Facile Synthesis of Octahydrobenzo[h]isoquinolines: Novel and Highly Potent D₁ Dopamine Agonists

Abstract

The octahydrobenzo[h]isoquinoline scaffold is of interest as a conformationally-restricted phenethylamine that may be useful for constructing biologically active products. Surprisingly, however, no tractable synthesis of this ring system has been reported. We now describe a facile method for obtaining this framework, and illustrate that our approach is easily amenable to substitutions at the 5-position. Importantly, we demonstrate that the 7,8-dihydroxy-5-phenyl-substituted ligand is an extremely potent, high-affinity, full D₁ dopamine receptor-selective agonist.

1. Introduction

Dopamine (DA) is a monoamine neurotransmitter that is important in locomotor control, reward circuitry, cognitive and endocrine function, and plays a role in a variety of other key physiological processes. Dopaminergic dysfunctions have been implicated in Parkinson’s disease, schizophrenia, addiction, attention deficit hyperactivity disorder (ADHD), and certain sexual disorders.¹ Useful dopaminergic therapeutics result, however, only when a thorough understanding is gained of the particular system and dopamine receptor isoforms that are involved. One approach that we have found most useful to aid in identifying the critical receptor types involves the design and use of conformationally-restricted analogues.^2–8 Conformationally-restricted analogues can be especially powerful when combined with computationally-derived receptor models and conformational analysis,^9–11 as well as site-directed mutagenesis.^{12, 13}

Nearly three decades ago, Joseph Cannon and his colleagues investigated the pharmacological activities of different rotamers of DA using rigid analogues designed around an octahydrobenzoquinoline or an octahydrobenzoisoquinoline framework. One of his conclusions was that the amine nitrogen needed to be coplanar with, and anti with respect to the catechol ring¹⁴ (Figure 1). He also showed that trans ring fusions, which confer a rigid and relatively planar structure, were more active than the corresponding cis ring fusions, which cannot simultaneously adopt both an anti and planar conformation.¹⁵ His conclusions¹⁶ were extremely important in the early SAR work on DA pharmacology and many have been consistently validated over the years, but his studies were carried out in an era prior to more modern insight into the existence of different DA receptor subtypes (although Cannon does suggest that multiple receptor types would explain some of his observations.¹⁶)

Figure 1.

Trans-β-dopamine

About the same time as Cannon’s work, Kebabian and Calne discovered that there were two classes of DA receptor, which they named D₁ and D₂.¹⁷ In order to study the different receptor classes, highly selective agonists and antagonists were needed. Because of their potential for treating Parkinson’s disease¹⁸ and improving cognition,¹⁹ selective D₁ dopamine receptor agonists (Figure 2) should be prime therapeutic candidates for the pharmaceutical industry and have been a major focus of our research for more than three decades. The first high-affinity D₁-selective agonist discovered was SKF38393,^{20, 21} but it proved to be only a partial agonist at DA D₁ receptors. Abbott Laboratories subsequently developed a series of potent isochroman compounds, many of which showed significant D₁ selectivity.^22,23 Our laboratory discovered the first D₁-selective full agonist, dihydrexidine,^{24, 25} followed by dinapsoline,^26,27 dinoxyline,²⁸ and more recently the highly D₁-selective full agonist, doxanthrine.²⁹

Figure 2.

Known D₁-like dopamine agonists

Much effort has been invested by our laboratory, and others, to determine the requirements for D₁ receptor subtype selectivity. Mottola and coworkers³⁰ used the Active Analogue Approach to map out the spatial requirements of the D₁ pharmacophore. It was proposed to include a catechol ring with the meta hydroxyl 7 Å away from the amine nitrogen, with the ethylamine side chain in the trans β rotameric conformation, as first defined by Cannon.¹⁶ Interestingly, Cannon asserted that this was the “‘wrong’ conformation of dopamine”¹⁶ for the assays he was using, which one may now conclude to have been D₂-like mediated biological responses. The D₁ pharmacophore model also calls for an accessory ring, typically a phenyl ring, attached at the side chain β carbon, and in near coplanarity with the catechol ring.

Taking all of these points into consideration, as well as prior SAR studies, we proposed the synthesis of 7,8-dihydroxyoctahydrobenzo[h]isoquinoline compounds (Figure 3), all of which possess the trans-β-rotameric conformation of dopamine, and are the subject of this report. We predicted that the cis compound 1 would have low affinity at both DA receptor subtypes, but that the trans phenyl compound 3 would be a D₁-selective agonist due to the presence of the phenyl ring, which we anticipated was positioned to engage the postulated accessory binding region in the receptor. Although the appended phenyl ring is not directly connected to the β carbon of the embedded dopamine moiety, we still predicted that 3 would possess D₁ selectivity because the overall distance from the centroid of the appended phenyl ring to the meta hydroxyl group is not significantly different from our working model. Furthermore, potent and D₁-selective isochroman compounds prepared at Abbott laboratories^31,32 possessed accessory groups in the comparable position.

Figure 3.

Target compounds: octahydrobenzo[h]isoquinolines 1, 2, and 3

Oppolzer originally published a method for the synthesis of benzo[h]isoquinolines,³³ which was subsequently adapted by Cannon and his coworkers³⁴ for the preparation of an 8,9-dioxygenated compound. Oppolzer’s method, however, relies on intramolecular thermal rearrangements to build the tricyclic ring system, and difficultly-accessible benzocyclobutene intermediates are required. The cis ring junctions were often the major products and the cyclic rearrangements were highly sensitive to heteroatom substitutions. Cannon’s adaptation worked specifically for an 8,9-dioxygenation substitution pattern, but overall this approach was not a general one, and in particular did not allow for 5-substituted compounds. Subsequently, Napier and Griffith,³⁵ patented a series of 6-substituted octahydrobenzo[h]isoquinolines as antidepressant agents. Their general synthetic approach, however, was more broadly applicable than that of Oppolzer and was modified for the preparation of target compounds 1–3.

2. Results

2.1. Chemistry

An initial goal of this project was to develop an improved and high-yielding synthesis of tetralone 7 (Scheme 1).^36,37 We envisioned that this ketone could then be functionalized to allow annulation of the desired heterocyclic ring. The first step of our synthesis of 7 was the formation of paraconic acid 4 from commercially available 2,3-dimethoxybenzaldehyde and succinic anhydride.³⁸ Pure, crystalline 4 was heated at 180 °C to effect both ring opening and decarboxylation. The unsaturated acid 5 was then catalytically hydrogenated and the reduced acid was treated with polyphosphoric acid to form 7 in nearly quantitative yield over two steps.

Scheme 1.

