PDE4A and cancer: In the PDE4 inhibitory activity and anticancer cell activity assays, compounds 2, 3, 5, 8, 9, 11–14, and 16 exhibited weak PDE4 inhibitory activity at a concentration of 10 μM, Compound 11 demonstrated potent inhibitory effects against six cancer cell lines (MDA-MB-231, MDA-MB-435, HCT116, SNB-19, PC3, and A549), with IC50 values ranging from 3.4 to 23.7 μM.