Passerini–Smiles Pathways to Spirooxindoles: Isatin-Based Scaffolds in Anticancer Drug Design

The underexplored Passerini–Smiles reaction (PSR), a variant of the 3-component Passerini reaction (3CPR), was successfully employed to create a tailored library of phenoxy-indoline carboxamide derivatives based on a fragment-based hybrid drug design strategy. Under mild conditions, inexpensive and commercially available isatin was utilized as a privileged carbonyl core, combined with electron-deficient phenols to establish a highly functionalized framework. Post-Passerini–Smiles transformations leveraged this strategic layout to provide a step-economical route to a complementary library of three-dimensional spirooxindole hybrids derived from the PS adducts. This study reinforces the relevance of combining structural hybridization with multicomponent reaction strategies in the discovery of potential anticancer active pharmaceutical ingredients (APIs). Both libraries were evaluated against six human solid-tumor cell lines, including non-small cell lung carcinoma, cervical and colon adenocarcinoma, and breast and pancreatic cancers. The most active compound 4gaa exhibited GI50 values below 10 μM for most of the tested cancer cell lines.