Design,Synthesis,and Biological Evaluation Of ?-Endomorphin Mimics Based On Scaffold Modification

The occurrence of pain involves complex mechanisms,in which opioid receptors play an important role.Opioids drugs such as morphine,are regarded as the golden standard of pain treatment in clinic,but their side effects,including nausea,constipation,respiratory depression,mental blurring,sleepiness and addiction,will not only reduce the compliance of patients,but also seriously affect the quality of life of patients after long-term use.Endogenous analgesic peptides existing in the cerebral cortex of mammals have been extensively studied in recent years.Compared with morphine,endomorphines not only has comparable analgesic effect,but also is not easy to produce side effects,so it is highly expected.However,the poor stability of enzymatic hydrolysis of endomorphine peptides and its inability to penetrate the blood-brain barrier limits its clinical use.The development of endomorphin analogues with analgesic activity and high stability,which can penetrate the blood-brain barrier,has become a research hotspot.The substitution of unnatural amino acids for endomorphin is an effective way to maintain its analgesic activity and improve its metabolic stability.We chose a-hydroxy-?pseudopeptide as a substitute molecule.Firstly different structures of endomorphin-2 analogues containing a-hydroxy-?-mimetic peptide were synthesized.On this basis,a library of lipid Endomorphin-2 derivatives and glycosylated derivatives was constructed.In addition,?-hydroxy-?-phenylalanine(AHPBA)and 2,6-dimethylty rosine(Dmt)were synthesized from natural amino acids and then they were used together to construct a leading analgesic compounds and their lipid or glycosylated derivatives.With the help of flexible docking of computer molecules,eight analogues of endomorphin-2 containing a-hydroxy-? seudopeptide were synthesized by liquid-phase synthesis after multiple-step reactions.Phe3 and Pro2 in the endomorphin-2 sequence were replaced with a-hydroxy-? pseudopeptide and unnatural amino acid respectively.On this basis,we focused on the structure modification of a-hydroxyl,and compared it with N-terminal glycosylation.A derivatives library containing 24 compounds was constructed.In vitro and in vivo bioactivity evaluation showed that the introduction of analogues of a-hydroxy-P pseudopeptide could retain the affinity of opioid receptors to vary degrees and improve the stability of enzymatic hydrolysis;Pro2 replacement with unnatural amino acids would affect the binding of analogues to receptors to vary degrees,but the stability of enzymatic hydrolysis would be further improved;analgesic experiments in vivo showed that 9a was more stable than endomorphine-2.Although its ED50 increased,the duration of analgesia lasted longer.In addition,9f obtained by Aib replacing Pro2 had a higher binding capacity of ? receptor than endomorphin-2,and showed a high degree of 8 receptor antagonism in vitro functional experiments,which was a potential 8 receptor antagonist.For the study of lipid or glycosylated derivatives,we found that the lipid derivatives at the a-hydroxyl position not only maintained receptor binding capacity,but also had a high stability to the enzymes,which met the requirements of peripheral administration,and improved the lipid solubility and membrane permeability in vary degrees.Although the glycosylated derivatives had a weak binding capacity to opioid receptors,they were more stable in serum and showed positive results in the Caco-2 permeation experiments.We applied the lipidation and glycosylation method to the structural modification of 26,a leading compound with good analgesic activity,which was discovered earlier.Three derivatives were designed and synthesized for its hydroxyl and N-terminal respectively.Biological activity evaluation showed that not only the receptor binding ability of a-hydroxyl and N-terminal lipid derivatives could be maintained to a certain extent,but also the membrane permeability could be improved to vary degrees.In mice analgesic model,N-terminal lipid derivative 28 showed analgesic activity after peripheral administration.It is a potential analgesic compound with high enzymatic stability and can penetrate the blood-brain barrier.The construction of drug-like compounds library is an important link in the development of new drugs and the discovery of lead compounds.The key technology development of drug-like fragments provides guidance for the selection of chemical routes and the establishment of molecular diversity.We have developed a new method for the synthesis of 2,4,5-trisubstituted imidazole.With the help of computer-aided design,we have designed and synthesized potential opioid receptor agonists containing imidazole skeleton.In addition,we have developed a new synthesis method of Mn(?)-catalyzed ?-ketophosphine oxides using olefin azide as starting material.?-ketophosphine oxides is one of the substrates for Wittig-Homer reaction and can be used for the synthesis of unnatural amino acids.Using this method,we synthesized different substituents of ?-ketophosphine oxides,which provided support for the construction and the further biological screening is still undergoing.