Synthesis and structure activity relationship studies of 3-biaryl-8-oxa-bicyclo[3.2.1]octane-2-carboxylic acid methyl esters

Abstract

Stille cross coupling protocols were utilized for the synthesis of 3-(biaryl)-8-oxabicyclo[3.2.1]oct-2-ene-2-carboxylic acid methyl esters, which furnished products in high yields where in some cases Suzuki coupling under the conditions utilized provided complex reaction mixture. Samarium iodide reduction of the resulting coupling products produced both of the 2β-carbomethoxy-3-biaryl-8-oxabicyclo[3.2.1]octane diastereomers and the 2α-carbomethoxy-3-biaryl-8-oxabicyclo[3.2.1]octane diastereomers. Among the series synthesized, the benzothiophene substituted compounds demonstrated significant binding profiles of inhibition of WIN 35,438 with 177 fold selectivity for DAT vs. SERT.

1. Introduction

Cocaine abuse is a serious international public health problem that results from its powerful psychostimulant and reinforcing effects. Chronic use of cocaine can impair central nervous system function by blockade of neurotransmitter uptake by dopamine, serotonin and norepinephrine reuptake systems [1-5]. Cocaine abuse has profound effects on other organ systems, in particular the cardiovascular system.

Considerable research has been devoted to gaining an understanding of the mechanism of action by which cocaine produces its pharmacological effects. In the brain, the neurotransmitter dopamine (DA) is released by presynaptic neurons into the synapse for signal transduction, where it can then bind at dopamine receptors of neighboring neurons. Under normal circumstances, excess synaptic DA is recycled back into the presynaptic neurons by the dopamine active transporter (DAT). Cocaine (1) binds to the DAT and thus inhibits dopamine reuptake from the synapse, thereby causing an accumulation of dopamine in the synapse. This, in turn, leads to an increase in dopaminergic neurotransmission and continuous stimulation of receiving postsynaptic neurons.

Cocaine's addictive properties are thought to depend largely on its ability to inhibit DAT [1,6-10]. In addition to the DAT, cocaine also binds at the serotonin reuptake transporter (SERT) and norepinephrine (NET) transporters with moderate affinity [11,14].

The DAT has been a prime focus for development of medications for cocaine abuse and there have been intensive research efforts over the last few decades toward discovery of cocaine pharmacotherapies based on this dopamine hypothesis [1]

The prototypical tropane (-)-2β-carbomethoxy-3β-(4-fluorophenyl)tropane (WIN35,428, compound 2), an analog of cocaine (Figure 1), has provided a lead for many researchers working in this field [15]. These analogues of WIN35,428 have provided significant insights and a large number of analogues have been reported to manifest selective and potent binding to monamine reuptake systems [16-20].

Figure 1.

Structures of cocaine and WIN 35,428.

Despite extensive research on this subject [11,12], a comprehensive understanding of the mechanism of action of cocaine and its tropane analogues at the molecular level has been elusive. We [21,22] have reported that the 8-amine functionality present in WIN35,428 is not essential for inhibitory potency at the DAT. Indeed, this amine can be exchanged for an ether [23], a thioether [22] and even a methylene [24] with very limited effect on DAT or SERT inhibition [25]. Davies [26] and Fu [27] have reported the synthesis and binding profile of 3-heterobiaryl systems in the 8-azabicyclo[3.2.1]octane series and shown a preferred selectivity of the SERT over the DAT for 4-(2-pyrrolyl)phenyl [10] and 4-(2-thiophenyl)phenyl [17] at the 3- position. In contrast 3-monoaryl systems demonstrated DAT selectivity [28].

We have reported that within the broad class of 8-heterobicyclo[3.2.1]octane systems, the 2β-carbomethoxy-β-aryl configured compounds showed interesting structure activity relationship (SAR) profiles [29-31]. The chair configured diastereomers demonstrated potency at DAT and SERT while the 2β-carbomethoxy-3α-aryl ones manifested far weaker potency at SERT.

To further develop a comprehensive picture about the substituent role in the inhibition effect of DAT and SERT, the synthesis of the ligands with the para- and meta-aryl phenyl groups and various heteroaryl substituents at the 3- position of oxatropanes would be important. In this regard, the present study undertook the synthesis of several oxatropene series and evaluated SAR profiles of both oxatropenes synthesized and some of their corresponding SmI₂ reduction products. We now present synthesis and binding profiles of series of II-V.

2. Results and Discussion

2.1. Chemistry

The primary goal of this study was to develop a broader understanding about the type and the nature of the side groups at the 3- position of the oxatropane skeleton on the effect of inhibiting DAT and SERT. The derivatives of the first series contained benzene units with 5-membered heteroaryl groups at the para- position. The second series provided compounds with heteroaryl substituents at the meta- position of the benzene unit. Series III furnished derivatives with heterobiarly substituents. In series IV and V, the biaryl substituents were directly connected to the tropane skeleton through the heteroring of the side groups. We recently reported the synthesis and DAT and SERT inhibitory potencies of a small series of 3-biaryloxatropanes (Series I, in Figure 2) [32]. We now report an extension of this study to include remaining series (Figure 2).

Figure 2.

Structures of 8-oxa[3.2.1]octan(en)es.

Syntheses of organostannane building blocks used to construct the targeted compounds are presented in Scheme 1. Compounds 3a-d were prepared under Stille conditions in the presence of Pd[P(Ph₃)]₄ in dioxane by the treatment of 3-bromo-1-iodobenzene with the corresponding arylstannanes and purified by column chromatography. These compounds were then treated with n-BuLi at – 70 °C in THF and reacted with Bu₃SnCl to furnish the intermediates 4a-d. Compound 4d was obtained along with 5 in approximately 1:1 ratio from the reaction of 3d as evidenced by the presence of (M+H)⁺ peaks at 452 and 529 in the mass spectra of the mixture, which correspond to the protonated molecular ion peaks of 4d and 5, respectively. In addition the coupling between compound 13 and mixture of 4d and 5 resulted in the formation of the corresponding compounds 14i and 14j in 42 % and 40 % yields, respectively, providing conclusive evidence for the ratio of compounds 4d and 5. Purification of the organostannane intermediates 4a-d by chromatographic methods resulted in significant destannylation. Therefore, they were used without purification and in slight excess in the subsequent coupling reactions. Intermediate stannanes 7a-d could be purified by fractional distillation at reduced pressure. Intermediates 10 and 12a-d were synthesized similarly.

Scheme 1.

Synthesis of organostannane intermediates.

Synthesis of the target compounds was readily achieved by the Stille cross-coupling protocol (Scheme 2). Thus reaction of triflate 13 [30] with the corresponding arylstannane intermediates in Scheme 1 produced the desired products 14a-u in high yields. Reactions were carried out in 1-methyl-2-pyrrolidinone at room temperature in the presence of ZnCl₂, tri-2-furylphosphine and tris(dibenzylideneacetone)dipalladium(0) for overnight or in dioxane at reflux temperature in the presence of tetrakis(triphenylphosphine)palladium(0) (Pd[(PPh₃)]₄) for overnight. The crude reaction mixtures were treated with 10 % aq KF to remove the tin by-product by converting it into insoluble tributyltin fluoride. Further purification was accomplished by flash chromatography on silica gel with ethyl acetate:hexane (1:9) as the eluent. When necessary, products were further purified by recrystallization. The compounds were characterized by ¹H NMR, mass spectrometry and elemental analysis.

Scheme 2.

Synthesis of 3-biaryloxatropenes via Stille coupling.

The Stille cross-coupling reaction conditions were quite successful in producing the target compounds (14e-u) in reasonably high yields (67-93 %) as seen in Table 1, comparable to the reported reactions of series I [32] (14a-d). The exception was the reaction with the benzoxazole stannane 7c intermediate for the synthesis of 14k which was obtained in 10 % yield [33].

Table 1.

The 3-biaryloxatropenes 13a-u.

R
	X	Y	% Yield		X	Y	% Yield		X	Y	% Yield		X	Y	Z	% Yield
14a	O	C	82	14e	O	C	75	14j	O	C	81	14o	S	C	H	85
b	S	C	85	f	S	C	91	k	O	N	10	P	O	C	H	93
c	NMe	C	79	g	NMe	C	93	l	S	N	67	q	NMe	C	H	80
d	S	N	79	h	S	N	42	m	S	C	78	r	S	N	H	85
								n	NH	C	56	s	O	C	Ph	80
												t	S	C	Ph	85
												u	NMe	C	Ph	80

Compounds 14h and 14i were obtained nearly equal quantities. The unintended compound 14i was the product from the coupling with the intermediate 5. The reaction with indolestannane 10 produced the target compounds 14n with 56 % yields as the major product along with lactam 15 in 10 % yields, which was conceivably formed via intramolecular lactamization. Structures of the compounds synthesized were confirmed by spectroscopic means and spectral data are provided in the experimental section.

We also utilized Suzuki conditions for the synthesis of some oxatropenes. Under the Suzuki conditions employed (Pd(PPh₃)₄, LiCl, Na₂CO₃, dioxane, reflux, 4 h) the reaction between triflate 13 and benzofuranboronic acid provided compound 14j in 82 % yield. On the other hand, the reaction between compound 13 with thiophenboronic acid furnished a complex reaction mixture. H NMR spectrum of the crude reaction mixture showed three well-resolved carbomethoxy signals with comparable intensities, indicating the presence of 14m (2,3-unsaturated) and two other products, which are presumably 3,4-unsaturated compounds one with 2α-CO₂CH₃ and the other with 2β-CO₂CH₃ orientation.

