Bicyclo-oligonucleotides with inverted configuration at C(5′): synthesis and properties

5′-Epi-bicyclothymidine and oligodeoxynucleotides thereof were prepared using solid phase phosphoramidite chemistry. UV-melting curves with complementary DNA and RNA furnish values of ΔTm/mod. of −2.7° to −6.5°C compared to the natural reference system. The reduction of pairing affinity can directly be correlated with a change of the orientation of the C(4′)–C(5′) bond in the duplexes.