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2,5-Dimethyl-2'-hydroxy-9 alpha- and 9 beta-(3-methylbutyl)-6,7-benzomorphans and N-substituted compounds in the 9 alpha-(3-methylbutyl) series: chemistry, pharmacology, and biochemistry.

2,5-Dimethyl-2'-hydroxy-9 alpha-(3-methylbutyl)-6,7-benzomorphan, the 9 beta-analogue, and 9 alpha-N-substituted (N-ethyl, propyl, butyl, pentyl, hexyl, phenylethyl, allyl, and cyclopropylmethyl) compounds were synthesized and evaluated biochemically and pharmacologically. The 9 beta N-methyl compound was found to be as potent as morphine in the mouse hot plate assay and had one-seventh the affinity of morphine for the opioid receptor. The N-alkyl and N-phenethyl 9 alpha-substituted compounds were either inactive or relatively ineffective as antinociceptive agents. None of the examined compounds substituted for morphine in single-dose suppression studies in the rhesus monkey. The N-cyclopropylmethyl compound in the 9 alpha series had half the narcotic antagonist potency of nalorphine and one-eighth of its affinity for the opioid receptor. The 9 alpha-(3-methylbutyl) moiety, unlike bulky substituents in the 9 beta position of 6,7-benzomorphans, generally lowers affinity for the mu opioid receptor and diminishes their in vivo activity as agonists or antagonists.

Analgesics↗

(+)-6,7-benzomorphan sigma ligands stimulate dopamine synthesis in rat corpus striatum tissue.

The benzomorphan sigma ligands, (+)-N-allylnormetazocine (NANM) and (+)-pentazocine, but not (+)-cyclazocine, stereospecifically stimulated dopamine synthesis in minces of rat corpus striatum by 15-23% over basal values at 0.1-1.0 microM. The effect of (+)-NANM and (+)-pentazocine was blocked by the reported sigma antagonist, BMY-14802 but not by the opiate antagonist naloxone. These results suggest that these (+)-benzomorphans may act as agonists at putative sigma heteroreceptors on striatal nerve terminals, or through an indirect mechanism, to modulate dopamine synthesis.

Animals↗

Benzomorphan binding sites in rat lumbo-sacral spinal cord.

The rat lumbo-sacral spinal cord contains a homogeneous population of opiate binding sites labelled with high affinity (KD = 0.21 +/- 0.04 nM) by [3H]etorphine and lower affinity (KD = 2.2 +/- 0.4 nM) by [3H]ethylketocyclazocine. Benzomorphan drugs are potent competitors for these binding sites while morphine and enkephalin display a low affinity. These binding sites have binding properties which are distinct from the mu-, delta-, and also kappa-sites but are very similar to those of the benzomorphan sites characterized in rat brain.

Animals↗

Effects of elevated calcium and calcium antagonists on 6,7-benzomorphan-induced analgesia.

The hypothesis that the nociceptive state and opiate-induced antinociception are generally regulated by Ca2+ brain levels has been tested. In this context, the effects of intracerebroventricular injections of CaCl2 (0.1-0.5 mumol), D600 (5.0-10.0 micrograms) and EGTA (0.5-1.0 mumol) on ethylketocyclazocine (EKC), ketocyclazocine (KC), Mr-2033, pentazocine (PTC), bremazocine (BMC) and SKF 10,047-induced antinociception were investigated in the mouse tail immersion test. Simultaneous treatment with either D600 or EGTA resulted in a significant and dose-related enhancement in the activities of the kappa-agonists: EKC, KC and Mr-2033, whilst the activities of PTC, BMC and SKF 10,047 remained unchanged. CaCl2 readily blocked the activities of all benzomorphans tested except that of SKF 10,047 against which CaCl2 was less effective. In addition a dose-related hyperalgesia was observed when CaCl2 was given alone. Although the results obtained from the kappa-agonists and CaCl2 per se support the hypothesis in question, data obtained from PTC, BMC and SKF 10,047 tends to oppose it. Additionally the present results taken together indirectly substantiate the notion that benzomorphan-induced analgesia may involve different opiate-sensitive neuronal substrates.

Analgesia↗

Synthesis and in vitro and in vivo activity of (-)-(1R,5R,9R)- and (+)-(1S,5S,9S)-N-alkenyl-, -N-alkynyl-, and -N-cyanoalkyl-5, 9-dimethyl-2'-hydroxy-6,7-benzomorphan homologues.