The ¹H NMR spectral data for the bicyclic skeleton of compounds 14e-u are in good agreement with the previous assignments for the 2-carbomethoxy-3-(4-heteroaryl)-8-oxa-[3.2.1]octene systems (14a-d). The chemical shifts of diagnostic skeletal protons are given in Table 2. The H₁ proton shows a doublet between δ 4.97-5.01 while H₅ appears as multiplet at δ 4.65-4.68. In addition, H_4β appears as a double doublet at δ 2.98-3.09 with the H_4α proton as a doublet at δ 2.08-2.18.

Table 2.

Diagnostic ¹H NMR data for compounds 14e-u.

Chemical shifts (ppm)
Compounds	H1	H4β(dd)	H4α(d)	H5	Compounds
O-2784	14e	5.03	2.98	2.16	4.65
O-2550	14f	4.94	3.05	2.25	4.68
O-2569	14g	5.02	2.99	2.15	4.64
O-2755	14h	4.97	3.08	2.26	4.68
O-2738	14i	4.97	3.09	2.22	4.68
O-2551	14j	4.86	3.04	2.30	4.71
O-2835	14k	4.87	3.15	2.49	4.76
O-2695	14l	4.94	3.13	2.43	4.74
O-2688	14m	4.95	3.08	2.26	4.68
O-2856	14n	5.02	3.25	2.53	4.64
O-2799	14o	4.92	3.03	2.23	4.65
O-2785	14p	4.83	2.95	2.23	4.66
O-2800	14q	5.08	2.90	2.14	4.61
O-2786	14r	4.81	3.02	2.33	4.64
O-2810	14s	4.87	2.99	2.25	4.69
O-2811	14t	4.93	3.04	2.24	4.65
O-2809	14u	5.11	2.95	2.21	4.64

The saturated target compounds (16a-u) were obtained by reduction of the 2,3-ene precursors (14a-u). Catalytic reduction provides mainly 2α-COOCH₃ compounds (diastereomer C, Figure 3) due to the preferred β-face reduction. As previously reported, 2α-COOCH₃ diastereomers are generally not effective inhibitors of DAT and SERT [6]. Therefore our method of choice employed SmI₂ in a protic solvent, which furnished 2β-carbomethoxy configured compounds (Table 4) as the predominant reduction products [30,34]. This route produced the biologically more interesting 2β,3α-configured diastereomer (A, Figure 3) in minor quantity.

Figure 3.

Synthesis of 3-(biaryl)-8-oxabicyclo[3.2.1]octane-2-carboxylic acid methyl esters.

Table 4.

2α,β-Carbomethoxy-3α,β-8-oxabicyclo[3.2.1]octanes 16a-u. Inhibition of [³H]WIN35,428 binding to the human dopamine transporter (hDAT) and [³H]citalopram binding to the human serotonin transporter (hSERT).^a

Series	Org#	Cpd	X,Y	Diastb,d (Scheme 3)	DAT	SERT
					IC50 (nM)		DAT/SERTc
	O-2504	16a	O,C	A: 2β, 3α	139	32	4
	O-2501	16b	S,C	A: 2β, 3α	356	35	10
	O-2570	16c	NCH3,C	A: 2β, 3α	>1μM	395	>2.5
	O-2993	16d	S,N	A: 2β, 3α	>1μM	128	>7
	O-2502	16e	O,C	B: 2β, 3β	64	30	2
	O-2823	16f	NCH3,C	B: 2β, 3β	>1μM	566	>2
	O-2608	16g	O,C	A: 2β, 3α	>1μM	77	>13
	O-2572	16h	S,C	A: 2β, 3α	>1μM	287	> 4
	O-2573	16j	NCH3,C	B: 2β, 3β	>1μM	142	> 7
	O-3232	16k	S,N	C: 2α, 3β	>1μM	>1μM	1
	O-2607	16l	O,C	C: 2α, 3α	39	>1μM	<0.04
	O-3245	16m	S,C	A: 2β, 3β	9	10	1
	O-2758	16n	S,C	D: 2α, 3β	18	79	0.2
	O-2967	16o	NH,C	C: 2α, 3α	350	>1μM	<0.3
	O-2969	16p	NH,C	B: 2β, 3β	110	556	0.2
	O-2968	16q	NH,C	D: 2α, 3β	370	>1μM	0.4
	O-2918	16r	S	C: 2α, 3α	487	78	6
	O-2917	16s	O	C: 2α, 3α	>1μM	640	<2
	O-3230	16t	S	D: 2α, 3β	>1μM	>1μM	1
	O-3231	16u	S	A: 2β, 3α	>1μM	>1μM	1

^aEach value is the mean of two or more independent experiments, each conducted in triplicate.

^bCompounds are racemic.

^cRatio of SERT inhibition to DAT inhibition.

^dA-D refer to the diastereomers (Figure 3)

Reduction of the bicyclo[3.2.1]octene systems with SmI₂ in THF:MeOH at –78 °C led to substrate dependent product distributions. For example, biaryl groups attached to the bicyclooctene skeleton through the phenyl ring, as in 14a-h,produced the 2β,3α (Diastereomer A) compounds 16a-d, 16g and 16h and the 2β,3β Diastereomer B) compounds 16e, 16f and 16j as the two isolable diastereomers, with the 2β,3β-chair conformer dominating (ca. 3:1 ratio). These two diastereomers (A and B) have the C2-carbomethoxyl group pointing toward the 8-oxygen of the bicyclic system. The thiazole substituent on the 3-aryl ring had a significant influence on the SmI₂ reduction. For example, compound 14d (4-thiazole: Series I) produced diastereomer A, compound 16d, in 9 % yield as compared to compound 14h (3-thiazole) in Series II provided diastereomer C, compound 16k in 23 % yield as the only isolable products.

The trend of the diastereoselectivity is less clear and the product distribution is more complex with compounds 14j-u where the heterocyclic ring is attached to the bicyclic skeleton. For example, the diastereofacial selectivity was reversed in the case of thiofuran 14o producing 2α3β (diastereomer D, 16t) as the major product with 74 % yield and 2β,3α (diastereomer A, 16u; 9 % yield), while the indole substituted compound 14n resulted in diastereomers B, C and D (16o-q) in comparable yields (14, 20 and 15 % yields, respectively). In contrast, the benzofuran derivative 14j, produced diastereomer C, 16l, as the only isolable product in 60 % yield, while the benzothiofuran derivative 14m provided A and D diastereomers, compounds 16m and 16n, with 48 % and 6 % yields, respectively.

3. Discussion

There has been extensive research in the developing potential medications for cocaine abuse. Much effort has been devoted for synthesis and biological evaluation of cocaine-like compounds where substituents at certain position were systematically changed. In this regard 3β-aryl-8-azabicyclo[3.2.1]octane-2β-carboxylates are among the most widely studied oxatropanes. Introduction of a naphthyl group into the tropane-based cocaine analogues established much significant effect in SERT affinity. Davies et. al. showed that 2- naphthyl derivative at the 3β position resulted in a very potent tropane analogue [35]. In addition, the 4-isopropyl phenyl derivative demonstrated good selectivity for SERT transporter [28]. The N-methylated 3β-(4(2-pyrrolyl)phenyl derivative showed 585-fold selectivity for SERT transporter over DAT (1.05 nM vs 614 nM), respectively [26]. On the other hand, the 3β-(5-indlyl)-8-azabicyclo[3.2.1]octanes showed binding affinities to both DAT and SERT transporters at 0.7-5.5 nM range with lack of selectivity [26,41]. In contrast, Dutta et. al. showed that replacement of the benzylic group by naphthyl moiety in structurally constrained 1,4-diazabicyclo[3.3.1]nonane systems resulted in reduction of the affinity for DAT [36]. However, the 2- naphthyl derivatives demonstrated about 3-fold more potency as compared to the 1- naphthyl derivative.

Fu and coworkers reported binding profiles of series of tropane analogues of cocaine. They saw that introduction of aryl or heteroaryl groups in the para position of 3β-phenylazatropane ring provided an increase in affinity and selectivity for SERT versus DAT and NET transporters [37].

From our laboratories, we reported high inhibition profile for 2β-carbomethoxy-3β-(2-naphthyl)-8-aza-bicyclo[3.2.1]octanes (0.49 nM for DAT and 2.19 nM for SERT) [21]. In addition, we also observed remarkable binding profiles of 2β-carbomethoxy-3β-(3,4-dichlorophenyl)-8-aza-, 8-oxa-, and 8-thiabicyclo[3.2.1]octanes, which showed comparable nanomolar potency at DAT and SERT (1.1, 3.3, 2.0 for DAT and 2.5, 4.7, 3.0 for SERT, respectively) [25].

A preliminary report [32] from these laboratories described the synthesis and DAT and SERT inhibitory potencies of compounds in Series I (Scheme 2). We reported that within a series of carboxylic acid methyl esters of (R,S)3-(4-heteroarylphenyl)-8-oxabicyclo[3.2.1]octan(en)e, the saturated 3α-aryl and 3β-aryl diastereomers were more potent inhibitors of the SERT compared with their inhibition of the DAT. We have now extended the SAR in this class by introduction of new aryl substituents at the 3-position of the 8-oxabicyclo[3.2.1]octane systems.

In this study we synthesized new series of 2,3-ene compounds 14e-u, and 2,3-oxatropanes, compounds 16e-u, and investigated their inhibitory potencies of DAT and SERT. Triflate 13 was reacted under Stille conditions with arylstannanes in Scheme 1 to obtain corresponding oxatropese 14e-u in high yields, which then were subjected to SmI₂ reduction conditions to obtain the 2,3-oxatropane diastereomers 16e-u.

