Pharmacologically, the novel LUXendins behave as full antagonists at the GLP1R, with similar potency to benchmark Exendin4(9-39). These studies further validate the robustness of the synthetic approach used and highlight the advantages of the S39C C-terminally substituted backbone used previously for Exendin4(9-39) and Exendin4(1-39) . We envisage that a similar backbone might in the future be amenable to functionalization with biotin, complexed lanthanides, singlet oxygen generators or even nanogold particles, for example to allow non-fluorescent labeling for mass spectrometry, magnetic resonance imaging or electron microscopy. With our observation that cyanine fluorophores behave more 'cleanly' in microscopic experiments, we are eager to find out how other molecular markers and tracers behave, and these endeavours are of ongoing interest in our laboratories.