Synthesis and analgesic properties of N-phosphorylated derivatives of Phe-Ala and Phe-Gly

N-Phosphoryl dipeptides derived from Phe-Ala, Phe-Ala-NH2 and Phe-Gly-NH2 were synthesized and their analgesic activity was evaluated in mice. Intracere-broventricular administration of P-Phe-Ala-NH2 produced a 100-fold increase in the analgesic potency of Phe-Ala and led to a potentiation and prolongation of the analgesic effect of the exogenously administered Met-enkephalin.