Beside azide-bearing 2a, other hypervalent iodine reagents could be used as labelling reagents under the same reaction conditions (Scheme 4). EBX with alkyne (2b), chlorine (2c) and alcohol (2d) functional groups as well as a rhodamine fluorophore (2e), were successfully added to the N-terminal tyrosine of β-casomorphin human peptide (3r) to give VBXs 3rb-3re. In addition, jagaricin 3w, was labeled with a fluorescent rhodamine 2e and the isolated O-VBX (3we) could be used as a fluorescent stain in Candida albicans cells (see Supporting Information for microscopy images). Interestingly, TMS-EBX (2f) led to unsubstituted bioconjugate 3rg. Such a result was previously observed on cysteine, and is due to a fast and complete desilylation of TMS-EBX (2f) to give the free EBX (2g). However, unlike with cysteine, where the generated S-VBX underwent a slow rearrangement into the ethynylated product, the unsubstituted O-VBX 3rg remained stable over time. During screening of EBX reagents, some limitations were observed. TIPS-and Ph-EBX (2h and 2i) did not provide the expected labelled product 3rh and 3ri. No reaction occurred, which could be due to the low solubility of these reagents in aqueous media. Similarly, low conversion was obtained with p-NO2 substituted EBX 2j to give product 3rj. When the water soluble EBX 2k was used, no improvement was observed and less than 5% of bioconjugate 3rk was formed. Scheme 4. Scope of EBX reagents on β-casomorphin human peptide 1r and jagaricin (1w). HPLC-MS yields are given as indicated in Scheme 1.