Strong Feedback Inhibition of Key Enzymes in the Morphine Biosynthetic Pathway from Opium Poppy Detectable in Engineered Yeast

Systematic screening of morphine pathway intermediates in engineered yeast revealed key biosynthetic enzymes displaying potent feedback inhibition: 3'-hydroxy-N-methylcoclaurine 4'-methyltransferase (4'OMT), which yields (S)-reticuline, and the coupled salutaridinol-7-O-acetyltransferase (SalAT) and thebaine synthase (THS2) enzyme system that produces thebaine. The addition of deuterated reticuline-d1 to a yeast strain able to convert (S)-norcoclaurine to (S)-reticuline showed reduced product accumulation in response to the feeding of all four successive pathway intermediates. Similarly, the addition of deuterated thebaine-d3 to a yeast strain able to convert salutaridine to thebaine showed reduced product accumulation from exogenous salutaridine or salutaridinol. In vitro analysis showed that reticuline is a noncompetitive inhibitor of 4'OMT, whereas thebaine exerts mixed inhibition on SalAT/THS2. In a yeast strain capable of de novo morphine biosynthesis, the addition of reticuline and thebaine resulted in the accumulation of several pathway intermediates. In contrast, morphine had no effect, suggesting that circumventing the interaction of reticuline and thebaine with 4'OMT and SalAT/THS2, respectively, could substantially increase opiate alkaloid titers in engineered yeast.

Discovery of an M-Substituted N-Cyclopropylmethyl-7α-phenyl-6,14-endoethanotetrahydronorthebaine as a Selective, Potent, and Orally Active κ-Opioid Receptor Agonist with an Improved Central Nervous System Safety Profile

The search for selective kappa opioid receptor (κOR) agonists with an improved safety profile is an area of interest in opioid research. In this work, a series of m-substituted analogs were designed, synthesized, and assayed, resulting in the identification of compound 6c (SLL-1206) as a κOR agonist with single-digit nanomolar activities. The subtype selectivity of compound 6c appeared to be a consequence of an enormous decrease in the affinity for μOR and δOR, rather than a significant increase in the affinity for κOR, which was not the case for SLL-039, another selective and potent κOR agonist identified in our previous work. Besides reduced central nervous system effects, SLL-1206 exhibited substantially improved physicochemical and pharmacokinetic properties compared with SLL-039, with increases of over 20-fold in aqueous solubility and approximately 40-fold in oral bioavailability in rats.

Effects of methyl jasmonate and phloroglucinol on thebaine and sanguinarine production in cell suspension culture of Persian poppy (Papaver bracteatum Lindl.)

The biosynthesis path engineering could be very promising for mass production of alkaloids by applying elicitors in the cell suspension culture of Persian poppy (Papaver bracteatum Lindl.). In this work, the effects of different concentrations of methyl jasmonate (MJ) and phloroglucinol (PG) on thebaine and sanguinarine productions in vitro were investigated. Roots as explant and supplementing 3 mg L-1 2,4-Dichlorophenoxyacetic acid with 0.5 mg L-1 Benzyl amino purine to modified MS medium were selected to achieve the most efficient combination for callus induction and production of callus fresh and dry weights. At 48 h after treatment, the addition of PG and MJ individually and in combination together significantly increased both thebaine and sanguinarine contents than the control. The results of high-performance liquid chromatography (HPLC) detection indicated that the highest production rate has been achieved through a synergic effect of two elicitors after 48 h. Results revealed that adding 200 μM of MJ and 100 mg L-1 PG increased thebaine and sanguinarine contents by 56.36 and 107.71-fold than control cells, respectively.

