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The opioid inactive isomer (+)-naltrexone is one of the rare Toll-like receptor 4 (TLR4) antagonists with good blood-brain barrier (BBB) permeability, which is a lead with promising potential for treating neuropathic pain and drug addiction. (+)-Naltrexone targets the lipopolysaccharides (LPS) binding pocket of myeloid differentiation protein 2 (MD-2) and blocks innate immune TLR4 signaling. However, the details of the molecular interactions of (+)-naltrexone and its derivatives with MD-2 are not fully understood, which hinders the ligand-based drug discovery. Herein, in silico and in vitro assays were performed to elucidate the innate immune recognition of the opioid inactive (+)-isomers. The results showed that the conserved LPS binding pocket of MD-2 accommodated these opioid inactive (+)-isomers. The calculated binding free energies of (+)-naltrexone and its derivatives in complex with MD-2 correlated well with their experimental binding affinities and TLR4 antagonistic activities. Hydrophobic residues in the MD-2 cavity interacted directly with these (+)-naltrexone based TLR4 antagonists and principally participated in ligand binding. Increasing the hydrophobicity of substituted group at N-17 improved its TLR4 antagonistic activity, while charged groups disfavored the binding with MD-2. Molecular dynamics (MD) simulations showed the binding of (+)-naltrexone or its derivatives to MD-2 stabilized the "collapsed" conformation of MD-2, consequently blocking the binding and signaling of TLR4. Thermodynamics and dynamic analysis showed the topology of substituted group at N-17 of (+)-naltrexone affected the binding with MD-2 and TLR4 antagonistic activity. This study provides a molecular insight into the innate immune recognition of opioid inactive (+)-isomers, which would be of great help for the development of next-generation of (+)-opioid based TLR4 antagonists.

Kappa-opioid receptor (κ) antagonists are potential therapeutic agents for a range of psychiatric disorders. The feasibility of developing κ-antagonists has been limited by the pharmacodynamic properties of prototypic κ-selective antagonists; that is, they inhibit receptor signaling for weeks after a single administration. To address this issue, novel trans-(3R,4R)-dimethyl-4-(3-hydroxyphenyl) piperidine derivatives, based on JDTic, were designed using soft-drug principles. The aim was to determine if the phenylpiperidine-based series of κ-antagonists was amenable to incorporation of a potentially metabolically labile group, while retaining good affinity and selectivity for the κ-receptor. Opioid receptor binding affinity and selectivity of three novel compounds (BU09057, BU09058, and BU09059) were tested. BU09059, which most closely resembles JDTic, had nanomolar affinity for the κ-receptor, with 15-fold and 616-fold selectivity over μ- and δ-receptors, respectively. In isolated tissues, BU09059 was a potent and selective κ-antagonist (pA2 8.62) compared with BU09057 (pA2 6.87) and BU09058 (pA2 6.76) which were not κ-selective. In vivo, BU09059 (3 and 10 mg/kg) significantly blocked U50,488-induced antinociception and was as potent as, but shorter acting than, the prototypic selective κ-antagonist norBNI. These data show that a new JDTic analogue, BU09059, retains high affinity and selectivity for the κ-receptor and has a shorter duration of κ-antagonist action in vivo.

On the basis of a mu opioid receptor (MOR) homology model and the isosterism concept, three generations of 14-heteroaromatically substituted naltrexone derivatives were designed, synthesized, and evaluated as potential MOR-selective ligands. The first-generation ligands appeared to be MOR-selective, whereas the second and the third generation ones showed MOR/kappa opioid receptor (KOR) dual selectivity. Docking of ligands 2 (MOR selective) and 10 (MOR/KOR dual selective) to the three opioid receptor crystal structures revealed a nonconserved-residue-facilitated hydrogen-bonding network that could be responsible for their distinctive selectivity profiles. The MOR/KOR dual-selective ligand 10 showed no agonism and acted as a potent antagonist in the tail-flick assay. It also produced less severe opioid withdrawal symptoms than naloxone in morphine-dependent mice. In conclusion, ligand 10 may serve as a novel lead compound to develop MOR/KOR dual-selective ligands, which might possess unique therapeutic value for opioid addiction treatment.