Synthesis of intermediate 7 by paraconic acid decarboxylation

We envisioned that the phenyl tetralone 8 could be made in a parallel manner using phenyl succinic anhydride and 2,3-dimethoxybenzaldehyde. The paraconic acid formed as expected; however, all of our decarboxylation attempts yielded decomposed material, with no evidence of gas evolution. We were able to synthesize large quantities of 8, however, using a procedure similar to one reported by Abbott Laboratories.³⁹

Scheme 2 illustrates construction of the tricyclic ring system from the alpha tetralone. Our approach was inspired by Simonelli and coworkers,⁴⁰ who used lithiated 2,4,4-trimethyl-2-oxazoline to prepare γ amino acids. Realizing that unsaturated nitriles can serve as Michael acceptors for carbon nucleophiles,^41,42 we envisioned that this method could be modified to prepare desired lactam 15. That is, tetralone 7 was converted into unsaturated nitrile 9 by treatment with trimethylsilylcyanide and boron trifluoride etherate (Scheme 2).⁴³ Lithiation of 2,4,4-trimethyl-2-oxazoline, followed by addition of the resulting carbanion to 9, afforded nearly equal amounts of the diastereomers from both the cis and the trans addition. This reaction also was attempted with an organocuprate reagent, anticipating that it might favor the desired trans addition, but it also yielded a nearly equal mixture of diastereomers, albeit in much lower yield. Fortunately, the cis and the trans addition products could be cleanly separated by column chromatography and each was carried forward in parallel syntheses. The stereochemistry of the addition products was confirmed by the ¹H MNR signal corresponding to the methine proton alpha to the cyano group. The cis addition product appeared as a doublet with a J value of 4.5 Hz, whereas the stereoisomer identified as trans had an equivalent signal with a J value of 9.3 Hz.

Scheme 2.

Synthesis of target compounds 1, 2, and 3 by conjugate addition to unsaturated nitriles

We were able to reduce the nitriles 9 to the amines 11 in high yield using cobalt boride⁴⁴ without the epimerization that occurred when lithium aluminum hydride or Raney nickel were employed. Highest yields were achieved using potassium borohydride, rather than sodium borohydride, possibly due to its higher stability in methanol. The lactams 15 were then formed in one step by hydrolysis of the oxazoline moiety in acidic ethanol, followed by quenching in aqueous sodium hydroxide. Reduction to the isoquinolines 17, followed by demethylation yielded the catechols 1 and 2 as hydrobromide salts.

The synthesis of the phenyl substituted isoquinoline followed the same steps as the unsubstituted compounds. The only notable difference was that the separation of the cis and trans oxazoline-addition products was readily accomplished by fractional crystallization. The trans isomer was the only one carried forward through the rest of the synthesis because the prior literature had shown that cis-fused polycyclic dopamine analogues invariably lacked biological activity. The hydrobromide salt of catechol 3 was prepared, and all three compounds were submitted for pharmacological assessment.

2.2. Pharmacology

The receptor binding properties of these new compounds at dopamine receptors are presented in Table 1. As anticipated, cis compound 1 had poor affinity at both classes of receptors, whereas 2 had slightly higher affinity at D₂-like receptors than at D₁-like receptors. When the phenyl substituent was incorporated into the ligand, 3, the affinity at D₁-like receptors increased significantly, with a K_i of 6 nM, 3-fold better than doxanthrine (DOX).⁴⁵

Table 1.

Binding affinity at porcine striatal homogenates^a

Ligand	D1-like (Ki, nM)	D2-like (Ki, nM)	Fold D1-like selectivity
DOX	18 ± 0.6	4400 ± 620	240
1	6800 ± 490	2800 ± 210	0.4
2	850 ± 65	670 ± 36	0.8
3	6 ± 0.2	440 ± 72	73
SCHb	0.79 ± 0.1	ND
CPZc	ND	3.2 ± 0.5

^aAll results shown are the mean ± SEM for at least three independent experiments.

^bSCH23390.

^cchlorpromazine.

Because 3 had such high affinity at D₁-like receptors, its potency and intrinsic activity at cloned human D₁ receptors also was evaluated in comparison with DHX and DOX (Table 2). These results indicate that not only is 3 a full agonist at D₁ receptors, but it also is 6–7-fold more potent at these receptors than either DHX or DOX. The compound was then submitted to the NIMH-sponsored PDSP program for screening against a panel of other brain receptors HTTP://PDSP.MED.UNC.EDU. It had low affinities (> 1 μM) for all but a small subset of targets, which included the following (K_i value, nM): 5-HT₃ (870), 5-HT₇ (220), α_1A (340), α_2A (3.5), α_2B (6.4), α_2C (1.1), and KOR (820). Affinities reported from the PDSP screens for dopamine receptors were: D₁ (18), D₂ (750), D₃ (130), D₄ (2650), and D₅ (2.8). Thus, based on affinities, the D₁-like affinity that we measured in porcine striatal homogenate likely reflects a large high-affinity component contributed by the D₅ receptor. We might note that to date no one has yet succeeded in discovering a D₁- or D₅-selective agonist molecule, and all known “D₁ agonists” are nonselective D₁/D₅ agonists, most often with a small preference for D₅ receptors. The affinities at the α₂ subtypes are similar to what we have found with other D₁ agonists, and may reflect some structural similarities between the D₁ and α₂ receptors. For example, Doxanthrine has affinities at the α_2B and α_2C receptors of 10 and 2 nM, respectively.⁴⁵ Surprisingly, resolution of the enantiomers of that compound revealed that the affinity for the D₁ receptor resides primarily in the (+) enantiomer, whereas the affinity for the α_2C receptor was in the (−) enantiomer.⁴⁶ Thus, studies are now underway to resolve 3 into its enantiomers to determine whether a similar reversed stereoselectivity occurs.

Table 2.

Potency^a at cloned hD₁ receptors

Ligand	EC50 (nM)	I.A. (%)
dopamine	20 ± 1	100 ± 0
DHX	3.9± 0.5	107 ± 3
DOX	4.3 ± 0.6	98 ± 3
3	0.64 ± 0.1	103 ± 7

^aAll results shown are the mean ± SEM for at least four independent experiments. I.A. is intrinsic activity, the maximum stimulation observed relative to the response of dopamine, which is defined as 100% I.A.

3. Discussion

Our concepts of the binding requirements in the orthosteric binding site of D₂-like versus D₁-like receptors have been further validated by the results of the present study, which are consistent with our initial predictions. That is, that cis compound 1 would have the lowest affinity at either class of receptors, and that the phenyl substituent on 3 would interact favorably with the accessory binding region of the D₁ receptor binding pocket to afford a ligand with increased affinity at D₁-like receptors. Not only does 3 possess higher affinity at the D₁-like receptors than other ligands such as DOX, it is 73-fold selective for D₁-like receptors over D₂-like receptors, and is 6–7-fold more potent than any previous full D₁ dopamine agonist discovered. We can say with confidence that our new ring system constricts the ethylamine side chain of the imbedded dopamine moiety into the conformation required to activate the D₁-like receptors, further refining our model of the D₁-like receptor binding pocket.

4. Conclusion

We have developed a tractable method for synthesizing the previously unreported 7,8-dihydroxyoctahydrobenzo[h]isoquinolines. This method is amenable to preparing analogues bearing substituents at the 5-position, as illustrated by the synthesis of 3. This latter molecule is a novel, rigid dopaminergic full agonist ligand with high affinity and very high potency at D₁-like receptors and significant selectivity over D₂-like receptors. In addition, screening indicated that 3 also has high affinity at α₂ adrenergic receptors. The practical consequences of this finding are unclear but it is known that stimulation of α₂ adrenergic receptors in prefrontal cortex has a beneficial effect on spatial working memory performance (reference 47 and citations contained therein). Thus, this framework will serve as the lead scaffold for further structure-activity relationship studies of ligands for the various dopamine receptor isoforms.

