The design, synthesis and biophysical evaluation of two highly-constrained tricyclic analogues of locked nucleic acid (LNA), which restrict rotation around the C4′–C5′-exocyclic bond (torsion angle γ) and enhance hydrophobicity in the minor groove and along the major groove, are reported. A structural model that provides insights into the sugar–phosphate backbone conformations required for efficient hybridization to complementary nucleic acids is also presented.