Microneedle-enhanced transdermal drug delivery greatly improves the subset of pharmacologically active molecules that can be transported across the skin. Formulation pH plays an important role in all drug delivery systems; however, for transdermal delivery it becomes specifically significant since a wide range of pH values can be exploited for patch formulation as long as it does not lead to skin irritation or sensitization issues. Wound healing literature has shown significant pH effects on barrier recovery. Stability and solubility of the drug, and thus transport across skin, are all affected by formulation pH. The current study examined the role of ionization state of the drug naltrexone on transdermal flux and permeability across microneedle treated skin, as compared to intact skin. Impedance spectroscopy was done in pigs in vivo to assess the role of formulation pH on the rate of micropore closure under the influence of three different pH conditions. The data indicated that while there was significant advantage of using a lower pH formulation in terms of total transport across microneedle treated skin, the pH however did not have any significant effect on the rate of micropore closure beyond the first 24 h.

To be useful, a system which predicts the metabolic fate of a chemical should predict the more likely metabolites rather than every possibility. Reasoning can be used to prioritize biotransformations, but a real biochemical domain is complex and cannot be fully defined in terms of the likelihood of events. This paper describes the combined use of two models for reasoning under uncertainty in a working system, METEOR-one model deals with absolute reasoning and the second with relative reasoning.

The importance of the indole scaffold of GNTI 3 in directing its address (5'-guanidinium group) to associate with the Glu297 residue of the kappa-opioid receptor was investigated by the synthesis and biological evaluation of its 4'- (4a), 6'- (4b), and 7'- (4c) regioisomers. The finding that only the 5'-regioisomer (GNTI) possessed potent kappa-opioid antagonist activity and high affinity at kappa-receptors illustrates the importance of the 5'-position in orienting the guanidinium group to the proper recognition locus (Glu 297) for potent kappa-antagonist activity. The discovery that the 6'-regioisomer of GNTI was a potent kappa-agonist, together with the results of site-directed mutagenesis studies that are consistent with association between the 6'-guanidinium group and Glu297, suggest that the transition from an inactive to an active state of the kappa-receptor involves a conformational change of TM6. We propose that association of the 6'-guanidinium group of 4b with Glu297 promotes axial rotational motion of transmembrane helix VI which leads to receptor activation via a conformational change of inner loop 3.

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.

Molecular modifications of both the kappa opioid antagonist norbinaltorphimine (norBNI, 1) and the kappa receptor have provided evidence that the selectivity of this ligand is conferred through ionic interaction if its N17' protonated amine group (an "address") with a nonconserved acidic residue (Glu297) on the kappa receptor. In the present study, we have examined the effect of structural modifications on the affinity of norBNI analogues for wild-type and mutant kappa and mu opioid receptors expressed in COS-7 cells. Compounds 2, 3, and 7, which have an antagonist pharmacophore and basic N17' group in common with norBNI, retained high affinity for the wild-type kappa but exhibited greatly reduced affinity for mutant kappa receptors (E297K and E297A). Modification of the phenolic or N-substituent groups of the antagonist pharmacophore (4 and 5) or removal of basicity at the address N17' center (6) led to greatly reduced affinity for the wild-type and mutant receptors. The reduced affinity upon modification of the kappa receptor is consistent with the ionic interaction of the protonated N17' group of kappa antagonists (1-3, 7) with the carboxylate group of E297 at the top of TM6. This was supported by the greatly enhanced affinity of compounds 1-3 for the mutant mu receptor (K303E), as compared to the wild-type mu receptor, given that residue K303 occupies a position equivalent to that of E297 in the kappa receptor. In view of the high degree of homology of the seven TM domains of the kappa and mu opioid receptors, it is suggested that the antagonist pharmacophore is bound within this highly conserved region of the kappa or mutant mu receptor and that an anionic residue at the top of TM6 (E297 or K303E, respectively) provides additional binding affinity.

