Synthesis and Monoamine Transporter Binding Properties of 3β-(3 ', 4

3β-(3'-Methyl-4'-chlorophenyl)tropane-2-carboxylic acid methyl ester (3b, RTI-112) is a 3-phenyltropane analogue that has high affinity for both the ...
0 downloads 0 Views 94KB Size
Download PDF
J. Med. Chem. 2005, 48, 2767-2771

2767

Articles Synthesis and Monoamine Transporter Binding Properties of 3β-(3′,4′-Disubstituted phenyl)tropane-2β-carboxylic Acid Methyl Esters F. Ivy Carroll,*,† Bruce E. Blough,† Zhe Nie,† Michael J. Kuhar,‡ Leonard L. Howell,‡ and Hernan A. Navarro† Chemistry and Life Sciences, Research Triangle Institute, Research Triangle Park, North Carolina 27709, and Yerkes National Primate Center of Emory University, 954 Gatewood Road NE, Atlanta, Georgia 30329 Received October 15, 2004

3β-(3′-Methyl-4′-chlorophenyl)tropane-2-carboxylic acid methyl ester (3b, RTI-112) is a 3-phenyltropane analogue that has high affinity for both the dopamine and serotonin transporters (DAT and 5-HTT, respectively). Compound 3b shows significant reduction of cocaine selfadministration in rhesus monkeys, yet fails to maintain robust drug self-administration. PET studies revealed that unlike more DAT selective analogues such as GBR 12 909 and 3-(4-chlorophenyl)tropane-2-carboxylic acid phenyl ester (RTI-113), 3b shows no detectible DAT occupancy when dosed at its ED50 for reduction of cocaine self-administration. In contrast, it highly occupies the 5-HTT at this dose. In this study, we report the synthesis and monoamine transporter binding potency of several new 3-(3′,4′-disubstituted phenyl)tropane-2-carboxylic acid methyl esters (3c-k), which have binding properties very similar to 3b. With the exception of the 3′,4′-dimethyl analogue 3k, all of the compounds possess subnanomolar IC50 and Ki values at the DAT and 5-HTT, respectively. The 3′-chloro-4′-bromo analogue 3e (IC50 ) 0.12 nM) and the 3′-bromo-4′-iodo analogue 3i (Ki ) 0.14 nM) are the most potent analogues at the DAT and 5-HTT, respectively. These compounds will be useful to further characterize the highly interesting behavioral profile of 3b. Introduction Even though cocaine (1) binds to the dopamine, serotonin, and norepinephrine transporters (DAT, 5-HTT, NET, respectively) with similar affinities, the psychomotor stimulant and reinforcing effects in animals have been attributed to its action at the DAT.1-4 The site where cocaine binds to the DAT has been referred to as the cocaine receptor.1,5 Much effort has been devoted to the characterization of the pharmacophore for this site (for reviews, see refs 6-9).6-9 For example, 3β-phenyltropane-2β-carboxylic acid methyl ester (2), WIN 35,065-2 was a lead structure for conducting structureactivity relationship (SAR) studies that provided insight into the nature of this binding site on the DAT.6,7 Early studies demonstated that in vitro binding affinity was highly dependent on the nature of the substituents on the 3β-aromatic ring.10,11 For example, the 3′,4′-disubstituted analogues such as the 3′,4′-dichloro (3a, RTI111) and 3′-methyl-4′-chloro (3b, RTI-112) compounds were the first analogues reported to show subnanomolor affinity at the DAT. Later reports showed that 3a and 3b also possessed subnanomolar affinity at the 5-HTT.12 Inhibiting 5-HT uptake may be an important characteristic of these compounds since a number of reports have suggested 5-HT indirectly modulates nucleus accumbens DA release.13,14 Importantly, since animal * To whom correspondence should be addressed. Research Triangle Institute, P.O. Box 12194, Research Triangle Park, NC 27709-2194. Phone: 919-541-6679. Fax: 919-541-8868. E-mail: [email protected]. † Research Triangle Institute. ‡ Yerkes National Primate Center of Emory University.

