Development of MS Binding Assays targeting the binding site of MB327 at the nicotinic acetylcholine receptor

The bispyridinium compound MB327 has been shown previously to have a positive pharmacological effect against poisoning with organophosphorous compounds (OPCs). The mechanism by which it exerts its therapeutic effect seems to be directly mediated by the nicotinic acetylcholine receptor (nAChR). In the present study, the development of mass spectrometry based binding assays (MS Binding Assays) for characterization of the binding site of MB327 at the nAChR from Torpedo californica is described. MS Binding Assays follow the principle of radioligand binding assays, but do not, in contrast to the latter, require a radiolabeled reporter ligand, as the readout is in this case based on mass spectrometric detection. For [²H₆]MB327, a deuterated MB327 analogue employed as reporter ligand in the MS Binding Assays, an LC-ESI-MS/MS method was established allowing for its fast and reliable quantification in samples resulting from binding experiments. Using centrifugation for separation of non-bound [²H₆]MB327 from target-bound [²H₆]MB327 in saturation and autocompetition experiments (employing native MB327 as competitor) enabled reliable determination of specific binding. In this way, the affinities for [²H₆]MB327 (K_d=15.5±0.9μmolL^-1) and for MB327 (K_i=18.3±2.6μmolL^-1) towards the nAChR could be determined for the first time. The almost exactly matching affinities for MB327 and [²H₆]MB327 obtained in the MS Binding Assays are in agreement with potencies previously found in functional studies. In summary, our results demonstrate that the established MS Binding Assays represent a promising tool for affinity determination of test compounds towards the binding site of MB327 at the nAChR.

Evaluation of GABA uptake in subcellular fractions of bovine frontal cortex and brainstem

GABA uptake as well as the distribution of GAT-1, GAT-2 and GAT-3 were investigated in bovine brain membrane fractions. GABA uptake was characterised by kinetic constants and IC50-values for a series of known inhibitors in subcellular fractions of frontal cortex and brainstem obtained by subsequent centrifugations on sucrose gradients. Additionally, the immunoreactivity for rGAT-1, rGAT-2 and rGAT-3 antibodies was studied in these fractions. The pharmacological profile for GABA uptake inhibition as well as results from immunoblotting indicated that GABA uptake in a selected subcellular fraction of frontal cortex (P2B) is almost exclusively due to GAT-1 whereas GABA uptake performed with a selected subcellular fraction of brainstem (P2A) in the presence of NNC 711 is mainly attributable to GAT-3.

Synthesis and opioid-receptor binding of novel amino-substituted morphan analogues

Starting with methyl 4,6-O-benzylidene-alpha-D-glucopyranoside (4), an optimized procedure is reported for preparation of the bromide 7, which is transformed into the N-acylated heptopyranosamine 9. After introduction of an axially positioned azido moiety in position 3 intramolecular N/O-acetal formation succeeds to provide the morphan analogue 17. In receptor binding studies with radioligands the amines 18b-18d reveal higher affinity for mu-receptors than for kappa-receptors. The most mu-active compound 18b (Ki = 14 nM) contains two aryl substituents, which presumably may occupy both aryl binding sites of mu-receptors.

Azagrevellins, Part I. Grevellin analogs with affinity to the N-methyl-D-aspartate (glycine site) receptor, a novel lead structure

A series of piperidine-2,3,5-triones (azagrevellins) has been prepared. A new synthesis has been introduced using the rearrangement of spiroepoxides in the presence of triethyloxonium tetrafluoroborate. The binding affinity toward the N-methyl-D-aspartate (glycine site) receptor has been measured to provide a basis for more detailed structure-activity studies. Azagrevellin 18d showed the highest binding potency.

Synthesis and resolution of racemic eliprodil and evaluation of the enantiomers of eliprodil as NMDA receptor antagonists

A short synthesis of the NMDA receptor antagonist (rac)-Eliprodil (9) and its resolution into the enantiomers by chiral HPLC is described. The enantiomers (R)-9 and (S)-9 were found to exhibit markedly different affinities for NR2B subunit containing NMDA receptors.