5. Experimental

5.1. Chemistry

5.1.1. General

All reagents were commercially available (Aldrich, Alfa Aesar) and were used without further purification unless otherwise indicated. Dry THF was distilled immediately before use from benzophenone-sodium under argon. Column chromatography was carried out using SiliCycle SiliaFlash P60 silica gel (230–400 mesh). J.T. Baker flexible thin layer chromatography sheets (silica gel IB2-F) were used to monitor reaction progress. Melting points were determined using a Mel-Temp apparatus and are reported as uncorrected values. ¹H NMR spectra were recorded using a 300 MHz Bruker ARX300 NMR spectrometer or 500 MHz Bruker DRX500 NMR spectrometer, as noted. Chemical shifts are reported in δ values (ppm) relative to an internal reference (0.03%, v/v) of tetramethylsilane (TMS) in CDCl₃, except where noted. Abbreviations used to report NMR peaks are as follows: bs = broad singlet, d = doublet, dd = doublet of doublets, m = multiplet, q = quartet, s = singlet, t = triplet. Chemical ionization mass spectra (CIMS) using isobutane as a carrier gas were obtained with a Finnigan 4000 spectrometer. Elemental analyses were performed by the Purdue University Microanalysis Laboratory or Midwest Microlabs. All reactions were carried out under an argon atmosphere, unless noted otherwise.

5.1.1.1. 2-(2,3-Dimethoxyphenyl)-5-oxo-tetrahydrofuran-3-carboxylic Acid, 4

To a flame-dried 3-neck flask fitted with a condenser and dried addition funnel were added 25.0 g (0.184 mol) of anhydrous, powdered zinc chloride. To this solid were added 100 mL CH₂Cl₂, followed by 15.3 g (0.092 mol) of 2,3-dimethoxybenzaldehyde and 13.8 g (0.138 mol) succinic anhydride. Triethylamine (25.6 mL, 0.184 mol) was added dropwise to the flask with rapid stirring. The reaction was heated at reflux for 4 days, then cooled to room temperature and poured over ice-cold 6N HCl. The organic component was extracted with EtOAc (3 × 250 mL), then washed with 2 N HCl (1 × 250 mL), and brine (1 × 250 mL). The product was extracted with saturated NaHCO₃ (4 × 200 mL) until TLC indicated no product remained in the organic layer. The aqueous layer was washed with CH₂Cl₂ (1 × 200 mL) and acidified with conc HCl. The white, milky solution was extracted with CH₂Cl₂ (3 × 250 mL), dried over Na₂SO₄, and evaporated under vacuum to afford 18.0 g (0.068 mol, 74%) of pale yellow solid that was recrystallized from EtOAc-hexanes; mp 129–130 °C (lit.⁴⁸ mp 132 °C). ¹H NMR: (300 MHz, CDCl₃): δ 7.01 (t, 1H, J = 7.5 Hz, ArH); 6.89 (dd, 1H, J = 2.5, 8.1 Hz, ArH); 6.82 (dd, 1H, J = 2.5, 8.1 Hz, ArH); 5.73 (d, 1H, J = 6.6 Hz, ArCH); 3.81 (s, 3H, ArOCH₃); 3.80 (s, 3H, ArOCH₃); 3.44 (dt, 1H, J = 6.6, 8.5 Hz, CHCO₂H); 2.90 (d, 2H, J = 8.5 Hz, COCH₂). EIMS: (M⁺) = 266.

5.1.1.2. 4-(2,3-Dimethoxyphenyl)but-3-enoic Acid, 5

To a one-neck round bottom flask were added 8.6 g (0.032 mol) of recrystallized 4 and the solid was heated on a 180 °C oil bath for 6 h. Carbon dioxide was observed bubbling out of the dark brown liquid. After 6 h, the reaction was cooled to room temperature and dissolved in CH₂Cl₂. The product and any unreacted starting material were extracted into 2 N NaOH (3 × 100 mL). The pKa of the butenoic acid is approximately 4.2, whereas the pKa of the paraconic acid is approximately 3.6, so the two compounds are separable by titration. The aqueous extract was therefore carefully acidified with 2 N HCl, with monitoring by a calibrated pH meter. At pH 4.0 the solution became very cloudy and was extracted with CH₂Cl₂. The titration and extraction were repeated until there was no turbidity at pH 4.0. Unreacted starting material was then recovered by acidifying to pH 3.0 and extracting with CH₂Cl₂. The organic extracts containing product were dried over Na₂SO₄, and evaporated under reduced pressure to yield pure 11, which solidified under reduced pressure to provide a yellow solid (4.7 g, 0.021 mol, 65%) that was used without further purification; mp 84–86 °C (no lit.⁴⁹ mp reported). ¹H NMR: (300 MHz, CDCl₃): δ 7.08 (dd, 1H, J = 1.2, 8.0 Hz, ArH); 6.99 (t, 1H, J = 8.0 Hz, ArH); 6.80 (m, 2H, ArH and ArCH=CH); 6.29 (dt, 1H, J = 7.2, 15.9 Hz, ArCHCH); 3.84 (s, 3H, ArOCH₃); 3.78 (s, 3H, ArOCH₃); 3.32 (dd, 2H, J = 1.2, 7.2 Hz, CH₂COOH). ESIMS: (M+Na⁺) = 245.

5.1.1.3. 4-(2,3-Dimethoxyphenyl)butanoic Acid, 6

A 500 mL Parr hydrogenation flask containing 0.6 g of 10% Pd/C and 5 (3.7 g, 0.017 mol) dissolved in 100 mL absolute EtOH was pressurized with H₂ gas and shaken at 25 psi H₂ for 2 h. The contents were filtered through Celite, the solvents were evaporated, and the resulting oil was dried under high vacuum to yield a grey solid (3.7 g, 0.017 mol, quant. yield). The solid was recrystallized from EtOAc-hexanes to produce fine white needles (2.2 g, 59.5%); mp 58–59 °C (lit.³⁶ mp. 58.5–60 °C). ¹H NMR: (300 MHz, CDCl₃): δ 6.97 (t, 1H, J = 8.1 Hz, ArH); 6.76 (d, 1H, J = 8.1 Hz, ArH); 6.75 (d, 1H, J = 8.1 Hz, ArH); 3.84 (s, 3H, ArOCH₃); 3.80 (s, 3H, ArOCH₃); 2.67 (t, 2H, J = 7.2 Hz, CH₂CH₂CO₂H); 2.37 (t, 2H, J = 7.2 Hz, ArCH₂); 1.92 (p, 2H, J = 7.2 Hz, CH₂CH₂CO₂H). ESIMS: (M+Na⁺) = 247.

5.1.1.4. 5,6-Dimethoxy-3,4-dihydronaphthalen-1(2H)-one, 7

A mechanically stirred flask charged with 15 g polyphosphoric acid was heated on a 60 °C oil bath for 20 min. Powdered 6 (1.0 g, 4.46 mmol) was added in small portions to the center of the stirring vortex. After 30 min the reaction was a rust color and no starting material remained (TLC). The reaction was quenched by pouring over ice with vigorous stirring, whereupon the desired product crystallized. The crystals were collected by filtration and washed with water to yield pearly off-white plates (900 mg, 4.37 mmol, 98 %); mp 103–104 °C (lit.³⁶ mp 104–105 °C) ¹H NMR: (300 MHz, CDCl₃): δ 7.79 (d, 1H, J = 8.7, ArH); 6.81 (d, 1H, J = 8.7, ArH); 3.86 (s, 3H, ArOCH₃); 3.75 (s, 3H, ArOCH₃); 2.89 (t, 2H, J = 6.3 Hz, ArCH₂); 2.53 (t, 2H, J = 6.3 Hz, C(O)CH₂); 2.05 (p, 2H, J = 6.3 Hz, CH₂CH₂CH₂). EIMS: (M⁺) = 206.

