Watson–Crick Base‐Pairing Properties of Nucleic Acid Analogues with Stereocontrolled α and β Torsion Angles (α,β‐D‐CNAs)

Constrained nucleic acids (α,β-D-CNAs) have an ethylene bridge that locks the α and β backbone torsion angles of DNA in the canonical (gauche(−),trans) conformation, as in B-form DNA (see picture), or in the noncanonical (gauche(+),trans) conformation. Canonical α,β-D-CNAs enhance the duplex-forming ability of oligonucleotides with complementary DNA, while noncanonical α,β-D-CNAs stabilize distorted B-DNA structures.