To conclude, we have demonstrated that SCALP can be used as a mild site-selective C-C bond forming bioconjugation for -oxo aldehydes biomolecules and simple aldehyde probes that bear acidic α-protons, without the need for catalysts. SCALP donors that bear electron-withdrawing substituents undergo conjugation more rapidly than SCALP donors bearing electrondonating substituents, which we attribute to the lowering of the pKa of the α-proton by electron-withdrawing groups making the enolate form of the SCALP donor more accessible. We also demonstrate the potential utility of SCALP for the preparation of protein bioconjugate therapeutics by selectively biotinylating the PSMA binding nanobody JVZ007. Furthermore, we demonstrate the suitability of SCALP in conjunction with established downstream bioconjugation methodologies by installing azide functionality onto JVZ007 and subsequently subjecting the resultant azide-JVZ007 bioconjugate to successive copper-catalysed Huisgen cycloaddition and copperfree strain-promoted azide-alkyne Huisgen cycloadditions. We anticipate that SCALP may find wide applications for the construction of the protein-small molecule bioconjugates where the stability of the targeted protein scaffold is compromised in the presence of excess small reagents such as catalysts, or by acidic/basic pH.