[3H]ifenprodil binding to NMDA receptors in porcine hippocampal brain membranes

(+/-)-2-(4-Benzylpiperidino)-1-(4-hydroxyphenyl)propan-1-ol ([3H]ifenprodil) binding to a subcellular fraction of porcine hippocampus, which was obtained by centrifugation on a discontinuous sucrose gradient, was investigated with the objective to label selectively the ifenprodil recognition site of native NMDA receptors. Saturation experiments revealed high-affinity sites for [3H]ifenprodil in this membrane fraction which could be characterised by a K(d) value of 23.0+/-1.8 nM using a one-site model. Calculation of saturation isotherms on the basis of a two-site model yielded a K(d1) value of 10.4+/-2.4 nM and a K(d2) value of 2200+/-1300 nM, respectively. Inhibition of [3H]ifenprodil binding by NR2B subunit-selective NMDA receptor antagonists, by polyamines, by sigma receptor ligands, by a variety of ligands acting at different NMDA receptor recognition sites and by several cations was studied and compared with the effects of these compounds on (5R,10S)-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5, 10-imine ([3H]MK-801) binding under non-equilibrium conditions. It turned out that sigma receptor ligands such as 1, 3-di(2-tolyl)-guanidine (DTG), (+)-3-(3-hydroxyphenyl)-N-propylpiperidine (R)-3-PPP, (S)-3-PPP and (1-¿2-[bis(4-fluorophenyl)methoxy]ethyl¿)(-4-[3-phenylpropyl]piperazi ne) (GBR-12909) did not affect [3H]ifenprodil binding in the nanomolar range or only slightly. In contrast, ifenprodil, eliprodil, nylidrin and haloperidol inhibited [3H]ifenprodil binding in the nanomolar range and in the same rank order and with the same potency as observed for the inhibition of the high-affinity fraction of [3H]MK-801 binding. The polyamines, which activate NMDA receptors, inhibited [3H]ifenprodil binding in a biphasic manner. Their potency to inhibit the high-affinity fraction of [3H]ifenprodil binding was found to be in the same range as their potency to enhance [3H]MK-801 binding. In the presence of 10 microM spermine a significantly enhanced (P=0.0097) rate of dissociation of [3H]ifenprodil binding was found, suggesting that inhibition of [3H]ifenprodil binding by spermine is not, or at least not exclusively mediated by a competitive interaction.

Stereoselective synthesis and receptor binding of conformationally restricted and flexible 2,4-disubstituted 1,3-dioxanes derived from benzomorphans

The key steps in the stereoselective synthesis of the tricyclic aminomethyl derivatives 19 and 20 and the aminoethyl substituted 1,3-dioxanes 24 and 25 are nucleophilic addition of aryllithium intermediates to the nitroalkene 13, intramolecular transacetalization of the addition products 15 and 16 (only for the tricyclic derivatives 19 and 20) and subsequent reduction of the nitro group. The affinities of the secondary and tertiary amines 19c,d, 20c,d, 24c,d, and 25c,d for the ion channel binding site of the NMDA receptor, for mu-, kappa-, and sigma-receptors have been investigated. In the group of tricyclic compounds only 19d shows remarkable sigma-receptor affinity (Ki = 21.6/1.10 microM). In the 1,3-dioxane series the moderate mu- (Ki = 27.8 microM) and kappa-receptor affinity (Ki = 36 microM) as well as the high sigma-receptor affinity (Ki = 3.3 microM) of the (S,S,S)-configurated methylamine 24c should be emphasized. The pentan-1-ol 26, the side product isolated during the synthesis of 24c, is of particular interest because of its considerable affinity to mu- (Ki = 16.0 microM), kappa- (Ki = 2.8 microM), and sigma-receptors (Ki = 14.5/1.26 microM). The biphasic competition curves obtained during sigma-receptor binding studies of 19d and 26 (two Ki values) may be explained by different interaction with sigma-receptor subtypes.

