The N7 imidazole nitrogen of purine nucleosides is known to take part in non-Watson-Crick hydrogen bonding and in metal chelation. "Deleting" the N7 nitrogen by replacing it with a CH group is a useful modification that has been accomplished in DNA oligonucleotides using the phosphoramidite of 2'-deoxytubercidin, namely 7-Deaza-dA CE-Phosphoramidite,⁽¹⁾, which was useful in showing that N7 of dA is an important hydrogen bond acceptor site for the endodeoxyribonuclease EcoRI.

Ref:

1. (a) Seela, F.; Kehne, A. Biochemistry, 1987 26, 2232-2238. (b) Seela, F.; Berg, H.; Rosemeyer, H. Biochemistry, 1989, 28, 6193-6198.