behavior studies have demonstrated that selective serotonin uptake inhibitors as well as selective dopamine uptake inhibitors can attenuate cocaine-induced stimulant and reinforcing effects, compounds showing high affinity for both the DAT and 5-HTT are of particular interest.15-18 In this paper, we report the synthesis and monoamine transporter binding properties of several new 3β-(3′,4′-disubstituted phenyl)tropane-2β-carboxylic acid methyl esters (3c-k). With the exception of the 3′,4′-dimethyl analogue 3k, all of the compounds showed subnanomolor affinity at both the DAT and 5-HTT. Chemistry The synthesis of compounds 3c-j starting with the appropriate 3-amino-4-halo compounds 4, 5, and 7 is

10.1021/jm040185a CCC: $30.25 © 2005 American Chemical Society Published on Web 03/18/2005

2768

Journal of Medicinal Chemistry, 2005, Vol. 48, No. 8

Carroll et al.

Table 1. Monoamine Transporter Binding Properties of 3β-(3′,4′-Disubstituted)tropane-2β-carboxylic Acid Methyl Esters

IC50, nM (Ki, nM) compd cocaine 2a 3a 3b 3c 3d 3e 3f 3g 3h 3i 3j 3k

X

Cl Cl Cl Cl Br Br Br I I I CH3

Y

DAT [3H]WIN 35 428

5-HTT [3H]paroxetine

NET [3H]nisoxetine

Cl CH3 Br I Cl Br I Cl Br I CH3

89.1 23 ( 5 0.79 ( 0.08 0.82 ( 0.05 0.42 ( 0.02 0.41 ( 0.09 0.12 ( 0.04 0.27 ( 0.01 0.21 ( 0.06 0.26 ( 0.05 0.20 ( 0.04 0.98 ( 0.05 0.43 ( 0.07

1050 (45) 1060 ( 61 (178 ( 5.5) 3.13 ( 0.36 (0.29 ( 0.03) 10.5 ( 0.41 (0.95 ( 0.04) 0.78 ( 0.04 (0.19 ( 0.01) 1.39 ( 0.23 (0.34 ( 0.06) 0.94 ( 0.09 (0.23 ( 0.02) 0.71 ( 0.03 (0.18 ( 0.01) 1.14 ( 0.26 (0.25 ( 0.04) 1.04 ( 0.14 (0.63 ( 0.05) 0.58 ( 0.07 (0.14 ( 0.02) 2.0 ( 0.56 (0.19 ( 0.05) 9.88 ( 1.11 (2.42 ( 0.27)

3300 (1990) 920 ( 70 (550 (44) 18 ( 0.85 (11 ( 0.51) 36.2 ( 1.02 (21.8 ( 0.62) 7.24 ( 0.69 (3.62 ( 0.34) 15.1 ( 0.59 (7.74 ( 0.29) 1.31 ( 0.13 (0.65 ( 0.07) 2.80 ( 0.16 (1.10 ( 0.08) 10.4 ( 1.5 (5.12 ( 0.77) 1.26 ( 0.09 (0.63 ( 0.05) 1.96 ( 0.17 (0.98 ( 0.09) 40.4 ( 3.56 (24 ( 2.1) 107 ( 11 (44 ( 4.7)

Scheme 1a

Scheme 2a

a Reagents: (a) 3,4-dimethylphenylmagnesium iodide, (C H ) O, 2 5 2 -45 °C; (b) CF3CO2H, -78 °C.

Biology The binding affinities of the target compounds 3c-j along with reference compounds cocaine, 2a, and 3a-b at the DAT, 5-HTT, and NET were determined via competition binding assays using the previously reported procedures.20 The results are listed in Table 1. Some of the data was taken from previous reports.10,11 The final concentration of radioligands in the assays was 0.5 nM [3H]WIN 35,428 for the DAT, 0.2 nM [3H]paroxetine for the 5-HTT, and 1.0 nM [3H]nisoxetine for the NET. a Reagents: (a) NCS, CH CN, reflux; (b) C H ONO, CuCl , 3 4 9 2 CH3CN, 65 °C; (c) C4H9ONO, CuBr2, CH3CN, 65 °C; (d) (CH3)2CHCH2CH2ONO, CH2I2, 80 °C.

shown in Scheme 1. The 4′-amino-3′-iodo (4) and 4′amino-3′-bromo (5) starting materials were prepared as previously reported.19 The 4′-amino-3′-chloro (7) material was prepared by chlorination of the 4′-amino compound 6 with N-chlorosuccimide in acetonitrile. Diazotization of 4, 5, and 7 with butyl nitrite in acetonitrile followed by treatment with the appropriate copper(II) halide provided the compounds 3c-g. The 4′iodo analogues 3h-j were prepared by diazotization of 4, 5, and 7 with isoamyl nitrite in the presence of diiodomethane. The 3′,4′-dimethyl analogue 3k was obtained by the addition of 3,4-dimethylphenylmagnesium iodide to anhydroecgonine methyl ester (8) using conditions similar to that used for the synthesis of other analogues10 (Scheme 2).