Pyrrolidine-2,4-diones with affinity to the N-methyl-D-aspartate (glycine site) receptor, Part II. 5-Arylidene-pyrrolidine-2,3,4-trione 3-oximes as NMDA receptor antagonists

A series of oximes deriving from 5-arylidene-pyrrolidine-2,3,4-triones and pyridine-2,3,4-triones has been prepared. The presence of the tautomeric nitrosoenol was proven in solutions of alpha-ketooxime 7a. The binding affinity of the new oximes toward the N-methyl-D-aspartate (glycine site) receptor has been measured as a basis for more detailed structure-activity relationship studies. Oxime 13b showed the highest binding potency acting as glycine antagonist in nanomolar concentration.

5-Arylidene-3-aryl-pyrrolidine-2,4-diones with affinity to the N-methyl-D-aspartate (glycine site) receptor, Part I

A series of new 5-arylidene 3-aryl-pyrrolidine-2,4-diones has been prepared. Their binding affinity toward the N-methyl-D-aspartate (glycine site) receptor has been measured as a basis for more detailed structure-activity relationship studies.

Syntheses of novel pyrazolomorphinans and their binding to mu- and kappa-opioid-receptors

A number of novel pyrazolomorphinans have been synthesized in excellent yields by the reaction of the enolic morphinan diketones 6 with various hydrazines. Hydrazine dihydrochloride led to the N-unsubstituted tautomeric pyrazoles 7a in equilibrium with 9a and 8a in equilibrium with 10a which could not be separated. Arylhydrazines on the other hand furnished the regioisomeric pyrazolomorphinans 7 and 9 as well as 8 and 10, which could be isolated and characterized. The structures of the new compounds were clarified by their spectra, the assignment of the regioisomeres was achieved by determination of NOE enhancements. Compounds 6a, 7c, 8b and 10c have been evaluated for their affinity at mu and kappa opioid receptors in radioligand binding assays. Their ability to inhibit [3H] DAMGO binding to mu and [3H] U 69,593 binding to kappa opioid receptors has been found to be comparable with that of codeine.

Noncompetitive NMDA antagonists: a novel synthesis of 1-phenyltetrahydro-3-benzazepines

The key step in the synthesis of the pharmacologically interesting 1-phenyltetrahydro-3-benzazepine skeleton is the Michael addition of (2-lithiophenyl)acetaldehyde acetals, which are generated in situ upon treatment of the bromo acetals 5a,b with n-butyllithium, to beta-nitrostyrene (6). The reductive ring closure of the nitro acetals 7a,b succeeded with zinc dust and hydrochloric acid to give the 3-benzazepines 11a,b in good yields. The unsubstituted 3-benzazepine 11a showed a considerable affinity for the phencyclidine binding site of the NMDA receptor (Ki = 6.41 microM), whereas donor substituents in the aryl moiety (11b,c) reduce the affinity for the NMDA receptor.

Syntheses of novel pyridazinomorphinans by inverse electron demand cycloaddition and their binding to mu and kappa receptors

A number of novel pyridazinomorphinans have been synthesized by the inverse electron demand Diels-Alder reaction of various 3,6-disubstituted 1,2,4,5-tetrazines with enamines derived from dihydrocodeinone and with codeinone. Reduction of some of the pyridazinomorphinans did not furnish the expected pyrroloepoxymorphinans; in all cases investigated reductive cleavage of the epoxybridge was observed to yield dihydropyridazino- or pyrrolomorphinans. The structures of all new compounds were assigned by the spectral data, that of the cycloadduct of codeinone was additionally verified by X-ray crystallography. Compounds 5a, 8, 11a and 16 have been evaluated for their affinity at mu and kappa opioid receptors in radioligand binding assays. Their ability to inhibit [3H]DAMGO binding at mu and [3H]U 69.593 binding at kappa receptors, respectively as compared to codeine has been found to be lower.