Two of the synthesized (-)-(1R,5R,9R)-N-homologues (N-but-3-enyl- and N-but-3-ynyl-5,9-dimethyl-2'-hydroxy-6,7-benzomorphan (9, 13)) were found to be about 20 times more potent than morphine in the mouse tail-flick assay (ED(50) = 0.05 mg/kg), and (-)-(1R,5R, 9R)-N-but-2-ynyl-5,9-dimethyl-2'-hydroxy-6,7-benzomorphan ((-)-(1R, 5R,9R)-N-but-2-ynylnormetazocine, 12) was about as potent as the opioid antagonist N-allylnormetazocine (AD(50) in the tail-flick vs morphine assay = 0.3 mg/kg). All of the homologues examined had higher affinity for the kappa-opioid receptor than the mu-receptor except (-)-N-but-2-ynyl-normetazocine (12), which had a kappa/mu ratio = 7.8 and a delta/mu ratio = 118. The (-)-N-2-cyanoethyl (3), -allyl (8), and -but-3-ynyl (13) analogues had good affinity (<10 nM) for delta-opioid receptors. Two homologues in the (+)-(1S,5S,9S)-normetazocine series, N-pent-4-enyl (24) and N-hex-5-enyl (25), were high-affinity and selective sigma(1)-ligands (K(i) = 2 nM, sigma(2)/sigma(1) = 1250, and 1 nM, sigma(2)/sigma(1) = 750, respectively); in contrast, N-allylnormetazocine (22) had relatively poor affinity at sigma(1), and its sigma(1)/sigma(2) ratio was <100.

Analgesics↗

Electrophilic gamma-lactone kappa-opioid receptor probes. Analogues of 2'-hydroxy-2-tetrahydrofurfuryl-5,9-dimethyl-6,7-benzomorphan diastereomers.

Benzomorphans with an electrophilic group in the nitrogen substituent were prepared as potentially irreversible ligands for the kappa-opioid receptor. These were synthesized from products of the reaction of normetazocine with the enantiomers of 5-(iodomethyl)-gamma-butyrolactone (11). alpha-Methylene gamma-lactones 5 and 7 and endocyclic alpha,beta-unsaturated gamma-lactones 8 and 9 were prepared from the corresponding saturated gamma-lactones 13 and 23 possessing the "active" (1R,5R,9R)-benzomorphan stereochemistry. Only gamma-lactones 8, 9, 13, and 23, lacking the exocyclic methylene group, retain significant affinities for opioid receptor binding sites when compared with the reference compounds (2"S)-3 and (2"R)-3. As observed with these references compounds, greater binding affinity is also seen with gamma-lactone diastereomers having the 2"S stereochemistry in the nitrogen substituent. Although the gamma-lactones do not bind irreversibly in opioid receptor preparations, they do show kappa-receptor selectivities comparable to those observed for the reference compounds.

Animals↗

5-allyl-9-oxobenzomorphans. 3. Potent narcotic antagonists and analgesics-antagonists in the series of substituted 2',9beta-dihydroxy-6,7-benzomorphans.

5-Allyl-2'-methoxy-2-methyl-9-oxo-6,7-benzomorphan methiodide (1) has been converted in a selective two-step process to the corresponding 9beta-hydroxy intermediates 4 and 6, which in turn were transformed via modified von Braun demethylation-acylation to the amides 11 and 21, respectively. These were reduced and demethylated to give a series of 5-allyl-2',9beta-dihydroxy-2-substituted 6,7-benzomorphans 13 and 23, some of which have been found to be highly potent narcotic antagonists and/or analgesics. The resolution of the most interesting compounds (23a and 23b) and pharmacological properties of the optical isomers are also described. Reduction of the double bond in 13 and 23 to give 14 and 24, with one exception, did not appreciably alter pharmacological profiles, while cyclization to the tetrahydrofuranobenzomorphans 25 substantially reduced the level of activities.

Analgesics, Opioid↗

Synthesis and pharmacological activity of some N-alkyl-substituted 9alpha-ethyl-2'-hydroxy-5-methyl-6,7-benzomorphans.

