Supramolecular chemistry .68. Nucleotide complexes with azoniacyclophanes containing phenyl-, biphenyl- or bipyridyl-units

Three cyclophanes (1-3) with p-phenyl, p-biphenyl- and m-bipyridyl spacers between diethylenetriamine units are studied by NMR titrations in water (D2O) with naturally occurring mononucleotides in the form of monophosphates. The biphenyl host 1 shows association constants K (in mol dm(-3) units) of 2200 with AMP5', 1270 with the isomeric AMP3', and smaller constants with G, C and U derivatives. An exception is GMP5' with 3, which in contrast to most host compounds shows a four-fold stronger binding than AMP5'. Thymidine (TMP5') is complexed with K = 2050 dm(3) mol(-1); the intracavity immersion of the T methyl substituent is visible also in the observed upheld NMR shifts. With the smaller hosts 2 and 3, constants of approximately 100-200 dm(3) mol(-1) are observed, indicating essentially salt bridge contributions. Structural conclusions are supported by the observed NMR shieldings and by selected molecular mechanics calculations.