Two new routes for alkylsubstituton of one in four amino groups in 1,4
,7,10-tetraazacyclododecane (cyclen) are described, isomeric N-tris(hy
droxy)butylcyclens 4 and 6 have been obtained in very good yields. Fur
ther carboxymethylation of other three amino groups afforded ris(hydro
xy)butyl-1,4,7-tris(carboxymethyl)cyclens 1 and 2.