N-2-SUBSTITUTED AND C-8-SUBSTITUTED OLIGODEOXYNUCLEOTIDES WITH ENHANCED THROMBIN INHIBITORY ACTIVITY IN-VITRO AND IN-VIVO

2'-Deoxyguanosine (G) analogues carrying various hydrophobic substitue nts in the N-2 and C-8 positions were synthesized and introduced throu gh solid-phase synthesis into 15-mer oligodeoxynucleotide, GGTTGGTGTGG TTGG, which forms a chairlike structure consisting of two G-tetrads an d is a potent thrombin inhibitor. The effects of the substitutions at N-2 and C-8 of the G-tetrad-forming G residues on the thrombin inhibit ory activity are relatively small, suggesting that these substitutions cause relatively small, perturbations on the chairlike structure form ed by the oligodeoxynucleotide. Introduction of a benzyl group into N- 2 of G(6) and G(11) and naphthylmethyl groups into N-2 of G(6) increas ed the thrombin inhibitory activity, whereas other substituents in the se positions had almost no effect or decreased the activity. Particula rly, the oligodeoxynucleotide carrying a 1-naphthylmethyl group in the N-2 position of G(6) showed an increase in activity by about 60% both in vitro and in vivo. Substitutions on the N-2 position of other G re sidues had little effect or decreased the activity. Introduction of a relatively small group, such as methyl and propynyl, into the C-8 posi tions of G(1), G(5), G(10), and G(14) increased the activity, presumab ly due to the stabilization of a chairlike structure, whereas introduc tion of a large substituent group, phenylethynyl, decreased the activi ty, probably due to the steric hindrance.