Definition: Peptides whose amino and carboxy ends are linked together with a peptide bond forming a circular chain. Some of them are ANTI-INFECTIVE AGENTS. Some of them are biosynthesized non-ribosomally (PEPTIDE BIOSYNTHESIS, NON-RIBOSOMAL).
GE 2270 A [ GE 2770,GE-2270,GE-2270A,GE2270,GE2270 A,GE2270A,MDL 62879 ] from Planobispora rosea; inhibits bacterial protein synthesis in vitro by affecting specifically the GTP-bound form of elongation factor Tu; structure given in first source