Protein/peptide bioconjugation α-oxo aldehyde LYRAG was prepared and characterised exactly as previously reported. Conversion experiments. To α-oxo aldehyde LYRAG 2 in pH 7.5 sodium phosphate buffer was added a stock of SCALP donor in DMSO such that the final concentrations/conditions of the reaction solution were 0.1 mM 2, 2 mM SCALP donor, 20 mM sodium phosphate, pH 7.5. The resultant solutions were incubated at 37 °C for 1 h prior to analysis by mass spectrometry. Percentage conversions were calculated from the relative integrals of the UV chromatogram traces of α-oxo aldehyde LYRAG and SCALP-LYRAG products in HPLC-traces (Figure , Figure ).