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Abstract: The reaction of the nca [18F]fluoride ion was investigated toward a series of N6-benzoyl 2",3"-isopropylidene-adenosine-5"-sulfonates including the methane-(mesylate), p-toluene-(tosylate), p-nitro-benzene-(nosylate)- and 2,2,2-trifluoro-ethane-sulfonate (tresylate) derivatives under usual nucleophilic substitution conditions. In these reactions cyclisation of the title compounds was observed whilst the radiofluorination took place only with low yield. The fluorine-18 uptake was found to be 1.17% for mesylate, 1.46% for tosylate, 0.99% for nosylate and 0.40% for tresylate under the conditions applied.

5'-N-(2-[¹⁸F]Fluoroethyl)-carboxamidoadenosine ([¹⁸F]FNECA), a promising ¹⁸F-labelled adenosine agonist has been prepared by two different synthetic routes. In the first, [¹⁸F]fluoride was reacted with 5'-N,N-ethylene-2,',3'-O-isopropylidenecarboxamido-adenosine and after removing the protective group [¹⁸F]FNECA was obtained in a low radiochemical yield (1±1%, means±sd, n=7, decay corrected). In the second, 2-[¹⁸F]fluoro-ethylamine was synthesised according to the literature and reacted with 2',3'-O-isopropylideneadenosine-5'-uronic acid in the presence of a coupling agent. The following hydrolysis step provided the [¹⁸F]FNECA with a modest radiochemical yield (24±9%, n=17, based on [¹⁸F]fluoride-activity). After purification by preparative reverse phase HPLC 18·9–166·5 MBq (0·51–4·5 mCi) [¹⁸F]FNECA was obtained with a specific activity of 2·35±1·14 TBq/mmol (63·5±30·9 Ci/mmol, n-3). The total synthesis took 200 min and the decay corrected radiochemical yield based on [¹⁸F]F⁻ activity was 17±9% (n=5) with more than 99·9% radiochemical purity. This second route provides sufficient [¹⁸F]FNECA for the subsequent biological evaluation using PET-technique. Copyright © 2000 John Wiley & Sons, Ltd.

Abstract: [11C]-labeled form of ten A2a adenosine receptor specific 8-styryl-7-methyl-xanthine derivatives ([11C]-caffeines) were synthesised by N-methylation of the corresponding 8-styryl-xanthine derivatives using [11C]-methyl iodide in optimized reaction conditions. The results show that the [11C]-methylations take place with excellent radiochemical yields (35–93%), and can be utilised easily in online preparations. These labeled ligands may facilitate the positron emission tomographic (PET) investigation of adenosine A2a receptors.

We carried out spectrofluorimetric and flow cytometric measurements to investigate the effect of hypo-osmotic shock on cell membranes of common carp sperm. The time course of the permeability of the sperm cell membrane, as monitored by DNA-related propidium iodide (PI) fluorescence, was followed for 30 min after dilution of semen in hypo-osmotic environments of different ionic strengths. Spectrofluorimetric measurements indicated a continuous increase in the total PI emission intensity of a sperm suspension. Cell-by-cell flow cytometric measurements suggested that the permeability changes were of the all-or-none type. The permeabilized fraction of cells in the individual samples was time and osmolality dependent. The number and percentage of cells in which DNA was stained by PI increased gradually over time and reached a steady-state plateau value after 5-15 min. This equilibrium fraction of cells with a PI-permeable cytoplasmic membrane displayed an inverse relationship with the osmolality of the diluent, having a near 100% value for fresh water and distilled water. Dilution of sperm in hypo-osmotic medium brought about a fast decrease in the forward light-scattering signal on a short time scale compared to the pre-steady-state time of the permeabilization. With the addition of extracellular Ca2+ (1.8 mM), restoration of the light scattering signal was observed. Permeabilization of the membrane and restoration of light scattering were not coincident in time. We propose a two-dimensional reorganization of the lipid structure as the underlying mechanism of the latter process.

5′-Deoxy-5′-[18F]fluoro-adenosine was synthesised by nucleophilic radiofluorination reactions of 5′-deoxy-5′-haloadenosines. The homogeneous isotope exchange in 5′-deoxy-5′-fluoro-adenosine was also investigated. The conversion of these reactions was found to be rather low and depends on the strength of the halogen-carbon bond: 0.248% for chloride-, 0.488% for bromide- and 1.070% for iodide-derivative; there was no reaction observed in the case of fluoro-compound.