The data obtained for inhibition of ligand binding at both DAT and SERT for the compounds in Table 3 and Table 4 are striking. In general, these compounds show very limited, if any, inhibitory potencies. Thus, within these series of 2,3-unsaturated compounds in Table 3, all the compounds are, at best, weak inhibitors of the DAT, 14a (102 nM), 14b (248 nM), 14j (349 nm), 14n (336 nm) and SERT (14a (248 nm), 14b (242 nm). The remaining compounds are effectively inactive at both transporters (IC₅₀ > 1μM). This is quite unlike the activity profiles we previously reported for 8-oxatropanes devoid of a 3-biaryl or a 3-(5-membered ring) system [25]. In that case, 2,3-ene-3-phenyl-(or 3-naphthyl)-8-oxatropanes manifest substantial inhibition of the DAT, as well as some considerable selectivity vs. SERT inhibition.

Table 3.

2-Carbomethoxy-3-aryl-8-oxabicylclo[3.2.1]octenes, 17a-u: Inhibition of [³H]WIN35,428^a binding to the human dopamine transporter (hDAT) and [³H]citalopram binding^b to the human serotonin transporter (hSERT).^c

Series	Org#	Cpd	X,Y	DAT	SERT
				IC50 (nM)		DAT/SERTc
	O-2546	14a	O,C	102	248	0.4
	O-2783	14b	S	272	242	1
	O-2547	14c	NCH3,C	>3μM	>3μM	1
	O-2861	14d	S,N	>3μM	>3μM	1
	O-2784	14e	O,C	>10μM	710	>14
	O-2550	14f	S,C	>10μM	>1μM	<0.7
	O-2569	14g	NCH3,C	>3μM	870	>14
	O-2755	14h	S,N	>3μM	>3μM	1
	O-2738	14i		>3μM	>3μM	1
	O-2551	14j	O,C	349	>3μM	<0.1
	O-2835	14k	O,N	>3μM	>3μM	1
	O-2695	14l	S,N	>1μM	>3μM	<0.5
	O-2668	14m	S,C	13	>2μM	<0.004
	O-2856	14n	NH,C	336	>3μM	<0.1
	O-2799	14o	S,C	>3μM	>3μM	1
	O-2785	14p	O,C	>3μM	>3μM	1
	O-2800	14q	NCH3,C	>3μM	>3μM	1
	O-2768	14r	S,N	>3μM	>3μM	1
	O-2810	14s	O	>3μM	>3μM	1
	O-2811	14t	S	>3μM	>3μM	1
	O-2809	14u	NCH3	>3μM	>3μM	1
	O-2862	15		>3μM	>3μM	1

^aBinding affinity³⁸ DAT: 12.9 nM; SERT: 160 nM.

^bBinding affinity DAT³⁹: 17.7 μm, SERT²³: 2.43 nM.

^cCompounds are racemic. Each value is the mean of two or more independent experiments, each conducted in triplicate.

^dOnly heteroatoms are identified; unidentified atoms are carbon.

^eRatio of SERT inhibition to DAT inhibition.

The exception was observed with benzothiophene substituted compound 14m in Series III with 13 nm potency and significant selectivity (< 0.004) at the DAT. The benzufora 14j, benzoxazole 14k, benzothiazole 14l and indole 14n analogues have IC₅₀ values at the DAT of 349 nM, > 3 μM, > 1 μM and 336 nM, respectively, which showed the loss of selectivity and potency. The high binding affinity of benzothiophene could be due to electronic or interaction with distant binding location or both.

In the case of 2,3-“ane” compounds, although not selective, the most potent tropane analogues are and found in series III. In this series, the benzothiophene substituted 2,3-saturated 2β3β–benzothiophene 16m demonstrated 9 nM and its 2α3β counterpart 16n showed 18 nM potencies at the DAT while they manifest IC₅₀ values of 10 and 79 nM, respectively for SERT. It is noteworthy to mention that the azatopane derivative of compound 16e as reported by Tamagnan et al demonstrated significantly higher binding profile and SERT selectivity [39]. 2β-Carbomethoxy-3 β-[2-furylphenyl]-8-azabicyclo[3.2.1]tropane and its N-methylated derivative showed 3.76 nM and 7.14 nM for DAT and 0.15 nm and 1.13 nM for SERT, respectively. In contrast, compound 16e showed 64 nM for DAT and 30 nM for SERT potencies.

It is also clear that the influence of substituent bulk at the C3 position is important. A comparison of the IC₅₀ values of the meta substituted compounds 14e,f and 16g,h to the para substituted counterparts 14a,b and 16a,b, respectively, shows that the extension site of the 5-membred heteroring, which increases bulkiness of the ligand as in the case of meta substitution, resulted in the significant loss of the binding ability to the DAT. Similar results were also reported for oxatropene with 1-naphthyl (1720 nM), 2-naphthyl (20 nM), and 2-anthracenyl (> 40,000 nM) substitution at the C3 position. The least bulkier 2-naphthyl manifests substantial DAT inhibitory potency [40]. Accordingly, these results support the notion that there is a significant sterik barrier to binding if the substituents lay transverse to the tropane skeleton as in the compounds in series II.

4. Conclusions

In this report we utilized Stille protocols for the synthesis of four novel series of oxabicyclo[3.2.1]octenes containing aryl substituents at the 3-position. SmI₂ reduction of the series II furnished 2β3α and 2β3β diastereomers as the isolable products while the remaining series produced complex product distributions. Analysis of the inhibition data obtained for these compounds demonstrates that the biaryl substitution at the 3- position of the bicyclooctene 14a-u did not have significant effect on the inhibition of WIN 35,438 nor the selectivity between DAT vs. SERT. Compound 14m was striking in that it was a DAT inhibitor (IC₅₀ = 13 nM) and quite selective (SERT IC₅₀ = >3 μM, 177 fold), while its saturated counterpart, 16m, was the most potent, but non-selective DAT and SERT inhibitor (DAT IC₅₀ = 9 nM; SERT IC₅₀ = 10 nM) in all series. The bicyclic aryl substituted oxatropenes, series III in general, and the corresponding reduction products have the strongest interaction with the binding site of DAT as compared to the remaining series.

It is important to note the fact that the relative positions of the heteroatoms in 14j-l and less so 16l-q have such an impact on potency and selectivity. In addition, compounds 14m and 16m are more similar to our 3-naphthyl compounds [21] in the earlier 8-hetero series, in contrast to that compounds in Series I, II, IV and V look very different that our earlier 3-aryl analogs [40]. This difference could be the subject of further studies including perhaps modeling studies.

5. Experimental Section

All compounds are racemates (1R/1S). NMR spectra were recorded in CDCl₃ on a JEOL 300 NMR spectrometer operating at 300.53 MHz for ¹H and 75.58 MHz for ¹³C. TMS was used as internal standard. Melting points are uncorrected and were measured on a Gallenkamp melting point apparatus. Thin-layer chromatography (TLC) was carried out on Baker Si250F plates. Visualization was accomplished with either UV exposure or treatment with phosphomolybdic acid (PMA). Flash chromatography was carried out on Baker silica gel 40 mm. Elemental analyses were performed by Atlantic Microlab, Atlanta, GA. All reactions were conducted under an inert (N₂) atmosphere.

5.1. General procedure for organostannane building blocks

A mixture of 1-bromo-3-iodobenzene (25 mmol), 1.0 equivalent of arylstannanes and 0.05 equivalent of Pd(PPh₃)₄ was refluxed under nitrogen for 5 h in dioxane (100 mL) (Scheme 1). After cooling and evaporation of the volatiles, the residue was dissolved in EtOAc (100 mL). KF solution (10 %, 50 mL) was added and the solution was stirred at room temperature for 30 min. The resultant precipitate was removed by suction filtration. The organic layer was washed with water (3 × 50 mL), dried over Na₂SO₄ and concentrated. The product was purified by flash column chromatography (eluent: hexane)

The resulting biarylbromides 2a-d (5 mmol) were treated in THF (25 mL) with n-BuLi (1.05 eq., 2.5 M in THF) at - 70 °C for 1 h followed by addition of tributyltin chloride (1.0 equiv.) via syringe. The reaction was allowed to warm to room temperature with stirring over 30 min. Hexane (50 mL) was added and the solution was washed with KF solution (10 %, 20 mL) and brine (2 × 30 mL). The organic layer was dried over Na₂SO₄ and concentrated. Attempts to purify the crude materials by column chromatography on deactivated silica or neutral alumina resulted in significant decomposition of the stannanes. Therefore, the resulting crude materials were used in the coupling reactions with the triflate without further purification.

5.1.1. 2(3-Bromophenyl)furan (3a)

Colorless oil, 80 %. ¹H NMR (CDCl₃) 7.80-7.79 (m, 1H), 7.57-7.54 (dt, 1H), 7.45-7.44 (d, 1H), 7.34-7.33 (m, 1H), 7.23-7.18 (t, 1H), 6.64-6.63 (d, 1H), 6.46-6.45 (m, 1H). ¹³C NMR δ 152.3, 142.6, 132.7, 130.2, 130.1, 126.6, 122.8, 122.2, 111.8, 106.0. Mass (M+H)⁺ = 223/225.

5.2. 2(3-Bromophenyl)thiophen (3b)

Pale yellow oil. 66 %. ¹H NMR (CDCl₃ 7.74-7.72 (m, 1H), 7.50-7.47 (m, 1H), 7.39-7.35 (m, 1H), 7.28 (s, 1H), 7.26 (s, 1H), 7.22-7-16 (t, 1H), 7.06-7.03 (m 1H). Mass (M+H)⁺ = 239/241.

