2.1. Peptide Solid Phase Synthesis

All peptide derivatives were synthesized according to standard SPPS (solid-phase peptide synthesis) procedures using the Fmoc/tBu strategy [27]. The Rink amide MBHA resin (substitution 0.71 mmol/g) was selected as the solid-phase support to provide amidated peptides at the C-terminus. Each peptide was synthetized using a scale of 0.20 mmol in DMF. The resin was allowed to swell for 30 min in the reactor, and then the Fmoc group was deprotected by treating the resin with 30% (v/v) piperidine in DMF (two cycles of 10 min). The coupling of each amino acid was performed by adding a 2-fold molar excess of the protected Fmoc-amino acid, with equimolar amounts of 1-hydroxybenzotriazole (HOBt), benzotriazol-1-yl-oxytris-pyrrolidino-phosphonium (PyBOP), and a 4-fold molar excess of diisopropylethylamine (DIPEA) in DMF/NMP. All couplings were performed twice for 40 min. At the end of the synthesis, crude peptides were fully cleaved from the resin with a TFA (trifluoroacetic acid)/TIS (triisopropylsilane)/H₂O (92.5/5/2.5 v/v/v) mixture at room temperature for 3 h. All the peptides were precipitated with cold ether and freeze-dried for three times. The purification of the crude products was carried out by RP-HPLC. Mass spectra confirmed the identity of the products (see Table 1 for analytical data of peptides).

Formula, theoretical and experimentally found molecular weight (MW) and retention time of investigated peptides.