Search results for "radioisotope"
showing 10 items of 300 documents
18F-Labeling Using Click Cycloadditions
2014
Due to expanding applications of positron emission tomography (PET) there is a demand for developing new techniques to introduce fluorine-18 (t1/2=109.8 min). Considering that most novel PET tracers are sensitive biomolecules and that direct introduction of fluorine-18 often needs harsh conditions, the insertion of18F in those molecules poses an exceeding challenge. Two major challenges during18F-labeling are a regioselective introduction and a fast and high yielding way under mild conditions. Furthermore, attention has to be paid to functionalities, which are usually present in complex structures of the target molecule. The Cu-catalyzed azide-alkyne cycloaddition (CuAAC) and several copper…
Ventilation-Perfusion Ratio in Perflubron During Partial Liquid Ventilation
2010
BACKGROUND: Functional magnetic resonance imaging (fMRI) of fluorine-19 allows for the mapping of oxygen partial pressure within perfluorocarbons in the alveolar space (Pao(2)). Theoretically, fMRI-detected Pao(2) can be combined with the Fick principle approach, i.e., a mass balance of oxygen uptake by ventilation and delivery by perfusion, to quantify the ventilation-perfusion ratio (Va/Q) of a lung region: The mixed venous blood and the inspiratory oxygen fraction, which are equal for all lung regions, are measured. In addition, the local expiratory oxygen fraction and the end capillary oxygen content, both of which may differ between the lung regions, are calculated using the fMRI-detec…
P-Glycoprotein Influence on the Brain Uptake of a 5-HT2A Ligand: [18F]MH.MZ
2010
<i>Background/Aims:</i> The serotonergic system, especially the 5-HT<sub>2A</sub> receptor, is involved in various diseases and conditions. We have recently developed a new [<sup>18</sup>F]-5-HT<sub>2A</sub> receptor ligand using an analogue, MDL 100907, as a basis for molecular imaging with positron emission tomography. This tracer, [<sup>18</sup>F]MH.MZ, has been shown to be an adequate tool to visualize the 5-HT<sub>2A</sub> receptors in vivo. However, [<sup>18</sup>F]altanserin, similar in chemical structure, is a substrate of efflux transporters, such as P-glycoprotein (P-gp), of the blood-brain barrier…
SYNTHESIS AND IN VITRO AFFINITIES OF VARIOUS MDL 100907 DERIVATIVES AS POTENTIAL 18F-RADIOLIGANDS FOR 5-HT2A RECEPTOR IMAGING WITH PET
2008
Radiolabelled piperidine derivatives such as [(11)C]MDL 100907 and [(18)F]altanserin have played an important role in diagnosing malfunction in the serotonergic neurotransmission. A variety of novel piperidine MDL 100907 derivatives, possible to label with (18)F-fluorine, were synthesized to improve molecular imaging properties of [(11)C]MDL 100907. Their in vitro affinities to a broad spectrum of neuroreceptors and their lipophilicities were determined and compared to the clinically used reference compounds MDL 100907 and altanserin. The novel compounds MA-1 (53) and (R)-MH.MZ (56) show K(i)-values in the nanomolar range towards the 5-HT(2A) receptor and insignificant binding to other 5-HT…
(18) F-labeled folic acid derivatives for imaging of the folate receptor via positron emission tomography.
2013
The folate receptor (FR) is already known as a proven target in diagnostics and therapy of cancer. Furthermore, the FR is involved in inflammatory and autoimmune diseases. The major advantage as a valuable target is its strongly limited expression in healthy tissues. Over the past two decades, several folic acid-based radiopharmaceuticals addressing the FR have been developed, and some of them show great potential for applications in clinical routine. However, most of these radiofolates were developed for single photon emission computed tomography imaging, and only a few can be used for positron emission tomography (PET) imaging. The development of suitable (18) F-labeled derivatives for PE…
Selective binding to monoamine oxidase A: in vitro and in vivo evaluation of (18)F-labeled β-carboline derivatives.
