Purity >99% by HPLC. Cell-permeable. A histone deacetylase (HDAC) inhibitor (Ki values are 0.41, 0.75, >100 and >100 μM for HDAC1, HDAC3, HDAC6 and HDAC8 respectively). Displays significant antitumor activity in vitro and in vivo against a broad spectrum of murine and human tumor models.