Antimicrobially active cycloundecapeptides related to gramicidin S having a novel turn structure with cisD-Phe-Pro peptide bond

Antimicrobially active cycloundecapeptides related to gramicidin S, cyclo(-Val1-Orn2-Leu3-X4-D-Phe5-Pro6-Val7-Orn8- Leu9-D-Phe10-Pro11-) (X= Leu (1), Ala (2), Orn (3), Lys (4) and Arg (5)), were synthesized. From the CD and NMR studies, 1–5 possess antiparallel β-sheet conformation linked by a type II’β-turn around D-Phe10-Pro11 and a novel turn structure around X4-D-Phe5-Pro6 sequence with cisD-Phe-Pro peptide bond. The structural modifications at position 4 of 1–5 are beneficial to identification of novel antibiotic candidates without hemolytic activity.