Radiochemical yield

Generally, labeled compounds are prepared by procedures which introduce the radionuchde at a late stage of the synthesis. This allows for maximum radiochemical yields, and reduces the handling time of radioactive material. When dealing with short half-life isotopes, a primary consideration is the time required to conduct synthetic procedures and purification methods. 

Substrate Methoef Synthesis Time (mmf Radiochemical Yield (%f Ref... 

Ammo And Agent Radiochemical Yield (%f 2- Isomer Distribution (%) - 4-... 

F-Labeled pirenperone (9) was prepared with high radiochemical yield (72%) and high purity (99%) for PET studies from pirenperone using a [ F] fluoride-cryptand-oxalate system (95CL835). 

Methyl- C]thymine ([ C]FMAU) could be obtained in modest radiochemical yields via cross-coupling of [ CJmethyl iodide with l-(2 -deoxy-2 -fluoro-/3-D-arabinofuranosyl)-5-(trimethylstannyl)uracil. Optimal power was found to be 70W, since an increase to 100 W as well as a decrease to SOW resulted in lower radiochemical yields (Scheme 6). 

The radiochemistry of ruthenocene has been studied by Baumgartner and Reichold (9) and by Harbottle and Zahn (29). It is found that neutron irradiation of crystalline RuCp2 yields about 10% of the radioactive ruthenium as RuCp2- More specifically, an isotopic difference in the radiochemical yield is found Ru, 9.6 0.1% Ru, 10.7 0.2% and Ru, 9.9 0.2% (29). In liquid solution the isotopic effect is much more pronounced, although the yields are lower. This was suggested by Harbottle as a general principle the greatest isotope effects are associated with the lowest yields. While this principle has not yet been substantiated, it seems reasonable since any thermal reactions which may increase the yields would not likely show any isotope effect. 

Radiochemical Yields in some Manganese Compounds, Following Neutron Activation... 

A specialized application of microwave-assisted organic synthesis involves the preparation of radiopharmaceuticals labeled with short-lived radionuclides, particularly for use in positron emission tomography [70-72]. This represented an excellent application of microwave technology, where the products must be prepared quickly and in high radiochemical yield, on a small scale. 

A particularly useful application of MW-assisted synthesis at elevated pressure has been in the preparation of radiopharmaceuticals containing isotopes with short half-lives, such as C-ll (half-life 20 min) and F-18 (half-life 110 min) [25-27]. Clearly, these compounds have to be synthesized very rapidly in order to give products with high radiochemical yield. For example, [1-11C] tyrosine 12 was synthesized using the two step Bucher-Strecker method by the reaction of p-hydroxyphenylacetaldehyde bisulfite adduct 11 with K11CN and (NH4)2C03 followed by hydrolysis with aqueous NaOH (Scheme 4.7)... 

Using conventional heating each step involved heating at 170 °C for 10 min, giving an overall radiochemical yield of 40-60%. In contrast, MW heating in a closed Pyrex tube gave a radioactivity gain of 91 % in a total reaction time of 1 min. 

Ballestra et al. [32] described a radiochemical measurement for determination of "technetium in rain, river, and seawater, which involved reduction to technetium (IV), followed by iron hydroxide precipitation and oxidation to the heptavalent state. Technetium (VII) was extracted with xylene and electrode-posited in sodium hydroxide solution. The radiochemical yield was determined by gamma counting on an anticoincidence shield GM-gas flow counter. The radiochemical yield of 50 to 150 litre water samples was 20-60%. 

Holm et al. [74] used a spectrometry for the determination of 237neptunium in seawater. The actinides are preconcentrated from a large seawater sample by hydroxide precipitation. The neptunium was isolated by ion exchange, fluoride precipitation, and extraction with TTA. 238Neptunium or 235neptunium was used to determine the radiochemical yield. 

The radiochemical oxidation of PS in a chloroform solution is accompanied by its destruction and formation of products of styrene oxidation, namely, benzaldehyde and styrene oxide [136]. The radiochemical yield of these products was equal to the radiochemical yield of PS macromolecule cleavages. Butyagin [137] analyzed the products of decomposition of the peroxyl radicals of PS and polyvinyIcyclohexane. Alkyl macroradicals were produced mechano- or photochemically, volatile products were evaporated in vacuum, and alkyl radicals were converted into peroxyl radicals using labeled lsO. Peroxyl radicals were then... 

At room temperature the chemical and radiochemical yields of 155 were different. The chemical yields were in the 30-40% range, while the radiochemical, not very reproducible yields were in the 6-15% range. Cattel and coworkers122 assigned these differences to tritium isotope effect in the Wittig reaction. No correlation between the specific activity of 155 and the degree of chemical conversion of 157 into 155 has been presented. The temperature dependence of the observed secondary tritium isotope effect has also not been... 

Starting with 3 GBq [nC]carbon dioxide produced in a 14N(p,a)11C nuclear reaction, the radiochemical yield of 165 was 0.5 GBq at the end of preparative purification performed in Sep-Pak C18 columns. The methyl esters of prostaglandins have a high affinity for the specific binding sites141. 

R1 = 14 (XXII I2CI, R2 = Me, specific activity 55 mCimmol, radiochemical yield 26.1%... 

This potent inhibitor of cholesterol biosynthesis has been synthesized178 by one-pot esterification of the alcohol 210 with the acid chloride of 2,2-dimethylbutanoic[l-14C] acid, obtained by carbonation of the Grignard reagent prepared from 2-chloro-2-methylbutane (equation 74). Desilylation of 211 afforded [14C]simvastatin 209 in 29% radiochemical yield from 14C-labelled C02. This 14C-labelled drug was needed for elucidation of its metabolic fate in experimental animals. 

I] 214) 52% radiochemical yield after HPLC, specific activity 27 Ci mmol ( 100% radiochemical purity... 

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