Three new cyclotetrapeptides isolated from Streptomyces sp. 447

Three new cyclotetrapeptides, named cyclo-(L-Leu-L-Glu-L-Leu-L-Glu) (1) cyclo-(L-Ile-L-Glu-L-Ile-L-Glu) (2) and cyclo-(L-Val-L-Glu-L-Val-L-Glu) (3), were isolated from Streptomyces sp. 447 obtained from endophytic actinobacteria. The producer strain was characterized as Streptomyces sp. by 16s rDNA sequencing. The structures of the three peptides were successfully assigned on the basis of 1D and 2D NMR spectroscopic and mass spectrometry analysis, while the absolute configuration of the amino acid residues was established by amino acid hydrolysis followed by derivatization and GC-MS experiments. Antimicrobial activities of the new compounds were studied.