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).
cyclo(Trp-Asp-Pro-Val-Leu) [ BQ 123,BQ-123,BQ123,cyclo(D-Trp-D-Asp-Pro-D-Val-Leu) ] derived from the modification of a natural lead of BE-18257B, an endothelin A receptor antagonist; has neuroprotective activity; amino acid sequence given in first source