Enkephalin analogs containing the dipeptide unit Tyr-Arg (kyotorphin).

Abstract
Eight Met- and Leu-enkephalin analogs substituted with L- or D-Arg at position 2 were synthesized using NG-mesitylene-2-sulfonylarginine. Among them, H-Tyr-D-Arg-Gly-Phe-Met-OH was found to possess an analgesic effect 2.4 times higher than that of morphine on a molar basis, when injected intracisternally. This compound was also found to produce analgesia when administered intravenously.