Invariant properties of upper limb movement trajectory control.

Positron emission tomography (PET) is a sensitive molecular imaging technique that can provide quantitative information on the distribution of specific proteins in living animals or humans and on their physiological functions and interactions with experimental and clinically useful drugs. Examples of such proteins include enzymes, receptors, transporters, and pathological plaques. The imaging of each protein requires a radiotracer that binds or interacts specifically with the protein of interest. Fluorine-18 is widely incorporated into PET tracers because of its favorable physical and chemical properties. These include decay with a half-life of 109.8 minutes by 97% emission of a relatively low-energy positron (mean energy 250 keV) and an ability to make strong bonds to carbon in place of a hydrogen or a hydroxy substituent. Moreover, fluorine-18 can be prepared as [F]fluoride ion from biomedical cyclotrons in exceptionally high amounts and at high molar activities by the O(p,n)F nuclear reaction on O-enriched water. This allows the [F]fluoride or derived tracers to be shipped to PET imaging centers lacking a cyclotron if they are within a few hours travel from a central cyclotron facility. The global market for F-labeled tracers is very high and was set to exceed $3bn in 2023. In the case of the most popular F-labeled tracer, [F]2-fluoro-2-deoxy--glucose (commonly known as [F]FDG or FDG), this distribution model underpins a billion-dollar industry for biomedical diagnosis. To further uncover the immense potential of PET for biomedical imaging, there is a growing need for the development of new methods for introducing fluorine-18 into bioactive molecules. Many experimental tracers that carry fluorine-18 at an alkyl carbon are prone to radiodefluorination , which can lead to [F]fluoride uptake in bone and to compromised PET imaging of nearby tissue. By contrast, [F]fluoroarenes usually resist radiodefluorination. Therefore, considerable effort has been made to devise methods for fast and efficient radiofluorination at aryl carbon, irrespective of aryl group electron density. As recently comprehensively reviewed, successful methods include the use of nitroarenes, diaryliodonium salts, aryliodonium ylides, arylboronic acids, arylboronic esters, arylstannanes, aryl sulfoxides, or triarylsulfonium salts as precursors. Radiofluorination yields from these precursors depend on many factors, including the nature, position, and accessibility of the leaving group on the aryl ring, and the nature and effect of proximal functional groups. Many of the methods require a metal mediator or catalyst, such as a palladium, nickel, ruthenium, or copper species, but catalyst-free methods are keenly sought for economy and simplicity and for easier regulatory compliance when producing PET tracers for clinical use. One such method is the radiofluorination of triarylsulfonium salt precursors. The utility of triarylsulfonium salts as precursors for F-labeling has recently been exemplified in the syntheses of promising PET tracers, including: [F]FAMTO, a radiotracer for imaging CYP11B1 and CYP11B2 enzymes in adrenal glands; [F]fluorobenzyl-candesartan, a radiotracer for the AT1 receptor; and [F]Aldoview a tracer for imaging aldosterone synthase (hCYP11B2) in primary hyperaldosteronism ().