Infectious diseases caused by drug-resistant bacteria are one of the most serious problems currently facing the medical field, as warned by the CDC1 and the WHO.2,3 Among these drug-resistant bacteria, methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus faecalis/faecium (VRE) are two of the most intractable nosocomial pathogens that show broad-range drug resistance. Vancomycin has been used as the last resort for the treatment of infectious diseases caused by S. aureus and enterococci; however, since 1986, VRE strains have emerged and become widespread.4,5 Since the beginning of this century, vancomycin intermediate-resistant S. aureus have been frequently isolated6 and 33 strains of vancomycin high-level resistant S. aureus have also emerged in Asian countries and in the United States.7 Effective drugs against these pathogens are urgently needed.During the course of our screening for antibiotics active against both methicillin-resistant S. aureus and VRE, pargamicin A (PRG-A, Figure 1) was discovered from the fermentation broth of soil actinomycete strain Amycolatopsis sp. ML1-hF4.8 PRG-A is a structurally unique cyclic peptide consisting of N-methyl-3-hydroxy valine, 4-hydroxy piperazic acid (4-OH-Pip), sarcosine, phenylalanine, N-hydroxy isoleucine (NOH-Ile) and piperazic acid (Pip), which shows excellent in vitro antibacterial activity that is either comparable to, or more potent than, that of other currently available drugs, including vancomycin.8 Our previous studies revealed that PRG-A exerted rapid bactericidal activity against staphylococci and enterococci via a mechanism that involved disruption of the membrane integrity of the target cells,9 a mode of action distinct from that of daptomycin.9,10 During the process of optimization of PRG-A production, we discovered new active components PRG-B, -C and -D (Figure 1) in the culture broth of the PRG-A-producing strain Amycolatopsis sp. ML1-hF4. This present study investigates the fermentation, isolation, structural elucidation and antimicrobial activities of these new PRG-A-analogs and discusses the structure–activity relationship of PRGs.