. . "The starting compound of formula IIP can be prepared by reaction of a 1,4,7,10-tetraazacyclo- dodecane having one amine nitrogen protected by a protecting group, e.g. a benzyl group, with a compound HalCH 2 X ' , e.g. ethyl bromoacetate, and subsequently removing the protecting group, e.g. using standard debenzylation conditions." . .