Capping group modifications likely exploit structural differences at the entrance of the active
site of each isoform to afford class selectivity or isoform selectivity (section I.A). In the case
of modification near the metal-binding moiety, the high sequence similarity near the catalytic
metal among the HDAC isoforms makes a similar approach problematic. However, selective
inhibitor design has centered in some cases on the presence of distinct binding pockets adjacent
to the catalytic metal.