Synthesis and structure-activity relationship of thiol-based histone deacetylase 6 inhibitors.

Selective histone deacetylase 6 (HDAC6) inhibitors are safe and well-tolerated with less off-target effect. However, most available HDAC6 inhibitors contain hydroxamate as a zinc-binding group (ZBG), and their unfavorable pharmacokinetic properties along with potential genotoxicity limited wide application in diverse diseases. Therefore, we designed and synthesized a series of selective HDAC6 inhibitors utilizing thiol as the ZBG and discussed their structure-activity relationship based on molecular docking. In particular, compound 21, obtained by constantly step-by-step simplification and evolution based on Ricolinostat, a specific HDAC6 inhibitor in Phase II, unexpectedly showed high selectivity (29-fold) and moderate potency (73 nM). Utilizing pyrimidine as a linker in thiol-based HDAC6 inhibitors produces an utterly novel structure, which might display different pharmacokinetic properties and genotoxicity.