Morphine biosynthesis in opium poppy involves two cell types: sieve elements and laticifers

Immunofluorescence labeling and shotgun proteomics were used to establish the cell type-specific localization of morphine biosynthesis in opium poppy (Papaver somniferum). Polyclonal antibodies for each of six enzymes involved in converting (R)-reticuline to morphine detected corresponding antigens in sieve elements of the phloem, as described previously for all upstream enzymes transforming (S)-norcoclaurine to (S)-reticuline. Validated shotgun proteomics performed on whole-stem and latex total protein extracts generated 2031 and 830 distinct protein families, respectively. Proteins corresponding to nine morphine biosynthetic enzymes were represented in the whole stem, whereas only four of the final five pathway enzymes were detected in the latex. Salutaridine synthase was detected in the whole stem, but not in the latex subproteome. The final three enzymes converting thebaine to morphine were among the most abundant active latex proteins despite a limited occurrence in laticifers suggested by immunofluorescence labeling. Multiple charge isoforms of two key O-demethylases in the latex were revealed by two-dimensional immunoblot analysis. Salutaridine biosynthesis appears to occur only in sieve elements, whereas conversion of thebaine to morphine is predominant in adjacent laticifers, which contain morphine-rich latex. Complementary use of immunofluorescence labeling and shotgun proteomics has substantially resolved the cellular localization of morphine biosynthesis in opium poppy.

The biosynthesis of papaverine proceeds via (S)-reticuline

Papaverine is one of the earliest opium alkaloids for which a biosynthetic hypothesis was developed on theoretical grounds. Norlaudanosoline (=tetrahydropapaveroline) was claimed as the immediate precursor alkaloid for a multitude of nitrogen containing plant metabolites. This tetrahydroxylated compound was proposed to be fully O-methylated. The resulting tetrahydropapaverine should then aromatize to papaverine. In view of experimental data, this pathway has to be revised. Precursor administration to 8-day-old seedlings of Papaver followed by direct examination of the metabolic fate of the stable-isotope-labeled precursors in the total plant extract, without further purification of the metabolites, led to elucidation of the papaverine pathway in vivo. The central and earliest benzylisoquinoline alkaloid is not the tetraoxygenated norlaudanosoline, but instead the trihydroxylated norcoclaurine that is further converted into (S)-reticuline, the established precursor for poppy alkaloids. The papaverine pathway is opened by the methylation of (S)-reticuline to generate (S)-laudanine. A second methylation at the 3' position of laudanine leads to laudanosine, both known alkaloids from the opium poppy. Subsequent N-demethylation of laudanosine yields the known precursor of papaverine: tetrahydropapaverine. Inspection of the subsequent aromatization reaction established the presence of an intermediate, 1,2-dihydropapaverine, which has been characterized. The final step to papaverine is dehydrogenation of the 1,2-bond, yielding the target compound papaverine. We conclusively show herein that the previously claimed norreticuline does not play a role in the biosynthesis of papaverine.

Investigation of abiogenic stress-induced alterations in the level of secondary metabolites in poppy plants (Papaver somniferum L.)

We aimed to understand the effects of water stress on the alkaloid production in various developmental stages of poppy plants and the effect of stress on the alkaloids content in the capsules. Three stages of the life cycle of Papaver somniferum L. were selected in our studies: Rosette, Flowering and Lancing developmental stages. Four types of water conditions were examined: Control, Withdrawal of Water, 50% Water Supply and Inundation. The morphological monitoring, results of Relative Water Content and proline content were used as indicators of stress. The result of the measurements in poppy leaves show that the secondary metabolites dramatically respond to these stress conditions. The constant water supply was beneficial for the accumulation of alkaloids in the capsules.

Analgesia: morphine-pathway block in top1 poppies

The opium poppy is a source of the pharmaceuticals codeine, morphine and their derived analgesics. Here we describe the initial characterization of the poppy mutant known as top1 (for 'thebaine oripavine poppy 1'), which accumulates the morphine and codeine precursors thebaine and oripavine and does not complete their biosynthesis into morphine and codeine. The original discovery of top1 stimulated a re-engineering of the opioid industry in the island state of Tasmania, which grows over 40% of the world's licit opiates, in order to produce thebaine and oripavine efficiently from morphine-free poppy crops to provide precursors for highly effective analgesics and for treatment of opioid addiction.

