Peptides occupy a unique chemical space and role within the pharmaceutical landscape, within which they can outperform small molecules and larger biologics. The ability to modify peptides and proteins chemoselectively remains of significant interest, with peptide conjugation, lipidation, stapling and disulfide engineering at the forefront of modern peptide chemistry. We have developed a robust method for the incorporation of an allenamide functional group to the N-terminus or side chain amino group of a peptide in solid-phase.1 Previously unexplored as a peptide functional group, the allenamide offers a versatile tool for chemoselective inter- or intramolecular bridging reactions with thiols, e.g. conjugation, lipidation or cyclisations, including disulfide mimicry. The bridging reaction is biocompatible, occurring spontaneously at pH 7.4 in catalyst free aqueous or organic media. Employing this “click” approach, a model peptide was successfully modified with a diverse range of alkyl and aryl thiols with excellent conversions. Furthermore, this technique was demonstrated as a valuable tool to induce spontaneous intramolecular cyclisation by preparation of an oxytocin analogue, where the native disulfide bridge was replaced by a vinyl sulfide moiety, formed via thia-Michael addition of a cysteine thiol to an allenamide handle. Building upon these findings, we have more recently employed the allenamide modification in solution phase during a semi-synthetic preparation of polymyxin B analogues, aiming to reduce the nephrotoxicity of the parent antimicrobial cyclic lipopeptide. Taking a common allenamide bearing precursor, we further optimised the thia-Michael addition to effect lipidation with less reactive alkyl thiols to yield rapid and near quantitative conversions to vinyl sulfide linked lipopeptides. Leveraging this platform, we prepared a series of semi-synthetic polymyxin B analogues in up to 20 % overall yield, over five synthetic steps. Their antimicrobial activity was assessed towards Gram negative bacteria and their nephrotoxicity evaluated in a leading kidney organoid model.