Cyclic nucleotide phosphodiesterases (PDEs) control the intracellular concentrations of cAMP and cGMP in virtually all mammalian cells. Accordingly, the PDE family regulates a myriad of physiological functions, including cell proliferation, differentiation and apoptosis, gene expression, central nervous system function, and muscle contraction. Along this line, dysfunction of PDEs has been implicated in neurodegenerative disorders, coronary artery diseases, chronic obstructive pulmonary disease, and cancer development. To date, 11 PDE families have been identified; however, their distinct roles in the various pathologies are largely unexplored and subject to contemporary research efforts. Indeed, there is growing interest for the development of isoform-selective PDE inhibitors as potential therapeutic agents. Similarly, the evolving knowledge on the various PDE isoforms has channeled the identification of new PET probes, allowing isoform-selective imaging. This review highlights recent advances in PDE-targeted PET tracer development, thereby focusing on efforts to assess disease-related PDE pathophysiology and to support isoform-selective drug discovery.

The reaction of enamine compounds with disulfides in the presence of tert-butyl hydroperoxide and a catalytic amount of tetrabutylammonium iodide conveniently afforded a variety of a-thioenamine compounds through the intermolecular oxidative C(sp 2 ) À S coupling. Incorporating both of the sulfide moieties in the disulfides into the final products under oxidative conditions, this novel approach exhibits the feature of atom efficiency. A radical mechanistic pathway for the reaction process has been proposed.

The reaction of o-nitroiodobenzene and mCPBA in AcOH was found to afford a novel hypervalent iodine compound which both iodine(iii) and iodine(v) moieties coexist. This new reagent is proved to be effective in realizing the synthesis of 2H-azirines.

Various chromeno[2,3-b]indol-11(6H)-ones were conveniently constructed via phenyliodine(III) diacetate (PIDA)-mediated intramolecular oxidative annulation. This method, while realizing a direct oxidative C–N bond formation between an aromatic ring and a pendent free-NH2 moiety, features a metal-free protocol, mild reaction conditions, simple workup, and the ready availability of the starting substrates.