Endogenous formation of morphine in human cells

Morphine is a plant (opium poppy)-derived alkaloid and one of the strongest known analgesic compounds. Studies from several laboratories have suggested that animal and human tissue or fluids contain trace amounts of morphine. Its origin in mammals has been believed to be of dietary origin. Here, we address the question of whether morphine is of endogenous origin or derived from exogenous sources. Benzylisoquinoline alkaloids present in human neuroblastoma cells (SH-SY5Y) and human pancreas carcinoma cells (DAN-G) were identified by GC/tandem MS (MS/MS) as norlaudanosoline (DAN-G), reticuline (DAN-G and SH-SY5Y), and morphine (10 nM, SH-SY5Y). The stereochemistry of reticuline was determined to be 1-(S). Growth of the SH-SY5Y cell line in the presence of (18)O(2) led to the [(18)O]-labeled morphine that had the molecular weight 4 mass units higher than if grown in (16)O(2), indicating the presence of two atoms of (18)O per molecule of morphine. Growth of DAN-G cells in an (18)O(2) atmosphere yielded norlaudanosoline and (S)-reticuline, both labeled at only two of the four oxygen atoms. This result clearly demonstrates that all three alkaloids are of biosynthetic origin and suggests that norlaudanosoline and (S)-reticuline are endogenous precursors of morphine. Feeding of [ring-(13)C(6)]-tyramine, [1-(13)C, N-(13)CH(3)]-(S)-reticuline and [N-CD(3)]-thebaine to the neuroblastoma cells led each to the position-specific labeling of morphine, as established by GC/MS/MS. Without doubt, human cells can produce the alkaloid morphine. The studies presented here serve as a platform for the exploration of the function of "endogenous morphine" in the neurosciences and immunosciences.

Identification of rat faecal, urinary and biliary metabolites of thionorphine, a novel mixed agonist-antagonist analgesic, using liquid chromatography/electrospray ionization tandem mass spectrometry

The biotransformation of thionorphine (N-cyclopropylmethyl-7alpha-[(s)-1-hydroxy-1-methyl-3-(2thiophene)-propyl]-6,14-endo-ethano tetrahydrooripavine), a new analgesic, was in-vestigated in rats. The results of metabolite analysis by liquid chromatography/electrospray ionization tandem mass spectrometry with positive ion mode, in which a mobile phase of 10 mM ammonium acetate (pH 3.0)/acetonitrile (25/75) was used, suggested that thionorphine is biotransformed to two potentially active metabolites, the N-dealkylated thionorphine (M-I) and the oxidized thionorphine (M-II), and subsequently form conjugates with glucuronic acid of both thionorphine and the metabolites.

A novel regiospecific N to O-methyl transferase activity in the biotransformation of a thebaine derivative with Cunninghamella echinulata NRRL 1384

A novel regiospecific N- to O-methyl transfer reaction has been characterised in the biotransformation of an N-CD3-thebaine derivative with the fungus Cunninghamella echinulata NRRL 1384.

The [4+2]] addition of singlet oxygen to thebaine: new access to highly functionalized morphine derivatives via opioid endoperoxides

The photooxidation of thebaine (3) with a sun lamp affords two main products: hydrodibenzofuran 10 (major) and benzofuran 11 (minor). The latter compound becomes predominant if a Hg lamp is used instead of a sun lamp. The formation of 10 proceeds via an endoperoxide intermediate that undergoes oxidation at the nitrogen atom. Protection of the nitrogen either by protonation or quaternization prevents its oxidation and thus the photooxidation of 3 in acid media constitutes a one-pot procedure for the preparation of 14-hydroxycodeinone 35. Photooxidation of the thebaine ammonium salt 31 allows the isolation in good yields of the corresponding to thebaine endoperoxide 32. The selective protection and reduction of the keto, aldehyde, and olefinic groups of hydrodibenzofuran 10 allowed the preparation of several diol and keto alcohol derivatives. This is the first report on the use of photooxidation to functionalize thebaine at C(6) and C(14) and also the first on the isolation of opioid endoperoxides.