Characterisation of the binding of [3H]MDL 105,519, a radiolabelled antagonist for the N-methyl-D-aspartate-associated glycine site, to pig cortical brain membranes

Binding of [3H]MDL 105,519 to glycine sites on N-methyl-D-aspartate (NMDA) receptors of pig cortical brain membranes was evaluated. [3H]MDL 105,519 labelled a homogeneous population of binding sites with a Kd-value of 3.73 +/- 0.43 nM and a Bmax-value of 3030 +/- 330 fmol/mg protein. Clear correlations between the affinity (Ki) to [3H]MDL 105,519 labelled sites and the potency (EC50) to enhance or inhibit non-equilibrium [3H]MK-801 binding in the nominal absence of glycine were shown for a variety of glycine site agonists, partial agonists and antagonists. The ratio of Ki to EC50 was >1 for agonists and partial agonists and <1 for antagonists. Various cations as well as glutamate and polyamine site ligands were shown to be able to influence [3H]MDL 105,519 binding to pig cortical brain membranes substantially.

Stereoselective syntheses and CNS activity of novel tricyclic amines

The enantiomerically pure amines (+)-5, (-)-9, (+)-11 and (+)-12 are stereoselectively prepared by reductive amination of the ketone (-)-4 [-->(+)-5], LiAlH4 reduction of the oxime (-)-7 followed by reductive methylation [-->(-)-9], SN2-substitution of the benzenesulfonate 10 [-->(+)-11] and reductive methylation of (+)-11 [-->(+)-12]. In the same way the racemic amines (+/-)-5, (+/-)-9, (+/-)-11 and (+/-)-12 are accessible starting from the racemic ketone (+/-)-4. Kinetic resolution of the racemic ketone (+/-)-4 with baker's yeast leads to the dextrorotatory ketone (+)-4 (86% ec), which is transformed via the methanesulfonate 16 into the tricyclic amines (-)-11 and (+)-17. Weak sedative effects are observed after application of the amines (+)-5, (+/-)-5, 0-9, (+/-)-9(+)-12, and (+/-)-12 to mice. Strong sedation is caused by (+/-)-11 with the dextrorotatory enantiomer (+/-)-11 being more effective than the levorotatory enantiomer (-)-11.

Characterisation of [3H]MK-801 binding and its cooperative modulation by pig brain membranes

Cooperative modulation of [3H]MK-801 binding to extensively washed pig cortical brain membranes in the presence of various concentrations of L-glutamate, glycine, spermine, CPP and DCKA was evaluated in association experiments. In saturation experiments [3H]MK-801 labelled a homogeneous population of binding sites with a Kd-value of 1.26 +/- 0.18 nmol 1(-1) and a Bmax-value of 2130 +/- 200 fmol/mg protein. The pharmacological profile of this site was further evaluated in competition experiments with known NMDA receptor channel blockers. In nonequilibrium binding experiments EC50-values of reference compounds acting at the L-glutamate, at the glycine, and at the polyamine site, were determined by increasing or decreasing [3H]MK-801 binding. Ifenprodil reduced [3H]MK-801 binding in a biphasic manner. All the data obtained are in agreement with results from [3H]MK-801 binding to rodent as well as human brain membranes. This study therefore strongly suggests, that pig cortical membranes are a suitable alternative to rodent brain membranes, and an acceptable substitute for human brain membranes in [3H]MK-801 binding experiments.

Species differences in [3H]linopirdine (DuP 996) binding to brain membranes

Binding of [3H]linopirdine was evaluated in membranes prepared from rat, mouse, calf, pig, and human brain tissue. Saturation and homologous competition experiments with freshly prepared and subsequently frozen brain membranes of young adult rats yielded biphasic binding curves. Analysing binding data with two-site models confirmed the existence of specific, high-affinity binding sites for [3H]linopirdine with a Kd value of 7.8 +/- 3.5 nM and revealed that another site with micromolar affinity for the radioligand may exist. Almost identical data were obtained with mouse brain membranes. However, high-affinity binding of [3H]linopirdine could not be detected in cerebral cortical membranes from calf, pig or an aged human subject, respectively. In these tissues [3H]linopirdine bound only with moderate affinity (Kd about 200 nM). In subsequent experiments using brain membranes either freshly prepared from aged (25-month-old) rats or prepared from young adult (3-month-old) rats after a post-mortem delay of up to 15 h, it could be excluded that the factors age or post-mortem delay were responsible for the lack of high-affinity [3H]linopirdine binding sites in calf, pig or human brain. It is concluded that [3H]linopirdine binding data obtained from rodent studies, and consequently physiological drug effects mediated by this drug target, cannot be readily extrapolated to other species including man.