5.1.1.5. 5,6-Dimethoxy-3,4-dihydronaphthalene-1-carbonitrile, 9

TMSCN (1.42 mL, 10.7 mmol) was added dropwise to a slurry of 7 (1.7 g, 8.25 mmol) in freshly distilled toluene (25 mL). After stirring for 10 min, BF₃·OEt₂ (1.57 mL, 12.38 mmol) was added all at once, producing an immediate color change from yellow to brown. The reaction was stirred at room temperature for 3 h, until no starting material remained, and was then quenched by pouring over 30 mL ice water with vigorous stirring. To this aqueous mixture were added 20 mL of Et₂O. The layers were separated, and the aqueous layer was extracted twice more with Et₂O and once with EtOAc. The combined organic layers were dried over Na₂SO₄, filtered, and evaporated under reduced pressure to yield a tan solid (1.7 g, 7.9 mmol, 96%) that could be recrystallized from MeOH to yield fine, colorless needles in 84% yield over three crops; mp 138–140 °C (lit.⁵⁰ mp 137–139 °C). ¹H NMR: (300 MHz, CDCl₃): δ 7.18 (d, 1H, J = 8.1 Hz, ArH); 6.80 (d, 1H, J = 8.1 Hz, ArH); 6.75 (t, 1H, J = 4.6 Hz, ArCH₂CH₂CH); 3.88 (s, 3H, ArOCH₃); 3.76 (s, 3H, ArOCH₃); 2.87 (t, 2H, J = 8.1 Hz, ArCH₂); 2.44 (m, 2H, ArCH₂CH₂). EIMS: (M⁺) = 215.

5.1.1.6. 5,6-Dimethoxy-3-phenyl-3,4-dihydronaphthalene-1-carbonitrile, 10

TMSCN (1.20 mL, 9.22 mmol) was added to a solution of phenyl tetralone 8 (2.00 g, 7.09 mmol) in dry toluene (100 mL). BF₃·OEt₂ (1.34 mL, 10.6 mmol) was then added slowly through a syringe and the reaction was stirred at ambient temperature overnight. The mixture was poured into 100 mL cold H₂O and extracted with EtOAc (3 × 50 mL). Column chromatography (2:1 EtOAc:hexanes) was used to purify the product and also to recover 0.674 g (2.39 mmol) of unreacted starting tetralone. The unsaturated nitrile (1.31 g, 4.50 mmol, 63.6%; 96% BRSM) was obtained as a white powder; mp 106–107 °C. ¹H NMR: (300 MHz, CDCl₃): δ 7.36–7.21 (m, 6H, PhH, ArH); 6.84 (d, 1H, J = 8.7 Hz, ArH); 6.78 (d, 1H, J = 3.9 Hz, C=CH); 3.90 (s, 3H, ArOCH₃); 3.81 (ddd, 1H, J = 3.9, 7.2, 11.4 Hz, ArCH₂CH); 3.71 (s, 3H, ArOCH₃); 3.35 (dd, 1H, J = 7.2, 16.5 Hz, ArCH₂); 2.92 (dd, 1H, J = 11.4, 16.5 Hz, ArCH₂). EIMS: (M⁺) = 291. Anal. Calc. for C₁₉H₁₇NO₂: C, 78.33; H, 5.88; N, 4.81. Found: C, 78.21; H, 5.91; N, 4.89.

5.1.1.7. Cis- and Trans-2-((4,4-dimethyl-2-oxazolin-2-yl)methyl)-5,6-dimethoxy-1,2,3,4-tetrahydro-naphthalene-1-carbonitrile, 11a, 11b

A solution of 2,4,4-trimethyloxazoline (Aldrich) (1.80 mL, 14.2 mmol) in 50 mL distilled THF was placed in a flask on a dry ice/acetone bath. A 2.0M solution of n-BuLi in cyclohexane (7.55 mL, 15.1 mmol) was then added dropwise with a syringe. The solution slowly turned bright yellow and was stirred at −78 °C for 1 h. Nitrile 9 (2.03 g, 9.44 mmol) dissolved in distilled THF (50 mL) was added dropwise to the solution of lithiated oxazoline. The yellow color faded and the mixture was stirred at −78 °C for 2 h, followed by 1 h at ambient temperature. The reaction was then quenched by the addition of 50 mL of 10% NH₄OH in saturated aqueous NH₄Cl. The solution was extracted with Et₂O (3 × 25 mL), and the organic layers were combined and extracted with 2N HCl (4 × 25 mL). The aqueous layer was basified with NaHCO₃, extracted with Et₂O, and the organic extract was dried over Na₂SO₄, filtered, and evaporated. This residue was separated by column chromatography (7:1 EtOAc:hexanes) to give the cis (R_f = 0.35, 0.990 g, 3.02 mmol, 32%) and trans (R_f = 0.28, 1.10 g, 3.35 mmol, 35.5%) addition products. The cis addition product was a colorless oil, but the trans product formed colorless needlelike crystals upon standing; mp 92–94 °C. Cis 11a: ¹H NMR: (300 MHz, CDCl₃): δ 6.96 (d, 1H, J = 8.7 Hz, ArH); 6.77 (d, 1H, J = 8.7 Hz, ArH); 4.18 (d, 1H, J = 4.5 Hz (cis), ArCHCN); 3.93 (s, 2H, OCH₂C(CH₃)₂); 3.83 (s, 3H, ArOCH₃); 3.77 (s, 3H, ArOCH₃); 3.00 (ddd, 1H, J = 2.4, 5.7, 18.0 Hz, ArCH₂); 2.72–2.60 (m, 1 H, ArCH₂); 2.56 (dd, 1H, J = 8.4, 15.9 Hz, CH₂C(N)O); 2.47 (dd, 1H, J = 6.3, 15.9 Hz, CH₂C(N)O); 2.46–2.32 (m, 1H, ArCH₂CH₂); 1.99–1.90 (m, 1H, ArCH(CN)CH); 1.83–1.68 (m, 1H, ArCH₂CH₂); 1.28 (s, 3H, C(CH₃)₂); 1.26 (s, 3H, C(CH₃)₂). EIMS: (M⁺) = 328. Anal. Calc. for C₁₉H₂₄N₂O₃: C, 69.49; H, 7.37; N, 8.53. Found: C, 69.41; H, 7.34; N, 8.36. Trans 11b: ¹H NMR: (300 MHz, CDCl₃): δ 7.11 (d, 1H, J = 8.4 Hz, ArH); 6.80 (d, 1H, J = 8.4 Hz, ArH); 3.93 (s, 2H, OCH₂C(CH₃)₂); 3.85 (d, 1H, J = 9.3 Hz (trans), ArCHCN); 3.83 (s, 3H, ArOCH₃); 3.77 (s, 3H, ArOCH₃); 2.90 (dt, 1H, J = 5.1, 17.7 Hz, ArCH₂); 2.75–2.63 (m, 1 H, ArCH₂); 2.59 (dd, 1H, J = 4.8, 13.5 Hz, CH₂C(N)O); 2.50–2.33 (m, 2H, ArCH₂CH₂, CH₂C(N)O); 2.16–2.07 (m, 1H, ArCH(CN)CH); 1.59–1.45 (m, 1H, ArCH₂CH₂); 1.27 (s, 3H, C(CH₃)₂); 1.26 (s, 3H, C(CH₃)₂). EIMS: (M⁺) = 328. Anal. Calc. for C₁₉H₂₄N₂O₃: C, 69.49; H, 7.37; N, 8.53. Found: C, 69.21; H, 7.49; N, 8.39.

