Direct C-H Phosphonylation of Electron-Rich Arenes and Heteroarenes by Visible-Light Photoredox Catalysis.

The direct transformation of ubiquitous, but chemically inert C-H bonds into diverse functional groups is an important strategy in organic synthesis that improves the atom economy and faclitates the preparation and modification of complex molecules. In contrast to the wide applications of aryl phosphonates, their synthesis via direct C-H bond phosphonylation is a less explored area. We report here a general, mild, and broadly applicable visible-light photoredox C-H bond phosphonylation method for electron-rich arenes and heteroarenes. The photoredox catalytic protocol utilizes electron-rich arenes and biologically important heteroarenes as substrates, [Ru(bpz)3 ][PF6 ]2 as photocatalyst, ammonium persulfate as oxidant, and trialkyl phosphites as the phosphorus source to provide a wide range of aryl phosphonates at ambient temperature under very mild reaction conditions.

Sensitization-Initiated Electron Transfer for Photoredox Catalysis.

Photosynthetic organisms exploit antenna chromophores to absorb light and transfer excitation energy to the reaction center where redox reactions occur. In contrast, in visible-light chemical photoredox catalysis, a single species (i.e., the photoredox catalyst) absorbs light and performs the redox chemistry. Mimicking the energy flow of the biological model, we report a two-center photoredox catalytic approach in which the tasks of light energy collection and electron transfer (i.e., redox reactions) are assigned to two different molecules. Ru(bpy)3 Cl2 absorbs the visible light and transfers the energy to polycyclic aromatic hydrocarbons that enable the redox reactions. This operationally simple sensitization-initiated electron transfer enables the use of arenes that do not absorb visible light, such as anthracene or pyrene, for photoredox applications. We demonstrate the merits of this approach by the reductive activation of chemical bonds with high reduction potentials for carbon-carbon and carbon-heteroatom bond formations.

New fluorinated agonists for targeting the sphingosin-1-phosphate receptor 1 (S1P(1)).

The sphingosine-1-phosphate receptor type 1 (S1P1) is involved in fundamental biological processes such as regulation of immune cell trafficking, vascular barrier function and angiogenesis. This Letter presents multistep syntheses of various fluorine substituted 12-aryl analogues of the drug fingolimod (FTY720) and a seven-steps route to 2-amino-17,17-difluoro-2-(hydroxymethyl)heptadecan-1-ol. In vitro and in vivo tests proved all these compounds as potent S1P1 receptor agonists.

Synthesis of new ligands for targeting the S1P1 receptor.

Sphingosine-1-phosphate (S1P) influences various fundamental biological processes by interacting with a family of five G protein-coupled receptors (S1P1-5). FTY720, a sphingosine analogue, which was approved for treatment of relapsing forms of multiple sclerosis, is phosphorylated in vivo and acts as an agonist of four of the five S1P receptor subtypes. Starting from these lead structures we developed new agonists for the S1P1 receptor. The biological activity was tested in vivo and promising ligands were fluorinated at different positions to identify candidates for positron emission tomography (PET) imaging after [(18)F]-labelling. The radioligands shall enable the imaging of S1P1 receptor expression in vivo and thus may serve as novel imaging markers of S1P-related diseases.

Synthesis and evaluation of fluorinated fingolimod (FTY720) analogues for sphingosine-1-phosphate receptor molecular imaging by positron emission tomography.

Sphingosine-1-phosphate (S1P) is a lysophospholipid that evokes a variety of biological responses via stimulation of a set of cognate G-protein coupled receptors (GPCRs): S1P1-S1P5. S1P and its receptors (S1PRs) play important roles in the immune, cardiovascular, and central nervous systems and have also been implicated in carcinogenesis. Recently, the S1P analogue Fingolimod (FTY720) has been approved for the treatment of patients with relapsing multiple sclerosis. This work presents the synthesis of various fluorinated structural analogues of FTY720, their in vitro and in vivo biological testing, and their development and application as [(18)F]radiotracers for the study of S1PR biodistribution and imaging in mice using small-animal positron emission tomography (PET).