C—末端截短δ阿片受体的结合特征

目的：研究δ阿片受体Ｃ－末端在受体结合配体的亲和力及选择性中的作用。方法：在中国苍鼠卵巢细胞（ＣＨＯ细胞）中分别稳定表达Ｃ末端截短３１个氨基酸残基及野生型δ阿片受体，用受体结合分析法研究了表达产物与配体的结合特征，结果：表达得到典型突变受体克隆ＣＨＯ－Ｔ及野生型受体克隆ＣＨＯ－Ｗ，ＣＨＯ－Ｔ结合（＾３Ｈ）ｄｉｐｒｅｎｏｒｐｈｉｎｅ（Ｄｉｐ）及（＾３Ｈ）（Ｄ－Ａｌａ＾２，Ｄ－Ｌｅｕ＾５）ｅｎｋｅｐｈ     

Selectivity of ligand binding to opioid receptors in brain membranes from the rat, monkey and guinea pig

Conditions for the equilibrium binding to opioid receptor of [3H]sufentanil (mu selective), [3H][D-Pen2,D-Pen5]enkephalin (delta selective), and [3H]U69,593 (kappa selective) were established in membranes from rat brain cerebrum, monkey cortex, or guinea pig cerebellum. The selectivity index of various opioid alkaloids and peptides in binding to the mu, delta, or kappa opioid receptors was expressed as the ratio of their EC50 values in displacing two selective radiolabeled ligands: [3H]sufentanil/[3H](D-Pen2,D-Pen5)enkephalin (selectivity: mu/delta), [3H]sufentanil/[3H]U69,593 (selectivity: mu/kappa), or [3H][D-Pen2,D-Pen5]enkephalin/[3H]U69,593 (selectivity: delta/kappa). High resolution in binding selectivity was observed: in rat brain the mu/delta selectivity for Tyr-D-Ala-Gly-(Me)Phe-Gly-ol and sufentanil were 0.02 and 0.03, whereas for [D-Pen2,D-Pen5]enkephalin and ICI 174,864 they were 1,200 and 998. Compared to mu opiates, the specific binding of delta and kappa agonists was less sensitive to sodium. The results describe a routinely applicable methodological approach for the assessment of selective ligand binding to the mu, delta and kappa opioid receptors in rodent and monkey brain membranes.     

Investigation of the selectivity of oxymorphone- and naltrexone-derived ligands via site-directed mutagenesis of opioid receptors: exploring the "address" recognition locus

The delta-selective opioid antagonist naltrindole (NTI), as well as the kappa-selective opioid antagonists norbinaltorphimine (norBNI) and 5'-guanidinonaltrindole (GNTI), are derived from naltrexone, a universal opioid antagonist. Previous studies have indicated that extracellular loop III is the key region for discrimination by naltrexone-derived selective ligands between the delta, mu, and kappa opioid receptor types. It has been proposed that selective ligands could bind to all three receptor types if the appropriate portions of the extracellular loops were eliminated. To investigate this possibility, several single-point mutant opioid receptors have been generated with the aim of conferring enhanced affinity of selective ligands for their nonpreferred receptor types. Mutations were made in all three types of opioid receptors with the focus on two positions at the extracellular end of transmembrane regions (TM) VI and VII. It was found that the delta-selective NTI could bind both mu and kappa receptors with significantly enhanced affinity when an aromatic residue in TM VII was replaced with alanine (mu[W318A] and kappa[Y312A]). Similarly, kappa-selective antagonists, norBNI and GNTI, showed enhanced affinity for the mu[W318A] mutant and for both mu and delta receptors when a glutamate residue was incorporated into the extracellular end of TM VI (mu[K303E] and delta[W284E]). These results demonstrate that naltrexone-derived selective ligands achieve their selectivity via a combination of enhanced affinity of the address for a particular subsite along with loss of affinity due to steric interference at nonpreferred types. The results reveal key residues in the "address" recognition locus that contribute to the selectivity of opioid ligands and support the hypothesis that recognition of the naltrexone moiety is essentially the same for all three receptor types.     