A series of N-substituted 9alpha-ethyl-2'-hydroxy-5-methyl-6,7-benzomorphans was synthesized and evaluated for their narcotic analgesic and antagonistic activities. Compounds 2a and 22 were as potent as morphine in the writhing (PPQ) and hot-plate tests, while a number of compounds demonstrated antagonistic activities greater than nalorphine. Generally, the compounds in this series show activities somewhat greater than the comparable compounds in the 5,9alpha-dimethyl-6,7-benzomorphan series for analgesic effect and similar or slightly less antagonistic potency.

Analgesics, Opioid↗

Synthesis and pharmacology of 5-noralkyl-9beta-methyl-6,7-benzomorphans and stereochemistry of some intermediates.

2,9beta-Dimethyl-2'-hydroxy-6,7-benzomorphan (18) has been synthesized from m-methoxyphenylacetone (6a) or m-methoxyphenylacetonitrile (1) via bromo-alpha-tetralone (10). Isomeric bromo-alpha-tetralone 9, instead of undergoing cyclization to a 6,7-benzomorphan, gave aromatization product 12. The structures and stereochemical assignments of 9, 10 (and thus 7 and 8), and 18 follow from analogy and from NMR data of 9, 10, 17, and 18. Compound 18 and the deoxy analog 16 are as potent as morphine and codeine, respectively, as analgetics (mice) and are without physical dependence capacity (monkeys).

Analgesics↗

Synthesis and pharmacological characterization of (+/-)-5,9 alpha-dimethyl-2-[2-(4-fluorophenyl)ethyl]-2'-hydroxy-6,7-benzomorphan (fluorophen), a ligand suitable for visualization of opiate receptors in vivo.

A fluorinated derivative of the benzomorphan opiate agonist phenazocine, (+/-)-5,9 alpha-dimethyl-2-[2-(4-fluorophenyl)ethyl]-2'-hydroxy-6, 7-benzomorphan (fluorophen), was prepared by N-acylation of (+/-)-5,9 alpha-dimethyl-2'-hydroxybenzomorphan with (p-fluorophenyl)acetyl chloride, followed by diborane reduction of the resulting amide. Fluorination produces only a twofold opiate receptor affinity loss when measured either by bioassay or receptor binding (selectivity mu congruent to delta greater than kappa). Labeled with 18F, fluorophen should be sufficiently potent to be useful as an in vivo probe for visualizing opiate receptors by positron emission transaxial tomography (PETT).

Animals↗

Synthesis and structure-activity relationships of 6,7-benzomorphan derivatives as antagonists of the NMDA receptor-channel complex.

We have synthesized a series of stereoisomeric 6,7-benzomorphan derivatives with modified N-substituents and determined their ability to antagonize the N-methyl-D-aspartate (NMDA) receptor-channel complex in vitro and in vivo. The ability of the compounds to displace [3H]-MK-801 from the channel site of the NMDA receptor in rat brain synaptosomal membranes and to inhibit NMDA-induced lethality in mice was compared with their ability to bind to the mu opioid receptor. Examination of structure-activity relationships showed that the absolute stereochemistry is critically important for differentiating these two effects. (-)-1R,9 beta,2"S-enantiomers exhibited a higher affinity for the NMDA receptor-channel complex than for the mu opioid receptor. The aromatic hydroxy function was also found to influence the specificity of the compounds. Shift of the hydroxy group from the 2'-position to the 3'-position significantly increased the affinity for the NMDA receptor-channel complex and considerably reduced the affinity for the mu opioid receptor. From this series of 6,7-benzomorphan derivatives, the compound 15cr.HCl [(2R)-[2 alpha, 3(R*),6 alpha]-1,2,3,4,5,6-hexahydro-3-(2-methoxypropyl)-6,11,11-trimethyl -2,6-methano-3-benzazocin-9-ol hydrochloride] was chosen as the optimum candidate for further pharmacological investigations.

Animals↗

Phencyclidine ("angel dust") analogs and sigma opiate benzomorphans cause cerebral arterial spasm.