5.2.1. 2-(3-Bromophenyl)-1-meyhyl-1H-pyrrole (3c)

Colorless oil 58 %. ¹H NMR δ 7.55-7.54 (t, 1H), 7.42-7.38 (dt, 1H), 7.33-7.30 (dt, 1H), 7.26-7.20 (t, 1H), 7.71-7.69 (t, 1H), 6.24-6.22 (m, 1H), 6.19-6.17 (m, 1H), 3.64 (s, 3H). δ 135,3, 132.9, 131.2, 129.8, 129.5, 126.9, 124.3, 122.4, 109.4, 107.9, 35.0. Mass (M+H)⁺ = 236/238 (100 %).

5.2.2. 2-(3-Bromophenyl)thiazole (3d)

Colorless oil 57 %. ¹H NMR (CDCl₃) δ 8.13-8.12 (t, 1H), 7.86-7.85 (d, 1H), 7.83-7.82 (m, 1H), 7.53-7.49 (m, 1H), 7.33-7.32 (d, 1H), 7.29-7.24 (t, 1H). ¹³C NMR (CDCl₃) δ 166.4, 143.8, 135.3, 132.7, 130.3, 129.3, 125.0, 123.0, 119.9. Mass (M+H)⁺ = 240/242 (100 %).

5.2.3. Tributyl-(3-furan-2-yl-phenyl)-stannane (4a)

Mass (M+H)+ = 435. The stannyl intermediate was used directly in the following step without further purification.

5.2.4. Tributyl-(3-thiophen-2-yl-phenyl)-stannane (4b)

Mass (M+H)⁺ = 451, The stannyl intermediate was used directly in the following step without further purification.

5.2.5. 1-Methyl-2-(3-tributylstannyl-phenyl)-1H-pyrrole (4c)

Mass (M+H)⁺ = 448. The stannyl intermediate was used directly in the following step without further purification.

5.2.6. 2-(3-Tributylstannanyl-phenyl)-thiazole (4d) and 2-(3-Tributylstannanyl-phenyl)-5-bromothiazole (5)

Brown oil. (M+H)⁺ = 529/531, (M+H)⁺ = 449/451. The stannyl intermediates were used directly in the following step without further purification.

5.2.7. Benzofuran-2-yl-tributylstannane (7a)

Pale yellow oil, 90 %. Bp 164 °C at 0.13 mm Hg. ¹H NMR (CDCl₃) δ 7.56-7.48 (m, 2 H), 7.22-7.16 (m, 2 H), 6.90-6.89 (m, 1 H), 1.65-1.54 (m, 6 H), 1.39-1.29 (m, 6 H), 1.27-1.12 (m, 6 H), m 0.92-0.87 (m, 9 H). ¹³C NMR (CDCl₃) 165.34, 158.62, 128.03, 123.29, 121.98, 120.22, 117.99, 110.94, 28.95, 27.19, 13.65, 10.14. Mass spectrum did not have (M+H)⁺ peak at m/z = 408. A common fragment ion at m/z = 291 for (C₁₂H₂₇Sn)⁺ was present (100 %). Anal. (C₂₀H₃₂OSn) C, H.

5.2.8. Benzo[b] thiophen-2-yl-tributylstannane (7b)

Pale yellow oil, 67.4 %, bp 174 °C at 0.13 mm Hg. ¹H NMR (CDCl₃) δ 7.90-7.87 (m, 1 H), 7.82-7.80 (m, 1 H), 7.42-7.23 (m, 3 H), 1.69-1.50 (m, 6 H), 1.42-1.30 (m, 6 H), 1.27-1.05 (m, 6 H), m 0.93-0.88 (m, 9 H). ¹³C NMR (CDCl₃) 144.31, 141.03, 139.74, 132.03, 123.66, 123.27, 122.68, 121.79, 28.97, 27.27, 13.67, 10.75. Mass spectrum did not have (M+H)⁺ peak at m/z = 424. A common fragment ion at m/z = 291 (C₁₂H₂₇Sn)⁺ was present (100 %). Anal. (C₂₀H₃₂SSn) C, H.

5.2.9. 2-Tributylstannyl-benzooxazole (7c)

Pale yellow oil, 49 %, bp > 140 °C at 0.13 mm Hg. ¹H NMR (CDCl₃) δ 7.79-7.75 (m, 1 H), 7.57-7.54 (m, 1 H), 7.32-7.26 (m, 2 H), 1.68-1.57 (m, 6 H), 1.42, 1.20 (m, 12 H), 0.92-0.87 (t, 9 H) ¹³C NMR (CDCl₃) 175.92, 152.01, 141.34, 124.32, 123.43, 119.64, 110.28, 28.76, 27.11, 13.60, 10.74. Mass (M+H)⁺ = 410 (100 %).

5.2.10. 2-Tributylstannyl-benzothoazole (7d)

Pale yellow oil, 84 %, bp 165 °C at 0.13 mm Hg. ¹H NMR (CDCl₃) δ 8.18-8.16 (m, 1 H), 7.97-7.94 (m, 1 H), 7.46-7.43 (m, 1 H), 7.39-7.33 (m, 1 H), 1.67-1.58 (m, 6 H), 1.40-1.23 (m, 12 H), 0.94-0.86 (m, 9 H). ¹³C NMR (CDCl₃) 177.66, 156.06, 136.25, 125.26, 124.35, 122.76, 121.28, 28.82, 27.20, 13.61, 11.23. Mass: (M+H)⁺ = 426 (100 %). Anal. (C₁₉H₃₁NSSn) C, H.

5.2.11. Synthesis of Tributylstannanylindol-1-carboxylic Acid Lithium Salt (10)

n-Butyllithium (2.5 M, 36 mL) was added to indole solution (10.0 g, 85.5 mmol) in THF (170 mL) under nitrogen at - 70 °C. After stirring for 30 min, excess of dry ice was added and stirring was continued at that temperature for 1 h and then allowed to warm to room temperature. Volatiles were removed to dryness and 21.5 g of white/gray solid was obtained. The solid was then dissolved in 200 mL of anhydrous THF and cooled to - 70 °C. n-BuLi (36 mL, 2.5 M), was added and mixture was stirred for 2 h. Bu₃SnCl (23.2 mL) was added via syringe and mixture was allowed to warm to room temperature. Ethyl acetate (150 mL) were added and mixtures was washed with brine (100 mL) and water (2 × 50 mL), dried over Na₂SO₄ and concentrated. The reddish oil (44.8 g) was used in the next step.

5.2.12. 2-Phenylfuran (11a)

Pale yellow oil, 79 %. ¹H NMR (CDCl₃) δ 7.70-7.66 (m, 2H), 7.47-7.46 (m, 1H), 7.41-7.35 (m, 2H), 7.28-7.23 (m, 1H), 6.65-6.64 (d, 1H), 6.43-6.46 (m, 1H). ¹³C NMR (CDCl₃) δ 153.9, 141.9, 130.8, 128.2, 127.3, 123.7, 111.6, 104.9.

5.2.13. 2-Phenylthiophen (11b)

White solid, 84 % yield, mp 33-34 °C. ¹H NMR (CDCl₃) δ 7.63-7.60 (m, 2H), 7.41-7.35 (m, 2H), 7.32-7.25 (m, 3H), 7.09-7.07 (m, 1H). ¹³C NMR (CDCl₃) δ 144.3, 134.3, 128.8, 127.9, 127.4, 125.8, 124.7, 123.

5.2.14. 1-Methyl-2-phenylpyrrole (11c)

Colorless oil, 78 %. ¹H NMR (CDCl₃) δ 7.39-7.33 (m, 4H), 7.31-7.25 (m, 1H), 6.69-6.68 (m, 1H), 6.24-6.17 (m, 2H), 3.63 (s, 3H). Mass (M+H)⁺ = 158 (100 %).

5.2.15. Tributyl-(5phenyl-furan-2-yl)-stannane (12a)

1H NMR (CDCl3) δ 7.69-7.66 (m, 2H), 7.39-7.34 (m, 2H), 7.24-7.19 (m, 1H), 6.68-6.67 (dt, 1H), 6.22-6.21 (d, 1H), 1.66-1.55 (m, 6H), 1.42-1.30 (m, 6H), 1.14-1.09 (m, 6H), 0.94-0.88 (t, 9H). ¹³C NMR CDCl₃) δ 160.9, 158.4, 131.4, 131.4, 128.6, 123.7, 123.4, 204.9, 28.9, 27.2, 13.7, 10.2.

5.2.16. 1-Methyl-2-phenyl-5-tributylstannanyl-1H-pyrrole (12c)

(M+H)⁺ = 448.

5.3. General synthesis of (R/S), 3-aryl-8-oxabicyclo[3.2.1]oct-2-ene-2-carboxylic acid methyl esters

5.3.1. Method I

Triflate 13 (1.75 g, 5.5 mmol), arylstannane (1.2 equivalent) and tetrakis(triphenylphosphine)palladium(0) (0.6 g, 10 mol %) were refluxed under nitrogen in dioxane (100 mL) for overnight. Ethyl acetate (150 mL) and 10 % aqueous KF (100 mL) were added and stirring was continued for 20 min. Precipitate formed was filtered off and the filtrate was washed with water (3 × 500 mL), dried over Na₂SO₄ and concentrated in vacuo. Further purification was done on silica gel column using EtOAc:Hexanes (1:9) as the eluent. Hexanes (1:9) as the eluent.