Synthesis of highly mu and delta opioid receptor selective peptides containing a photoaffinity group

A series of cyclic, conformationally constrained photolabile peptides related to the enkephalins and to somatostatin were designed and synthesized in an effort to develop highly selective and potent peptides for the delta and mu opioid receptors. The following new peptides were prepared and tested for their delta opioid receptor potency and selectivity in the guinea pig ileum assay, the mouse vas deferens assay, and the rat brain binding assay: H-Tyr-D-Pen-Gly-p-NH2Phe-D-Pen-OH (1, [p-NH2Phe4]DPDPE) and H-Tyr-D-Pen-Gly-p-N3Phe-D-Pen-OH (2, [p-N3Phe4]-DPDPE). The following new peptides were prepared and tested for their mu opioid receptor potency and selectivity in the same assays: H-D-Phe-Cys-p-NH2Phe-D-Trp-Lys-Thr-Pen-Thr-NH2 (3, [p-NH2Phe3]CTP) and D-Phe-Cys-p-N3Phe-D-Trp-Lys-Thr-Pen-Thr-NH2 (4, [p-N3Phe3]CTP). The delta selective photoaffinity peptide 2 displayed both high affinity (IC50 = 9.5 nM) and good selectivity (IC50 mu/IC50 delta = 1053) as an agonist at delta opioid receptors in bioassays, and 2 also displayed moderate affinity (33 nM) and excellent selectivity (IC50 mu/IC50 delta = 110) for rat brain delta opioid receptors. The mu selective photoaffinity peptide 4 displayed very weak affinity (8% contraction at 300 nM) at mu opioid receptors in bioassays, but good affinity (IC50 = 48.6 nM) and excellent selectivity (IC50 delta/IC50 mu = 412) for the rat brain mu opioid receptors. These conformationally constrained cyclic photoaffinity peptides may be useful tools to investigate the pharmacology of delta and mu opioid receptors.     

Dermenkephalin (Tyr-D-Met-Phe-His-Leu-Met-Asp-NH2): a potent and fully specific agonist for the delta opioid receptor

Dermorphin, Tyr-D-Ala-Phe-Gly-Tyr-Pro-Ser-NH2 is an extraordinarily potent and highly mu-selective opioid heptapeptide isolated from amphibian skin. It is unique among peptides synthesized by animal cells in having an amino acid residue in the D-configuration. At least two different preprodermorphin cDNAs were cloned from skin of Phylomedusa sauvagei; their predicted amino acid sequences contained four to five homologous repeats of 35 amino acids, each repeat including one copy of the dermorphin progenitor sequence. Tyr-Ala-Phe-Gly-Tyr-Pro-Ser-Gly, flanked by Lys-Arg at the amino end and by Glu-Ala-Lys-Lys at the carboxyl end [Science (Wash. D. C.) 238:200-202 (1987)]. The D-Ala in position 2 in dermorphin is encoded by a usual Ala codon in the precursor sequence. Of the two prodermorphin molecules, one has a dermorphin copy replaced with a distinct heptapeptide same processing signals. Assuming the same pathway as for the release of dermorphin, processing of this precursor may yield, beside dermorphin, a copy of a new peptide, Tyr-D-Met-Phe-His-Leu-Met-Asp-NH2. We have synthetized this peptide together with its (L-Met2)-counterpart and evaluated their respective opioid receptor selectivity in the mouse vas deferens and guinea pig ileum assays and in rat brain membrane binding assays. Overall, the data collected demonstrate that the putative prodermorphin product Tyr-D-Met-Phe-His-Leu-Met-Asp-NH2 named dermenkephalin, behaves as a potent delta opioid agonist exhibiting high affinity and high selectivity for the delta opioid receptor. Prodermorphin, thus, offers a surprising example of an opioid biosynthetic precursor that might simultaneously generate highly potent and fully selective agonists for the mu- (morphine) and the delta (enkephalin) opioid receptors, respectively. In addition, because dermenkephalin has no structural features in common with the sequence of all the hitherto known opioid peptides, it should be a useful tool for identifying conformational determinants for high affinity and selective binding of opioids to the delta receptor.     

Ring substituted and other conformationally constrained tyrosine analogues of [D-Pen2,D-Pen5]enkephalin with delta opioid receptor selectivity.