A series of analogues of the delta opioid receptor antagonist naltrindole (1) possessing a phenyl, phenoxy, or benzyloxy group at the 4'-, 5'-, 6'-, or - 7'-positions (4-15) and a 2-(2-pyridinyl)ethenyl group at the 5'-position (16) on the indolic benzene ring were synthesized through Fischer indolization of naltrexone. Compounds 4-16 were evaluated for their affinities in opioid receptor binding assays in rat or guinea pig brain membranes and for their opioid antagonist and agonist activities in vitro on the guinea pig ileum (GPI) and mouse vas deferens (MVD) preparations. All of the compounds displayed delta selectivity in binding to the delta, mu, and kappa opioid receptors. The binding potencies of most of the compounds at the delta, mu, and kappa sites, however, were lower than that of 1. Among positional isomers, the 7'-substituted compounds in general had higher affinities than 6'-, 5'-, or 4'-substituted analogues, indicating that bulky groups are tolerated better at the 7'-position than at other positions. The affinity of the compounds were also determined at putative subtypes of the delta and kappa receptors: deltacx-1 (mu-like), deltacx-2 (delta-like), and the kappa2b site in an attempt to identify subtype selective agents. Although none were identified, the data revealed a different rank-order of potency beteween mu vs deltacx-1, deltacx-2 vs delta, and the kappa2b vs mu, delta, and kappa1. The antagonist potencies of the compounds in the MVD were in agreement with their binding affinities at the delta site in rat brain membrane. The most potent member of the series, the 7'-phenoxy compound 14, binds to the delta site with a Ki of 0.71 nM, shows >40-fold delta over mu and delta over kappa binding selectivity, and exhibits delta receptor antagonist potency in the MVD with a Ke of 0.25 nM, properties which are comparable to the delta receptor affinity and antagonist potency of naltrindole (Ki = 0.29 nM, Ke = 0. 49 nM). Interestingly, many members of the series were found to possess significant partial to full agonist activities in the MVD (6, 9, 10, 13, 16) or GPI (6, 11, 14, 15). Among the compounds studied, the highest agonist activity in the MVD was displayed by 16 (IC50 = 220 nM), and the highest agonist activity in the GPI was displayed by 14 (IC50 = 450 nM). The overall affinity and activity profile of compound 14 is, therefore, that of a nonpeptide ligand possessing mixed mu agonist/delta antagonist properties. Recently there has been considerable interest in such compounds possessing mu agonist/delta antagonist activities because of their potential therapeutic usefulness as analgesics with low propensity to produce tolerance and dependence side effects. The results of the present study suggest that morphinan derivatives related to 16 and 14 may provide useful leads for the development of potent nonpeptide ligands possessing delta agonist or mixed delta antagonist/mu agonist activities.

A series consisting of spiroindanyl (5-7), benzospiroindanyl (8-10), and spiroperinaphthyl (11) derivatives of naltrexone and oxymorphone were synthesized in order to investigate the role of an orthogonal-oriented "address" for delta opioid receptors. All of the ligands exhibited a preference for delta receptors in vitro. The 7-benzospiroindanyl derivative 8 (BSINTX) was the most selective delta opioid receptor antagonist in vitro. In mice BSINTX antagonized the delta 1-selective agonist, [D-Pen2,D-Pen5]enkephalin without significantly affecting the antinociceptive potency of delta 2, mu, and kappa agonists. The results of this study are consistent with an orthogonally-oriented address favoring delta 1 activity.

The E-isomer of 7-benzylidenenaltrexone (BNTX, la) was reported by Portoghese as a highly selective delta-opioid antagonist. The corresponding Z-isomer 1b was not readily available through direct aldol condensation of naltrexone (6) with benzaldehyde. Using the photochemical methods employed by Lewis to isomerize cinnamamides, we have obtained Z-isomer 1b in good yield from E-isomer 1a. A series of (E)- and (Z)-7-arylidenenaltrexone derivatives was prepared to study the effect of larger arylidene groups on opioid receptor affinity in this series. By aldol condensation of naltrexone (6) with benzaldehyde, 1-naphthaldehyde, 2-naphthaldehyde, 4-phenylbenzaldehyde, and 9-anthracaldehyde, the (E)-arylidenes were readily obtained. Photochemical isomerization afforded the corresponding Z-isomers. These compounds were evaluated via opioid receptor radioligand displacement assays. In these assays, the Z-isomers generally had higher affinity and were more delta-selective than the corresponding E-isomers. The (Z)-7-(1-naphthylidene)naltrexone (3b) showed the greatest selectivity (delta:mu ratio of 15) and highest affinity delta-binding (Ki = 0.7 nM). PM3 semiempirical geometry optimizations suggest a significant role for the orientation of the arylidene substituent in the binding affinity and delta-receptor selectivity. This work demonstrates that larger groups may be incorporated into the arylidene portion of the molecule with opioid receptor affinity being retained.

