NMR studies on oligo‐deoxyribonucleotides containing N6‐methyladenine

500 MHz 1H‐NMR and NOE measurements of d(GGATCC) and d(GGm6ATCC) show that both oligo‐nucleotides assume a B‐DNA conformation at low temperature. Around the melting temperature, however, the single and double strands of the N‐methylated form are in slow exchange on the NMR time scale. The preferred conformation of the adenine methyl group, cis to N1, retards base pairing and also destabilizes the double helix.