The conformationally restricted, cyclic disulfide-containing delta opioid receptor selective enkephalin analogue [D-Pen2,D-Pen5] enkephalin (DPDPE) was modified by 2' (CH3) and 3' (I, OCH3, NO2, NH2) ring substitutions and by beta-methyl conformationally constrained beta-methyltyrosine derivatives in the 1 position. The potency and selectivity of these analogues were evaluated by bioassay in the mouse vas deference (MVD, delta receptor assay) and guinea pig ileum (GPI, mu receptor assay) assays and by radioreceptor binding assays in the rat brain using [3H]CTOP (mu ligand) and [3H][p-ClPhe4]DPDPE (delta ligand). The analogues showed highly variable potencies in the binding assays and in the bioassays. Aromatic ring substituents with positive Hammett constants had decreased potency, while substituents with negative Hammett constraints has increased potency for the opioid receptor. The most potent and most selective compound based on the binding was [2'-MeTyr1]DPDPE (IC50 = 0.89 nM and selectivity ratio 1310 in the binding assays). The 6-hydroxy-2-aminotetralin-2-carboxylic acid-containing analogue, [Hat1]DPDPE, also was highly potent and selective in both assays, demonstrating that significant modifications of tyrosine in enkephalins are possible with maintenance of high potency and delta opioid receptor selectivity. Of the beta-methyl-substituted Tyr1 analogues, [(2S,3R)-beta-MeTyr1]DPDPE was the most potent and the delta receptor selective. The results with substitution of beta-MeTyr or Hat instead of Tyr also demonstrate that topographical modification in a conformationally restricted ligand can significantly modulate both potency and receptor selectivity of peptide ligands that have multiple sites of biological activity.     

Novel D3 selective dopaminergics incorporating enyne units as nonaromatic catechol bioisosteres: synthesis, bioactivity, and mutagenesis studies

Enynes of type 4 and 5 as long chain derivatives of the nonaromatic dopamine D 3 receptor agonist 3 (FAUC 73) were prepared by exploiting chemoselective functionalization of the azido-substituted vinyl triflate 9. Radioligand binding studies indicated excellent D 3 affinity and selectivity over related GPCRs for the terminal alkynes 4c (FAUC 460) and 5c. Biphasic displacement curves gave picomolar K i values for the high affinity binding site of D 3. According to mitogenesis experiments and bioluminescence based cAMP assays, the biphenylcarboxamide 4c and its click chemistry derived triazole analogue 5c behaved as strong partial agonists but relative ligand efficacy significantly depended on the type of functional assay. Site directed mutagenesis involving the mutants D 3 D3.32E, and D 3 F6.51W implied that ligand interactions with D3.32 and F6.51 are highly crucial, giving rise to analogous binding modes for dopamine, classical and enyne type agonists.     

Bivalent ligands for G protein-coupled receptors

Bivalent ligands have been developed for a variety of G protein-coupled receptor targets, including opioid, dopamine, serotonin and muscarinic receptors. The most successful application of the bivalent ligand approach has been in the development of selective opioid antagonists, such as norbinaltorphimine. Several important principles have emerged from the study of norbinaltorphimine and related compounds, including the utility of bivalent ligands for targeting particular receptor classes and serving as a scaffold for specific interactions with unique amino acid residues that render receptor subtype selectivity. In recent years, several novel bivalent compounds were synthesized and characterized for activity at muscarinic receptors. The compounds display an interesting profile of high binding affinity, strong agonist potency and receptor subtype selectivity. Bivalent ligands represent an important starting point for the development of selective muscarinic agonists with potential utility in treating a variety of neurological disorders, including Alzheimer's disease and schizophrenia. The bivalent ligand approach may be generally applicable to other G protein-coupled receptors.     

