Synthesis and antiviral activity of ethidium-arginine conjugates directed against the TAR RNA of HIV-1

The regulatory protein Tat is essential for viral gene expression and repli cation of the human immunodeficiency virus type 1 (HIV-1). Tat transactivat es the HIV-1 long terminal repeat(LTR) via its binding to the transactivati on responsive element(TAR) and increases the viral transcription. Studies h ave shown that the binding of arginine and arginine derivatives induces a c onformational change of the TAR RNA at the Tat-binding site. The unpaired A 17 residue delimits a small cavity which constitutes a receptor site for sm all molecules, especially for ethidium bromide. These binding characteristi cs have prompted us to design a series of ethidium-arginine conjugates capa ble of interacting with the TAR RNA. Here we report the synthesis of six et hidium derivatives equipped with arginine side chains. These molecules were biologically evaluated, and two compounds (17 and 20) exhibited in vitro a nti-HIV-1 activity at micromolar concentration, without toxicity (up to 100 mu M concentration). Melting temperature studies indicated that the most a ctive molecule (20) bound strongly to TAR in vitro. RNase protection experi ments agreed with the molecular modeling studies which suggested that the e thidium moiety of 20 was inserted next to the A17 residue while the arginin e side chain occupied the pyrimidine bulge.