NITROGEN-15-LABELED OLIGODEOXYNUCLEOTIDES .4. TETRAPLEX FORMATION OF D[G(7-N-15)GTTTTTGG] AND D[T(7-N-15)GGGT] MONITORED BY H-1 DETECTED N-15 NMR

We have synthesized two molecules containing [7-N-15]-labeled 2'-deoxyguanosine, d[G(N-15(7))GTTTTTGG], and d[T(N-15(7))GGGT] which, under appropriate conditions, will form tetramolecular complexes. The N-15 chemical shifts of these molecules and of their Watson-Crick duplexes, d[G(N-15(7))GTTTTTGG].d[CCAAAAACC] and d[T(N-15(7))GGGT].d[ACCCA], were monitorod as a function of temperature. The N-15 chemical shift of the labeled N7 atom in each tetramolecular complex shows a similar temperature dependence, and the chemical shifts are not signal-averaged. The similarity of the chemical shifts for the tetraplex and single strand structures, and the difference seen for the two duplexes, are consistent with the different degrees of hydrogen bonding to the N7 which could be expected in each case. Thus, although more examples will be required to establish the generality of these observations, a purine [7-N-15] label appears to be able to monitor major groove interactions, including hydration.