Click for PET. Click chemistry as a tool for 18F radiolabelling

PhD ceremony: Ms. L.S. Campbell-Verduyn, 12.45 uur, Academiegebouw, Broerstraat 5, Groningen

Dissertation: Click for PET. Click chemistry as a tool for 18F radiolabelling

Promotor(s): prof. B.L. Feringa, prof. P.H. Elsinga, prof. R.A. Dierckx

Faculty: Mathematics and Natural Sciences

This thesis explores the application of ‘click’ chemistry in the field of [18F]-radiolabelling for positron emission tomography, a nuclear imaging technique. Radiochemistry presents a unique set of challenges: short synthetic time frames, small amounts of reagents, and limited available methods of characterization. Superimposed on these challenges is the requirement that the products be consistently pure and the results reproducible as ultimately the protocols may be used to prepare compounds for injection in patients. The copper-catalyzed 1,3-dipolar cycloaddition of alkynes and azides (CuAAC) and its copper-free counterpart promoted by ring strain have both proven to be reliable and orthogonal ligations. The CuAAC in particular is rapid, amenable to a wide range of conditions, selective and robust. In a field where simplicity and speed of reaction are crucial, ‘click’ chemistry began to emerge as an excellent radiolabelling technique. Two main goals were pursued; first to accelerate the rate of the CuAAC and secondly to explore ways to avoid using copper in the ‘click’ reaction to allow for in vitro and in vivo labeling. The first goal was achieved by using the phosphoramidite MonoPhos as a ligand which dramatically increased the reaction rate. The second goal was achieved using in situ generated benzyne to react with azides yielding benzotriazoles, as well as by synthesizing a strained cyclooctyne. Both methodologies, copper-catalyzed and copper-free were used to label bombesin, a peptide frequently used for imaging certain types of cancer, with [18F].