To determine the capability of the synthesized compounds to inhibit HDAC enzymes, we carried out an HDAC inhibition assay (Table ). We tested our compound set against two human isoforms, hHDAC1 (class I) and hHDAC6 (class IIb). Notably, all compounds exposed a preferential inhibition of HDAC1 over HDAC6 (selectivity indices: SI 6/1 = (HDAC6 IC50) / (HDAC1 IC50) ranging from 2 to 44). The inhibitors of type A showed low nanomolar inhibitory activity against HDAC1 (IC50 values ranging from 0.010 to 0.017 µM) and moderate inhibition of HDAC6 (IC50 values ranging from 0.16 to 0.44 µM). Again, the compounds of type B had a weaker inhibitory activity on HDAC1 compared to type A (IC50 values range: 0.043 to 0.12 µM), while the inhibition of HDAC6 was similar to type A (IC50 values range: 0.15 to 0.50 µM). The compounds of type C showed similar activity against HDAC1 compared to type B, with IC50 values ranging from 0.021 to 0.19 µM, and against HDAC6, with IC50 values ranging from 0.24 to 0.64 µM. The most potent HDAC1 inhibitor among the synthesized compounds was 9d (IC50 = 0.010 µM), which also stood out as the most selective HDAC1