D-Pyrohomoglutamic acid (R-6-oxopiperidine-2-carboxylic acid) is a δ-lactam formed by the head-to-tail cyclisation of D-homoglutamic acid. Unlike pyroglutamic acid, D-pyrohomoglutamic acid is reported as a pyrolysis product but is re-named to better reflect the compound’s structural relationship to D-homoglutamic acid, the “unnatural” optical isomer of L-homoglutamic acid. D-Pyrohomoglutamic acid has found limited application as a terminal amino acid analogue in the structure-activity relationships of small linear peptides such as substance P and as a chemical synthon. The biological and pharmacological properties of D-pyrohomoglutamic acid have not been extensively investigated.