SYNTHETIC AND BIOLOGICAL APPLICATIONS OF TRICYCLIC ANALOGS OF GUANOSINE

Tricyclic nucleosides incorporating the 9-oxo-imidazo[1,2-a]purine (1, N-2-ethenoguanine) system, natural prototypes of which occur in tRNA a s nucleosides of the wyosine series, were used for synthetic, structur al and biological purposes. 1,N-2-(Prop-1-ene-1,2-diyl) guanosine deri vatives used as intermediates allowed to enforce on guanosine the subs titution at the N-3 position and at the N-2 exo-amino group, not possi ble to be performed directly. Wyosine and 2'-deoxywyosine together wit h 4,5'-anhydro-4-desmethylwyosine and its congeners were used as, resp ectively, 100% anti and 100% syn conformation standards in a new graph ical method for the syn-anti conformational analysis of nucleosides by 1D IH NOE difference spectroscopy. Substitution at the appended third ring allowed to modify the biological and physical properties of anti viral agents acyclovir and ganciclovir, e.g. to develop their fluoresc ent analogues.