Several psychotomimetic phencyclidine (PCP) analogs--N-ethyl-l-phenylcyclohexylamine (PCE), N-[1-(2-thienyl)cyclohexyl]piperidine (TCP), N-[1-(thienyl)cyclohexyl ))pyrrolidine (THP), ketamine, and N,N-dimethyl-l-phenyl-cyclohexylamine (PCDEA)--were tested on basilar and middle cerebral arteries of the dog in vitro and found to induce contraction in these blood vessels with a maximal contractile activity (i.e., intrinsic activity) similar to that of PCP. The concentration-effect curves of these compounds were found to be parallel to the curve of PCP (P less than 0.01). The relative potency was PCE greater than TCP greater than PCP greater than THP greater than PCDEA greater than ketamine. A PCP analog with no psychotomimetic activity, 1-piperidinocyclohexanecarbonitrile (PCC), did not induce the blood vessels to contract, nor did the opiate morphine. Three psychotomimetic benzomorphans--pentazocine, cyclazocine, and N-allylnorcyclazocine--were found to: (i) also produce contraction; and (ii) have concentration--effect curves parallel to the curve of PCP, but with reduced intrinsic activities (i.e., maximal tensions were lowered) compared to PCP. A kappa opiate, ethylketocyclazocine, relaxed the blood vessels in a dose-dependent manner. This study provides direct evidence for a distinct PCP receptor on cerebral blood vessels and suggests that certain benzomorphans may produce cerebral vasospasm via PCP-receptor interactions.

Animals↗

Irreversible activation of the opiate receptor of neuroblastoma X glioma hybrid cells by an alkylating benzomorphan derivative.

The benozomorphan derivative (-)-2-[2-(p-bromoacetamidophenyl)ethyl]-5,9 alpha-dimethyl-2'-hydroxy-6,7-benzomorphan (BAB), capable of reacting with nucleophilic groups, acts on neuroblastoma X glioma hybrid cells as a potent, irreversible opiate agonist. Its potency in inhibiting the increase in cellular cyclic AMP, evoked by prostaglandin E1, is comparable to that of Leu-enkephalin. This also applies to its capacity to compete with [3H]D-Ala2-Met-enkephalinamide ([3H]DAEA) in binding on cell membrane preparations. The comparatively lower potency of (-)-2-[2-(p-acetamidophenyl)-ethyl]-5,9 alpha-dimethly-2'-hydroxy-5,7-benzomorphan (AB), which differs from BAB in the substitution of the bromoacetamido group by an acetamido group, is of the same order of magnitude as that of morphine. The covalent interaction of BAB with the opiate receptors is deduced from the observations that (1) it is not possible to wash away this compound from the receptors, (2) the potency of BAB in inhibiting the specific binding of [3H]DAEA increases with prolonged preincubation time, and (3) AB behaves as a reversible agonist.

Affinity Labels↗

Identification of benzomorphan-kappa opiate receptors in cerebral arteries which subserve relaxation.

Several 'so-called' kappa-opiate receptor agonists e.g., ketocyclazocine (Kc), ethylketocyclazocine (Ekc), bremazocine, MR-2034 and U-50488H, were tested on basilar and middle cerebral arteries of the dog in vitro for relaxant or contractile activities. Ekc, Kc and bremazocine were found to produce concentration-dependent reductions in basal tone and to relax cerebral arteries contracted with prostaglandin F2 alpha (PGF2 alpha). All three agonists appear to act on benzomorphan-kappa opiate receptors which subserve relaxation in cerebral blood vessels. MR-2034 and U-50488H were found to induce contraction in the cerebral arteries. These opiate agonists appear to act on phencyclidine (PCP) or sigma-opiate receptors which subserve contraction. A variety of pharmacological antagonists (phentolamine, propranolol, methysergide, atropine, diphenhydramine, cimetidine, naloxone) did not modify any of the cerebral vascular effects produced by the opiates. These results suggest: (1) specific benzomorphan-kappa opiate receptors which subserve relaxation exist in cerebral blood vessels; (2) some kappa agonists appear to produce, primarily, contraction in cerebral vessels via PCP or sigma-opiate receptors: and cerebral vascular muscle may provide a useful tool to analyse the molecular constitution of these two distinct and opposite-acting opiate receptors.

3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cycloh↗

Site of anti-nociceptive action of a new benzomorphan derivative ID-1229.