The presence of a molecular scaffold to orient a basic group is important for potent and selective kappa opioid antagonist selectivity. An attempt to determine how the geometry of the scaffold affects this selectivity has led to the synthesis of a bivalent ligand (5) whose linker constrains the N17' basic nitrogen (the "address") to a position that is 6.5 A from N17' in the kappa antagonist norBNI (1) when these molecules are superimposed. The fact that compound 5 was found to be a highly selective and potent mu-selective antagonist supports the idea that the position of N17' in 5 precludes effective ion pairing with the nonconserved residue Glu297 on outer loop 3 of the kappa opioid receptor. The high mu receptor binding affinity and in vitro pharmacological selectivity of 5 coupled with its presumed low central nervous system bioavailability suggest that it may be a useful antagonist for the investigation of peripheral mu opioid receptors.

A series of regioisomeric substituted 6-O-benzyl ethers of 6 beta-naltrexol (12) in which isothiocyanate groups were attached directly to or one carbon removed from the aromatic ring of the benzyl group were prepared. These agents were prepared to obtain electrophilic opioid ligands potentially useful in the characterization of opioid receptors and drug-receptor interactions. Preparation of these ligands was accomplished from 3-O-trityl-6 beta-naltrexol (13) via phase transfer-catalyzed alkylation of the regioisomeric o-, m-, and p-nitrobenzyl halides and the o-, m-, and p-cyanobenzyl halides. The intermediates were deprotected and reduced, and formation of the isothiocyanates from the corresponding amines completed the synthesis. The ligands (6-11) were tested in radioligand displacement assays in guinea pig brain homogenate for opioid receptor binding affinity and irreversibility. All six of the isothiocyanates demonstrated significant affinity in the displacement assays for all three opioid receptors. They also appeared to be irreversibly bound at each of the receptor types. Compound 6, the o-isothiocyanatobenzyl ether analog, had the highest affinity, and it demonstrated significant irreversibility at very low concentration. It appears to be suitable for further investigation.

A series of 6-O-ethers of 6 beta- and 6 alpha-naltrexol (6 and 7) were prepared to examine the effect of large aralkyl groups on affinity of the ligands for opioid receptors. The affinities of the 6 beta- and 6 alpha-O-ether with benzyl, biphenylmethyl, 1- and 2-naphthylmethyl, and 9-anthracylmethyl groups were determined. Preparation of the ligands was accomplished from suitably 3-O-protected derivatives of 6 and 7 by phase transfer catalyzed alkylation using aralkyl halides, followed by deprotection. Both 3-O-trityl and -benzyl protecting groups were used. In radioligand displacement assays, compounds from the 6 alpha-O ether series had higher affinity than the analogous diastereomers in the 6 beta-O series, with few exceptions. In the 6 alpha-O series, the benzyl ether (29) and the biphenylmethyl ether (30) had the highest affinity, similar to naltrexone. In the 6 beta-O series, the benzyl ether had the highest affinity. The larger aralkyl ethers had slightly less affinity. Large lipophilic 6 beta-O- and 6 alpha- O-aralkyl groups are readily accommodated in the drug-receptor interaction.

A series of norbinaltorphimine congeners (2-12) which contain different groups at the N17'-position have been synthesized in order to evaluate the role of N17' in conferring kappa opioid antagonist selectivity at opioid receptor sites. The compounds that contain a basic N17' nitrogen (2-9) were found to be selective kappa antagonists. Amidation of N17' afforded congeners 10-12 with feeble kappa antagonist potency and low selectivity. The fact that potent antagonism and selectivity were observed only when members of the series contain a basic N17' nitrogen suggests that it interacts with extracellular domains of the kappa receptor that contain acidic amino acid residues. The N-terminal domain and extracellular loop 2, both of which contain acidic residues, are candidates for this interaction and may be components of the kappa address subsite of the receptor.