Results and Discussion Despite extensive efforts directed toward the development of pharmacotherapies to treat cocaine abuse, no effective drug is currently in clinical use.21-24 Since the DAT is the critical recognition site for cocaine and contributes to its abuse liability, DAT inhibitors represent a promising approach in drug development.21-23 A number of preclinical studies in nonhuman primates provide evidence that DAT inhibitors can effectively attenuate cocaine self-administration.20,25-28 Recently, we reported that 3b and 3β-(4′-chlorophenyl)tropane2β-carboxylic acid phenyl ester (9, RTI-113) were highly effective in reducing cocaine self-administration in rhesus monkeys and had no adverse behavioral effects.25,26 Positron emission tomography (PET) studies in rhesus monkeys showed that doses of the relatively DAT-selective 9 that decrease cocaine self-administration resulted in high occupancy of the DAT.26 In contrast, even though 3b showed greater than 70% DAT occupancy at the highest dose tested, DAT occupancy

Monoamine Transporter Binding of Phenyltropane Analogues

Journal of Medicinal Chemistry, 2005, Vol. 48, No. 8 2769

was below the limit of detection at the ED50 for reduction of cocaine self-administration.25 Surprisingly, 3b, which has about equal affinity for the DAT and 5-HTT, showed 84% occupancy of the 5-HTT at the ED50 dose.25 Importantly, 3b failed to maintain robust drug selfadministration in any of the three rhesus monkeys studied.25 These results strongly indicate that the interesting behavioral profile of 3b may be due to its interaction at both the DAT and 5-HTT. Compound 3b also has high affinity for the NET (Table 1), and thus it is possible that interaction at the NET may contribute to 3b induced decrease in cocaine self-administration. However, this seems unlikely since selective norepinephrine uptake inhibitors such as desipramine failed to reduce cocaine self-administration in nonhuman primates.15,18 Thus, the synthesis and pharmacological study of compounds possessing monoamine transporter binding properties similar to 3b should lead to a better understanding of the biochemical mechanism underlying cocaine abuse and could lead to new pharmacotherapies for treatment. The data listed in Table 1 show that compounds 3c-k all have monoamine transporter binding properties very similar to 3b. With the exception of the 3′,4′-dimethyl analogue 3k, they all show subnanomolar IC50 and Ki values at the DAT and 5-HTT, respectively. In addition, similar to 3b, they have appreciable affinity for the NET. The IC50 values at the DAT ranged from 0.12 to 0.98 nM with the 3′-chloro-4′-bromo analogue 3e (IC50 ) 0.12 nM) possessing the highest affinity at the DAT. The Ki values at the 5-HTT for 3c-j ranged from 0.14 to 0.63 nM. The 3′-bromo-4′-iodo analogue 3i with a Ki of 0.14 nM possessed the highest affinity at the 5-HTT. The Ki for the 3′,4′-dimethyl analogue 3k was 2.42 nM. The compounds showed slightly higher Ki values at the NET with a range of 0.98-44 nM. From an SAR viewpoint, it is interesting to note that all of the compounds possessed similar potency at the DAT and 5-HTT regardless of the size and electrostatic properties of the compounds at either the 3′- or 4′- position. One exception was the dimethyl analogue 3k, which had a somewhat larger Ki value at the 5-HTT. In summary, previous studies showed that the mixed action monoamine transporter inhibitor 3b reduced cocaine self-administration at a high level of 5-HTT occupancy with no detectable DAT occupancy and showed limited reinforcing effects. In this study, a number of compounds possessing monoamine-binding properties similar to but slightly different from that of 3b have been produced. All of the compounds showed subnanomolar potency at the DAT and 5-HTT. These compounds can serve as pharmacological tools to further characterize the highly interesting behavioral profile found for 3b and may lead to new pharmacotherapies for treating cocaine abuse.

