[CH2:1]1[N:8]([CH2:9][CH2:10][NH+:11]([CH2:22][C:23]([O-:25])=[O:24])[CH2:12][CH2:13][N:14]2[CH2:21][C:19](=[O:20])[O:18][C:16](=[O:17])[CH2:15]2)[CH2:7][C:5](=[O:6])[O:4][C:2]1=[O:3].C1CN2C(=NCCC2)C1.[NH2:35][NH2:36]>CS(C)=O>[C:16]([CH2:15][N:14]1[CH2:21][C:19](=[O:20])[NH:36][NH:35][C:5](=[O:6])[CH2:7][N:8]([CH2:1][C:2]([OH:4])=[O:3])[CH2:9][CH2:10][N:11]([CH2:22][C:23]([OH:25])=[O:24])[CH2:12][CH2:13]1)([OH:18])=[O:17]A 500 mL three-neck flask is charged with 150 mL of dry DMSO and flushed with nitrogen. Two syringes are charged separately with solutions of diethylenetriaminepentaacetic acid dianhydride (2.82 g, 7.89 mmol) and DBN (2.94 g, 2.92 mL, 23.67 mmol) in 122 mL of DMSO and anhydrous hydrazine (0.25 g, 0.25 mL, 7.89 mmol) in 125 mL DMSO. The two solutions are added simultaneously at the rate of 40 mL/hour to the flask at ambient temperature, employing a syringe pump. After the completion of addition the reaction mixture is stirred for 48 hours, concentrated under vacuum to 10 mL, and water (10 mL) is added. The solution at pH 10.5 is applied to AGIX-8 (100-200 mesh, acetate form) resin and the column is eluted with 1N acetic acid. The product is obtained by removal of acetic acid, followed by lyophilization.
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