Phosphoinositide-3-kinase (PI3K) overexpressed in many tumors is a promising target for cancer therapy. However, due to toxicity from the ubiquitous expression of PI3K in many tissues, the development of PI3K inhibitors with high selectivity and low toxicity has become an urgent need for tumor treatment. Herein, based on the <i>HipHop</i>, we designed and synthesized a series of 6-(4,6-dimorpholino-1,3,5-triazin-2-yl)benzo[<i>d</i>]oxazol-2-amine derivatives as potent, selective, and long-acting PI3Kα inhibitors. Compound <b>27</b> was determined with potent PI3Kα inhibitory activity (IC<sub>50</sub> = 4.4 nM), which exhibited excellent selectivity for homologous PI3K enzymes and a 370 kinome panel. Meanwhile, <b>27</b> featured favorable stability (<i>T</i><sub>1/2</sub> > 10 h) and high bioavailability (130%). Importantly, compound <b>27</b> exerted great antigastric cancer activity <i>in vivo</i> when combined with taxol. Collectively, these characteristics suggested <b>27</b> to be a promising PI3K agent for cancer treatment.