An iterative synthesis of radiolabelled polyethylene glycol oligomers

A synthetic method has been developed for the iterative preparation of unlabelled and 3H-polyethylene glycol (PEG) oligomers. The strategy involved alkylating the sodium anion of mono-tritylated ethylene glycol oligomers (Ph3C[OCH2CH2]nOH, n=1-28) with O-tosyl-O-allyl-triethylene glycol or O-tosyl-O-allyl-pentaethylene glycol. Subsequent ozonolysis of the terminal olefin followed by reduction with NaBH4 or NaB[3H]4 provided the next higher mono-tritylated ethylene glycol oligomer which could be deprotected to the final glycol oligomer (H[OCH2CH2]nOH, n=4-34) or carried on in the iterative process. The method provides discrete PEG oligomers of high specific activity (20.6-48.6 mCi/mmoL) in 96-98% radiochemical purity. (author)