New Sequential‐Assignment Routes of Nucleic Acid NMR Signals Using a [5′‐13C]‐Labeled DNA Dodecamer

NMR signal assignments for DNA oligomers have been performed by the well‐established sequential assignment procedures based on NOESY and COSY. The H4′/H5′/H5″ resonance region is congested and difficult to analyze without the use of isotope‐labeled DNA oligomers. Here a DNA dodecamer constructed with 2′‐deoxy[5′‐13C]ribonucleotides, 5′‐d(*C*G*C*G*A*A*T*T*C*G*CG)‐3′ (*N = [5′‐13C]Nucleotide), was prepared in an effort to analyze the H4′/H5′/H5″ resonance region by 2D 1H‐13C HMQC‐NOESY. In the C5′ and H1′ resonance region, weak and strong cross peaks for C5′(i)‐H1′(i) and C5′(i)‐H1′(i‐1), respectively, were found, thus enabling the sequential assignment within this region. A similar sequential assignment route was found between C5′ and H2″. Proton pair distances evaluated from the canonical B‐DNA as well as A‐DNA indicated that these sequential‐assignment routes on a 2D 1H‐13C HMQC‐NOESY spectrum work for most nucleic acid stem regions. †In honor and celebration of the 70th birthday of Professor Leroy B. To...