Characterization and histone deacetylase inhibitory activity of three novel fluorescent benzamide derivatives

New fluorescent benzamide derivatives were developed by using four different aromatic groups with expanding sizes from thiophene to naphthalene, anthracene, and pyrene in an attempt to identify a novel histone deacetylase (HDAC) inhibitor. The compounds exhibited red shift absorption and emission dependent on the size of the aromatic group as well as a high fluorescence efficiency with high quantum yields. However, the HDAC binding affinity of the compounds with polyaromatic modification of the substituent was very low (IC₅₀ ranging from 46 to 101 μM) in contrast to that of the monoaromatic substituted compound (<0.12 μM). Likely, the modification of the aromatic substituent results in the enzyme's inability to bind the inhibitors due to space limitation at the binding site. Nevertheless, we believe that these results will be useful in the design of new fluorescent HDAC inhibitors based on the benzamide scaffold with diverse applications as diagnostic tools targeting the HDAC enzyme, which has an important role in the prevention of a number of diseases.