Dibenzothiophene sulfonium salts as leaving groups for aromatic [18F] fluorination-exemplified by highly efficient direct labeling of the mGluR5 PET tracer [18F] FPEB

peer reviewe

Imaging tau pathology in Alzheimer's disease with positron emission tomography: lessons learned from imaging-neuropathology validation studies

Though the presence of both amyloid-β (Aβ) plaques and tau neurofibrillary tangles is necessary for neuropathologic diagnosis of Alzheimer’s disease (AD), it is now widely recognized that tau burden correlates more strongly with neurodegeneration and cognitive impairment in life than the development of Aβ plaques [1]. Recent developments of tau-sensitive radiotracers for imaging with positron emission tomography (PET) have, for the first time, enabled visualisation, mapping, and quantification of inclusions of aggregated, paired helical filament (PHF) tau associated with AD in the living brain [2]. In-depth characterisation of tau PET tracers, and in particular comparison of antemortem PET readings with postmortem neuropathologic findings, were of paramount importance to understand the clinical potential and limitations of the new imaging tools. In the case of [18F]flortaucipir, the most widely used tau PET ligand, these cross-validation studies, together with autoradiography evaluations, provided information about the specificity of this tracer to PHF-tau in AD but also revealed substantial undesired (off-target) binding and limited ability to detect PHF-tau at the earliest Braak stages [3,4,5,6,7]. The combined data subsequently underpinned the implementation of an effective method for the clinical interpretation of [18F]flortaucipir PET scans [3]. Ultimately, these efforts have led to the approval of [(18)^F]flortaucipir by the US Food and Drug Administration (FDA) as the first PET radiopharmaceutical indicated to ‘estimate the density and distribution of aggregated neurofibrillary tangles in patients with cognitive impairment who are being evaluated for AD (Tauvid prescribing information, https://www.accessdata.fda.gov/drugsatfda_docs/label/2020/212123s000lbl.pdf)

Functionalized Triarylsulfonium Salts for Aromatic [18F] Fluorination of Drug-like Small Molecules

peer reviewe

Ring-closing synthesis of dibenzothiophene sulfonium salts and their use as precursors for aromatic [18F]fluorination – Application to direct labeling of the mGluR5 PET tracer [18F]FPEB

peer reviewe

A Practical Iron-Based Newman-Kwart Rearrangement Under Oxidative Conditions

Herein, we report that iron(II)/ammonium persulfate in aqueous acetonitrile mediates the Newman-Kwart rearrangement of O-aryl carbamothioates. Electron-rich substrates react rapidly under moderate heating to afford the rearranged products in excellent yields. The mild conditions, rapid reaction rates, and suitability for scale up offer immediate practical benefits to access functionalised thiophenols