Synthesis of Purine-1,4,7,10-Tetraazacyclododecane Conjugate and Its Complexation Modes with Copper(II)

Purine-1,4,7,10-tetraazacyclododecane (cyclen) conjugate was designed to study its Cu(2+) ions complexation capability. Several synthetic approaches were tested to achieve the target compound. The optimal approach involved stepwise modifications of purine N9, C8, and C6 positions that, in nine consecutive steps, provided purine-cyclen conjugate. The synthetic sequence involved Mitsunobu-type alkylation at N9 and iodination at C8, followed by Stille, S(N)Ar, CuAAC, and alkylation reactions. The designed purine-cyclen conjugate is able to complex Cu(2+) ions in both the cyclen part and between the purine N7 and triazole N2 positions. The complexation pattern and equilibrium were studied using the NMR titration technique in MeCN-d(3) and absorption spectra.