Asymmetric synthesis and enantiospecificity of binding of 2-(1,2,3,4-tetrahydro-1-isoquinolyl)-ethanol derivatives to mu and kappa receptors

A number of 2-(1,2,3,4-tetrahydro-1-isoquinolyl)-ethanol derivatives 7a-e have been synthesized in diastereomerically and enantiomerically pure form and have been evaluated for their binding affinity at mu and kappa opioid receptors. The amido ketones 5a-c and ent-5a-c, which were accessible by employing 3b and ent-3b for Asymmetric Electrophilic Amidoalkylation reactions, served as starting compounds. Upon reduction of 5a-c and ent-5a-c the amido alcohols l-6a-c, u-6a-c, ent-l-6a-c and ent-u-6a-c were obtained. Hydrolysis of these compounds yielded the secondary amino alcohols l-7a-c, u-7a-c, ent-l-7a-c and ent-u-7a-c and upon reductive methylation of l-7b-c, u-7b-c, ent-l-7b-c and ent-u-7b-c with CH2O and NaCNBH3 the tertiary amino alcohols l-7d-e, u-7d-e, ent-l-7d-e and ent-u-7d-e were obtained. The binding affinities of the final compounds l-7a-e, u-7a-e, ent-l-7a-e and ent-u-7a-e at both the mu and the kappa receptor were strongly dependent on their stereochemistry. In each case isomers exhibited higher affinity at the mu than at the kappa receptor. For the secondary amino alcohols 7a-c the affinity at the mu receptor followed the stereochemical order l-7 > ent-l-7 > ent-u-7 > u-7 whereas for the tertiary amino alcohols the order l-7 > u-7 > ent-l-7 > ent-u-7 was found. The stereoisomers l-7d and l-7e of the tertiary amino alcohols were found to be the most active compounds the latter exhibiting a Ki value of 7.17 which is close to that of Morphine (Ki = 1.64). In an in vivo model, the Writhing Test, both compounds l-7d and l-7e displayed high analgetic activity.

Synthesis, pharmacological investigation and computational studies on a tricyclic ergoline analog with selective dopamine autoreceptor activity

The novel aminobenzindolone 8 was prepared and evaluated as a potential antipsychotic agent. The target compound was synthesized in eight steps starting from the tetrahydrobenzindolone 9. The key step of the synthesis was an electrophilic amination of the aromatic ketone 11 followed by reductive degradation when the diethoxymethyl group was employed for protection of the lactam nitrogen and also for the benzylic position 2a. Dopamine and serotonin receptor binding studies revealed 8 to be a potent and selective ligand at the D-2 autoreceptor (ki = 4.0 nM). Further in vivo studies including the GBL-test and locomotor activity measurements indicated agonistic activity of 8 at the prejunctional binding sites. Comparison of ab initio based molecular electrostatic isopotential maps corroborates our hypothesis that the dopamine structure 6, containing an intramolecular hydrogen bond donating effect of the meta-HO-group, represents the conformation which is active at the dopamine D-2 autoreceptor.