The site of anti-nociceptive action of a new benzomorphan derivative ID-1229, 2-[3-(p-fluorobenzoyl)-1-propyl]-5 alpha, 9 alpha-dimethyl-2'-hydroxyl-6, 7-benzomorphan was investigated using electrophysiological methods. In rabbits, ID-1229 (0.1-0.5 mg/kg) caused slowing in the EEG, and depressed the evoked potentials recorded from the sensory cortex and the Nucleus ventralis posterolateralis of the thalamus elicited by sciatic stimulation. A small dose (1 mg/kg) of ID-1229 decreased the bradykinin-induced unitary discharges of lamina V neuron of the spinal dorsal horn in intact rabbits but not in spinal rabbits. These results suggest that ID-1229 inhibits the sensory transmission of bradykinin-induced pain at the dorsal horn of the spinal cord, through its facilitatory action on the descending inhibitory system from the supra-spinal structure.

Analgesics↗

Demonstration and affinity labeling of a stereoselective binding site for a benzomorphan opiate on acetylcholine receptor-rich membranes from Torpedo electroplaque.

The interaction of an optically pure benzomorphan opiate, (-)-N-allyl-N-normetazocine [(-)-ANMC], with the nicotinic acetylcholine receptor from Torpedo electroplaque was studied by using radioligand binding and affinity labeling. The binding was complex with at least two specific components having equilibrium dissociation constants of 0.3 microM and 2 microM. The affinity of the higher affinity component was decreased by carbamoylcholine but not by alpha-bungarotoxin. The effect of carbamoylcholine was not blocked by alpha-bungarotoxin. In comparison, the affinity of [3H]phencyclidine, a well-characterized ligand for a high-affinity site for noncompetitive blockers on the acetylcholine receptor, is increased by carbamoylcholine and the increase is blocked by alpha-bungarotoxin. The binding of (-)-[3H]ANMC was inhibited by a number of other benzomorphans, with (-) isomers being 4- to 5-fold more potent than (+) isomers. Phencyclidine inhibits the binding of (-)-[3H]ANMC to its high-affinity site by a mechanism that is not competitive. UV-catalyzed affinity labeling indicated that the high-affinity-binding site for (-)-[3H]ANMC is at least partially associated with the delta subunit. Tryptic degradation of the Torpedo marmorata delta chain suggested that (-)-ANMC labeled a 16,000-dalton COOH-terminal portion of the subunit. In contrast, 5-azido-[3H]trimethisoquin, a photoaffinity label of the high-affinity site for noncompetitive blockers, labels a 47,000-dalton NH2-terminal fragment of the delta subunit. These results suggest that (-)-[3H]ANMC binds to sites completely distinct from the binding sites for acetylcholine. The high-affinity-binding site for (-)-ANMC and that for phencyclidine and 5-azidotrimethisoquin are allosterically coupled but are regulated differently and are probably physically distinct.

Affinity Labels↗

8-Carboxamidocyclazocine: a long-acting, novel benzomorphan.

To obtain benzomorphans with a longer duration of action that may be potential therapeutics for treating cocaine abuse, 8-carboxamidocyclazocine was synthesized. The pharmacological properties of 8-carboxamidocyclazocine were compared with the parent compound cyclazocine. Changing the 8-hydroxyl group on cyclazocine to an 8-carboxamido group resulted in only a 2-fold decrease in the affinity of the compound for the kappa-receptor, and no change in the affinity for the mu-opioid receptor, with both compounds having K(i) values of less than 1 nM, based on radioligand binding assays. In the guanosine 5'-O -(3-[(35)S]thio)triphosphate ([(35)S]GTPgammaS) binding assay, the two compounds produced moderate stimulation of GTP binding to the human kappa- and mu-receptors. When given by i.c.v. injection, the compounds produced less than 60% antinociception in the mouse 55 degrees C warm-water tail-flick test. However, in the mouse writhing test, the compounds had high potency in producing antinociception. Antinociception induced by either 8-carboxamidocyclazocine or cyclazocine was mediated by both kappa- and mu-opioid receptors. Cyclazocine acted as a mu-antagonist in addition to its agonist properties at the mu-receptor, as measured by the inhibition of morphine-induced antinociception. In contrast, 8-carboxamidocyclazocine did not inhibit morphine-induced antinociception, demonstrating that it was not a mu-opioid receptor antagonist in this assay. An i.p. injection of an ED(70) dose of 8-carboxamidocyclazocine produced antinociception that lasted for 15 h in contrast to cyclazocine, which produced antinociception, lasting 2 h. 8-Carboxamidocyclazocine is a novel, long-acting benzomorphan, which possesses pharmacological properties that are distinct from the properties of cyclazocine.

3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cycloh↗