Prototypical selective δ-opioid receptor agonist peptide. Inhibits electrically stimulated contraction of mouse vas deferens in vitro (EC50 = 5.2 nM), and is antinociceptive in vivo.

Mesoxalic acid is primarily located in the cytoplasm within the cell. Mesoxalic acid can be biosynthesized from malonic acid. Outside of the human body mesoxalic acid can be found in cereals and cereal products common pea and herbs and spices.

H-D-Phe-Pip-Arg-pNA (S-2238) dihydrochloride, a chromogenic substrate, is patterned after the N-terminal portion of the A alpha chain of fibrinogen, which is the natural substrate of thrombin. H-D-Phe-Pip-Arg-pNA dihydrochloride is specific for thrombin and is used to measure antithrombin-heparin cofactor (AT-III). The AT-III assay using H-D-Phe-Pip-Arg-pNA dihydrochloride is sensitive, accurate, and easy to perform.