Naltrindole (1) (NTI) is a highly potent and selective delta-opioid receptor antagonist. In an effort to understand the origin of the high potency, affinity, and selectivity of NTI, we have examined the conformational role of its indolic benzene moiety through the synthesis of related naltrexone derivatives 3-8, which contain the benzene moiety in different orientations and at different attachments in the molecule. One of these naltrexone derivatives, 5, whose 7-indanyl benzene moiety is orthogonal to ring C of the morphinan system, is a potent delta-opioid receptor antagonist in vitro and in vivo. Computer-assisted molecular overlay studies of the minimized structures (2-8) revealed the importance of the position of the benzene moiety for effective interaction with delta-opioid receptors. In compounds 2, 4, and 5, the aromatic ring falls in the same region of space as that of the indolic benzene moiety of NTI, and all of these ligands possessed significant activity at delta-opioid receptors. Analogues (3 and 6-8) which were shown to have relatively weak delta-opioid receptor antagonist potency have their aromatic groups located in a space that is different from that of the more potent analogues.

The isothiocyanate group was attached to the 4'-, 5'-, 6'-, or 7'-position of naltrindole in an effort to determine the importance of the position of this electrophilic group on the selectivity for subtypes of delta opioid receptors. All of the ligands were delta-selective when tested against standard agonists in smooth muscle preparations. However, the rank-order delta antagonism of antinociception in mice did not parallel the in vitro pharmacologic data. The 5'-isothiocyanate 2 was the most potent and selective antagonist in vivo, causing a 52-fold increase of the ED50 for [D-Ser2,D-Leu5]enkephalin-Thr6 (DSLET) and no increase for [D-Pen2,D-Pen5]enkephalin (DPDPE). The effect of each of the ligands on the binding of [3H]DSLET and [3H]DPDPE to guinea pig brain membranes clearly differentiated between the binding sites that recognize these radioligands. These studies provide additional evidence for the presence of two subtypes of delta opioid receptors.

A series of fatty acid derivatives of naltrexamine and naltrexhydrazine were synthesized and evaluated for their persistent binding to opioid receptors. Members of this series were found to require greater than five washes for removal from mouse brain membranes when the fatty acyl chain was saturated. The presence of unsaturation in the fatty acyl groups enhanced the persistent binding. In this regard the persistent binding increased as a function of the number of double bonds, with the unsaturated congeners requiring greater than 10 washes for removal of the ligand from the membranes. The results of this study are consistent with the apparently important role of polyunsaturated fatty acids in the binding of ligands to opioid receptors.

Alpha- and beta-naltrexol derived esters 9 and 10 and ethers 11 and 12, each containing the alpha, beta-unsaturated ester functionality, were prepared as conformationally more flexible analogues of spiro-alpha-methylene-gamma-lactones 5 and 6. All were active in the opioid radioreceptor binding assay against [3H]bremazocine and more active against [3H]DAGO, indicating mu-subtype selectivity, but only ether 12 showed significant irreversible activity. We conclude that small structural changes, made in very closely related electrophilic opioids, lead to changes in receptor binding. All four compounds were long-acting antagonists to morphine in mice, with ester 10 being approximately equipotent with naltrexone.

The diastereomeric 6-desoxy-6-spiro-alpha-methylene-gamma-butyrolactone derivatives of naltrexone (4a and 5a) and of oxymorphone (4b and 5b) were prepared from their parent ketones. Diastereomers 4a and 4b were obtained from the 3,14-diacetate derivatives of naltrexone (6a) and oxymorphone (6b) by reaction with the Reformatsky reagent prepared from methyl alpha-(bromomethyl)acrylate. Deacetylation with methanol completed the synthesis. Diastereomers 5a and 5b were obtained from oxiranes 8a and 8b, respectively. The oxiranes were allowed to react with the sodium salt of ethyl acetoacetate, followed by methenation and deprotection to complete the synthesis of 5a and 5b, respectively. Compound 5a was the most potent agent tested in competition against [3H]naltrexone in the opioid radioreceptor assay. At a concentration of 5 nM this compound produced a 50% inhibition of binding. The majority of this inhibition (30%) was irreversible, i.e., it remained even after extensive washing of the membrane preparation in the presence and absence of Na+. Naloxone protected against this irreversible effect. The data suggest a receptor nucleophile, perhaps a sulfhydryl group, is located where it can add to the alpha, beta-unsaturated carbonyl system of 5a.