Tricyclic CNS active agents by intramolecular Oxa-Pictet-Spengler reaction

Mitsunobu inversion of the (S)-configurated lactate (S)-7, which is prepared in four steps starting from (S)-tyrosine, leads to the (R)-configurated lactate (R)-7. The key step in the transformation of the enantiomeric lactates (S)-7 and (R)-7 into the benzomorphan analogous tricycles (R,S)-16a,b, (S,R)-16a,b, (S,S)-22, and (R,R)-22 is an intramolecular Oxa-Pictet-Spengler reaction: The amides (S)-13, (R)-13, (S)-19 and (R)-19, in which the carbonyl moiety-masked as an acetal-is linked to the 2-phenylethanol moiety, are cyclized to give the tricyclic amides (R,S)-15, (S,R)-15, (S,S)-21, and (R,R)-21, respectively. In a concentration of 100 microM both enantiomers of 16a, 16b, and 22 are not able to compete with 3H-(+)-MK 801 for the phencyclidine binding sites of NMDA receptors. In vivo, only (R,S)-16b and (S,S)-22 exhibit weak sedative and analgesic activity.

Synthesis and dopamine receptor binding of 3-phenylazepino[5,4,3-c,d]indole derivatives

The 3-phenylazepino[5,4,3-c,d]indole derivatives 5 and 9-11, representing heterocyclic analogs of the selective dopamine D-1 receptor ligands of the 3-phenylbenzazepine class, were synthesized starting from the indole-4-carboxylate 7. Receptor binding studies employing bovine striatal membranes demonstrated that the test compounds 5, 10, and 11 are able to displace the D-1 selective radioligand [3H]-SCH 23390 as well as the D-2 antagonist [3H]-spiperone. Compound 5b turned out to be the most potent and selective ligand (ki = 1.8 microM for D-1 and ki = 8.9 microM for D-2). It is assumed that the moderate selectivity of 5b is due to the conformational inequality of the 7-membered rings when compared to the benzazepines. This results in a spatial arrangement of the phenyl substituent which is not able to interact with a 'subtype selectivity-inducing site'.

Synthesis of (S)-3,4-diaminobutanenitriles as precursors for 3-amino-GABA derivatives

Starting from natural asparagine (1) a synthesis of the protected (S)-3,4-diaminobutanenitriles 5 and 8a-c via the beta-homoserine derivative 2 is described. The amino function in position 4 was introduced by Mitsunobu-coupling or by reductive amination when a strange deformylation of the amino aldehyde 7 was observed as a side reaction. The Mitsunobu-product 5 was converted into the dibenzylamine substituted GABA 6b which was investigated for its affinity at the GABA-A receptor.

[CNS-active pyrans: amine- and aryl- substituted dioxabicyclooctanes]

The amin- and phenyl substituted 6,8-dioxabicyclooctanes 10 and 11 show distinct CNS-activities. Intensity and profile depend on the type of amine and the stereochemistry of the products. Therefore, we have synthesized 6,8-dioxabicyclooctanes with different amine-phenyl distances and examined their CNS-activities on mice as well as by receptor binding studies with the PCP-binding site which is part of the NMDA-receptor-complex.

[Conformationally restricted pethidine analogs. 5. Synthesis and pharmacologic testing of cis-B-10b-acyl-1,2,3,4,4a,5,6,10b- octahydrobenzo(f)isoquinolines]

Cyanophenylcyclobuten (1a) gave the corresponding cis-B-configurated 10b-acyloctahydrobenzo[f] isoquinolines 3a-f by Grignard reaction. Cis-B-3b was demethylated to yield the secondary base 3g, which in turn was realkylated to the homologous allyl- and isopentenyl derivatives 3h and 3i. In the writing test the desoxyketobemidon analogon cis-B-3b exhibits a remarkable activity, whereas 3a, c-e are somewhat weaker and 3h and 3i are inactive.

[Synthesis of homochiral 5,9-epoxybenzocyclooctenes with amino substitutents: relationship between structure and CNS activity]

This paper deals with the synthesis and psychopharmacological effects of variations of the sedative and analgesic tricyclic amines 3a and 3b: Starting with the homochiral ketone 4 the amines 5 (primary amino group in equatorial position), 7 (axially oriented dimethylamino group), 9 (additional phenyl residue in position 7), 13b, and 14b (equatorially and axially arranged dimethylaminomethyl group) and 23 and 24 (axial amino group shifted to position 9) are prepared. BBr3 cleaves the phenolic ethers of the secondary amine (+/-)-3a to yield the aminodiphenol (+/-)-10. -Keeping mice under observation for behavioral anomalies (Irwin screen) and analgesic activity (writhing test) shows, that the amines 5, 7, 9, (+/-)-10, 13b, 14b, and 23 do not reach the sedative and analgesic effects of the amines 3a and 3b, described by us.

