Chiral and achiral macrocyclic diketal diamines, analogs of cyclams, were synthesized from the previously obtained corresponding diketal dilactams by reduction with lithium aluminum hydride in the presence of a trace amount of triethylamine. In the (15-30) × 10-3 M concentration range, the reaction led mainly to the expected doubly reduced compounds except in the trans-OMe substituted series (R = Ph, Me), in which it partially stopped at the single reduction stage. A conformational study conducted by liquid NMR spectroscopy and molecular mechanics calculations showed that the most stable conformations were either set in a rectangular [3434]-type structure for trans-OMe compounds 7b (R = Me) and 10b (R = H) or stabilized by two intramolecular NH···O hydrogen bonds for all the other macrocyclic diamines. Tc-99m radiolabeling with the nitrido-technetium core [TcN]2+ gave 10-20 % exchange yields