Rapid, one‐step, high yielding 18F‐labeling of an aryltrifluoroborate bioconjugate by isotope exchange at very high specific activity

Abstract

A rapid, single step, aqueous 18F‐labeling method that proceeds under mild conditions to provide radiotracers in high radiochemical yield and at high specific activity represents a long‐standing challenge. Arylboronates capture aqueous 18F‐fluoride ion in buffered pH 2–3 at moderate temperature to provide a highly polar 18F‐ArBF3− anion. Similarly, 19F‐18F isotope exchange on a 19F‐ArBF3− should create an 18F‐ArBF3−. We hypothesized that this reaction would proceed in volumes that would be amenable to the high levels of 18F‐activity used in clinical hospitals. In order to measure both radiochemical and chemical yields, along with specific activity, we linked an alkyne‐19F‐ArBF3− to rhodamine azide by standard click chemistry to afford a precursor Rh‐19F‐ArBF3−. This precursor was aliquoted in portions of 50 nmol and lyophilized for on‐demand use. Using robotic manipulators in a hot cell, we combined >29.6 GBq (800 mCi) and 50 nmol of the Rh‐19F‐ArBF3− in aqueous dimethylformamide at buffered pH 2–3. Following mild heating (40 °C) for 10‐15 min, the reaction was quenched and analyzed. We observed radiochemical yields of 50% and specific activities of nearly 555 GBq/µmol (15 Ci/µmol). Similar radiochemical yields and slightly lower specific activities were also obtained with ~400 mCi (n = 2). With radiochemical yields in the hundreds of millicuries and specific activities that are 3–10‐fold higher than most radiotracers, this method is very attractive method for preparing clinically useful radiotracers. Moreover, the ability to produce tracers at extraordinarily high specific activities expands the distribution time window from production labs to distant positron emission tomography scanners. Copyright © 2012 John Wiley & Sons, Ltd.