Differential binding properties of oripavines at cloned mu- and delta-opioid receptors

This study examines the possibility that oripavine opioid receptor agonists bind equally to both high and low affinity states of the mu-opioid receptor. Studies were performed in C6 cells expressing mu- or delta-opioid receptors; high and low agonist affinity states of the receptors were defined by the absence and presence, respectively of Na+ ions and the GTP analog Gpp(NH)p. At the mu-opioid receptor dihydroetorphine and etorphine were full agonists, buprenorphine had moderate efficacy while diprenorphine was an antagonist. At the delta-opioid receptor, dihydroetorphine, etorphine, and diprenorphine had moderate efficacy while buprenorphine was an antagonist. The binding affinities of the oripavines at the mu-opioid receptor decreased only one to 2-fold in the presence of NaCl and Gpp(NH)p. In contrast, decreases in oripavine affinity at the delta-opioid receptor correlated with delta-opioid receptor efficacy. The ability of oripavine agonists to bind with high affinity to the low agonist affinity state of the nu-opioid receptor may explain the high potencies of these compounds in vivo.

Stereoselective mu- and delta-opioid receptor-related antinociception and binding with (+)-thebaine

In vivo and in vitro binding studies with natural thebaine and its enantiomer, (+)-thebaine were conducted to elucidate further their interactions with the opioid system. (-)-Thebaine a key intermediate in the biosynthesis of morphine in the poppy plant (Papaver somniferum) and in mammalian tissue, was poorly effective antinociceptively in mice at doses to 30 mg/kg. Its principal behavioral manifestation was lethal convulsions. Naltrindole, at doses of 1 and 10 mg/kg did not block either the convulsions or lethal effects, suggesting that the delta-opioid receptor system was not involved in this action. Surprisingly, the dextrorotatory isomer exhibited significant antinociceptive activity in the tail-flick [ED50 = 8.9 (3.4-22.1) mg/kg], hot-plate [ED50 = 22.9 (10.9-48.1) mg/kg] and phenylquinone [ED50) = 1.9 (1.6-9.5) mg/kg] assays. Studies with opioid receptor-subtype antagonists, beta-funaltrexamine, nor-binaltorphimine and naltrindole, indicated that antinociception was associated with mu- and delta-opioid receptors. Results of displacement experiments supported the in vivo data. Significant competition for [3H]diprenorphine binding with both isomers for cloned mu- and delta-opioid receptors was observed. However, (-)-thebaine was more effective at the delta-opioid receptor (Ki = 1.02+/-0.01 microM) whereas (+)-thebaine was more effective at the mu-opioid receptor ( Ki = 2.75+/-0.01 microM). Opioid-induced antinociception associated with unnatural thebaine raises the possibility of additional mu- and delta-opioid receptor sites.

Acetyl coenzyme A:salutaridinol-7-O-acetyltransferase from papaver somniferum plant cell cultures. The enzyme catalyzing the formation of thebaine in morphine biosynthesis

Acetyl coenzyme A:salutaridinol-7-O-acetyltransferase, a highly substrate-specific enzyme, has been purified nearly 3,000-fold to homogeneity from Papaver somniferum plant cell suspension cultures. Purification was achieved by fractionated ammonium sulfate precipitation, dye-ligand affinity chromatography on matrex red A, gel filtration, ion exchange chromatography on Mono Q and a second dye-ligand affinity chromatography on fractogel TSK AF Blue. The purified enzyme was a single polypeptide with an M(r) = 50,000 displaying an isoelectric point of 4.8, a pH optimum between pH 6 and 9 and a temperature optimum at 47 degrees C. The Km values for the substrate salutaridinol and the co-substrate acetyl co-enzyme A were 7 and 46 microM, respectively. Salutaridinol-7-O-acetyltransferase catalyzes the stoichiometric transfer of the acetyl group from acetyl coenzyme A to the 7-OH group of salutaridinol yielding salutaridinol-7-O-acetate, which is a new intermediate in morphine biosynthesis. Salutaridinol-7-O-acetate undergoes a subsequent spontaneous allylic elimination at pH 8-9, leading to the formation of thebaine (1), the first morphinan alkaloid with the complete pentacyclic ring system, or at pH 7 leading to dibenz[d,f]azonine alkaloids that contain a nine-membered ring. Acetylation and subsequent allylic elimination is a new enzymic mechanism in alkaloid biosynthesis, which in the poppy plant can transform one precursor into alkaloids possessing markedly different ring systems, depending on the reaction pH.