[Synthesis and CNS-activity of spirocyclic pethidine and prodine analogs]

The bromoacetals 5a and 5b react with n-butyllithium and the piperidone 7 to yield the hydroxyacetals 8b and 8c, respectively. Cyclization of 8b and 8c followed by acid hydrolysis affords the spirocyclic hemiacetals 10b and 10c which are oxidized by PCC to give the spirocyclic prodine analogues 4b and 4c. The corresponding spirocyclic pethidine derivative 2 is prepared by alkylation of the 2-benzopyran-3-one 16 with N-Lost (17). In the mouse writhing test the spiropethidine 2 is not analgesic active up to a dose of 20 mg/kg body weight (bw). In the spirocyclic prodine series the methylated lactone 4c is the most active analgesic with an ED50-value (ED50 = 9.2 mg/kg bw) in the range of the ED50-value of tramadol.

[2,6-Epoxy-3-benzazocines: centrally acting N/O-acetals produced by cyclization of amino- and amidoacetals]

Under acidic conditions the secondary amines 10a and 10b, the primary amine 15, the amide 17a, and the urethane 17b were cyclized to yield the 2,6-epoxy-3-benzazocines 11a, 11b, 16, 18a and 18b, respectively. Ring closure of the inverse amide 5a, however, failed to give the tricyclic N/O-acetal 6. With LiAlH4 the epoxy bridge of the urethane 18b was opened to afford the bicyclic 3-benzazocine 20. While the N-(2-methoxyethyl) derivative 11b did not influence the behaviour of mice, the N-methyl derivative 11a showed strong central effects.

[Synthesis of enantiomerically pure 6,10-epoxybenzocycloocten-7-amines with CNS activity]

In an oxa-Pictet-Spengler reaction the methyl (S)-phenyllactate 6 and methyl levulinate (7a) are condensed to the 2-benzopyrans cis-8a and trans-8a, which react with CH3I to yield the dimethyl ethers cis-9a and trans-9a. Cis-9a and trans-9a can be separated by medium pressure liquid chromatography. In the subsequent Dieckmann-Cyclisation cis-9a is transformed to the laevorotatory beta-ketoester (-)-10a, while the dextrorotatory enantiomer (+)-10a is obtained from trans-9a after C-3-epimerisation. With Eu(hfc)3 the ketone (-)-11, prepared by saponification and decarboxylation of (-)-10a, proves to be enantiomerically pure. By reductive amination, ketone (-)-11 is transformed to the amines (-)-12a and (-)-12b. Symptoms typical for central damping are caused after i.p. application of (-)-12a and (-)-12b to mice. In the mouse writhing-test (-)-12a HCl affords an ED50-value of 7.0 mg/kg, comparable with the ED50-value of tramadol.

Tricyclic Azaergoline Analogues: Synthesis, Structural Modifications, and Pharmacological Studies

As an extension of previous investigations on synthesis and dopamine autoreceptor activity of bicyclic ergoline analogues the tricyclic azaergoline analogues 9a and 9b were synthesized. Furthermore, the geometry of the aromatic beta-ethylamine moiety of 9a,b was modified by stereoselective construction of the cycloheptenyl fused pyrazolopyridine derivative 7 and the aminomethyl substituted tricycle 10. Binding affinity of these compounds at dopamine (DA) receptor sites was investigated employing rat striatum homogenate: The compounds reveal modest to weak, but selective binding to a dopamine D-2 receptor when it is labelled with the DA-autoreceptor agonist [3H]-SND 919. In vivo studies with mice showed that 7, 9a,b, and 10 affect their CNS activity.