Synthesis of 3′-deoxy-3′-fluorothymidine (FLT) 5′-O-glucuronide: a reference standard for imaging studies with [18F]FLTDRN conceived this study; BTG, SJH and DRN wrote the manuscript; SJH and TR performed the chemical synthesis supervised by CC, BTG and RJG; MG performed the HPLC analysis

Reaction of methyl 2,3,4-tri- O -acetyl-1- O -(trichloroacetimidoyl)-α- d -glucopyranuronate with 3′-deoxy-3′-fluorothymidine in the presence of trimethylsilyl trifluoromethanesulfonate gave (2 R ,3 R ,4 S ,5 S ,6 S )-2-(((2 R ,3 S ,5 R )-3-fluoro-5-(5-methyl-2,4-dioxo-3,4-dihydropyrimidin-1(2 H )-yl)tetrahydrofuran-2-yl)methoxy)-6-(methoxycarbonyl)tetrahydro-2 H -pyran-3,4,5-triyl triacetate, which was hydrolysed to 3′-deoxy-3′-fluorothymidine-5′-glucuronide. Analysis of this reference standard by high performance liquid chromatography enabled the identification of [ 18 F]3′-deoxy-3′-fluorothymidine-5′-glucuronide in blood samples from six human patients who had been administered [ 18 F]3′-deoxy-3′-fluorothymidine. The de novo synthesis of 3′-deoxy-3′-fluorothymidine-5′- O -glucuronide enabled both the analysis of this reference standard by HPLC and identification of the metabolite in a blood sample from a patient administered [ 18 F]FLT.