1,4,7,10-Tetraazacyclododecane-4,7,10-triacetic acid tri-t-butyl ester (360 mg, 0.70 mmol) (Example 22 (a)) was dissolved in dimethylformamide (2.1 ml) . Sodium iodide (15 mg, 1 mmol), triethylamine (142 mg, 1.4 mmol) and 3-chloro-1-propanol (132 mg, 1.4 mmol) were added to the stirred mixture at ambient temperature. The mixture was stirred for 3 hours at ambient temperature, the temperature was then raised to 100° C. and kept there for 2 hours. The solvent was evaporated and the residue was dissolved in dichloromethane (3 ml) and washed with water (1 ml). Trifluoroacetic acid (2 ml) was added to the dichloromethane solution and the mixture was stirred at ambient temperature for 1 hour. The solvents were evaporated and the residue dissolved in water (6 ml). The aqueous solution was washed with ether (6×3 ml). The aqueous solution was acidified, the water was evaporated, and the title compound was isolated as a hygroscopic white powder. Yield 192 mg (68%), FAB MS: 405(M+1). The structure was confirmed by 1HNMR and 13CNMR.
