A series of hydroxamic acid derivatives bearing a cyclic amide/imide group as a linker and/or cap structure, prepared during our structural development studies based on thalidomide, showed class-selective potent histone deacetylase (HDAC)-inhibitory activity. Structure–activity relationship studies indicated that the steric character of the substituent introduced at the cyclic amide/imide nitrogen atom, the presence of the amide/imide ...