Design and Efficient Synthesis of RalA Inhibitors Containing the Dihydro‐α‐carboline Scaffold

Ras‐related protein RalA is a member of the Ras small GTPases superfamily. Its activation plays an important role in regulating tumor initiation, invasion, migration, and metastasis. In this study, we designed a new type of RalA inhibitor containing a dihydro‐α‐carboline scaffold. The structurally new dihydro‐α‐carboline derivatives could be efficiently synthesized in good yields through a newly developed three‐component [3+2+1] cyclization reaction. Evaluation of the biological activity showed that some of the dihydro‐α‐carboline derivatives can inhibit RalA/B and proliferative activities of NSCLC cell lines. The 4‐(pyridin‐3‐yl)‐dihydro‐α‐carboline compound ( 3 o ) was found to be the most potent derivative, with IC 50 values of 0.43±0.03, 0.64±0.07, 0.93±0.10, and 1.54±0.15 μM against A549, H1299, H460, and H1975 cells, respectively. Mechanism investigation suggested that 3 o inhibits the RalA/B activation of A549, down‐regulates Bcl‐2, stimulates cytochrome c and PARP cleavage, and induces cell apoptosis. A molecular docking study revealed that 3 o can form stable hydrogen bonds with residues of RalA. Moreover, amide‐π and alkyl‐π interactions also contributed to the affinity between 3 o and RalA.