The hypothesis that the dose-limiting side effects of PDE4 inhibitors could be mediated via the central nervous system prompted us to design and synthesize a hydrophilic piperidine analog to improve the side effect profile of Ariflo™ 1, which is an orally active second- generation PDE4 inhibitor. During evaluation of various water-soluble piperidine analogs, 2a–b, 11b–14b, and 17a showed therapeutic potential in cross-species comparison ...