D-Pyroaspartic acid ((2R)-4-oxoazetidine-2-carboxylic acid) is a head-to-tail cyclisation of D-aspartic acid to form the only amino acid derived azetidine. Synthetically, D-Pyroaspartic acid is prepared by cyclisation of the corresponding methyl esters. Unlike pyroglutamic acid, pyroaspartic acid is not a thermal degradation product but is re-named to better reflect the compound’s structural relationship to L-aspartic acid. Despite the intensive interest in beta-lactams spanning 70 years, D-pyroaspartic acid has received scant attention except for its role as a synthon to more complex molecules.