Additions of Thiols to 7-Vinyl-7-deazaadenine Nucleosides and Nucleotides. Synthesis of Hydrophobic Derivatives of 2′-Deoxyadenosine, dATP and DNA

Additions of alkyl- or arylthiols to 7-vinyl-7-deaza-2'-deoxyadenosine gave a series of 7-[2-(alkyl- or arylsulfanyl)ethyl]-7-deaza-2'-deoxyadenosines in 45-85% yields. The nucleosides were converted to 5'-O-mono-(dA SR MP) or triphosphates (dA SR TP) by phosphorylation. The modified triphosphates were also prepared by thiol addition to 7-vinyl-7-deaza-dATP. The triphosphates dA SR TP were good substrates for DNA polymerases useful in the enzymatic synthesis of base-modified oligonucleotides (ONs) or DNA containing flexibly linked hydrophobic substituents in the major groove. Primer extension was used for the synthesis of ONs with one or several modifications, PCR was used for the synthesis of heavily modified DNA, whereas terminal deoxynucleotidyl transferase was used for a single-nucleotide labeling of the 3'-end.