A number of pathogenic RNA viruses, such as HIV-1, have extensive folded RNA conformations with imperfect A-form duplexes that are essential for virus function, and could serve as targets for structure-specific antiviral drugs. A method for the discovery of such drugs involves evaluation of the interactions with RNA of a wide variety of compounds that are known to bind to nucleic acids by different mechanisms. This approach has been initiated by using corresponding sequence RNA and DNA polymers as initial test systems for analysis of RNA binding strength and selectivity. Compounds that bind exclusively in the minor groove in AT sequences of DNA do not have significant interactions with RNA. Polycations, however, can show significant RNA affinity and binding selectivity, probably through complex formation in the RNA major groove. Some intercalators and a group of diphenylfuran cations have strong interactions with RNA that are very dependent on compound structure. RNA hairpin model systems for the RRE binding site of HIV-1 Rev protein were constructed for more detailed investigations. The diphenylfuran cations bind strongly to RRE and selectively inhibit Rev binding. CD, NMR, and fluorescence binding studies indicate that the active compounds bind in the internal loop region of RRE (with binding constants >lO'M-'), and cause a conformational change in the RNA. None of the standard nucleic acid binding modes appears to fit the results for complexes of the active compounds with RRE, and it is proposed that the diphenylfuran system threads through the internal loop region of RRE. Such a model allows contacts of the furan cationic substituents with both grooves of RRE in addition to the intercalation interactions with the bases.