The Structure-Activity Relationships Of Endomorphin-1 And Its Analogues

Opioid peptides have long been used to relieve the symptoms of clinical pain, and these substances are mainly mediated through the central nervous system of its analgesic effect.In 1997, the endomorphin-1 (Tyr-Pro-Trp-Phe-NH2,EM-1) and endomorphin-2 (Tyr-Pro-Phe-Phe-NH2, EM-2) were firstly isolated from the human cortex and the bovine brain by Zadina et al.. According to numerous studies showed, endomorphin-1 and endomorphin-2 compared to morphine on the MOP receptor have a high selectivity and affinity, and therefore can produce a strong analgesic activity; but in the same time,there are many defects, such as enzymatic stability is poor, the analgesic effect of short-term, the lack of an orally active, difficultly through the blood-brain barrier, thus limiting the endomorphin widely used in clinical practice.In this study, a novel non-natural amino acids 2-furyl-α-amino methylene-β- alanine ((2-furyl)Map) was introduced into EM-1 structure and studied the structure-activity relationship. In addition, we also introduced other non-natural amino acid Dmt, D-Ala, N-Me-D-Ala into the EM-1 and used the EDC/HOBt liquid phase synthesis method for the synthesis of the five analogues. Then these analogs were carried out various pharmacological activity detection, including affinity experiments, in vitro biological activity tests, and enzymatic hydrolysis in vivo analgesic various experiments.We found that these analogues on mouse brain membrane stability have increased, while only analogue3 and7 exhibited higher MOP receptor affinity activity, selectivity and biological activity in vitro than EM-1. In these analogues,analogue3(Tyr-Pro-Trp-(2-furyl)Map-NH2) showed high affinity and activity, its dissociation constant Kiμ= 0.22nM,10 times higher than the EM-1. In GPI experiment, IC50 value of 2.92nM, about 5 times higher than the EM-1. In warm bath flick test, after intracerebroventricular(i.c.v.) administration analogues3 exhibit strong analgesic effect than the EM-1, and prolonged the duration of action; in other various analgesic experiments, analogue3 showed a significant analgesic activity in vivo after intravenous administration, and therefore we speculate analogue3 can produce analgesic effect through the blood brain barrier (BBB) into the brain.