Syntheses of low-hemolytic antimicrobial gratisin peptides.

Antibiotic and hemolytic activities of gratisin (GR), cyclo(-Val(1)-Orn(2)-Leu(3)-d-Phe(4)-Pro(5)-d-Tyr(6)-)(2), and fifteen GR analogues, which have various d-amino acid residues in place of d-Tyr(6,6') residues, were examined. Among them, [d-Orn(6,6')]-GR, [d-Lys(6,6')]-GR and [d-Arg(6,6')]-GR showed the strong activity against both Gram-positive and Gram-negative bacteria. In addition, the antibiotics showed significantly reduced toxicity against human blood cells compared with gramicidin S, cyclo(-Val(1)-Orn(2)-Leu(3)-d-Phe(4)-Pro(5)-)(2).