Pyrrolinone-based peptidomimetics, the first mimics of beta-strands, are potent inhibitors of HIV-1 protease. Importantly, the bis(pyrrolinones) described herein proved to be more active in cellular antiviral assays compared with an analogous peptide-derived inhibitor even though they are less effective in inhibiting the isolated protease. These results suggest that pyrrolinone inhibitors offer better transport properties than the corresponding peptide-based peptidomimetics; we attribute this effect to decreased solvation of the mimetics. Structure-activity relationships for the pyrrolinones correlate well with those reported for related peptides, consistent with similar modes of binding.