Solid-Phase Synthesis of Omiganan Peptide

Omiganan (ILRWPWWPWRRK-NH₂) was synthesized as described previously [38 (link)]. The peptide was synthesized manually by the solid-phase method using Fmoc chemistry on polystyrene Rink amide resin with a loading of 1.0 mmol/g (Orpegen Peptide Chemicals GmbH, Heidelberg, Germany). Single deprotection of the Fmoc group was performed with a 20% (v/v) piperidine (Merck, Darmstadt, Germany) solution in DMF (Honeywell, Seelze, Germany) for 15 min. Acylation of Fmoc-AA-OH was conducted in a DCM/DMF (1:1, v/v) solution with OxymaPure and DIC as coupling reagents (equimolar mixture of reagents) for 1.5 h using a threefold molar excess based on the resin. Every step was preceded by rinsing the resin and running the chloranil test. Cleavage of Omiganan was accomplished in TFA (Apollo Scientific, Denton, UK) and scavengers’ mixture—TIS (Sigma-Aldrich, St. Louis, MO, USA), phenol (Sigma-Aldrich, St. Louis, MO, USA), and deionized water (92.5:2.5:2.5:2.5, v/v/v/v) for 1.5 h with agitation. The cleaved peptide was precipitated with cold diethyl ether and lyophilized. Omiganan was purified by reversed-phase high-performance liquid chromatography, and its identity was confirmed by mass spectrometry (ESI-MS).