Endogenous morphine

This review surveys the discovery of endogenous alkaloids in mammals. The formation of morphine in mammalian brain was assumed in 1970. The existence of morphine was demonstrated by radioimmunoassay. Identification of morphine was performed by spectroscopic methods. The isolation of mammalian morphine raises the question of biosynthesis. Recently, it has been shown that the biosynthetic pathway is similar to that that exists in poppy.

Synthesis and characterization of 7-nitrobenzo-2-oxa-1,3-diazole (NBD)-labeled fluorescent opioids

Alkylation of sarcosine with 4-chloro-nitrobenzo-2-oxa-1,3-diazole (NBD-chloride) furnished a fluorescent tag that was coupled with a tetrahydrothebaine derivative and beta-naltrexamine, respectively, to yield the fluorescent opioids 7 alpha-(1R)-1-hydroxy-1-methyl-3-(4-hydroxyphenyl)-propyl]-6,14- endoethenotetrahydrothebaine NBD-sarcosinate (ASM-5-10) and N-cyclopropylmethyl-3-hydroxy-14 beta-hydroxy-6 beta-(NBD sarcosinyl)-amino-epoxymorphinan (ASM-5-67). The fluorescence intensity of the novel opioids allowed their detection at subnanomolar concentrations, and was dependent on the polarity of the solvent. Maximum quantum yield was obtained in ethyl acetate and ethanol, and minimal fluorescence in heptane and water. Compounds ASM-5-10 and ASM-5-67 displaced the opioid receptor binding of [3H]Tyr-D-Ala-Gly-(Me)Phe-Gly-ol in monkey brain membranes with IC50 values of 8.4 and 1.5 nM, respectively. Whereas ASM-5-67 bound to mu, delta, and kappa receptors with comparable affinities, ASM-5-10 was mu-selective, with selectivity indices (ratio of respective IC50 values) of 0.04 for both mu/delta and mu/kappa. The sodium response ratio in binding revealed a pronounced agonist property of ASM-5-10. Both opioids were lipophilic, with octanol-water partition coefficients (log Papp) of 2.8 (ASM-5-10) and 1.0 (ASM-5-67). ASM-5-10 exhibited particularly strong membrane retention that was not reversible by four washes. Their favorable characteristics in fluorescence, receptor binding, and membrane interaction make these newly developed ligands useful molecular probes to study opioid receptor mechanisms.

Thebaine O-demethylation to oripavine: genetic differences between two rat strains

1. Codeine O-demethylation to morphine is mediated by cytochrome P450 IID1 (rat), or P450 IID6 (man), and exhibits genetic polymorphism. Thebaine is a precursor in the formation of endogenous morphine and codeine in man, being O-demethylated to oripavine. 2. The objective of the present study was to ascertain whether the O-demethylation of thebaine to oripavine was mediated by cytochrome P450 IID1 in rat liver microsomes. 3. Thebaine O-demethylation showed strain differences in female Sprague-Dawley (SD) and female Dark-Agouti (DA) rats, which serve as a model for the human debrisoquine/sparteine metabolism phenotypes. 4. The total intrinsic clearance of thebaine to oripavine was high (19.7 ml/h per mg protein) in SD rats, indicating that oripavine is a major metabolite of thebaine. A 3-fold lower intrinsic clearance was observed in DA rats (6.7 ml/h per mg protein). 5. Thebaine O-demethylation was inhibited by quinine and known substrates of cytochrome P450 IID1/P450 IID6, supporting the major involvement of cytochrome P450 IID1 in oripavine formation in rats.

Microbial degradation of the morphine alkaloids: identification of morphine as an intermediate in the metabolism of morphine by Pseudomonas putida M10

A strain of Pseudomonas putida was isolated by selective enrichment with morphine that was capable of utilising morphine as a primary source of carbon and energy for growth. Experiments with whole cells showed that both morphine and codeine, but not thebaine, could be utilised. A novel NADP-dependent dehydrogenase, morphine dehydrogenase, was purified from crude cell extracts and was shown to be capable of oxidising morphine and codeine to morphinone and codeinone, respectively. This NADP-dependent morphine dehydrogenase was not observed in any other species of pseudomonads examined and was quite distinct from the beta-hydroxysteroid dehydrogenase found in Pseudomonas testosteroni, which had previously been shown to have activity against morphine.

