| Abstract
| - Five dinucleating ligands (1−5) and one trinucleating ligand (6) incorporating 1,5,9-triazacyclododecan-3-yloxy groups attached to an aromatic scaffold have been synthesized. The ability of the Zn2+complexes of these ligands to promote the transesterification of dinucleoside 3‘,5‘-monophosphates to a2‘,3‘-cyclic phosphate derived from the 3‘-linked nucleoside by release of the 5‘-linked nucleoside hasbeen studied over a narrow pH range, from pH 5.8 to 7.2, at 90 °C. The dinuclear complexes show markedbase moiety selectivity. Among the four dinucleotide 3‘,5‘-phosphates studied, viz. adenylyl-3‘,5‘-adenosine(ApA), adenylyl-3‘,5‘-uridine (ApU), uridylyl-3‘,5‘-adenosine (UpA), and uridylyl-3‘,5‘-uridine (UpU), the dimerscontaining one uracil base (ApU and UpA) are cleaved up to 2 orders of magnitude more readily thanthose containing either two uracil bases (UpU) or two adenine bases (ApA). The trinuclear complex (6),however, cleaves UpU as readily as ApU and UpA, while the cleavage of ApA remains slow. UVspectrophotometric and 1H NMR spectroscopic studies with one of the dinucleating ligands (3) verify bindingto the bases of UpU and ApU at less than millimolar concentrations, while no interaction with the basemoieties of ApA is observed. With ApU and UpA, one of the Zn2+−azacrown moieties in all likelihoodanchors the cleaving agent to the uracil base of the substrate, while the other azacrown moiety serves asa catalyst for the phosphodiester transesterification. With UpU, two azacrown moieties are engaged in thebase moiety binding. The catalytic activity is, hence, lost, but it can be restored by addition of a third azacrowngroup on the cleaving agent.
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