5.1.1.8. Trans-2-((4,4-dimethyl-2-oxazolin-2-yl)methyl)-5,6-dimethoxy-3-phenyl-1,2,3,4-tetrahydronaph-thalene-1-carbonitrile, 12

In a method analogous to the synthesis of 11 above, nitrile 10 (0.770 g, 2.65 mmol) was converted to the title compound. The trans isomer was crystallized from the crude mixture using 1:1 EtOAc:hexanes to yield 0.262 g (0.649 mmol, 25%) of a white powder. The mother liquor was further purified by column chromatography (1:1 EtOAc:hexanes) to isolate 0.378 g (0.936 mmol) of a mixture of the cis and trans isomers of the desired product, from which an additional 0.029 g (0.0718 mmol, 2.7%) of the trans isomer was crystallized; mp 131–133 °C. ¹H NMR: (300 MHz, CDCl₃): δ 7.39–7.19 (m, 6H, PhH, ArH); 6.88 (d, 1H, J = 8.7 Hz, ArH); 4.57 (d, 1H, J = 10.5 Hz (trans), ArCHCN); 3.87 (s, 3H, ArOCH₃); 3.88–3.75 (m, 2H, OCH₂C(CH₃)₂); 3.74 (s, 3H, ArOCH₃); 3.22 (dd, 1H, J = 4.5, 16.8 Hz, ArCH₂); 3.03 (dt, 1H, J = 4.5, 11.4 Hz, ArCH₂CH); 2.81 (dd, 1H, J = 11.4, 16.8 Hz, ArCH₂); 2.72–2.61 (m, 1H, ArCH(CN)CH); 2.55 (dd, 1H, J = 3.9, 16.2 Hz, CH₂C(N)O); 2.55 (dd, 1H, J = 6.3, 16.2 Hz, CH₂C(N)O); 1.27 (s, 3H, C(CH₃)₂); 1.22 (s, 3H, C(CH₃)₂). EIMS: (M⁺) = 404. Anal. Calc. for C₂₅H₂₈N₂O₃: C, 74.23; H, 6.98; N, 6.93. Found: C, 73.90; H, 7.01; N, 6.71.

5.1.1.9. Cis-(2-((4,4-dimethyl-2-oxazolin-2-yl)methyl)-5,6-dimethoxy-1,2,3,4-tetrahydronaphthalen-1-yl)-methanamine, 13a

A solution of cis nitrile 11a (0.880 g, 2.68 mmol) in MeOH (30 mL) was placed in a flask and stirred on an ice bath. Solid CoCl₂·6H₂O (1.28 g, 5.36 mmol) was added and the mixture was stirred until all solids dissolved. KBH₄ (1.45 g, 0.0268 mol) was then added carefully in three portions over 10 min. The black solution was removed from the ice bath and stirred at ambient temperature for 1 h. The reaction was then quenched by the addition of 10 mL of conc HCl, and the bright blue solution was evaporated to near dryness. The residue was re-dissolved in H₂O (50 mL) and washed once with Et₂O (10 mL). The aqueous layer was basified with NH₄OH and extracted with CH₂Cl₂ (3 × 20 mL). The organic layers were combined, dried over Na₂SO₄, filtered, and evaporated to yield the desired product (0.813 g, 2.45 mmol, 91%) as a white solid; mp 208 °C (dec.). ¹H NMR: (300 MHz, CDCl₃): δ 6.82 (d, 1H, J = 8.4 Hz, ArH); 6.76 (d, 1H, J = 8.4 Hz, ArH); 3.84 (s, 3H, ArOCH₃); 3.79 (s, 3H, ArOCH₃); 3.59 (dd, 1H, J = 6.0, 15.6 Hz, CH₂NH₂); 3.50 (s, 2H, OCH₂C(CH₃)₂); 3.22 (dd, 1H, J = 10.8, 15.6 Hz, CH₂NH₂); 3.04–2.95 (m, 1H, ArCH₂); 2.88–2.79 (m, 1H, ArCH); 2.72–2.55 (m, 2H, CH₂C(N)O); 2.22–2.13 (m, 1H, ArCH₂CH₂CH); 2.11–2.01 (m, 1H, ArCH₂); 1.77–1.65 (m, 2H, ArCH₂CH₂); 1.28 (s, 3H, C(CH₃)₂); 1.26 (s, 3H, C(CH₃)₂). EIMS: (M⁺) = 332. Anal. Calc. for C₁₉H₂₈N₂O₃ (0.5 eq MeOH): C, 67.21; H, 8.68; N, 8.04. Found: C, 66.86; H, 8.35; N, 8.07.

5.1.1.10. Trans-(2-((4,4-dimethyl-2-oxazolin-2-yl)methyl)-5,6-dimethoxy-1,2,3,4-tetrahydronaphthalen-1-yl)methanamine, 13b

A procedure identical to that above was used to convert 0.500 g of trans nitrile 11b (1.52 mmol) into the desired amine (0.480 g, 1.45 mmol, 94%), recovered as a white solid; mp 181 °C (dec.). ¹H NMR: (300 MHz, CDCl₃): δ 6.93 (d, 1H, J = 8.4 Hz, ArH); 6.78 (d, 1H, J = 8.4 Hz, ArH); 4.18 (dd, 1H, J = 5.1, 15.3 Hz, CH₂NH₂); 3.84 (s, 3H, ArOCH₃); 3.80 (s, 3H, ArOCH₃); 3.53 (d, 1H, J = 17.4 Hz, OCH₂C(CH₃)₂); 3.49 (d, 1H, J = 17.4 Hz, OCH₂C(CH₃)₂); 3.17 (dd, 1H, J = 11.1, 15.3 Hz, CH₂NH₂); 3.03 (dd, 1H, J = 3.9, 17.4 Hz, ArCH₂); 2.70–2.56 (m, 1H, ArCH₂); 2.49 (dt, 1H, J = 5.1, 11.1 Hz, ArCH); 2.30 (dd, 1H, J = 4.2, 15.9, CH₂C(N)O); 2.04 (dd, 1H, J = 12.0, 15.9, CH₂C(N)O); 1.94–1.87 (m, 1H, ArCH₂CH₂); 1.77–1.62 (m, 1H, ArCH₂CH₂CH); 1.38 (dq, 1H, J = 3.0, 12.6 Hz, ArCH₂CH₂); 1.27 (s, 3H, C(CH₃)₂); 1.25 (s, 3H, C(CH₃)₂). EIMS: (M⁺) = 332. Anal. Calc. for C₁₉H₂₈N₂O₃ (+ 0.33 eq MeOH): C, 67.68; H, 8.62; N, 8.16. Found: C, 67.81; H, 8.43; N, 7.96.