Electrophilic alpha-methylene-gamma-lactone and isothiocyanate opioid ligands related to etorphine

Isothiocyanate and alpha-methylene-gamma-lactone analogues of 6,14-endo-ethenotetrahydrothebaine and -oripavine were prepared with the electrophilic groups being located at C-19 in the C-7 alpha-side chain. Isothiocyanates were prepared in the N-Me and N-CPM (N-cyclopropylmethyl) series, both as the phenols and 3-O-methyl ethers from the diastereomeric amines formed from reductive amination of thevinone (2) and N-(cyclopropylmethyl)northevinone (13). Although addition of the organozinc reagent from methyl alpha-bromomethacrylate to 25 failed, addition to 3-O-protected aldehydes 27 and 35 produced, after subsequent deprotection, alpha-methylene-gamma-lactones 29 and 37, respectively. In the opioid receptor displacement assays against [3H]bremazocine as the radiolabeled ligand, the phenolic compounds were most potent with N-CPM isothiocyanates 20 and 21 showing IC50s of 0.32 and 0.76 nM, respectively, and N-CPM alpha-methylene-gamma-lactone 37 having an IC50 = 1.0 nM. Compound 37 showed irreversible effects in the binding assay which were mu-selective, as demonstrated by analogous experiments using [3H]DAGO, and naloxone was found to protect against the irreversible effects. This observation suggests that a receptor-bound nucleophile is located at a position where it can readily reach the alpha-methylene group of lactone 37.

A study of the interaction of the alkylating agent, NIH10236, with opioid receptors in vitro and in vivo

The series of experiments reported in this paper examined the spectrum of subtypes of opioid receptors alkylated in vitro by N-cyclopropylmethyl-7 alpha-methylfumaramido-6,14- endoethenotetrahydronororipavine (NIH10236) and four optical isomers of the methylfumaramidophenethyl derivatives of 3-methylfentanyl. Pretreatment of membranes with NIH10236 resulted in a wash-resistant inhibition of the binding of [3H]6 beta-fluoro-6-desoxyoxymorphone (mu binding sites), the binding of [3H][D-ala2,D-leu5]-enkephalin (both the higher and lower affinity delta binding sites) and was without effect on kappa binding sites labelled with [3H]bremazocine. All four potential alkylating derivatives of 3-methylfentanyl were inactive. Pretreatment of membranes with 1 microM of the reversible ligands, (+)-cis-3-methylfentanyl, but not its enantiomer, inhibited the binding of [3H]6 beta-fluoro-6-desoxyoxymorphone and the binding of [3H][D-ala2,D-leu5]enkephalin to the lower affinity binding sites by over 90%. This phenomenon is termed "pseudo-irreversible inhibition." Incubation of pretreated membranes for 60 min at 37 degrees C, in the presence of 200 mM NaCl and 50 microM GppNHp, only partially reversed the masking of opioid receptors by (+)-cis-3-methylfentanyl. For in vivo experiments, membranes were prepared 18-24 hr after the intracerebroventricular administration of 80 and 50 micrograms of NIH10236. This resulted in decreased labelling of mu binding sites, lower affinity [3H][D-ala2,D-leu5]enkephalin binding sites, as well as kappa binding sites, labelled by [3H]U69,593 and [3H]bremazocine. There was no apparent alteration in the higher affinity [3H][D-ala2,D-leu5]enkephalin binding site.(ABSTRACT TRUNCATED AT 250 WORDS)

Transformation of thebaine to oripavine, codeine, and morphine by rat liver, kidney, and brain microsomes

