Reaction Steps
To a 50-mL round bottom flask loaded with 2-(2-(2-(4-hydroxyphenyl)-N-(2-(2-(4,7,10-tris(2-(tert-butoxy)-2-oxoethyl)-1,4,7,10-tetraazacyclododecan-1-yl)acetamido)ethyl)acetamido)acetamido)acetic acid 3 (0.113 g, 0.131 mmol) was added 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (0.038 g, 0.198 mmol, 1.5 eq.) and 2-maleimidoethylamine.HCl (0.035 g, 0.198 mmol, 1.5 eq.). The mixture was dissolved in 10 mL of CH3CN and stirred for 12 hours at room temperature. After solvent removal in vacuo, purification was achieved by preparative reverse-phase HPLC (gradient from 100% 0.1% formic acid in water to 50% 0.1% formic acid in water/50% CH3CN) to give 4. 1H-NMR (300 MHz, CDCl3) δ 9.02 (m, 1H), 8.07 (m, 1H), 7.01 (m, 2H), 6.79 (m, 2H), 6.65 (s, 1H), 4.23-2.80 (m, 34H), 1.45 (s, 27H); 13C-NMR (75 MHz, CDCl3) δ 173.67, 173.43, 171.04, 170.33, 170.26, 170.08, 169.94, 169.86, 168.64, 156.55, 156.47, 134.16, 130.33, 130.06, 125.57, 125.09, 115.95, 115.84, 81.93, 81.87, 81.81, 81.70, 56.63, 56.08, 55.90, 53.12, 52.01, 50.95, 49.79, 49.41, 49.39, 47.22, 43.44, 43.07, 39.58, 39.15, 38.25, 38.10, 37.74, 37.34, 28.17.
