Synthesis And Analgesic Activities Of Endomorphin-2 And Its Analogues

Endomorphins including endomorphin-1(H-Tyr-Pro-Trp-Phe-NH₂, EM1) andendomorphin-2(H-Tyr-Pro-Phe-Phe-NH₂, EM2) were discovered, isolated anddemonstrated to have high selectivity and affinity forμ-opioid receptors in 1997.Endomorphins are thought to inhibit pain without some of the undesirable side effects ofmorphine, which encourages the application of natural and synthetic peptides as analgesicsinstead of morphine. In this dissertation, the synthesis and the determination ofantinociceptive activities of endomorphin-2 and its analogues were reported.The tetrapeptide of EM₂(H-Tyr-Pro-Phe-Phe-NH₂) and its trifluoroacetic acid salt(H-Tyr-Pro-Phe-Phe-NH₂-TFA), were synthesized from L-tyrosine, L-proline andL-phenylalanine by liquid phase condensation. Two novel analogues of EM2,H-Tyr-cAsn(CHPh)-Phe-Phe-NH₂(1) and H-Tyr-cAsn(CMe₂)-Phe-Phe-NH₂(2), wereprepared by replacing proline in EM2 with cyclic asparagines, cAsn(CHPh) andcAsn(CMe₂), respectively. The synthetic procedure included the synthesis of twodipeptides first and coupling of the two dipeptides to the tiffed tetrapeptides in CH₂Cl₂/DMF in the presence of 1-[3-(dimethylamino)propyl]-3-ethylcarbodiimide hydrochloride(EDCI), 1-hydroxybenztriazole (HOBO and N-methylmorpholine (NMM).The structures of the products and intermediates were characterized by IR, ¹H NMR,MS and HRMS. The antinociceptive activities of EM2 and its cyclic asparagine analogueswere assessed in HOAc-induced abdominal constriction tests in mice with i. p. injection.The results showed that both of the analogues were active in the tests. The antinociceptiveactivities of analogue 1 was higher than that of EM2, aspirine and meperidine. Analogue 1was observed to be a stronger analgesics with dose-dependence. The test mice did notshow any tendency to be addicted while administrated of analogue 1 repeatedly andregularly.