Phosphatidylinositol 3-kinase α (PI3Kα) is one of the most attractive therapeutic targets for cancer treatment. As our continuing endeavor to discover isoform and/or mutant selective class of PI3K inhibitors, herein we report the optimization of a structurally novel PI3Kα H1047R mutant inhibitor Hit-02 (EC50 = 115.3 μM), which was identified from a high-throughput screening campaign. Structure-activity relationship analysis enabled us to discover compound 7h, which strongly inhibited PI3Kα H1047R mutant with an EC50 value of 0.55 μM, over 200-fold more potent than Hit-02, while having little effect on other PI3K isoforms. Western blotting assay suggested that 7h decreased the phosphorylation level of AKT, another proof that 7h inhibited PI3Kα H1047R mutant function. Cell viability assay revealed that 7h inhibited HCT-116 cancer cell growth with an IC50 value of 10.9 μM. In addition, 7h was found to arrest cell cycle at G2 phase but did not show any cell apoptosis effect. Furthermore, 7h obviously induced cell autophagy, which might contribute to its anti-proliferation effect in cancer cell. Collectively, all these data demonstrated that 7h could be a promising lead for the development of structurally novel PI3Kα inhibitor.