A series of SAHA cap derivatives was designed and prepared in good-to-excellent yields that varied from 49% to 95%. These derivatives were evaluated for their antiproliferative activity in several human cancer cell lines. Antiproliferative activity was observed for concentrations varying from 0.12 to >100 μM, and a molecular modeling approach of selected SAHA derivatives, based on available structural information of human HDAC8 in complex with SAHA, was performed. Strikingly, two compounds displayed up to 10-fold improved antileukemic activity with respect to SAHA; however, these compounds displayed antiproliferative activity similar to SAHA when assayed against solid tumorderived cell lines. A 10-fold improvement in the leukemic vs peripheral blood mononuclear cell therapeutic ratio, with no evident in vivo toxicity toward blood cells, was also observed. The hereindescribed compounds and method of synthesis will provide invaluable tools to investigate the molecular mechanism responsible for the reported selectively improved antileukemic activity.

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A series of N-substituted amino caproic hydroxamic acid histone deacetylase inhibitors derivatives was designed in good-toexcellent yields and evaluated for their antiproliferative activity in a panel of human cancer cell lines, showing half maximum effective concentration varying from 700 nM to > 100 μM. Interestingly, the replacement of a furyl group by a thienyl one impacted very significantly the cap role on this antiproliferative activity and on histone acetylation induced by these drugs in cell-based but also in cell-free enzyme assays, suggesting an important role of the electronic density attached to the oxygen or sulfur atoms.