Synthesis, NMR and ultraviolet spectroscopy of [10](N6,9)-6-aminopurinophane; Calculation of the chemical shifts in the [n](N6,9)-6-aminopurinophane series

[10] (N6,9)-6-Aminopurinophane was prepared via a Mitsunobu reaction involving 6-chloropurine and 10-azido-1-decanol. Reduction of the azido moiety to an amine allowed for subsequent cyclization to the cyclophane. N6-Nonyladenine, 9-nonyladenine, and N6,9-dinonyladenine were also prepared using the established chemistry. Heating the [10](N6,9)-6-aminopurinophane to 90 degrees C allowed for a complete assignment of the proton and carbon spectra, while cooling the sample to -77 degrees C revealed additional isomers likely due to the anti-syn isomerization about the N6-C6 bond. A variable temperature proton NMR study revealed a Delta G(c)(not equal) of 59.4 +/- 5.5 kJ mol(-1) associated with the interchange between the two major conformers. The ultraviolet spectra of the [n](N6,9)-6-aminopurinophane series show a bathochromic shift and a hypochromic effect in the transitions as the methylene chain length decreases (i.e., n = 10 to 9 to 8). The aminopurinophanes are used to assess the relative merits of a semi-empirical model that allows for the calculation of the chemical shifts of the methylene bridge protons.