Thebaine, an intermediate of morphine biosynthesis in the poppy plant, Papaver somniferum, was transformed to oripavine, codeine, and morphine by rat liver, kidney, and brain microsomes in the presence of an NADPH-generating system. The formation of morphine, codeine, and oripavine was identified by a specific RIA, HPLC, and GCMS. Thebaine also gave rise to four other compounds, which for the moment are unidentified. NADH dramatically increased the formation of both codeine and morphine when used together with an NADPH-generating system, especially in liver microsomes. NADPH is essential in the formation of oripavine from thebaine and morphine from codeine, while NADH is critical in the conversion of thebaine to codeine and from oripavine to morphine. Carbon monoxide or SKF 525A inhibited the conversion, indicating a role of cytochrome P-450. These results provide evidence for the enzymatic in vitro conversion by mammalian tissues of thebaine to morphine. The pathway is similar to that which exists in plants.

Precursors of the mammalian synthesis of morphine: (+)-salutaridine and (-)-thebaine from (+)-6-demethylsalutaridine, and (-)-N-13CH3-thebaine from (-)-northebaine

Standard samples of pure (+)-salutaridine and (-)-thebaine required to study the mammalian origin of morphine, were prepared from (+)-6-demethylsalutaridine by published procedures and were characterized by CD spectra and physical data. Reductive N-methylation of (-)-northebaine afforded (-)-thebaine, and when 13C-labeled formalin was used, (-)-thebaine with a 13C label on the N-methyl carbon atom resulted. The latter represents a model procedure to prepare ultimately N-14CH3-labeled (-)-thebaine and 14C-labeled congeners.

In vivo binding of putative delta-selective opioid antagonists to central opiate receptors

The in vivo opiate receptor binding of three putative delta-selective opioid antagonists, the irreversible oripavine ligand NIH 10236 and two enkephalin analogs, ICI 154,129 and ICI 174,866, was studied in rat brain. Following i.c.v. injection, potent and apparently irreversible opiate receptor binding was observed for NIH 10236 with similar affinity for mu, delta and kappa sites. However, opiate receptor binding was not evident either after s.c. injection of NIH 10236 or ICI 154,129, or following i.c.v. administration of ICI 154,129 or ICI 174,864. The receptor sites that mediate the pharmacological effects of these drugs should be reevaluated.

Hybromet: a ligand for purifying 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 vivo opiate receptor binding of oripavines to mu, delta and kappa sites in rat brain as determined by an ex vivo labeling method

The relative in vivo receptor affinities of three oripavine drugs given subcutaneously were determined at the mu, delta and kappa type of opiate binding sites in rat brain. The oripavines include the agonist etorphine, the antagonist diprenorphine and the mixed agonist-antagonist buprenorphine. With the use of mu, delta and kappa specific labeling conditions in brain homogenates immediately after sacrifice (ex vivo labeling), the method relies on the assay of those receptor sites that remain unbound in vivo. Because of the slow receptor binding kinetics of the oripavines, little or no dissociation of the in vivo ligand occurs during the ex vivo labeling period. All three drugs displayed lower affinity in vivo at the delta sites relative to mu sites, whereas the kappa affinities were highly variable. Etorphine displayed considerable mu selectivity, while burpenorphine's affinity at the mu and kappa sites was similar. The apparent in vivo binding affinities obtained from the ex vivo labeling approach are compatible with previous results where tracers were applied in vivo. The dramatic differences of the in vivo and in vitro opiate receptor binding properties of the oripavines demonstrate the need for in vivo receptor binding parameters in the analysis of the function of individual receptor types.

Probes for narcotic receptor mediated phenomena. 10. Irreversible ligands to opioid receptors based on biologically potent endoethenooripavines. Reversible binding of fit to mu and delta opioid receptors

A p-isothiocyanatophenylacetylamino moiety at the C7alpha position on an endoethenooripavine (NIH 10358) was found to irreversibly bind to both the mu and delta opioid receptors in rat brain membrane preparations. However, the same endoethenooripavine nucleus with a p-methylfumaroylaminophenylacetylamino moiety at that position (NIH 10364) binds specifically and irreversibly to only mu opioid receptors. Hypotheses are being developed concerning receptor subclass alkylation specificity. For example, it has now been found that the delta receptor irreversible agonist, FIT, can interact with both mu and delta receptors in a reversible manner.