Development and validation of opioid ligand–receptor interaction models: The structural basis of mu vs. delta selectivity

Abstract: Opioid receptor binding conformations for two structurally related, conformationally constrained tetrapeptides, JOM‐6 (µ receptor selective) and JOM‐13 (δ receptor selective), were deduced using conformational analysis of these ligands and analogs with additional conformational restrictions. Docking of these ligands in their binding conformations to opioid receptor structural models, based upon the published rhodopsin X‐ray structure, implicates specific structural features of the µ and δ receptor ligand binding sites as forming the basis for the µ selectivity of JOM‐6 and the δ selectivity of JOM‐13. In particular, the presence of E229 in the µ receptor (in place of the corresponding D210 of the δ receptor) causes an adverse electrostatic interaction with C‐terminal carboxylate‐containing ligands, resulting in the observed preference of ligands with an uncharged C‐terminus for the µ receptor. In addition, the requirement that the Phe³ side chain of JOM‐13 assume a gauche orientation for optimal δ binding, whereas the Phe³ side chain of JOM‐6 must be in a trans orientation for high‐affinity µ binding can be largely attributed to the steric effect of replacement of L300 of the δ receptor by W318 of the µ receptor. Testing this hypothesis by examining the binding of JOM‐6 and several of its key analogs with specific µ receptor mutants is described. Our initial results are consistent with the proposed ligand–receptor interaction models.     

3-甲基芬太尼衍生物构效关系及受体结合特征研究

对3-甲基芬太尼的1-苯乙基、4-N-丙酰基进行了结构改造、测定了所合成化合物的镇痛活性及部分化合物的镇痛作用持续时间、阿片受体亲和力和对阿片受体亚型的选择性。结果表明,大部分化合物均有较强的吗啡样镇痛活性,强度约为吗啡的2～180倍。所试化合物的镇痛作用持续时间比芬太尼延长6～10倍。化合物1～4的受体亲和力(IC₅₀)约为10^-7～10^-3mol。化合物13对阿片μ-受体有较高的选择性,对大鼠脑膜的λ/δ比值大于700,对小鼠脑膜的μ/δ比值为1000。     

Topographically designed analogues of [D-Pen,D-Pen5]enkephalin.

The conformationally restricted, cyclic disulfide-containing delta opioid receptor selective enkephalin analogue [D-Pen2,D-Pen5]enkephalin (1, DPDPE) was systematically modified topographically by addition of a methyl group at either the pro-S or pro-R position of the beta carbon of an L-Phe4 or D-Phe4 residue to give [(2S,3S)-beta-MePhe4]DPDPE (2), [(2R,3R)-beta-MePhe4]DPDPE (3), [(2S,3R)-beta-MePhe4]DPDPE (4), and [(2R,3S)-beta-MePhe4]DPDPE (5). The four corresponding isomers were prepared in which the beta-methylphenylalanine residue was p-nitro substituted, that is with a beta-methyl-p-nitrophenylalanine (beta-Me-p-NO2Phe) residue, to give [(2S,3S)-beta-Me-p-NO2Phe4]DPDPE (6), [(2R,3R)-beta-Me-p-NO2Phe4]DPDPE (7), [(2S,3R)-beta-Me-p-NO2Phe4] DPDPE (8), and [(2R,3S)-beta-Me-p-NO2Phe4]DPDPE (9), respectively. The potency and selectivity (delta vs mu opioid receptor) were evaluated by radioreceptor binding assays in the rat brain using [3H]CTOP (mu ligand) and [3H]DPDPE (delta ligand) and by bioassay with mouse vas deferens (MVD, delta receptor assay) and guinea pig ileum (GPI, mu receptor assay). The eight analogues of DPDPE showed highly variable binding and bioassay activities particularly at the delta opioid receptor (4 orders of magnitude), but also at the mu opioid receptor, which led to large differences (3 orders of magnitude) in receptor selectivity. For example, [(2S,3S)-beta-MePhe4]DPDPE (2) is 1800-fold selective in binding to the delta vs mu receptor, making it one of the most selective delta opioid receptor ligands in the enkephalin series as assessed by the rat brain binding assay, whereas the corresponding (2R,3R)-beta-Me-p-NO2Phe-containing analogue 9 is only 4.5-fold selective (nonselective) in this same assay. On the other hand, in the bioassay systems, [(2S,3S)-beta-Me-p-NO2Phe4]DPDPE (5) is more potent than DPDPE and 8800-fold selective for the MVD (delta receptor) vs the GPI (mu receptor), making it the most highly selective ligand in this series for the delta opioid receptor on the basis of these bioassays. In these assay systems, the (2R,3S)-beta-MePhe4-containing analogue 5 had very weak potency and virtually no receptor selectivity (4.4-fold). These results demonstrate that topographical modification alone in a conformationally restricted peptide ligand can significantly modulate both potency and receptor selectivity of peptide ligands that have multiple sites of biological activity and suggest that this approach may have general application to peptide ligand design.     