In an effort to determine whether or not the basic nitrogens in the spacer of the bivalent ligand 6 beta,6 beta'-[ethylenebis(oxyethyleneimino)]bis[17-(cyclopropylmethyl)4,5 alpha-epoxymorphinan-3,14-diol] (TENA, 1) is responsible for its selective kappa opioid antagonist activity, we have synthesized monovalent analogues 2-4 that contain a C-6 side chain with basic nitrogens. Analogue 2 behaved as a potent opioid agonist in the guinea pig ileum preparation (GPI) and possessed no significant kappa opioid antagonist activity (IC50 ratio = 1) relative to TENA (IC50 ratio = 20). The agonist activity of 3 and 4 interfered with the opioid antagonist assay and therefore did not permit evaluation of antagonist activity in a concentration range where TENA is effective. Although the results obtained with 2 are consistent with the requirement of a second opiate pharmacophore (rather than a second basic nitrogen in the spacer) for the kappa antagonist activity of TENA, the potent agonism associated with these monomers do not allow a firm conclusion in this regard.

Chlornaltrexamine (CNA) produces ultralong-lasting (3--6 days) narcotic antagonism in mice and persistent stereospecific binding to rat-brain homogenate. Protection studies in mice suggest that CNA mediates its narcotic antagonist effects by interacting with the same receptors that are occupied by naloxone. A single icv dose of CNA also has been found to inhibit the development of physical dependence in mice for at least 3 days. These studies suggest that CNA exerts its sustained effects by selective covalent association with opioid receptors.

Ethylketocyclazocine (1) has greater kappa/mu selectivity than cyclazocine in brain binding assays. 10-Ketonaltrexone (11) and 10-ketooxymorphone (10) were prepared from naltrexone 3-methyl ether and oxycodone, respectively. Bioassays in the myenteric plexus longitudinal muscle preparation of the guinea pig ileum and in the mouse vas deferens, in addition to brain binding assays, demonstrated that 10 and 11 were far less potent than naltrexone (2) and oxymorphone (3) at mu sites and also had little affinity for kappa and delta sites. It is concluded that introduction of the 10-keto group in naltrexone and oxymorphone diminished opioid effects at all binding sites.

The anti-anti isomer of naltrexonazine (1) was synthesized, and its configuration was confirmed by X-ray crystallography. The syn-anti isomer is readily converted to 1 under acidic conditions. The apparent equal receptor binding of 1 and syn-anti isomer indicates that isomerization of the azine moiety may take place under the conditions of biological evaluation. Two possible explanations for wash-resistant binding of 1 to opioid receptors are presented. The first possibility involves a noncovalent interaction of the ligand with the opioid receptor, and the second considers covalent binding by a receptor-based sulfhydryl group.

3-O-tert-Butylmorphine (5) was prepared from 6-O-acetylmorphine (3) via alkylation with N,N-dimethylformamide di-tert-butyl acetal, followed by hydrolytic removal of the 3-(dimethylamino)-2-propenoate group. The same process was used to prepare the tert-butyl ether of levorphanol (6), (-)-3-tert-butoxy-N-methylmorphinan (8). Both 5 and 8 exhibited in vitro affinity for the opiate receptor comparable to codeine and had analgesic properties in the writhing test. Only 5 exhibited activity in the tail-flick procedure and neither compound showed significant antitussive activity.

Epimeric 6-amino derivatives of naloxone and naltrexone have been synthesized and the configuration at the C-6 chiral center was determined from NMR studies. All of the derivatives possess narcotic antagonist activity in mice, with each of the 6beta epimers having greater potency than the corresponding 6alpha epimers. In vitro binding experiments indicate that the affinities of these epimers parallel thier in vivo potencies. Slight antinociceptic properties were observed with three of the four compounds. The naloxone derivatives 3a and 3b appear to be attractive candidates for investigation as long-acting narcotic antagonists in view of their fourfold greater duration of action relative to the other antagonists (1, 2, 4a, and 4b).

