HDAC9 and cancer: They observed the structural similarity between urushiol and HDAC inhibitors, e.g., vorinostat, and, considering the known anti-cancer activity of urushiol, they designed three series of urushiol derivatives by: (i) adding the missing zinc binding group-hydroxamic acid group into the tail of the alkyl chain; (ii) introducing hydroxy, carbonyl, amino and methyl ether groups into the alkyl chain; and (iii) replacing the phenolic hydroxy groups by ether or ester groups substituents with different electronic or steric properties into the benzene ring and alkyl side chain.