Design of peptidomimetic delta opioid receptor antagonists using the message-address concept

Highly selective nonpeptide ligands with potent delta opioid receptor antagonist activity have been developed using the message-address concept. This approach envisaged the delta opioid receptor to contain two major recognition subsites; a message subsite which recognizes the pharmacophore, and an address subsite that is unique for the delta receptor type and confers selectivity. The message and address components of the delta-selective enkephalins were postulated to be Tyr1 and Phe4, respectively, with Gly2-Gly3 functioning as a spacer. The message component of the target compounds in this study was derived from naltrexone and related structures. An indole system was fused to the C ring of naltrexone as a mimic of the address component. The benzene moiety of indole was viewed as the delta address component, mimicking the phenyl group of Phe4, and the pyrrole portion was used as a rigid spacer. Members of the series (1-23) were evaluated for opioid antagonist activity on the guinea pig ileum (GPI) and mouse vas deferens (MVD) preparations. Naltrindole (NTI, 1) was the most potent member of the series, with Ke values of approximately 0.1 nM at delta receptors. The antagonism by NTI was approximately 220- and 350-fold greater at delta than at mu and kappa opioid receptors. The binding of NTI and selected members of the series to guinea pig brain membranes was qualitatively consistent with their pharmacologic antagonist activity profiles in the MVD and GPI, but the Ki values were not in the same rank order. The selectivity of NTI arises mainly as a consequence of increased affinity at delta receptors. Thus, the Ke and Ki values of NTI were 1/530 and 1/90 that of the delta antagonist enkephalin analogue, ICI 174864. In contrast to NTI, ICI174864 derives its selectivity through greatly decreased recognition at mu and kappa receptors. The implications of the high affinity and selectivity of NTI as a consequence of its conformational rigidity are discussed. It is suggested that any attempt to model a receptor-bound conformation of an opioid peptide should consider affinity and potency at multiple receptor sites rather than selectivity alone.     

Pharmacological properties of a proenkephalin A-derived opioid peptide: BAM 18

BAM 18 is a derivative of the opioid precursor proenkephalin A. Although it exists in rat and guinea-pig brain in relatively high concentrations, its physiological function is presently unknown. In the present study we have determined the opioid receptor selectivity of this peptide using radioligand binding and peripheral tissue bioassay. When selective binding conditions were used, BAM 18 bound to the mu opioid receptor with an affinity three times that of the kappa opioid receptor and over 10 times that of the delta opioid receptors (Ki = 0.29, 0.75, and 3.2 nM respectively). BAM 18 also displayed mixed receptor selectivity in in vitro bioassay. Ke values for naloxone antagonism of BAM 18 agonist activity in the electrically stimulated guinea-pig ileum and the mouse vas deferens were 4.3 and 9.9 nM, respectively. These data indicate that BAM 18 binds to all three opioid receptor subtypes with a selectivity profile of mu greater than kappa greater than delta.     

Synthesis and evaluation of N,N-dialkyl enkephalin-based affinity labels for delta opioid receptors

To develop affinity labels for delta opioid receptors based on peptide antagonists, the Phe(4) residues of N,N-dibenzylleucine enkephalin and N,N-diallyl[Aib(2),Aib(3)]leucine enkephalin (ICI-174, 864) were substituted with either Phe(p-NCS) or Phe(p-NHCOCH(2)Br). A general synthetic method was developed for the conversion of small peptide substrates into potential affinity labels. The target peptides were synthesized using Phe(p-NH(2)) and a Boc/Fmoc orthogonal protection strategy which allowed for late functional group conversion of a p-amine group in the peptides to the desired affinity labeling moieties. A key step in the synthesis was the selective deprotection of a Boc group in the presence of a tert-butyl ester using trimethylsilyl trifluoromethanesulfonate (TMS-OTf). The target peptides were evaluated in radioligand binding experiments in Chinese hamster ovary (CHO) cells expressing delta or mu opioid receptors. The delta receptor affinities of the N, N-dibenzylleucine enkephalin analogues were 2.5-10-fold higher than those for the corresponding ICI-174,864 analogues. In general, substitution at the para position of Phe(4) decreased binding affinity at both delta and mu receptors in standard radioligand binding assays; the one exception was N, N-dibenzyl[Phe(p-NCS)(4)]leucine enkephalin (2) which exhibited a 2-fold increase in affinity for delta receptors (IC(50) = 34.9 nM) compared to N,N-dibenzylleucine enkephalin (IC(50) = 78.2 nM). The decreases in mu receptor affinities were greater than in delta receptor affinities so that all of the analogues tested exhibited significantly greater delta receptor selectivity than the unsubstituted parent peptides. Of the target peptides tested, only N, N-dibenzyl[Phe(p-NCS)(4)]leucine enkephalin (2) exhibited wash-resistant inhibition of radioligand binding to delta receptors. To our knowledge, 2 represents the first peptide-based affinity label to utilize an isothiocyanate group as the electrophilic affinity labeling moiety. As a result of this study, enkephalin analogue 2 emerges as a potential affinity label useful for the further study of delta opioid receptors.     

