Synthetic Receptors for Metal Cations

A series of related building blocks have been prepared based on this design [114, 

The use of the three template metal ions and the three diamines at the same time led to the formation of several target macrocycles. For instance, by simultaneously adding Mg, Ca, and Sr, compounds 45a-c were amplified (45a = 60-84%, 45b = 22%, and 45c = 27-62%). 

The macrocycle 51 can be converted into 52 by addition of an excess of Cd salt to the complex of 51 with Ba. Upon reduction with NaBH4, the resulting [3 + 3] amine macrocycle was the only product observed [55]. 

ESI-MS, ultraviolet, and NMR were used to study templating effects on the DCLs, and proved that metal ion binding is the driving force. Recently, the same group reported a highly diastereoselective amplification induced by Cd of the heterochiral form of macrocycle 52 starting from a mixture of (R,R)- and (S,S)-trans-cyclohexane-l,2-diamine [56], 

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