2015
In this study we synthesized four different (18)F-labeling precursors for the visualization of the monoamino oxidase A using harmol derivatives. Whereas two are for prosthetic group labeling using [(18)F]fluoro-d2-methyl tosylate and 2-[(18)F]fluoroethyl-tosylate, the other three precursors are for direct nucleophilic (18)F-labeling. Additionally the corresponding reference compounds were synthesized. The syntheses of [(18)F]fluoro-d2-methyl-harmol and 2-[(18)F]fluoroethyl-harmol were carried out using harmol as starting material. For direct nucleophilic (18)F-labeling of the tracers carrying oligoethyled spacers (PEG), a toluenesulfonyl leaving group was employed. The radiolabeling, purifi…
Total synthesis and evaluation of [18F]MHMZ.
2007
Radiochemical labeling of MDL 105725 using the secondary labeling precursor 2-[(18)F]fluoroethyltosylate ([(18)F]FETos) was carried out in yields of approximately 90% synthesizing [(18)F]MHMZ in a specific activity of approximately 50MBq/nmol with a starting activity of approximately 3GBq. Overall radiochemical yield including [(18)F]FETos synthon synthesis, [(18)F]fluoroalkylation and preparing the injectable [(18)F]MHMZ solution was 42% within a synthesis time of approximately 100 min. The novel compound showed excellent specific binding to the 5-HT(2A) receptor (K(i)=9.0 nM) in vitro and promising in vivo characteristics.
Efficient microwave-assisted direct radiosynthesis of [(18)F]PR04.MZ and [(18)F]LBT999: selective dopamine transporter ligands for quantitative molec…
2009
Abstract PR04.MZ 8-(4-fluoro-but-2-ynyl)-3- p -tolyl-8-aza-bicyclo[3.2.1]octane-2-carboxylic acid methyl ester ( 1 ) and LBT999 8-(( E )-4-fluoro-but-2-enyl)-3b- p -tolyl-8-aza-bicyclo[3.2.1]octane-2β-carboxylic acid methyl ester ( 2 ) are selective dopamine reuptake inhibitors, derived from cocaine. Compounds 1 and 2 were labelled with fluorine-18 at their terminally fluorinated N-substituents employing microwave enhanced direct nucleophilic fluorination. K[ 18 F]F − Kryptofix ® 222 cryptate, tetrabutyl ammonium [ 18 F]fluoride and caesium [ 18 F]fluoride were compared as fluoride sources under conventional and microwave enhanced conditions. Fluorination yields were remarkably increased un…
Synthesis of No-Carrier-Added 4-[18F]Fluorophenol from 4-Benzyloxyphenyl-(2-thienyl)iodonium Bromide
2011
4-[(18)F]Fluorophenol is a versatile synthon for the synthesis of more complex radiopharmaceuticals bearing a 4-[(18)F]fluorophenoxy moiety. In order to prepare 4-[(18)F]fluorophenol in no-carrier-added (n.c.a.) form only a nucleophilic labelling method starting from [(18)F]fluoride is suitable. In this paper a new, two step radiosynthesis starting from 4-benzyloxyphenyl-(2-thienyl)iodonium bromide and [(18)F]fluoride with subsequent deprotection is described, yielding n.c.a. [(18)F]fluorophenol in 34 to 36% radiochemical yield.
Analysis of the spatial distribution of free radicals in ammonium tartrate by pulse EPR techniques
2009
Using pulse electron paramagnetic resonance (EPR) on a series of l(+)-ammonium tartrate (AT) dosimeters exposed to radiations with different linear energy transfer (LET), we assessed the ability of pulse EPR spectroscopy to discriminate the quality of various radiation beams such as (60)Co gamma-ray photons, protons and thermal neutrons at various doses by analyzing the local radical distributions produced by the different beams. We performed two types of pulse EPR investigations: two-pulse electron spin echo decay obtained by varying the microwave power, and a double electron-electron resonance (DEER) study. Both methods provide information about the dipolar interactions among the free rad…