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

Antimicrobially active cycloundecapeptides related to gramicidin S, cyclo(-Val(1)-Orn(2)-Leu(3)-X(4)-D-Phe(5)-Pro(6)-Val(7)-Orn(8)-Leu(9)-D-Phe(10)-Pro(11)-) (X=Leu (1), Ala (2), Orn (3), Lys (4) andArg (5)), were synthesized. From the CD and NMR studies, 1-5 possess antiparallel beta-sheet conformation linked by a type II' beta-turn around D-Phe(10)-Pro(11) and a novel turn structure around X(4)-D-Phe(5)-Pro(6) sequence with cis D-Phe-Pro peptide bond. The structural modifications at position 4 of 1-5 are beneficial to identification of novel antibiotic candidates without hemolytic activity.