The invention relates to a compound represented by the following formula (I): ##STR00001## and pharmaceutically acceptable salts, stereoisomers, enantiomers, prodrugs and solvates thereof. The compounds are useful as an agent for enhancing the neurite outgrowth and preventing or treating of diseases associated with HDAC in particular, tumor or cell proliferative diseases. In particular, the compounds of the invention can be used as an agent for anti-neurodegenerative diseases and human spinal muscular atrophy (SMA).