Probes for narcotic receptor mediated phenomena. 7. Synthesis and pharmacological properties of irreversible ligands specific for mu or delta opiate receptors

Syntheses of affinity reagents for opiate receptors based on the fentanyl, endo-ethenotetrahydrooripavine, and etonitazene carbon-nitrogen skeletons are described. The isothiocyanate, bromoacetamido, and methylfumaramido alkylating functions were employed in these compounds, some of which had previously been shown to be mu specific (12, BIT) and delta specific (8, FIT and 19, FAO) in vitro. Antinociceptive activity of the title compounds was determined in the mouse hot-plate test, which revealed that certain compounds in each class showed morphine-like activity. The binding EC50 values against [3H]Dalamid for opiate receptors in NG108-15 (delta receptors) and rat brain membranes (mu + delta receptors) are also reported. With this type of experiment, it was possible to independently measure the apparent affinity of the etonitazene congeners 12-14 for the mu and delta receptors.

Thebaine metabolites in the urine of rhesus monkeys

The metabolic fate of thebaine in rhesus monkeys was investigated. Using thin layer chromatography, more than four metabolites were detected in the urine of monkeys given thebaine (8 mg/kg, s.c.). Two of the metabolites isolated by high performance liquid chromatography were not consistent with those reported previously. With the use of gas chromatography-mass spectrometry, the structures were identified as oripavine (3-O-demethylthebaine) and nororipavine (3-O,N-di-demethylthebaine) from the mass spectra of their trimethylsilyl and propionyl derivatives. Further experiments with liver microsomes from rhesus monkeys showed that, in addition to these metabolites, northebaine was also formed from thebaine in the presence of NADPH.

Biosynthesis of morphine alkaloids in Papaver bracteatum Lindl

Administration of 1-3H-N-methyl-14C-(+/-)-reticuline to Papaver bracteatum gave good incorporation of carbon-14 into thebaine and a decrease in the tritium to carbon-14 ratio indicative of racemization. The incorporation of carbon-14 and the extent of tritium loss were the same whether reticuline was administered to the intact plant or to isolated leaves. Carrier dilution with cold codeine, codeinone, and morphine showed only insignificant incorporation of radioactivity into codeine and none at all into codeinone and morphine. When codeinone was administered to the living plant, it was converted to codeine rapidly and efficiently, but no O-demethylation to morphine could be detected. The experimental data indicate that the biosynthesis of thebaine in P. bracteatum proceeds by the same pathway as in the opium poppy. The limiting step in the sequence is the demethylation of the enol ether group of thebaine to neopinone.

Papaver bracteatum Lindley: thebaine content in relation to plant development

Four thebaine-rich varieties of P. bracteatum have been grown in the open over two seasons and the thebaine distribution in aerial parts examined to determine the most suitable source material for commercial production. The leaves contained only 0-1 to 0-15%; the capsules 0-5 to 3-0% and the bled latex 28 to 53%. The maximum for the latter occurred about 3-4 weeks after petal opening and during the day, at about 15,00 h. A product 'bractium' prepared exactly as opium from P. somniferum contained up to 55% thebaine and calculations from the 1974 results gave theoretical yields up to 58 k of thebaine per hectare. However this is a very labour intensive method; furthermore bled latex only represents about 46% of the total thebaine of the capsule. In addition the pedicels contain significant amounts of thebaine, so that fruiting tops may be recommended as source material. In the capsule the thebaine content reaches a peak 3 to 4 weeks after petal opening and again two weeks later. At this fully ripe stage there is a theoretical yield of 50 kg per hectare. Two further advantages accrue from collection at this time: the ripe seeds can probably be used for similar purposes as poppy seed; and the pericarps at this stage contain no 'bound thebaine' (i;e., thebaine insoluble in MeOH; NH4OH but soluble in acetic acid--in unripe capsules bound thebaine represents 18 to 36% of the total thebaine). There is some evidence that, as this perennial plant increases in age, the capacity for thebaine production seems to continue increasing. Storage of raw material, even in ideal conditions, led to a loss of thebaine of 12 to 20% in one year.