5.1.1.11. Trans-(2-((4,4-dimethyl-2-oxazolin-2-yl)methyl)-5,6-dimethoxy-3-phenyl-1,2,3,4-tetrahydro-naphthalen-1-yl)methanamine, 14

Using the method employed for 13, nitrile 12 (0.157 g, 0.389 mmol) was converted to the title compound (0.149 g, 0.365 mmol, 94%) as a white solid; mp 213 °C (dec.). ¹H NMR: (300 MHz, CDCl₃): δ 7.40–7.22 (m, 5H, PhH); 7.01 (d, 1H, J = 8.7 Hz, ArH); 6.83 (d, 1H, J = 8.7 Hz, ArH); 4.25 (dd, 1H, J = 5.4, 15.0 Hz, ArCHCH₂NH₂); 3.86 (s, 3H, ArOCH₃); 3.77 (s, 3H, ArOCH₃); 3.73 (bs, 2H, NH₂); 3.51–3.42 (m, 2H, OCH₂C(CH₃)₂); 3.30–3.21 (m, 2H, ArCH₂, ArCHCH₂NH₂); 2.85–2.46 (m, 3H, ArCHCH₂NH₂, ArCH₂CH); 2.01 (dq, 1H, J = 5.4, 11.1 Hz, ArCH₂CH(Ph)CH); 1.89–1.74 (m, 2H, CH₂C(N)O); 1.20 (s, 3H, C(CH₃)₂); 1.16 (s, 3H, C(CH₃)₂). ESIMS: (M+H⁺) = 409. Anal. Calc. for C₂₅H₃₂N₂O₃ (0.66 eq H₂O): C, 71.40; H, 7.99; N, 6.66. Found: C, 71.58; H, 7.70; N, 6.40.

5.1.1.12. Cis-7,8-dimethoxy-1,2,4,4a,5,6-hexahydrobenzo[h]isoquinolin-3(10bH)-one, 15a

Cis amine 13a (0.530 g, 1.60 mmol) was dissolved in 30 mL of a 10% solution of H₂SO₄ in absolute EtOH and the solution was heated at 85 °C for 48 h. The reaction was cooled to room temperature, 30 mL H₂O were added and, with stirring, 6 N NaOH was added until a white solid formed and the reaction pH > 12. The basic mixture was stirred for 15 min and the solid was collected by filtration to afford the desired lactam as an off-white solid (0.234 g, 0.870 mmol, 55%). The filtrate was extracted with EtOAc to recover an additional 0.100 g (0.372 mmol, 23%, total 78%) of product; mp 185–187 °C. ¹H NMR: (300 MHz, CDCl₃): δ 6.83 (d, 1H, J = 8.4 Hz, ArH); 6.75 (d, 1H, J = 8.4 Hz, ArH); 5.91 (bs, 1H, NH); 3.84 (s, 3H, ArOCH₃); 3.80 (s, 3H, ArOCH₃); 3.42–3.37 (m, 2H, CH₂NH); 3.19–2.99 (m, 2H, ArCH, ArCH₂); 2.80–2.63 (m, 2H, ArCH₂, C(O)CH₂); 2.33 (d, 1H, J = 17.1 Hz, C(O)CH₂); 2.32–2.21 (m, 1H, ArCH₂CH₂CH); 1.90–1.59 (m, 2H, ArCH₂CH₂). ESIMS: (M+H⁺) = 262. HR ESIMS: Calc. Mass = 262.1443, Actual Mass = 262.1445.

5.1.1.13. Trans-7,8-dimethoxy-1,2,4,4a,5,6-hexahydrobenzo[h]isoquinolin-3(10bH)-one, 15b

In an identical fashion, 1.24 g (3.73 mmol) of the trans amine 13b was converted into 0.656 g (2.51 mmol, 67%) of the trans lactam as a white solid; mp 240 °C (dec.). ¹H NMR: (300 MHz, CDCl₃): δ 6.86 (d, 1H, J = 8.4 Hz, ArH); 6.78 (d, 1H, J = 8.4 Hz, ArH); 6.09 (bs, 1H, NH); 3.94 (dt, 1H, J = 4.1, 11.4 Hz, CH₂NH); 3.85 (s, 3H, ArOCH₃); 3.81 (s, 3H, ArOCH₃); 3.18 (t, 1H, J = 11.4, CH₂NH); 3.09 (dd, 1H, J = 3.9, 17.7 Hz, ArCH₂); 2.78 (dt, 1H, J = 5.4, 11.4, ArCH); 2.71–2.59 (m, 1H, ArCH₂); 2.60 (dd, 1H, J = 4.8, 17.4, COCH₂); 2.19 (dd, 1H, J = 12.3, 17.4, C(O)CH₂); 2.03–1.93 (m, 1H, ArCH₂CH₂); 1.90–1.74 (m, 1H, ArCH₂CH₂CH); 1.42 (dq, 1H, J = 5.4, 12.4 Hz, ArCH₂CH₂). ESIMS: (M+H⁺) = 262. Anal. Calc. for C₁₅H₁₉NO₃: C, 68.94; H, 7.33; N, 5.36. Found: C, 68.60; H, 7.01; N, 5.38.

5.1.1.14. Trans-7,8-Dimethoxy-5-phenyl-1,2,4,4a,5,6-hexahydrobenzo[h]isoquinolin-3(10bH)-one, 16

Following the method for the synthesis of 15 above, amine 14 (0.200 g, 0.490 mmol) was converted into the desired lactam as a white solid (0.110 g, 0.326 mmol, 67%). The filtrate was extracted with EtOAc to recover an additional 0.032 g (0.095 mmol, 19%) of the product; mp > 250 °C. ¹H NMR: (300 MHz, CDCl₃): δ 7.38–7.19 (m, 5H, PhH); 6.93 (d, 1H, J = 8.7 Hz, ArH); 6.82 (d, 1H, J = 8.7 Hz, ArH); 5.98 (bs, 1H, NH); 4.00 (dt, 1H, J = 4.6, 11.4 Hz, CH₂NH); 3.86 (s, 3H, ArOCH₃); 3.78 (s, 3H, ArOCH₃); 3.37–3.21 (m, 2H, CH₂NHCOCH₂); 3.20 (dt, 1H, J = 5.1, 10.5 Hz, ArCHCH₂); 2.83 (dd, 1H, J = 12.3, 17.4 Hz, NHCOCH₂); 2.66 (dt, 1H, J = 4.2, 10.5 Hz, ArCH₂CH(Ph)CH); 2.23 (dd, 1H, J = 4.2, 17.1 Hz, ArCH₂); 2.17–2.04 (m, 1H, ArCH₂CH); 1.94 (dd, 1H, J = 12.6, 17.1 Hz, ArCH₂). ESIMS: (M+H⁺) = 338. HR ESIMS: Calc. Mass = 338.1756, Actual Mass = 338.1753.

