Regioselective Labeling Research Articles

Efficient regioselective labelling of the CFC alternative 1,1,1,2-tetrafluoroethane (HFC-134a) with fluorine-18

Efficient chemistry is described for the regioselective labelling of the CFC alternative 1,1,1,2-tetrafluoroethane with cyclotron-produced positron-emitting fluorine-18 ( t 1 2 = 109.7 min). [1- 18F]1,1,1,2-Tetrafluoroethane was prepared by nucleophilic addition of no-carrier-added [ 18F]fluoride to trifluoroethylene and [2- 18F]1,1,1,2-tetrafluoroethane by nucleophilic displacement of tosylate with [ 18F]fluoride in 2,2,2-trifluoroethyl p-toluenesulphonate. Each reaction was mediated by a potassium cation-Kryptofix ® 2.2.2 complex, with or without acetonitrile as solvent, in a sealed glassy carbon vessel. The selectivities were 97.2±0.4% for labelling in the 1-position by nucleophilic addition and 91.2±1.2% for labelling in the 2-position by nucleophilic substitution. GC separation afforded each labelled tetrafluoroethane in high radiochemical purity (>99.995%) and high chemical purity (>99.6%). Specific radioactivities of about 37 MBq (1 mCi) per μmol were obtained. Each synthesis was fully automated to cope safely with the high initial radioactivity and delivered purified product within one physical half-life of the fluorine-18 The products are suitable for pharmacokinetic studies in man.

Studies of the interaction of the maltose-binding protein of Escherichia coli, a closed-groove binder, with 4,6- O-ethylidenemalto-oligosaccharides (dp 2–5) and its regioselective labelling with 3-azibutyl 1-thio-α-(6- 3H)maltoside

Four malto-oligosaccharides (dp 2–5), each with a 4,6- O-ethylidene group on the glucosyl unit at the non-reducing terminus, were synthesised and used to prove that the maltose-binding protein (MBP) of E. coli is a closed-groove binder. α- d-Glucosylation of 3-azibutyl 1-thio-α- d-(6- 3H)glucopyranoside yielded a 3H-labelled, photolabile 1-thiomaltoside derivative that was used to chemically modify the binding site of MBP. The 3H-labelled peptide containing 83% of the total radioactivity, which was isolated after tryptic cleavage of the modified MBP and sequenced, is part of the closed end of the MBP groove.