Replacement of Ala by Aib improves structuration and biological stability in thymine-based alpha-nucleopeptides

Three thymine-based nucleo-heptapeptides, each containing two nucleo-amino acids and zero, one or four Aib residues, respectively, have been synthesized. A single Aib residue is enough to promote the adoption of a helical structure in our nucleopeptides and to increase significantly their resistance towards enzymatic degradation. The insertion of four Aib residues, out of seven residues in the sequence, affords a rigid, 310-helical nucleopeptide that is substantially unaffected by serum enzymes and is not cytotoxic.