To apply this technology to biomedically relevant peptides, the hormone oxytocin was synthesised with alGly replacing one of the Cys residues in the peptide to install a hydrocarbon 'brace' in place of the native disulfide (carba-oxytocin). This modification has been previously explored to enhance the proteolytic and hydrolytic stability of the hormone. Positioning alGly at the N-terminus and Cys at an internal position for this model (52, SI) failed to afford the desired product when applying the cyclisation conditions, instead producing desulfurised linear material only. Interestingly, Scanlan, Petracca and co-workers observed the same challenge when attempting to cyclise oxytocin via a thiol-ene reaction using an N-terminal alGly residue. We found that switching the positions of the Cys and alGly residues (sequence 53) reinstated the cyclisation, affording the desired macrocycle in moderate yield (54, 52% isolated yield, Figure ).