Design, Synthesis, and Biological Evaluation of Highly Potent Small Molecule–Peptide Conjugates as New HIV‑1 Fusion Inhibitors

The small molecule fusion inhibitors N-(4-carboxy-3-hydroxyphenyl)-2,5-dimethylpyrrole (NB-2) and N-(3-carboxy-4-hydroxyphenyl)-2,5-dimethylpyrrole (A12) target a hydrophobic pocket of HIV-1 gp41 and have moderate anti-HIV-1 activity. In this paper, we report the design, synthesis, and structure–activity relationship of a group of hybrid molecules in which the pocket-binding domain segment of the C34 peptide was replaced with NB-2 and A12 derivatives. In addition, the synergistic effect between the small molecule and peptide moieties was analyzed, and lead compounds with a novel scaffold were discovered. We found that either the nonpeptide or peptide part alone showed weak activity against HIV-1-mediated cell–cell fusion, but the conjugates properly generated a strong synergistic effect. Among them, conjugates Aoc−βAla–P26 and Noc−βAla–P26 exhibited a low nanomolar IC50 in the cell–cell fusion assay and effectively inhibited T20-sensitive and -resistant HIV-1 strains. Furthermore, the new molecules exhibited better stability against proteinase K digestion than T20 and C34.