CD Spectra and Cyclization of Linear Pentapeptides as Gramicidin S Precursors with a Benzyloxycarbonyl Group on the Side Chain of Orn Residue

Abstract

Abstract Five pentapeptides related to gramicidin S, H–Val–Orn(Z)–Leu–d-Phe–Pro–OH, H–Orn(Z)–Leu–d-Phe–Pro–Val–OH, H–Leu–d-Phe–Pro–Val–Orn(Z)–OH, H–d-Phe–Pro–Val–Orn(Z)–Leu–OH, and H–Pro–Val–Orn(Z)–Leu–d-Phe–OH, were cyclized with 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride and 1-hydroxybenzotriazole. The pentapeptide with a Pro residue at the C-terminal formed predominantly the cyclic dimer (diZ-gramicidin S), while the pentapeptide with an Orn(Z) residue at the C-terminal produced exclusively the cyclic monomer (Z-semigramicidin S). The reaction mode of those pentapeptides was correlated with their CD spectra.