Structures of the acylhydrazide (13), hydrazide (14), methyl-1,3,4-oxadiazole (15), monofluoromethyl-1,3,4-oxadiazole (16) and trifluoromethyl-1,3,4-oxadiazole (17) analogs. Inhibitory activities of prepared compounds against HDAC1–4 and HDAC6; IC50 [μM, mean ± SD] or percent inhibition at 10 μM; n.e.: no effect = < 15% inhibition at 10 μM.