alpha-DNA-III. Characterization by high field 1H-NMR, anti-parallel self-recognition and conformation of the unnatural hexadeoxyribonucleotides alpha-[d(CpApTpGpCpG)] and alpha-[d(CpGpCpApTpG)]. Alpha-oligodeoxynucleotides as potential cellular probes for gene control.

High field 2-D-1H-NMR techniques permitted the assignment of all non-exchangeable protons of the unnatural deoxyribonucleotides alpha-[d(CpApTpGpCpG)] and alpha-[d(CpGpCpApTpG)]. 1-D and 2-D NOESY experiments show strong H6H8-H4' dipolar interactions for all nucleotides in both sequences. These data, together with COSY and J-resolved spectra, indicate that these two alpha-oligomers adopt 3'-exo conformations of the sugar moieties in solution with anti conformations of the glycosyl linkages. Both 1H-NMR data, and hypochromocity comparison of alpha-CATGCG and beta-CATGCG, demonstrate a higher degree of base stacking in the case of the alpha-sequence. The UV hyperchromicity at 260 nm, and symmetry considerations in the imino proton NMR experiments reveal antiparallel self-recognition and duplex annealing at positions 1-4 for alpha-[d(CATGCG)] and positions 3-6 for alpha-[d(CGCATG)]. The temperature variation of the imino proton NMR signals suggests that the hydrogen bonding in self-recognition is comparable in strength with that in a beta-DNA duplex, and NOE data are in accord with Watson-Crick rather than Hoogsteen base pairing.