Synthesis and opioid radioreceptor assay data on analogues closely related to 6-desoxy-6-spiro-alpha-methylene-gamma-lactone 5a, a compound with irreversible activity in this assay, are reported. Saturated lactones (7a,b), endocyclic alpha, beta-unsaturated gamma-lactones (8a,b and 9a), and 6 alpha,7 alpha-fused alpha-methylene-gamma-lactones (10a and 11a) were prepared. Related 6-desoxy-6-methylene 6 beta- and 6 alpha-oxides (12a,b and 13a) and glycidate esters 14a,b and 15a,b were also prepared with use of naltrexone (1a) and oxymorphone (1b) as starting material. Compounds in the N-cyclopropylmethyl (N-CPM) series were more potent than those in the N-Me series in displacing [3H]naltrexone in the opioid radioreceptor assay, usually by 2-16-fold in the absence of Na ion. The most potent N-CPM analogues were epoxides 12a and 13a and glycidate esters 14a and 15a, showing IC50's of 2-6 nM, similar to that of 5a. Of the N-Me analogues, 6 beta-oxide 12b was most active, with an IC50 of 8 nM in the absence of Na ion. For the N-CPM analogues, the Na ion ratios were generally less than 1, with two exceptions. The N-Me analogues showed expected larger Na ion effects of 7 or greater. None of the lactone analogues had irreversible effects when preincubated in the rat brain membrane preparation, even at 37 degrees C for 30 min, i.e., washing restored [3H]naltrexone binding to control levels. These results clearly show that the alpha-methylene-gamma-lactone moiety of 5a is required for irreversible effects, consistent with it serving as a conjugate addition acceptor of a nucleophilic group from a ligand at or near the receptor. The epoxides and glycidate esters also had no irreversible activity, indicating more electrophilic functional groups are needed and/or these electrophiles are not properly aligned to react with nucleophilic groups at or near the opioid receptor.

The N-methyl analogues (2a, 2b) of the nonequilibrium mu opioid receptor antagonist beta-funaltrexamine (1b) were synthesized and evaluated in the guinea pig ileum preparation (GPI). These analogues are highly potent, reversible opioid agonists and possess no nonequilibrium antagonist activity. The ineffectiveness of 2b in protecting against irreversible blockage of mu opioid receptors by 1b and the fivefold lower reactivity of 2b with cysteine suggest that N-methyl substitution adversely affects both the first and second recognition steps that are essential for effective covalent blockage of opioid receptors.

Condensation of the Grignard reagent derive from 2-[4-(allyloxy)phenyl]ethyl bromide (4b) with 7 alpha-acetyl-6,14-endo-ethenotetrahydrothebaine (5) furnished the (R) tertiary carbinol, 7, which upon methoxymercuration followed by treatment with the KBr gave the bromomercurio compound 10 (Hybromet). The corresponding N-cyclopropylmethyl analogue, 11, was prepared also. The bromomercurio compound, 1, and the mercaptobenzothiazole derivative, 3, gave allyl phenyl ether when treated with BAL at room temperature. Similar treatment of 10 with BAL gave 7 in high yield. Binding studies using rat brain homogenates indicated that 7, 13, and 14 have moderately high affinities for mu rather than delta binding sites. Although much weaker, 10 showed preferential mu binding also. These results along with the fact that 10 reacted smoothly with sulfhydryl groups suggest that Hybromet would be a suitable ligand for use in affinity chromatography.

In an effort to develop selective antagonists for kappa opioid receptors, bivalent ligands that contain opioid antagonist pharmacophores derived from naltrexone or other morphinans were synthesized and tested on the guinea pig ileum (GPI) and mouse vas deferens (MVD) preparations. The minimum requirements for kappa selectivity are at least one free phenolic OH group and one N-cyclopropyl or N-ally substituent. Several compounds (3, 8, 10) with kappa selectivity as good as or better than norbinaltorphimine (nor-BNI, 2) were discovered. The structure-activity relationship revealed that the pyrrole ring functions strictly as a spacer and does not contribute to kappa selectivity. The pharmacologic data suggest that only one antagonist pharmacophore may be required for kappa selectivity and that the other morphinan portion of the molecule confers selectivity by interacting with a unique subsite proximal to the antagonist pharmacophore recognition locus.