Discovery ofNovel Oxazolo[4,3‑<i>f</i>]purine Derivatives asAntitumor Agents through PPIA Interaction

54 novel oxazolo [4,3-<i>f</i>]purine derivatives were designed, synthesized, and evaluated for antitumor activity, among which compound <b>20b</b> exhibited potent activity against several cancer cell lines. Compound <b>20b</b> inhibited cell metastasis, arrested the cell cycle in the G₀/G₁ phase, and induced apoptosis in HCT116 cells. Mechanistic studies revealed that <b>20b</b> increased ROS levels and led to DNA damage, endoplasmic reticulum (ER) stress, and mitochondrial dysfunction in HCT116 cells. Limited proteolysis-small molecule mapping (LiP-SMap), drug affinity responsive target stability (DARTS) assay, cellular thermal shift assay (CETSA), and surface plasmon resonance (SPR) experiments provided evidence that compound <b>20b</b> bound to PPIA with a KD value of 0.52 μM. siRNA assay indicated that <b>20b</b>-mediated antiproliferative and antimigration activities were abolished and that the PPIA/MAPK signaling pathway was inhibited when PPIA was silenced in HCT116 cells. Significantly, compound <b>20b</b> presented significant anticolorectal cancer efficacy <i>in vivo</i> without obvious toxicity. These results indicate that <b>20b</b> may serve as a novel anticancer agent targeting PPIA, meriting further attention in antitumor drug research.