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).
histidyl-proline diketopiperazine [ His-Pro-Dkp,cyclo(His-Pro),cyclo(histidyl-prolyl),histidyl-proline diketopiperazine, (3R-cis)-isomer,histidyl-proline diketopiperazine, (3S-cis)-isomer,histidyl-proline diketopiperazine, (3S-trans)-isomer,histidyl-proline-diketopiperazine ] biologically active cpd to which thyrotropin-releasing hormone (TRH) is metabolized; structure; RN given refers to cpd without isomeric designation