5.3.2. Method II

Triflate 13 (1.75 g, 5.5 mmol), arylstannane (1.2 equivalent), ZnCl₂ (11.0 mmol), tri-2-furylphosphine (0.25 g, 1.1 mmol) and tris(dibenzylideneacetone)dipalladium(0) (0.5 g, 0.5 mmol) were stirred in 1-methyl-2- pyrrolidinone (100 mL) at room temperature for overnight under nitrogen. Ethyl acetate (150 mL) and 10 % aqueous KF (100 mL) were added and stirring was continued for 20 min. Precipitate formed was filtered off and the filtrate was washed with water (3 × 500 mL), dried over Na₂SO₄ and concentrated in vacuo. Further purification was done on silica gel column using EtOAc:Hexanes (1:9) as the eluent. Hexanes (1:9) as the eluent.

5.3.3. Spectral Data

5.3.3.1. (R,S) 3-(3-Furan-2-yl-phenyl)-8-oxa-bicyclo[3.2.1]oct-2-ene-2-carboxylic acid methyl ester (14e)

White solid, 75 % yield, mp 81-81 °C. ¹H NMR (CDCl₃) δ 7.60-7.57 (m, 1H), 7.45-7.43 (m, 2H), 7.36-7.31 (t, 1H), 7.02-6.99 (m, 1H), 6.64-6.63 (d, 1H), 6.47-6.46 (m, 1H). 5.03-5.02 (d, 1H), 4.67-4.63 (m, 1H), 3.49 (s, 3H), 3.02-2.94 (dd, 1H), 2.22-2.13 (m, 4H), 1.84-1.78 (m, 1H). ¹³C NMR (CDCl₃) δ 166.4, 153.6, 144.6, 142.0, 141.4, 130.6, 128.3, 125.7, 122.9, 122.0, 11.7, 105.2, 73.4, 73.1, 51.3, 41.5, 35.6, 29.8. Mass (M+H)⁺ = 311 (60 %), (M-OCH₃)⁺ = 279 (100 %). Anal. (C₁₉H₁₈O₄) C, H.

5.3.3.2. (R,S) 3-(3-Thiophen-2-yl-phenyl)-8-oxa-bicyclo[3.2.1]oct-2-ene-2-carboxylic acid methyl ester (14f)

Pale yellow solid, 91 % yield, mp 93-94 °C. ¹H NMR (CDCl₃) δ 7.59-7.56 (m, 2H), 7.39-7.35 (m, 2H), 7.35-7.24 (m, 1H), 7.20-7.18 (d, 1H), 7.01-7.00 (m, 1H), 4.95-4.93 (d, 1H), 4.69-4.67 (m, 1H), 3.71 (s, 3H), 3.09-3.02 (dd, 1H), 2.29-2.05 (m, 4H), 1,84-1.72 (m, 1H). ¹³C NMR (CDCl₃) δ 167.5, 144.8, 140.5, 133.9, 133.1, 132.0, 128.9, 127.7, 127.4, 125.7, 122.8, 74.00, 73.1, 51.8, 40.5, 35.2, 29.6. Mass (M+H)⁺ = 327 (100 %), (M-OCH₃)⁺ = 295 (15 %). Anal. (C₁₉H₁₈O₃S ) C, H .

5.3.4. (R,S) 3-[3-(1-Methyl-1H-pyrrol-2-yl)-phenyl]-8-oxa-bicyclo[3.2.1]oct-2-ene-2-carboxylic acid methyl ester (14g)

Pale yellow oil, 93 % yield. ¹H NMR (CDCl₃) δ 7.37-7.29 (m, 2H), 7.14-7.13 (m, 1H), 7.06-7.02 (dt, 1H), 6.71-6.70 (t, 1H), 6.22-6.16 (m, 2H), 5.04-5.00 (d, 1H), 4.67-4.62 (m, 1H), 3.64 (s, 3H), 3.51 (s, 3H), 3.03-2.95 (dd, 1H), 2.26-2.04 (m, 4H), 1.83-1.73 (m, 1H). ¹³C NMR (CDCl₃) δ 166.3, 144.8, 141.0, 134.2, 133.0, 131.7, 128.0, 127.7, 127.0, 125.0, 123.7, 108.6, 107.7, 73.4, 73.1, 51.3, 41.7, 35.6, 35.0, 29.8 . Mass (M+H)⁺ = 324 (100 %). Anal. (C₂₀H₂₁NO₃) C, H, N.

5.3.4.1. (R,S) 3-(3-Thiazol-2-yl-phenyl)-8-oxabicyclo[3.2.1]oct-2-ene-2-carboxylic acid methyl ester (14h)

Pale yellow, 42 % yield, mp 92-94 °C. ¹H NMR (CDCl₃) δ 7.94-7.91 (m, 2H), 7.75 (s, 1H), 7.45-7.40 (m, 3H), 4.98-4.96 (d, 1H), 4.69-4.67 (m, 1H), 3.72 (s, 3H), 3.12-3.04 (dd, 1H), 2.28-2.04 (m, 4H), 1.80-1.78 (m, 1H). ¹³C NMR (CDCl₃) δ 168.4, 166.6, 142.5, 135.6, 133.6, 133.3, 130.9, 129.2, 128.9, 126.4, 73.8, 72.9, 51.9, 40.8, 35.1, 29.6. Mass (M+H)⁺ = 328 (100 %). Anal. (C₁₈H₁₇NO₃S) C, H, N.

5.3.4.2. (R,S)-3-[2-(3-Bromophenyl)-thiazol-5-yl]-8-oxa-bicyclo[3.2.1]oct-2-ene-2-carboxylic acid methyl ester (14i)

Pale yellow solid, 40 % yield, mp 92-94 °C. ¹H NMR (CDCl₃) δ 8.11-8.10 (t, 1H), 7.85-7.82 (m, 1H), 7.76 (s, 1H), 7.56-7.52 (m, 1H), 7.33-7.27 (t, 1H), 4.98-4.96 (d, 1H), 4.70-4.66 (m, 1H), 3.73 (s, 3H), 3.12-3.05 (dd, 1H), 2.28-2.05 (m, 4H), 1.79-1.72 (m, 1H). ¹³C NMR (CDCl₃) δ 166.4, 142.7, 136.3, 135.2, 134.0, 132.9, 130.9, 130.4, 129.2, 125.0, 123.1, 73.8, 72.9, 51.9, 40.9, 35.2, 29.6. Mass (M+H)⁺ = 406/408 (100 %). Anal. (C₁₈H₁₆BrNO₃S ) C, H, N.

5.3.4.3. Synthesis of (RS), 3 -Benzofuran-2-yl-8-oxa-bicyclo[3.2.1]oct-2-ene-2--carboxylic acid methyl ester (14j)

White solid 81 % yield, mp 95-96 °C. ¹H NMR (CDCl3) δ 7.55-7.52 (m, 1H), 7.40-7.37 (m, 1H), 7.30-7.25 (dt, 1H), 7.22-7.17 (dt, 1H), 6.74-6.71 (d, 1H), 4.87-4.85 (d, 1H), 4.74-4.69 (m, 1H), 3.81 (S, 3H), 3.08-3.01 (dd, 1H), 2.32-2.09 (m, 4H), 1.82-1.77 (m, 1H). ¹³C NMR (CDCl3) δ 168.4, 154.6, 153.3, 135.6, 133.1, 128.1, 125.0, 122.9, 121.3, 110.9, 105.6, 74.0, 72.9, 52.0, 35.4, 35.1, 29.4. Mass. (M+H)+ = 285 (70 %), (M-OCH3)+ = 253 (100 %). Anal. (C17H16O4) C, H.

5.3.4.4. Synthesis of (RS), 3 -Benzoxazol-2-yl-8-oxa-bicyclo[3.2.1]oct-2-ene-2--carboxylic acid methyl ester (14k)

Pale yellow solid, 10 % yield. mp 85-86 °C. ¹H NMR (CDCl₃) δ 7.75-7.70 (m, 1H), 7.50-7.45 (m, 1H), 7.38-7.31 (m, 2H), 4.88-4.86 (d, 1H), 4.79-4.74 (m, 1H), 3.81 (s, 3H), 3.19-3.11 (dd, 1H), 2.53-2.47 (d, 1H), 2.32-2.20 (m, 2H), 2.18-2.10 (m, 1H), 1.86-1.82 (m, 1H). ¹³C NMR (CDCl₃) δ. 167.4, 160.9, 150.3, 141.3, 141.1, 125.6, 124.6, 123.2, 120.3, 110.5, 73.9, 73.0, 52.4, 35.2, 29.5. Mass. (M+H)⁺ = 286 (100 %). Anal. (C₁₆H₁₅NO₄) C, H, N.

5.3.4.5. (R,S) 3-Thiazole-2-yl-8-oxa-bicyclo[3.2.1]oct-2-ene-2-carboxylic acid methyl ester (14l)

Method II, colorless oil, 67 % yield. ¹H NMR (CDCl₃) δ 8.03-8.00 (m, 1H), 7.89-7.86 (m, 1H), 7.55-7.45 (m, 1H), 7.42-7.36 (m, 1H), 4.95-4.93 (d, 1H), 4.76-4.72 (m, 1H), 3.70 (s, 3H), 3.17-3.09 (dd, 1H), 2.47-2.41 (d, 1H), 2.31-2.11 (m, 3H), 1.92-1.83 (m, 1H). . ¹³C NMR (CDCl₃) δ 166.8, 165.7, 153.1, 137.7, 135.2, 132.4, 126.2, 125.4, 123.4, 121.5, 73.7, 73.1, 52.1, 38.4, 35.2, 29.7. Mass. (M+H)⁺ = 302 (100 %), (M-OCH₃)⁺ = 270 (10 %).

