Synthesis of cyclen derivatives

摘要

The invention relates to an improved process for preparation of protected DO3A, such as DO3A-tri-t-butyl ester (1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid tri-t-butyl ester). The compound is prepared as a salt. The process includes a work-up procedure giving DO3A-tri-t-butyl ester as a salt of excellent purity.