inhibitor in this series was 9d with an IC50 of 0.0113 µM against HDAC2 and an IC50 of 0.0139 µM against HDAC3. HDAC4 could be inhibited by all of the tested compounds with low micromolar IC50 values comparable to the reference panobinostat. HDAC8 was inhibited by all compounds as well with submicromolar IC50 values. Taken together, the three hit compounds could inhibit all tested HDAC isoforms with a clear preference for HDAC1-3.