5.1.1.15. Cis-7,8-dimethoxy-1,2,3,4,4a,5,6,10b-octahydrobenzo[h]isoquinoline Hydrochloride, 17a

A flame-dried single-neck flask was charged with 50 mL of distilled THF, and 0.130 g (0.498 mmol) of the cis lactam 15a were added. A 1.0 M solution of BH₃ in THF (2.49 mL, 2.49 mmol) was added dropwise to the flask and the reaction was heated at reflux overnight. The reaction was then cooled to room temperature, quenched carefully with H₂O, and evaporated to about one-third the volume. Following the addition of 10 mL 2N HCl, the solution was stirred at ambient temperature for 4 h. The aqueous solution was washed once with Et₂O, basified with NH₄OH, and extracted with CH₂Cl₂ (3 × 25 mL). The organic layers were combined, dried over Na₂SO₄, filtered, and evaporated to yield a colorless residue, which was dissolved in Et₂O and acidified with 6N HCl in EtOH. The solid that formed was collected by filtration to yield 0.084 g (0.297 mmol, 60%) of isoquinoline HCl 17a as a white powder and crystallized from MeOH; mp 186 °C (dec.). ¹H NMR: (500 MHz, d₆-DMSO): δ 8.80 (bs, 2H, NH₂); 6.87 (m, 2H, ArH); 3.75 (s, 3H, ArOCH₃); 3.66 (s, 3H, ArOCH₃); 3.16 (dd, 1H, J = 4.2, 12.4 Hz, ArCHCH₂NH₂); 3.12–3.05 (m, 2H, CH₂NH₂CH₂); 2.99–2.82 (m, 3H, ArCHCH₂NH₂CH₂, ArCH₂); 2.59–2.48 (m, 1H, ArCH₂); 2.10–1.89 (m, 3H, ArCH₂CH₂CHCH₂); 1.72 (bd, 1H, J = 11.8 Hz, NH₂CH₂CH₂); 1.62–1.54 (m, 1H, ArCH₂CH₂). ESIMS: (M+H⁺) = 248. Anal. Calc. for C₁₅H₂₂ClNO₂: C, 63.48; H, 7.81; N, 4.94. Found: C, 63.37; H, 7.79; N, 5.00.

5.1.1.16. Trans-7,8-dimethoxy-1,2,3,4,4a,5,6,10b-octahydrobenzo[h]isoquinoline Hydrochloride, 17b

An identical procedure was used to convert 0.500 g (1.92 mmol) of trans lactam 15b into 0.325g (1.15 mmol, 60.0%) of the trans isoquinoline HCl 17b, obtained as a white powder that was crystallized from MeOH; mp 228 °C (dec.). ¹H NMR: (300 MHz, d₆-DMSO): δ 8.91 (bs, 2H, NH₂); 6.95 (d, 1H, J = 8.7 Hz, ArH); 6.86 (d, 1H, J = 8.7 Hz, ArH); 3.96 (d, 1H, J = 8.4 Hz, ArCHCH₂NH₂); 3.76 (s, 3H, ArOCH₃); 3.66 (s, 3H, ArOCH₃); 3.30 (d, 1H, J = 8.4 Hz, ArCHCH₂NH₂CH₂); 2.94–2.81 (m, 2H, ArCHCH₂NH₂CH₂CH₂); 2.74–2.55 (m, 3H, ArCH₂, ArCHCH₂); 1.90–1.79 (m, 2H, ArCH₂CH₂CHCH₂); 1.56–1.30 (m, 3H, ArCH₂CH₂CH). ESIMS: (M+H⁺) = 248. Anal. Calc. for C₁₅H₂₂ClNO₂ (0.33 eq MeOH): C, 62.54; H, 7.99; N, 4.76. Found: C, 62.78; H, 7.70; N, 4.78.

5.1.1.17. Trans-7,8-Dimethoxy-5-phenyl-1,2,3,4,4a,5,6,10b-octahydrobenzo[h]isoquinoline Hydrochloride, 18

Analogous to the procedure for 17, lactam 16 (0.190 g, 0.564 mmol) was converted into the title compound (0.169 g, 0.471 mmol, 84%) as a white powder; mp > 250 °C. ¹H NMR: (500 MHz, d₆-DMSO): δ 9.15 (bs, 1H, NH₂); 8.88 (bs, 1H, NH₂); 7.39–7.20 (m, 5H, PhH); 7.04 (d, 1H, J = 9.0 Hz, ArH); 6.92 (d, 1H, J = 9.0 Hz, ArH); 4.04 (bd, 1H, J = 11.0 Hz, CHCH₂NH); 3.78 (s, 3H, ArOCH₃); 3.64 (s, 3H, ArOCH₃); 3.21 (bd, 1H, J = 11.5 Hz, CH₂CH₂NH); 3.03 (d, 1H, J = 12.5 Hz, ArCH₂); 2.90 (bt, 1H, J = 11.0 Hz, ArCH); 2.85–2.68 (m, 4H, ArCH₂CH, CH₂NH₂CH₂); 1.91–1.83 (m, 1H, ArCH₂CH(Ph)CH); 1.39–1.31 (m, 1H, CH₂NH₂CH₂CH₂); 1.29–1.19 (m, 1H, CH₂NH₂CH₂CH₂). ESIMS: (M+H⁺) = 324. Anal. Calc. for C₂₁H₂₆ClNO₂: C, 70.08; H, 7.28; N, 3.89. Found: C, 69.71; H, 7.22; N, 3.73.

5.1.1.18. Cis-1,2,3,4,4a,5,6,10b-octahydrobenzo[h]isoquinoline-7,8-diol Hydrobromide, 1

A solution of 17a (0.050 g, 0.177 mmol) in dry CH₂Cl₂ (15 mL) in a flame-dried single-neck flask was cooled to −78 °C, and 0.55 mL of a 1.0 M solution of BBr₃ in CH₂Cl₂ (0.55 mmol) were added dropwise to the flask. The reaction was stirred at −78 °C for 2 h and then at room temperature for 2 h. The solution was returned to the dry ice/acetone bath and carefully quenched by the addition of 3 mL anhydrous MeOH. The quenched reaction was evaporated to dryness, keeping the water bath below 40 °C. The solid residue was redissolved in MeOH, and evaporated again, repeating this process a total of four times. The resulting tan solid was dried under high vacuum overnight and then crystallized from MeOH-Et₂O to yield a fine, white powder (0.043 g, 0.144 mmol, 81%); mp > 250 °C. ¹H NMR: (500 MHz, d₆-DMSO): δ 9.08 (s, 1H, ArOH); 8.47 (m, 1H, NH₂); 8.34 (m, 1H, NH₂); 8.19 (s, 1H, ArOH); 6.60 (d, 1H, J = 8.0 Hz, ArH); 6.43 (d, 1H, J = 8.0 Hz, ArH); 3.18–3.06 (m, 2H, ArCHCH₂NH₂CH₂); 2.99–2.88 (m, 3H, ArCHCH₂NH₂CH₂); 2.79 (dd, 1H, J = 3.5, 17.5 Hz, ArCH₂); 2.45–2.33 (m, 1H, ArCH₂); 2.04–1.87 (m, 3H, ArCH₂CH₂CHCH₂); 1.71 (bd, 1H, J = 16.0 Hz, ArCH₂CH₂CHCH₂); 1.58–1.52 (m, 1H, ArCH₂CH₂). ESIMS: (M+H⁺) = 220. Anal. Calc. for C₁₃H₁₈BrNO₂ (+ 0.66 eq MeOH) C, 51.05; H, 6.48; N, 4.36. Found: C, 51.02; H, 6.24; N, 4.32.