5.3.4.6. (R,S)-3-[2-Benzothiophen-2-yl] -8-oxa-bicyclo[3.2.1]oct-2-ene-2carboxylic acid methyl ester (14m)

White solid 78 % yield, mp 84-86 °C. ¹H NMR (CDCl₃) δ 7.79-7.76 (m, 1H), 7.74-7.71 (m, 1H), 7.37-7.30 (m, 2H), 7.18 (s, 1H), 4.96-4.94 (d, 1H), 4.70-4.66 (m, 1H), 3.65 (s, 3H), 3.11-3.04 (dd, 1H), 2.30-2.20 (m, 4H), 1.85-1.76 (m, 1H). ¹³C NMR (CDCl₃) δ 167.1, 141.6, 139.7, 139.4, 134.2, 133.8, 124.6, 124.4, 123.7, 122.4, 122.1, 73.9, 73.1, 51.9, 40.8, 35.3, 29.7. Mass. (M+H)⁺ = 301 (60 %), (M-OCH₃)⁺ = 269 (100 %). Analysis. (C₁₇H₁₆O₃S) C, H.

5.3.4.7. (RS), 3-(1H-Indol-2-yl)-8-oxa-bicyclo[3.2.1]oct-2-ene-2--carboxylic acid methyl ester (14n)

Method II, light yellow solid, 56 % yield. mp 132-134 °C. ¹H NMR (CDCl₃) δ 7.59-7.56 (d, 1H), 7.41-7.38 (m, 1H), 7.23-7.18 (m, 1H), 7.09-7.03 (m, 1H), 6.74-6.73 (m, 1H), 5.03-5.01 (m, 1H), 4.66-4.62 (m, 1H), 3.79 (s, 3H), 3.28-3.21 (dd, 1H), 2.56-2.50 (d, 1H), 2.16-2.-7 (m, 3H), 1.69-1.62 (m, 1H). ¹³C NMR (CDCl₃) δ 168.3, 136.4, 135.3, 127.2, 127.1, 123.7, 120.8, 119.8, 111.6, 105.6, 73.9, 72.8, 52.2, 37.9, 35.4, 29.3. Mass. (M+H)⁺ = 284 (100 %). Anal. (C₁₇H₁₇NO₄). C, H, N.

5.3.4.8. (R,S) 3-Thiophen-2-yl-8-oxa-bicyclo[3.2.1]oct-2-ene-2-carboxylic acid methyl ester (14o)

Method I, yellow solid, 85 % yield. ¹H NMR (CDCl₃) δ 7.29-7.26 (m, 1H), 7.01-7.98 (m, 2H), 4.92-4.91 (d, 1H), 4.67-4.63 (m, 1H), 3.67 (s, 3H), 3.07-2.99 (dd, 1H), 2.25-2.04 (m, 4H), 1.81-1.72 (m, 1H). ¹³C NMR (CDCl₃) δ 167.4, 1412.3, 133.3, 132.3, 126.8, 126.1, 125.8, 73.8, 73.1, 51.7, 40.8, 35.1, 29.6. Mass (M+H)⁺ = 251 (50 %) (M-OCH₃)⁺ = 219 (100 %). Anal. (C₁₃H₁₄O₃S). C, H, S.

5.3.4.9. (R,S) 3-Furan-2-yl-8-oxa-bicyclo[3.2.1]oct-2-ene-2-carboxylic acid methyl ester (14p)

Method I, yellow solid. 93 % yield, mp 56-57 °C. ¹H NMR (CDCl₃) δ 7.37-7.36 (d, 1H), 7.52-7.52 (d, 1H), 6.40-6.38 (m, 1H), 4.84-4.82 (d, 1H), 4.68-4.64 (m, 1H), 3.77 (s, 3H), 2.99-2.91 (dd, 1H), 2.26-2.02 (m, 4H), 1.78-1.72 (m, 1H) ¹³C NMR (CDCl₃) δ 168, 151.4, 142.5, 130.1, 111.1, 109.8, 73.7, 72.7, 51.6, 35.4, 35.3, 29.3. Mass (M+H)⁺ = 235 (100 %) (M-OCH₃)⁺ = 203 (80 %). Anal. (C₁₃H₁₄O₄) C, H.

5.3.4.10. (R,S) 3-(1-Methyl-1H-pyrrol-2-yl-8-oxa-bicyclo[3.2.1]oct-2-ene-2-carboxylic acid methyl ester (14q)

Method I, pale yellow oil, 80 % yield. ¹H NMR (CDCl₃) δ 6.65-6.63 (M, 1H), 6.15-6.13 (M, 1H), 6.01-5.99 (M, 1H), 5.09-5.07 (M, 1H), 4.63-4.59 (M, 1H), 3.62 (S, 3H), 3.41 (S, 3H), 2.94-2.86 (DD, 1H), 2.20-2.-06 (M, 4H), 1.79-1.69 (M, 1H). ¹³C NMR (CDCl₃) δ 165.5, 137.2, 133.4, 131.9, 107.8, 107.7, 73.4, 73, 71.7, 42.4, 33.9, 29.6. Mass (M+H)⁺ = 248 (100 %) (MOCH₃)⁺ = 216 (30 %). Anal. C₁₄H₁₇NO₃) C, H, N.

5.3.4.11. (R,S) 3-Thiazol-2-yl-8-oxa-bicyclo[3.2.1]oct-2-ene-2-carboxylic acid methyl ester (14r)

Method I, yellow oil, 85 % yield. ¹H NMR (CDCl₃) 7.81-7.80 (d, 1H), 7.35-7.34 (d, 1H), 4.89-4.87 (d, 1H), 4.74-4.70 (m, 1H), 3.72 (s, 3H), 3.13-3.05 (dd, 1H), 2.44-2.38 (d, 1H), 2.29-2.17 (m, 2H), 2.15-2.07 (m, 1H), 1.88-1.74 (m, 1H). ¹³C NMR (CDCl₃) 167.43, 165.1, 142.9, 135.9, 130.9, 119.7, 73.7, 73.1, 52, 38.1, 35.1, 29.5. Mass (M+H)⁺ = 252 (100 %) (M-OCH₃)⁺ = 220 (20 %). Anal. (C₁₂H₁₃NO₃S) C, H, S, N.

5.3.4.12. (R,S) 3-(5-Phenyl-furan-2-yl)-8-oxa-bicyclo[3.2.1]oct-2-ene-2-carboxylic acid methyl ester (14s)

Method I, white solid. 80 % yield, mp 85-87 °C. ¹H NMR (CDCl₃) δ 7.62-7.60 (m, 2H), 7.40-7.35 (m, 2H), 7.28-7.26 (m, 1H), 6.67-6.65 (d, 1H), 6.61-6.58 (d, 1H), 4.87-4.86 (d, 1H), 4.71-4.67 (m, 1H), 3.77 (s, 3H), 3.05-3.98 (dd, 1H), 2.30-2.04 (m, 4H), 1.82-1.67 (m, 1H). ¹³C NMR (CDCl₃) δ 169, 154, 150, 130.3, 130, 129, 128, 125, 124, 112, 107, 74, 73, 52, 35, 30. Mass (M+H)⁺ = 310 (100 %) (M-OCH₃)⁺ = 279 (30 %). Anal. (C₁₉H₁₈O₄) C, H.

5.3.4.13. (R,S) 3-(5-Phenyl-thiophrn-2-yl)-8-oxa-bicyclo[3.2.1]oct-2-ene-2-carboxylic acid methyl ester (14t)

Method I, yellow solid. 85 % yield, mp 92-93 °C. ¹H NMR (CDCl₃) δ 7.58-7.55 (m, 2H), 7.39-7.33 (m, 2H), 7.30-7.24 (m, 1H), 7.19-7.18 (d, 1H), 7.00-6.99 (d, 1H), 4.94-4.92 (d,1H), 4.68-4.63 (m, 2H), 3.70 (s, 3H), 3.08-3.01 (dd, 1H), 2.28-2.13 (m, 4H), 1.79-1.75 (m, 1H). ¹³C NMR (CDCl₃) δ 167.5, 144.8, 133.9, 133, 128.8, 127.7, 125.7, 122.8, 73.9, 73.1, 51.8, 40.4, 35.1, 29.6. Mass (M+H)⁺ = 327 (100 %) (M-OCH₃)⁺ = 295 (20 %). Anal. (C₁₉H₁₈O₃S). C, H, S.

5.3.4.14. (R,S) 3-(1-Methyl-1H-pyrrol-4-phenyl)-2-yl-8-oxa-bicyclo[3.2.1]oct-2-ene-2-carboxylic Acid Methyl Ester (14u)

Method I, pale yellow oil, 80 % yield. ¹H NMR (CDCl3) δ 6.65-6.63 (M, 1H), 6.15-6.13 (M, 1H), 6.01-5.99 (M, 1H), 5.09-5.07 (M, 1H), 4.63-4.59 (M, 1H), 3.62 (S, 3H), 3.41 (S, 3H), 2.94-2.86 (DD, 1H), 2.20-2.-06 (M, 4H), 1.79- 1.69 (M, 1H). ¹³C NMR (CDCl3) δ 165.5, 137.2, 133.4, 131.9, 107.8, 107.7, 73.4, 73, 71.7, 42.4, 33.9, 29.6. Mass (M+H)+ = 248 (100 %) (MOCH3)+ = 216 (30 %). Anal. (C14H17NO3) C, H, N.

