To DCBO-terminal alkyne linker S8 (1.0 mg, 1.1 µmol) was added (MeCN)4Cu(I)BF4 (1.5 mg, 4.8 µmol). The mixture was then dissolved in 40 µL of anhydrous DMF under nitrogen. The resultant solution was incubated in darkness under nitrogen at room temperature for 30 minutes, to ensure coordination of Cu(I) to the DBCO unit of S8, thereby prohibiting its ability to partake in strain-promoted azide-alkyne cycloaddition reactions. 1.8 µL of the S8 / (MeCN)4Cu(I)BF4 mixture was then delivered to the azide-JVZ007 solution, delivering an ~10-fold excess of copper-pretreated S8 relative to azide-JVZ007. 200 equivalents of (+)-sodium L-ascorbate was then delivered (using 10 µL of 100 mM stock solution). The reaction vessel was sealed shut to prevent excess oxygen diffusing into the sample, and the sample was incubated for 3 hours at 37 °C while the copper catalysed click reaction between the terminal alkyne of 17 and the aryl azide of azide-JVZ007 ensued. After this time, the sample was diluted to a volume of 1 mL using pH 7 100 mM sodium EDTA solution and then dialysed overnight into pH 7 100 mM sodium EDTA solution using 3.5 kDa dialysis tubing. During this step any copper coordinated to DBCO is removed, restoring the ability of the DBCO motif to partake in strain-promoted azide alkyne cycloaddition reaction. The sample was then dialysed into HPLC-grade water. This yielded DBCO-JVZ007 (SI, Figure ), which was characterised by UV-vis and mass spectrometry analyses (SI, Figure ). The DBCO-JVZ007 sample was then flash-frozen using liquid nitrogen and lyophilised.