Subsequently, 4-methyoxyphenyl)acetaldehyde 9 was selected as a scaffold upon which to construct a more complicated functionalised SCALP probe, as the phenol moiety could easily be derivatised. Accordingly, biotinylated SCALP donor probe S6 (SI, Figure ) was synthesised using solid phase peptide synthesis. SCALP bioconjugation between α-oxo aldehyde JVZ007 and biotinylated-SCALP donor probe S6 yielded biotin-JVZ007, and the successful biotinylation was verified by both western-blot and protein mass spectrometry analyses (Figure ). Protein mass spectrometry again showed the biotin-JVZ007 SCALP product to be present in several forms derived from the expected β-hydroxy aldehyde cross-aldol product; as a hydrate and a hemiacetal (Figure ). Finally, we used the biotin-JVZ007 bioconjugate in flow cytometry experiments to demonstrate that JVZ007 still bound to PSMA selectively when modified at its N-terminus using PSMA-positive LNCaP cells and PSMAnegative PC3 cells (Figure ), verifying that this labelling was indeed PSMA-specific via a competition experiment with unlabelled JVZ007 (Figure ).