5.3.4.15. Compound 15

Yellow solid, 10 % yield, mp 171-172 °C. ¹H NMR (CDCl₃) δ 7.64-7.61 (m, 1H), 7.36-7.33 (d, 1H), 7.26-7.20 (dt, 1H), 7.07-7.01 (dt, 1H), 6.28 (s, 1H), 4.94-4.92 (m, 1H), 4.78-4.73 (m, 1H), 3.03-2.95 (dd, 1H), 2.31-2.08 (m, 4H), 1.77-1.70 (m, 1H). ¹³C NMR (CDCl₃) δ 162.5, 140.7, 140.6, 138.6, 134.4, 133.5, 127.3, 122.8, 122.6, 112.0, 105.8, 72.3, 70.3, 35.6, 31.9, 29.8. Mass. (M+H)⁺ = 252 (100 %). Anal. (C₁₆H₁₃NO₂) C, H, N.

5.4. General procedure for SmI₂ reduction

Compounds 14 (2-5 mmol) were dissolved in THF:MeOH or THF:2-propanol (9:1, 30 mL) in pre-degassed flask and cooled to - 78 °C. Samarium iodide (0.1 M in pentane, 3 eq.) was added via syringe and, after stirring for 15 min., solution was allowed to warm up to room temperature. Solvent was removed and residue was taken into EtOH:brine, and washed with brine, dried over Na₂SO₄ and concentrated. Further purification was done on column (silica gel, ~100 g) using 10 % ethyl acetate in hexane as the eluent.

5.4.1. (R,S) 3α-(3-(2-Furyl)phenyl)-8-oxa-bicyclo[3.2.1]octane-2 β-carboxylic acid methyl ester (16g)

65 %. White solid, mp 94-96 °C. ¹H NMR (CDCl₃) δ 7.54-7.46 (m, 3H), 7.32-7.27 (t, 1H), 7.14-7.11 (d, 1H), 6.65-6.64 (dd, 1H), 6.48-6.46 (m, 1H), 4.55-4.50 (m, 2H), 3.58 (s, 3H), 3.35-3.26 (m, 1H), 2.61-2.57 (dd, 1H), 2.49-2.40 (m, 1H), 2.20-1.95 (m, 2H), 1.85-1.76 (m, 1H), 1.73-1.64 (m, 1H), 1.50-1.42 (dt, 1H). ¹³C NMR (CDCl₃) δ 174.5, 153.9, 143.4, 142.0, 130.9, 128.7, 126.7, 122.9, 122.1, 111.6, 105.0, 74.6, 72.3, 54.9, 51.8, 36.8, 36.1, 31.6, 31.5. Mass (M+H)⁺ = 313 (100 %), (M-OCH₃)⁺ = 285 (85 %), (M-COOCH₃)⁺ = 253 (7 %). Anal. (C₁₉H₂₀O₄) C, H.

5.4.1.1. (R,S) 3 α-(3-(2-N-Methylpyrrol)phenyl)-8-oxa-bicyclo[3.2.1]octane-2 β-carboxylic acid methyl ester (16h)

Colorless oil, 57 % yield. ¹H NMR (CDCl₃) δ 7.34-7.27 (m, 2H), 7.24-7.21 (m, 1H), 7.19-7.16 (m, 1H), 6.71-6.70 (t, 1H), 6.21-6.19 (m, 2H), 4.70-4.66 (m, 2H), 3.65 (s, 3H), 3.49 (s, 3H), 3.27-3.21 (m, 1H), 2.89-2.77 (m, 2H), 2.1902.01 (m, 2H), 1.98-1.89 (m, 1H), 1.85-1.78 (m, 1H), 1.69-1.63 (m, 1H). ¹³C NMR (CDCl₃) δ 171.6, 142.3, 134.7, 133.0, 128.1, 127.6, 126.6, 125.6, 123.5, 108.4, 107.7, 75.4, 51.6, 51.3, 35.0, 33.4, 32.3, 29.1, 28.1. Mass (M+H)⁺ = 326. Analysis. (C₂₀H₂₃ NO₃) C, H, N.

5.4.2. (R,S) 3 β-(3-(2-Furyl)phenyl)-8-oxa-bicyclo[3.2.1]octane-2 β-carboxylic acid methyl ester (16i)

¹H NMR (CDCl₃) δ 7.55 (s, 1H), 7.50-7.47 (dd, 1H), 7.45-7.44 (dd, 1H), 7.32-7.27 (t, 1H), 7.17-7.14 (m, 1H), 6.63-6.62 (dd, 1H), 6.46-6.44 (m, 1H), 4.71-4.66 (m, 2H), 3.48 (s, 3H), 3.28-3.20 (m, 1H), 2.89-2.76 (m, 2H), 2.22-1.90 (m, 3H), 1.85-1.77 (m, 1H), 1.68-1.62 (m, 1H). ¹³C NMR (CDCl₃) δ 171.6, 154.0, 142.7, 141.8, 130.6, 128.4, 126.1, 122.6, 121.8, 111.5, 104.8, 76.6, 75.3, 51.6, 51.2, 33.4, 32.2, 29.0, 28.0. Mass (M+H)⁺ = 313 (100 %), (M-OCH₃)⁺ = 285 (90 %). Anal. (C₁₉H₂₀O₄) C, H.

5.4.3. (R,S) 3 β-(3-(2-N-Methylpyrrol)phenyl)-8-oxa-bicyclo[3.2.1]octane-2 β-carboxylic acid methyl ester (16j)

Colorless oil, 17 % yield. ¹H NMR (CDCl₃) δ 7.33-7.21 (m, 3H), 7.18-7.15 (dt, 1H), 6.72-6.71 (t, 1H), 6.22-6.19 (m, 2H), 4.54-4.49 (m, 2H), 3.64 (s, 3H), 3.59 (s, 3H), 3.34-3.25 (m, 1H), 2.58-2.54 (dd, 1H), 2.47-2.40 (m, 1H), 2.16-2.09 (m, 1H), 2.06-1.95 (m, 1H), 1.83-1.75 (m, 1H), 1.70-1.61 (m, 1H), 1.49-1.38 (dt, 1H). ¹³C NMR (CDCl₃) δ 174.5, 143.0, 134.6, 133.3, 128.6, 128.1, 126.8, 123.6, 108.5, 107.7, 74.6, 72.2, 55.1, 51.8, 37.1, 36.1, 35.0, 31.7, 31.6. Mass (M+H)⁺ = 326. Anal. C₂₀H₂₃NO₃) C, H, N.

5.4.4. (R,S) 3 α-(3-(2-Thiazole)phenyl)-8-oxa-bicyclo[3.2.1]octane-2 α-carboxylic acid methyl ester (16k)

White solid, mp 134-135 °C. ¹H NMR (CDCl₃) δ 7.90-7.87 (m, 2H), 7.59 (s, 1H), 7.44-7.40 (m, 3H), 7.26 (s, 1H), 4.57-4.55 (m, 2H), 3.67-3.64 (m, 1H), 3.63 (s, 3H), 3.05-3.01 (dd, 1H), 2.09-1.97 (m, 3H), 1.96-1.87 (m, 3H). . ¹³C NMR (CDCl₃) δ 171.8, 166.7, 141.8, 140.5, 133.7, 129.8, 128.9, 128.8, 128.3, 126.2, 75.9, 75.1, 54.1, 53.9, 50.0, 39.6, 39.4, 30.0, 29.6, 28.4, 25.7. Mass (M+H)⁺ = 330. Anal. (C₁₈H₁₉NO₃S) C, H, N, S.

5.4.5. (R,S) 3 α-Benzofuran-2-yl-8-oxa-bicyclo[3.2.1]octane-2 α-carboxylic acid methyl ester (16l)

Semi solid, 60 % yield. ¹H NMR (CDCl₃). δ 7.51-7.48 (m, 1H), 7.42-7.39 (m, 1H), 7.26-7.17 (m, 2H), 6.53-6.52 (m, 1H), 4.80-4.48 (d, 1H), 4.50-4.46 (t, 1H), 3.86-3.81 (m, 1H), 3.80 (s, 3H), 3.21 (s, 1H), 2.54-2.46 (m, 1H), 2.07-2.02 (m, 1H), 1.98-1.81 (m, 2H), 1.78-1.71 (m, 1H), 1.65-1.57 (m, 1H). ¹³C NMR (CDCl₃). δ 173.4, 160.4, 154.2, 128.6, 123.5, 122.7, 120.3, 110.8, 101.3, 75.00, 74.0, 52.2, 48.0, 30.5, 29.2, 28.4, 28.1. Mass (M+H)⁺ = 287 (100 %), (M-OCH₃)⁺ = 255 (65 %), (M-CO₂CH₃)⁺ = 227 (35 %). Analysis. (C₁₇H₁₈O₄) Calc. C: 71.31, H: 6.34. Found. C: 71.39, H: 6.50

5.4.6. (R,S) 3 α-Benzo[b] thiophen-2-yl-8-oxa-bicyclo[3.2.1]-octane-2 β-carboxylic acid methyl ester (16m)

White solid, 48 % yield, mp: 117-119 °C. ¹H NMR (CDCl₃) δ 7.77-7.74 (m, 1H), 7.67-7.64 (m, 1H), 7.34-7.24 (m, 2H), 7.11-7.10 (d, 1H), 4.71-4.69 (d, 1H), 4.50-4.47 (m, 1H), 3.87-3.84 (m, 1H), 3.74 (s, 3H), 2.91-2.89 (d, 1H), 2.64-2.55 (m, 1H), 2.01-1.92 (m, 1H), 1.90-1.71 (m, 4H). ¹³C NMR (CDCl₃) δ 173.6, 149.5, 139.8, 138.6, 124.2, 123.7, 122.9, 122.0, 119.7, 74.9, 73.4, 52.8, 52.2, 34.8, 31.6, 29.3. Mass (M+H)⁺ = 303 (100 %), (MOCH₃)⁺ = 271 (60 %), (M+ CO₂CH₃)⁺ = 243 (10 %). Analysis. (C₁₇H₁₈O₃S) C, H, S.

