base triplet with the mismatch. the combined use of an acridine intercalator to pi-pi stack on the target gave a nanomolar binding affinity for tt or uu mismatches over others. along with high binding affinity, this molecule was shown to displace mbnl from the complex with r(cug) with a micromolar ki. additionally, hiv-1 rna has been targeted extensively in vitro by rna-binding small molecules. in 2007, miller and coworkers used dynamic combinatorial chemistry to screen a compound library against hiv-1 frameshift regulatory stem-loop rna. they identified a hit compound that was selective for the regulatory sequence with micromolar binding affinity. in 2011, butcher and colleagues discovered a frameshifting stimulator (db213) which bound to hiv-1 fs rna with moderate binding affinity. an nmr structure of the rna in complex with db213, showed that the small molecule bound to the major groove of the rna duplex. schneekloth and hargrove have taken a different approach by targeting the hiv-1 tar rna hairpin. in a small molecule microarray screening, the schneekloth group identified a thienopyridine derivative that interacts with hiv-1 tar rna hairpin. further sar studies provided more information on the structure and binding mode. the lead analogue was found to bind to the 5’-utr of hiv with an ic50 of 40 μm for displacing a tat-derived peptide. the hargrove group developed a small library of amiloride derivatives with changes at the c(5) and c(6) positions to improve the binding affinity of amiloride to the loop and bulge of the hiv-1 tar rna. using in vitro studies and modeling, they found a hit compound whose inhibition activity was increased by more than 100x compared to the parent amiloride. this compound is reported to be one of the tightest non-aminoglycoside tar ligands reported to date.