Development of conformationally constrained linear peptides exhibiting a high affinity and pronounced selectivity for delta opioid receptors

A series of linear conformationally constrained opioid peptides was designed in an attempt to develop highly selective and potent agonists for the delta opioid receptors. These enkephalin analogues corresponding to the general formula Tyr-D-X(OY)-Gly-Phe-Leu-Thr(OZ) were obtained by incorporating bulky residues (X = Ser or Thr; Y = tert-butyl or benzyl; Z = tert-butyl) into the sequence of the previously reported delta specific agonists DSLET (Tyr-D-Ser-Gly-Phe-Leu-Thr) and DTLET (Tyr-D-Thr-Gly-Phe-Leu-Thr). In binding studies based on displacement of mu and delta opioid receptor selective radiolabeled ligands from rat brain membranes, the two constrained hexapeptides, Tyr-D-Ser(O-t-Bu)-Gly-Phe-Leu-Thr (1, DSTBULET) (KI(mu) = 374 nM, Kr(delta) = 6.14 nM, KI(delta)/KI(mu) = 0.016) and in particular Tyr-D-Ser(O-t-Bu)-Gly-Phe-Leu-Thr(O-t-Bu) (7, BUBU) (KI(mu) = 475 nM, KI(delta) = 4.68 nM, KI(delta)/KI(mu) = 0.010) were shown to be among the most potent and selective delta probes reported to date. A roughly similar pattern of selectivity was obtained with the guinea pig ileum and mouse vas deferens bioassays. In addition, the analgesic potency (hot-plate test) of these peptides intracerebroventricularly administered in mice was shown to be significantly related to their mu-receptor affinity.     

Effect of N-alkyl and N-alkenyl substituents in noroxymorphindole, 17-substituted-6,7-dehydro-4,5alpha-epoxy-3,14-dihydroxy-6,7:2',3'-indolomorphinans, on opioid receptor affinity, selectivity, and efficacy

The N-alkyl analogues (N-ethyl through N-heptyl), branched N-alkyl chain analogues (N-isopropyl, N-2-methylpropyl, and N-3-methylbutyl), and N-alkenyl analogues ((E)-N-3-methylallyl (crotyl), N-2-methylallyl, and N-3,3-dimethylallyl) were prepared in the noroxymorphindole series (17-substituted-6,7-dehydro-4,5alpha-epoxy-3,14-dihydroxy-6,7:2',3'-indolomorphinans), and the effect of the N-substituent on opioid receptor affinity, selectivity, and efficacy was examined using receptor binding assays, [(35)S]GTPgammaS efficacy determinations, and smooth muscle functional assays (electrically stimulated mouse vas deferens and guinea pig ileum). All of the compounds acted as opioid antagonists, including those with N-substituents which usually confer either weak agonist-antagonist behavior (N-ethyl) or potent opioid agonist activity (N-pentyl) in morphinan-like ligands which interact with the mu-receptor. Several N-substituted noroxymorphindoles were found to be more mu/delta-selective than naltrindole (NTI). The N-2-methylallylnoroxymorphindole, in particular, was found to be more selective than NTI in receptor binding assays (mu/delta = 1700 vs 120; kappa/delta = 810 vs 140), as an antagonist in the GTPgammaS assay (mu/delta = 170 vs 140; kappa/delta = 620 vs 160), and considerably more selective than NTI in the functional assays (mu/delta > 2200 vs 90). It also had high affinity for the delta-opioid receptor (K(i) = 4.7 nM in the binding assay) and high antagonist potency (1.2 nM in the GTPgammaS assay; 8.9 nM in the MVD assay).     

