PDE4D and Alzheimer disease: Compounds 79, 84, and 87 are considered hybrids of clioquinol–rolipram and roflumilast as multitarget-directed ligands for the treatment of AD in terms of inhibition of phosphodiesterase 4D (PDE4D), the oxygen radical absorbance capacity (ORAC) value, and the experimental potential of the blood–brain barrier (BBB) permeability (Pe) of the selected compounds using parallel artificial membrane permeation assay (PAMPA).