The aim of this work was to synthesize 4-acetamido-, 4-amino- and 4-oxo-6-substituted aminoquinazolines and to evaluate them as phosphoinositide 3-kinases (PI3Ks) inhibitors. The respective chemotype was designed based on combining the structural features of two previously reported scaffolds acting as potent PI3Kγ inhibitors, which are quinazoline derivatives and amino-heterocyclic derivatives. In vitro enzymatic assay at 10 µM against all the eight human PI3K isoforms showed that an unsubstituted benzamide group at position 6 and an acetyl group at N(4) gave the best inhibitory activity on PI3Kγ. Interestingly, compounds 5a and 5e showed a significant, inhibitory effect on Class II PI3K-C2γ. This is of high value since there are very few inhibitors for this isoform reported in the literature.