5.1.1.19. Trans-1,2,3,4,4a,5,6,10b-octahydrobenzo[h]isoquinoline-7,8-diol Hydrobromide, 2

The same procedure as above was used to convert 0.076 g (0.269 mmol) of trans isoquinoline 17b into 0.056 g (0.187 mmol, 70.0%) of the trans catechol HBr salt 2, crystallized from MeOH-Et₂O as a fine, off-white powder; mp > 250 °C. ¹H NMR: (300 MHz, d₆-DMSO): δ 9.10 (bs, 1H, ArOH); 8.81 (bd, 1H, J = 10.5 Hz, NH₂); 8.46 (bd, 1H, J = 10.5 Hz, NH₂); 8.19 (bs, 1H, ArOH); 6.59 (d, 1H, J = 8.3 Hz, ArH); 6.49 (d, 1H, J = 8.3 Hz, ArH); 3.90 (d, 1H, J = 10.5 Hz, ArCHCH₂NH₂); 3.31 (d, 1H, J = 10.5 Hz, ArCHCH₂NH₂CH₂); 3.00–2.81 (m, 1H, ArCHCH₂NH₂CH₂); 2.76 (dd, 1H, J = 5.5, 17.5 Hz, ArCHCH₂NH₂); 2.65 (q, 1H, J = 11.0 Hz, ArCH₂CH₂CHCH₂); 2.59–2.48 (m, 2H, ArCH₂, ArCH); 1.88–1.77 (m, 2H, ArCH₂CH₂CHCH₂); 1.51–1.40 (m, 2H, ArCH₂CH₂CH); 1.39–1.29 (m, 1H, ArCH₂CH₂). ESIMS: (M+H⁺) = 220. Anal. Calc. for C₁₃H₁₈BrNO₂ (0.33 eq MeOH): C, 51.51; H, 6.27; N, 4.51. Found: C, 51.17; H, 5.89; N, 4.45.

5.1.1.20. Trans-5-Phenyl-1,2,3,4,4a,5,6,10b-octahydrobenzo[h]isoquinoline-7,8-diol Hydrobromide, 3

In a procedure analogous to that for 2, isoquinoline 18 (0.070 g, 0.195 mmol) was converted into the title compound, recrystallized from MeOH-Et₂O and isolated as a fine, white powder (0.044 g, 0.117 mmol, 60%); mp > 250 °C. ¹H NMR: (300 MHz, d₆-DMSO): δ 9.14 (s, 1H, ArOH); 8.81–8.72 (m, 1H, NH₂); 8.50–8.35 (m, 1H, NH₂); 8.26 (s, 1H, ArOH); 7.38–7.20 (m, 5H, PhH); 6.64 (d, 1H, J = 8.4 Hz, ArH); 6.58 (d, 1H, J = 8.4 Hz, ArH); 3.97 (bd, 1H, J = 9.6 Hz, CHCH₂NH); 3.22 (bd, 1H, J = 10.8 Hz, CH₂CH₂NH); 2.95 (d, 1H, J = 11.7 Hz, ArCH₂); 2.89–2.55 (m, 5H, ArCH₂CH, ArCHCH₂NH₂CH₂); 1.91–1.80 (m, 1H, ArCH₂CH(Ph)CH); 1.40–1.32 (bd, 1H, J = 12.6 Hz, CH₂NH₂CH₂CH₂); 1.28–1.12 (m, 1H, CH₂NH₂CH₂CH₂). ESIMS: (M+H⁺) = 296. Anal. Calc. for C₁₉H₂₂BrNO₂ (1 eq MeOH): C, 58.83; H, 6.42; N, 3.43. Found: C, 58.55; H, 6.77; N, 3.24.

5.2. Pharmcology

5.2.1. Materials

Affinity and functional data for all compounds were obtained using well-established methodology.^51–54 [³H]Spiperone (95 Ci/mmol) and [³H]SCH-23390 (81 Ci/mmol) were purchased from Amersham Biosciences (Piscataway, NJ). Butaclamol, SCH-23390, ketanserin, and most other reagents were purchased from Sigma-Aldrich Chemical Co. (St. Louis, MO).

5.2.1.1. Competition Binding Experiments

Fresh porcine striatal tissue was obtained from the Purdue Butcher Block and prepared as previously described.⁵¹ In brief, the striatal tissue was homogenized using a potter-type homogenizer, suspended in homogenization buffer (20 mM Hepes, 0.32 M sucrose, pH 7.4), and centrifuged at 1,000g for 10 min at 4 °C. The pellet (P1) was discarded, and the supernatant was spun at 30,000g for 10 min at 4 °C. The resulting pellet (P2) was resuspended in 50 mM Tris buffer (pH 7.4) by briefly using a Kinematica homogenizer, followed by centrifuging at 30,000g for 30 min at 4 °C. This pellet was resuspended again in 50 mM Tris buffer, dispensed into 1 mL aliquots, and spun again at 13,000g for 10 min at 4 °C. A BCA protein assay was used to quantify the final protein concentration in each pellet. The supernatant was removed, and the pellets were frozen at −80 °C until use.

The radioligand binding assays were performed as previously described,⁵⁵ with minor modifications. The pellets were resuspended (1 mg/mL) in receptor binding buffer (50 mM Hepes, 4 mM MgCl₂, pH 7.4), and 75 μg of protein was used per assay tube. Receptor isotherms were performed with [³H]SCH-23390 and [³H]spiperone to determine B_max and K_d for D₁-like and D₂-like receptor sites, respectively (760 fmol/mg and 0.44 nM for [³H]SCH-23390; 250 fmol/mg and 0.075 nM for [³H]spiperone). All D₂-like binding assays were performed with 50 nM ketanserin to mask 5-HT_2A binding sites. Nonspecific binding was defined with 5 μM butaclamol. Drug dilutions for competitive binding assays were made in receptor binding buffer and added to assay tubes containing 75 μg of protein and either 1 nM [³H]SCH-23390 or 0.15 nM [³H]spiperone. All binding experiments were incubated at 37 °C for 30 min and were terminated by harvesting with ice-cold wash buffer (10 mM Tris, 0.9% NaCl) using a 96-well Packard Filtermate cell harvester. After the samples were dried, 30 μL of Packard Microscint O was added to each well. Radioactivity was counted with a Packard Topcount scintillation counter.

5.2.1.2. Cyclic AMP Accumulation Assay

Assays were performed on confluent monolayers of cells in 48-well plates. All drugs were diluted in Earle’s balanced salt solution (EBSS) assay buffer (EBSS containing 2% bovine calf serum, 0.025% ascorbic acid, and 15 mM HEPES, pH 7.4) and added in duplicate on ice. cAMP stimulation assays were incubated for 15 min at 37 °C in the presence of 500 μM isobutylmethylxanthine (IBMX) and terminated with 3% trichloroacetic acid. cAMP levels in cell lysates were quantified using a previously published method.⁵⁶ Aliquots (15 μL) of cellular lysate was added in duplicate to cAMP binding buffer (100 mM Tris-HCl, pH 7.4, 100 mM NaCl, 5mM EDTA) in assay tubes containing [³H]cAMP (1 nM final concentration) and bovine adrenal gland cAMP binding protein (100–150 μg in 500 μL of buffer). These were incubated on ice at 4 °C for 2–3 h and terminated by harvesting with ice cold wash buffer (100 mM Tris, 0.9% NaCl) using a 96-well Packard Filtermate cell harvester. After the filter plates were dried overnight, 30 μL of Packard Microscint O was added to each well. Radioactivity was counted using a Packard Topcount Scintillation counter. Standard curves ranging from 0.01 to 300 pmol of cAMP were used to determine the concentration of cAMP in each sample.

5.2.1.3. Data Analysis

Graphpad Prism was used to generate dose-response, receptor saturation, and competition binding curves, and to perform statistical analyses (GraphPad Software, San Diego, CA). Data from D₁ cAMP stimulation assays were normalized to 10 μM dopamine. K_i values were calculated from competition binding experiments using the Cheng-Prusoff equation.