Nucleotide complexes with azoniacyclophanes containing phenyl-, biphenyl- or bipyridyl- units

Abstract

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 dm³ mol¹ the intracavity immersion of the T methyl substituent is visible also in the observed upfield NMR shifts. With the smaller hosts 2 and 3, constants of approximately 100–200 dm³ mol^–1 are observed, indicating essentially salt bridge contributions. Structural conclusions are supported by the observed NMR shieldings and by selected molecular mechanics calculations.