21.8 mg). MS (ESI), 883.2 (M/2+H)+.

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