Synthesis and application of a Sec2-containing oligopeptide for method evaluation purposes in selenium speciation

Sec2-containing oligopeptide was synthesized directly from Sec2 with the traditional liquid phase peptide synthesis without addressing the usually applied and complex solid phase (SPPS) protocol driving through a protected Sec residue and site-oriented oxidation into a diselenide bridge. Effective solubilization of Sec2 in dimethylformamide and its pH-controlled access to pentachlorophenol-activated peptides to couple with were of crucial importance to achieve good yield (>50%) of synthesis, monitored by HPLC-UV, SEC–ICP-MS and HPLC–ESI-MS techniques. To demonstrate the possible application of the new compound, (Boc-GGFG)–Sec2–(Boc-GGFG) (m/z 1173.3, [M+H]+), it was utilized to compare the effect of the two most addressed sample preparation techniques, i.e., methanesulphonic acid (MSA) based digestion and proteolytic digestion with protease XIV, on the Sec residue. The study revealed that the use of MSA resulted in the decomposition of Sec even after derivatization with iodoacetamide.