Synthesis and Electron Paramagnetic Resonance Studies of Oligodeoxynucleotides Containing 2-N-tert-Butylaminoxyl-2′-deoxyadenosines

Oligodeoxynucleotides (ODNs) containing 2‐N‐tert‐butylaminoxyl‐2′‐deoxyadenosine (A*) residues were synthesized to allow accurate monitoring of adenine motion by EPR spectroscopy through the agency of direct linkage of the acyclic aminoxyl group to the nucleobase, and EPR studies of the ODNs in single‐ and double‐stranded forms were performed. Upon duplex formation, peak broadening and decreases in peak height were observed in EPR spectra, and the synthesized ODNs were shown to be excellent monitors of hybridization. Comparison of peak height and the h1/h0 signal ratio provided information on the relative mobility of A* in duplexes with different stability. A second set of ODNs each containing two A* residues at different intervals and four dA residues were also synthesized. For these ODNs, correlations were observed between the EPR spectral shapes of the duplexes and the number of dA residues between A* residues, thus demonstrating the potential of A* residues in monitoring of the structures of nucleic acids. Spin‐labeled and doubly spin‐labeled ODNs containing 2‐N‐tert‐butylaminoxyl‐2′‐deoxyadenosine (A*), which contains an acyclic amoxyl radical directly connected to the adenine base, provided information on the relative mobility of A* (for single‐labeled) in ODNs and on the distances between A* residues (for doubly labeled) in duplexes by comparing peaks.