Figure 2.

Scheme for the synthesis of an oligonucleotide incorporating a covalent base pair (the hydrazone bond is indicated by the arrow). i, SnCl₄/HMDS/TCS/CH₃CN. ii, NaHCO₃. iii, POCl₃/DMF. iv, H₂O. v, MeONa/MeOH. vi, NH₂NH₂/NaHSO₃/phosphate buffer (pH 5). vii, F/phosphate buffer (pH 5). HMDS, hexamethyldisilazane; TCS, trimethylchlorosilane; Template, oligonucleotide template; Template′, oligonucleotide incorporating a N⁴-aminocytidine residue; Template⩵F, template covalently linked to the nucleoside analogue F by means of a hydrazone bond. Either T₃CT₃ or Tem (Table 1) can be used as the Template.