Discovery of novel triazole-based opioid receptor antagonists

We report the computer-aided design, chemical synthesis, and biological evaluation of a novel family of delta opioid receptor (DOR) antagonists containing a 1,2,4-triazole core structure that are structurally distinct from other known opioid receptor active ligands. Among those delta antagonists sharing this core structure, 8 exhibited strong binding affinity (K(i) = 50 nM) for the DOR and appreciable selectivity for delta over mu and kappa opioid receptors (delta/mu = 80; delta/kappa > 200).     

Stress prevents the chronic ethanol-induced delta opiod receptor supersensitivity in the rat brain

The effects of ethanol administration on binding characteristics of the highly selective mu and delta opioid receptor agonists 8H-[D-Ala2-MePhe4-Gly5-ol]enkephalin (3H-DAGO) and 3H-[D-Pen2, D-Pen5] enkephalin (3H-DPDPE), respectively, were investigated in the rat brain. Chronic but not acute ethanol administration profoundly increased affinity of 3H-DPDPE without changing the number of delta receptors. Stress, applied before each ethanol administration, prevents the above changes. On the other hand, chronic treatment with ethanol did not affect the binding characteristics of 3H-DAGO. These results suggest particular sensitivity of the delta opioid receptor to chronic ethanol administration. Furthermore, a possible involvement of endogenous opioid peptide systems in the enhancement of delta opioid receptor sensitivity is postulated.     

Pro(3)]Dyn A(1-11)-NH(2): a dynorphin analogue with high selectivity for the kappa opioid receptor

A proline scan at positions 2 and 3 of the opioid peptide dynorphin A(1-11)-NH(2) led to the discovery of the analogue [Pro(3)]Dyn A(1-11)-NH(2). This analogue possesses high affinity and selectivity for the kappa opioid receptor (K(i)(kappa) = 2.7 nM, K(i) ratio kappa/micro/delta = 1/2110/3260). The gain in selectivity is achieved through an overall reduction of opioid receptor affinity which is most pronounced at micro and delta receptors. The Pro(3) analogue exhibits antagonist properties. Despite its high kappa affinity, [Pro(3)]Dyn A(1-11)-NH(2) is a relatively weak antagonist in both the [(35)S]GTPgammaS assay (IC(50) = 380 nM) and the guinea pig ileum assay (K(e) = 244 nM). Discrepancies between GPI and binding assay have often been ascribed to differential kappa receptor subtypes prevailing in central vs peripheral neurons. Since the [(35)S]GTPgammaS assay uses the same membrane preparations as the binding assay, differential kappa subtypes can be ruled out as an explanation in this case, and the observed behavior rather seems to reflect an intrinsic property of the ligand.     

Synthesis and biological evaluation of 14-alkoxymorphinans. 17. Highly delta opioid receptor selective 14-alkoxy-substituted indolo- and benzofuromorphinans

14-Alkoxy analogues of naltrindole and naltriben differently substituted in positions 5 and 17 and at the indole nitrogen (compounds 28-44) have been synthesized in an effort to enhance the delta potency and/or delta selectivity and in order to further elaborate on structure-activity relationships of this class of compounds. Introduction of a 14-alkoxy instead of the 14-hydroxy group present in naltrindole resulted in somewhat lower delta binding affinity, while in many cases (compounds 31, 34, 37, 40, 41, 44, HS 378) the delta receptor selectivity was considerably increased. An ethoxy group in position 14 is superior to other alkoxy groups concerning delta affinity and selectivity (34, 41, 42, 44, HS 378). In [35S]GTP gamma S binding, compounds 34, 41, and HS 378 exhibited about one-tenth the antagonist potency of naltrindole at delta opioid receptors while their delta antagonist selectivity was considerably higher. 17-Methyl-substituted compounds 35 and 44 were found to be pure delta receptor agonists in this test.