Nucleoterpenes of thymidine and 2'-deoxyinosine: synthons for a biomimetic lipophilization of oligonucleotides.

2'-Deoxyinosine (1) and thymidine (7) were N-alkylated with geranyl and farnesyl moieties. These hydrophobic derivatives, 3a and 3b, and 9a and 9b, respectively, represent the first synthetic biomimetic nucleoterpenes and were subsequently 5'-protected and converted into the corresponding 3'-O-phosphoramidites, 5a and 5b and 11a and 11b, respectively. The latter were used to prepare a series of lipophilized oligonucleotide dodecamers, a part of which were additionally labelled with indocarbocyanine fluorescent dyes (Cy3 or Cy5), 18-23. The insertion of the lipooligonucleotides into, as well as duplex formation at artificial lipid bilayers was studied by single-molecule fluorescence spectroscopy and fluorescence microscopy.