Transcription-Inhibition and Antitumor Activities of N-Alkylated Tetraazacyclododecanes

A series of alkyl‐substituted tetraazacyclododecane congeners were synthesized, and their antitumor activities towards human HeLa cells as well as their effect on the in vitro transcription with T7 RNA polymerase were investigated. A structure–activity‐relationship (SAR) study identified the most‐active congeners as those with medium alkyl‐chain lengths. Three compounds, 5–7, were found to exhibit significant biological activities, with IC50 values towards HeLa cells in the low‐micromolar range.