5.4.7. (R,S) 3 β-Benzo[b] thiophen-2-yl-8-oxa-bicyclo[3.2.1]-octane-2 α-carboxylic acid methyl ester (16n)

Yellow oil, 6 % yield. ¹H NMR (CDCl₃) δ. 7.75-7.72 (m, 1H), 7.68-7.65 (m, 1H), 7.32-7.21 (m, 2H), 7.06 (s, 1H), 4.70-4.64 (m, 2H), 3.65 (s, 3H), 3.54-3.45 (m, 1H), 2.93-2.91 (d, 1H), 2.86-2.77 (m, 1H), 2.22-2.03 (m, 2H), 1.97-1.90 (m, 1H), 1.89-1.78 (m, 2H). ¹³C NMR (CDCl₃) δ. 171.4, 147.5, 139.9, 138.6, 124.1, 123.6, 122.1, 119.9, 76.5, 75.3, 51.7, 45.6, 33.9, 31.1, 28.8, 28.1. Mass (M+H)⁺ = 303.

5.4.8. (R,S) 3 α-(1H-Indol-2-yl)-8-oxa-bicyclo[3.2.1]-octane-2 α-carboxylic acid methyl ester (16o)

Pale yellow solid, 14 % yield. 176-178 °C. ¹H NMR (CDCl₃) δ 8.22 (s, 1H), 7.54-7.51 (d, 1H), 7.283-7.280 (d, 1H), 7.13-7.07 (m, 2H), 6.298-6.294 (d, 1H), 4.65-4.63 (d, 1H), 4.54-4.49 (m, 1H), 3.75 (s, 3H), 3.71-3.62 (m, 1H), 2.73-2.70 (dd, 1H), 2.61-2.52 (m, 1H), 2.07-1.93 (m, 1H), 1.92-1.83 (m, 1H), 1.82-1.70 (m, 3H), ¹³C NMR (CDCl₃) δ Mass. (M+H)⁺ = 286. Anal. (C₁₇H₁₉NO₃) C, H, N.

5.4.9. (R,S) 3 β-(1H-Indol-2-yl)-8-oxa-bicyclo[3.2.1]-octane-2- β-carboxylic acid methyl ester (16p)

Pale yellow solid. 20 % yield, mp 222-224 °C. ¹H NMR (CDCl₃) δ 8.95 (s, 1H), 7.53-7.50 (d, 1H), 7.35-7.32 (d, 1H), 7.12-7.05 (m, 2H), 6.278-6.273 (d, 1H), 4.72-4.68 (d, 1H), 4.62-4.58 (m, 1H), 3.65 (s, 3H), 3.48-3.40 (m, 1H), 2.83-2.73 (m, 2H), 2.21-2.05 (m, 2H), 2.02-1.82 (m, 2H), 1.57-1.55 (m, 1H). ¹³C NMR (CDCl₃) δ 173.4, 139.7, 136.0, 127.6, 121.2, 119.8, 119.4, 110.8, 100.5, 75.4, 51.7, 51.1, 34.2, 29.5, 29.6, 28.0. Mass. (M+H)⁺ = 286. Anal. (C₁₇H₁₉NO₃) C, H, N.

5.4.10. (R,S) 3 β-(1H-Indol-2-yl)-8-oxa-bicyclo[3.2.1]-octane-2- α-carboxylic acid methyl ester (16q)

Pale yellow solid. 15 % yield, mp decomposed > 150 °C. ¹H NMR (CDCl₃) δ 8.40 (s, 1H), 7.54-7.51 (d, 1H), 7.307-7.305 (d, 1H), 7.12-7.05 (m, 2H), 6.274-6.270 (d, 1H), 4.59-4.56 (m, 2H), 3.64 (s, 3H), 3.56-3.45 (m, 1H), 3.00-2.95 (dd, 1H), 2.24-2.15 (dt, 1H), 2.09-2.02 (m, 1H), 1.99-1.93 (m, 1H), 1.91-1.80 (m, 3H), ¹³C NMR (CDCl₃) δ Mass. (M+H)⁺ = 286. Anal. (C₁₇H₁₉NO₃) C, H, N.

5.4.11. (R,S) 3 α-(5-Phenyl-thiophen-2-yl)-8-oxa-bicyclo[3.2.1]octane-2 α-carboxylic acid methyl ester (16r)

Colorless semi-solid. ¹H NMR (CDCl₃) δ 7.56-7.54 (m, 2H), 7.37-7.32 (m, 2H), 7.32-7.24 (m, 1H), 7.13-7.11 (d, 1H), 6.85-6.84 (m, 1H), 4.68-4.66 (m, 1H), 4.50-4.48 (m, 1H), 3.79-3.69 (m, 4H), with a singlet at 3.74 for 3H), 2.82-2.80 (dd, 1H), 2.62-2.52 (m, 1H), 1.99-1.75 (m, 5H). ¹³C NMR (CDCl₃) δ: 173.8, 148.2, 141.9, 134.3, 128.8, 127.2, 125.4, 124.2, 123, 74.9, 73.3, 53.3, 52.2, 35.2, 31.2, 29.5. Mass (M+H)⁺ = 329 (100 %). Anal. (C₁₉H₂₀O₃S) C, H, S.

5.4.12. (R,S) 3 α-(5-Phenyl-furan-2-yl)-8-oxa-bicyclo[3.2.1]octane-2 α-carboxylic Acid Methyl Ester (16s)

Colorless oil. ¹H NMR (CDCl₃) 7.62-7.59 (m, 2H), 7.39-7.32 (m, 2H), 7.24-7.19 (m,2H), 6.59-6.56 (d, 1H), 6.18-6.17 (m, 1H), 4.78-4.76 (d, 1H), 4.45-4.42 (m, 1H), 3.78 (s, 3H), 3.12 (s, 1H), 2.49-2.41 (m, 1H), 1.99-1.87 (m, 2H), 1.87-1.71 (m, 1H), 1.68-1.65 (m, 1H), 1.65-1.60 (m, 1H). ¹³C NMR (CDCl₃) δ: 173.4, 156.7, 151.9, 130.7, 128.5, 126.9, 123.3, 106.4, 105.7, 74, 73.7, 52.1, 48, 30.5, 28.8, 27.9. Mass (M+H)⁺ = 313 (100 %). Anal. (C₁₉H₂₀O₄). C, H.

5.4.13. (R,S) 3 β-Thiophen-2-yl-8-oxa-bicyclo[3.2.1]octane-2 α-carboxylic Acid Methyl Ester (16t)

Pale yellow oil. 74 % yield. ¹H NMR (CDCl₃) δ 7.09-7.06 (m, 1H), 6.84-6.8-0 (m, 2H), 4.59-4.57 (m, 1H), 4.42-4.48 (m, 1H), 3.70-3.60 (m, 4H), 3.67 (s, 3H), 2.72-2.70 (dd, 1H), 2.54-2.44 (m, 1H), 1.94-1.60 (m, 6H). ¹³C NMR (CDCl₃) δ: 173.8, 148.6, 126.6, 123.2, 123, 74.9, 73.3, 53.7, 52.1, 35.5, 30.9, 29.5. Mass (M+H)⁺ = 252 (90 %) (M-OCH₃)⁺ = 221 (100 %). Anal. (C₁₃H₁₆O₃S). C, H, S.

5.4.14. (R,S) 3 α-Thiophen-2-yl-8-oxa-bicyclo[3.2.1]octane-2 α-carboxylic Acid Methyl Ester (16u)

White solid, 9 % yield, mp. 102-103 °C. ¹H NMR (CDCl₃) δ 7.12-7.10 (dd, 1H), 6.93-6.90 (m, 1H), 6.84-6.83 (m, 1H), 4.67-4.60 (m, 2H), 3.57 (s, 3H), 3.48-3.41 (m, 1H), 2.86-2.84 (d, 1H), 2.78-2.69 (dt, 1H), 2.20-2.00 (m, 2H), 1.94-1.86 (m, 2H), 1.83-1.71 (m, 2H). ¹³C NMR (CDCl₃) δ: 171.2, 146.7, 123.3, 122.9, 75.3, 52.1, 51.4, 34.4, 30.3, 28.8, 28. Mass (M+H)⁺ = 252 (90 %) (M-OCH₃)⁺ = 221 (100 %). Anal. (C₁₃H₁₆O₃S). C, H, S.

5.5. Biology

The affinities of 2,3-unstaurated “ene” and 2,3-saturated “ane” compounds for the DAT and SERT are presented in Table 3 and Table 4, respectively. The affinities (IC₅₀) for the dopamine and serotonin transporters were determined in competition studies using [³H]3β-(4-fluorophenyl)tropane-2β-carboxylic acid methyl ester (WIN 35,438) or [³H]CFT) to label the DAT and [³H]citalopram to label the serotonin transporter. Nonspecific binding was measured with fluoxetine (10μM) [41]. Each compound was tested 2-5 times in monkey striatum because these compounds were part of an ongoing SAR study of DAT in this tissue [9,21-23,29-31]. Competition studies were conducted with a fixed concentration of radioligand and a range of concentrations of test drug. All compounds inhibited [³H]WIN 35,438 and [³H]citalopram in a concentration dependent manner. All compounds tested are racemic.