F-Fluorothymidine FLT

18F-FLT is prepared by nucleophilic reaction between 18F-sodium fluoride and a precursor, 2,3 -anhydro-5,-0-benzoyl-2 -deoxylhymidine, which is prepared by standard organic synthesis (Machula et al, 2000). 18F-sodium fluoride is added to a mixture of Kryptofix 2.2.2 and potassium carbonate in acetonitrile, and the mixture is dried to a residue by heating at 120°C for 5 min. The precursor in dimethyl sulfoxide (DMSO) is added to the dried residue and heated at 160°C for 10 min. Hydrolysis of the 5 -0-protecling 

Since thymidine is incorporated into DNA and provides a measure of cell prohferation, 18F-FLT is commonly used for in vivo diagnosis and characterization of tumors in humans. 

This is an 18F-labeled pyridaben derivative that binds to mitochondrial complex I of the electron transport chain with high affinity. It is prepared by mixing dry 18F-containing Kryptofix 2.2.2 with BMS-747155-01 in dry acetonitrile and heating at 90°C for 10 min (Huisman et al, 2008). The product is then purified further by HPLC to give an overall radiochemical yield of 50-60% and radiochemical purity of 99%. 

18F-BMS-747158-02 is being evaluated for clinical use in humans for the measurement of myocardial perfusion by PET. 

The synthesis of 18F-FET is carried out in two steps (Wester et al, 1999) First, ethylene glycol-1,2-ditosylate in acetonitrile is reacted with dry 18F-containing Kryptofix 2.2.2 and potassium bicarbonate at 90°C for 10 min. The product is purified by absorbing it on a polystyrene cartridge and then eluting with dimethylsulfoxide. Second, the eluate is mixed with dipotassium sodium salt of L-tyrosine and heated at 90°C for 10min. The mixture is purified by HPLC and cation exchange to afford 18F-FET. The radiochemical yield is about 40-45% with purity between 97 and 99%. 

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The proliferation of tumor cells is the basic mechanism for malignant growth. Therefore, it has been tried to image this parameter, which is thought to be more specific for malignancy compared to, for example, glucose consumption. [ F]-fluorine-labeled thymidine analog 3 -deoxy-3 -[ F]-fluorothymidine (FLT) is retained in the cell after phosphorylation by thymidine kinase 1, whose levels correlate with cell proliferation. 

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