carried out on plates precoated with silica gel GHLF (250 µm thickness). TLC visualization was accomplished with a UV lamp or in an iodine chamber. All moisture sensitive reactions were performed under a positive pressure of nitrogen maintained by a direct line from a nitrogen source. Commercially available ultralow water THF (J. T. Baker) was used. 3β-(3′-Bromo-4′chlorophenyl)tropane-2β-carboxylic Acid Methyl Ester (3c) Tartrate. Anhydrous copper(II) chloride (250 mg, 1.88 mmol), butyl nitrite (272, µL, 2.3 mmol), and anhydrous acetonitrile (8 mL) were added to a threenecked round-bottom flask that was equipped with a reflux condenser, additional funnel, and a gas outlet tub. The resulting mixture was warmed to 65 °C. The amine (5, 550 mg, 2 mmol) in 2 mL of acetonitrile was added dropwise to the reaction solution. Lots of precipitate appeared, followed by the evolution of nitrogen. After 10 min the reaction mixture was allowed to cool to room temperature, poured into 25 mL of 20% aqueous HCl, and neutralized by the addition of saturated sodium carbonate solution. The aqueous layer was extracted by methylene chloride and dried (Na2SO4). Purification by flash column (elution with 1:3 ethyl acetate-hexane with1% TEA) gave 140 mg (24%) of product 3c as clear oil. 1H NMR (CDCl3, 300 MHz) δ (ppm) 1.57-1.69 (m, 3H), 2.012.21 (m, s, 5H, NCH3), 2.49 (dt, 1H, H-4), 2.87-2.91 (m, 2H), 3.35 (m, 1H), 3.51 (s, 3H, CO2CH3), 3.57 (m, 1H, H-1), 7.14 (dd, 1H, J ) 8.4 and 1.8 Hz, Ar H-6), 7.32 (d, 1H, J ) 8.4 Hz, Ar H-5), 7.47 (d, 1H, J ) 2.1 Hz, Ar H-2); 13C NMR (CDCl3 75 MHz) δ 25.57, 26.18, 33.58, 34.31, 42.30, 51.59, 52.88, 62.45, 65.60, 122.24, 127.88, 129.85, 130.89, 133.07, 144.20, 172.14. Tartrate salt had: mp 90-92 °C; [R]20D -90.2° (c 0.50, CH3OH); Anal. (C20H25BrClNO8): C, H, N. 3β-(4′-Chloro-3′iodophenyl)tropane-2β-carboxylic Acid Methyl Ester (3d) Tartrate. Anhydrous copper(II) chloride (81 mg, 0.6 mmol), butyl nitrite (88 µL, 0.75 mmol), and anhydrous acetonitrile (4 mL) were added to a three-necked round-bottom flask that was equipped with a reflux condenser, additional funnel, and a gas outlet tube. The resulting mixture was warmed to 65 °C. The amine (4, 200 mg, 0.5 mmol) in 1 mL of acetonitrile was added dropwise to the reaction solution. Lots of precipitate appeared, followed by the evolution of nitrogen. After 10 min, the reaction mixture was allowed to cool to room temperature, poured into 25 mL of 20% aqueous HCl, and neutralized by the addition of saturated sodium carbonate solution. The aqueous layer was extracted with methylene chloride and dried (Na2SO4). Purification by flash column (elution with 3:1 ethyl acetate-hexane with1% TEA) gave 150 mg (71%) of product 3d as light yellow oil. 1H NMR (CDCl3, 300 MHz) δ (ppm) 1.58-1.75 (m, 3H), 2.04-2.16 (m, s, 5H, NCH3), 2.49 (dt, 1H, H-4), 2.84-2.89 (m, 2H), 3.35 (m, 1H), 3.53 (s, 3H, CO2CH3), 3.57 (m, 1H, H-1), 7.20 (dd, 1H, J ) 9.0 and 3.0 Hz, Ar H-6), 7.32 (d, 1H, J ) 8.4 Hz, Ar H-5), 7.70 (d, 1H, J ) 2.1 Hz, Ar H-2); 13C NMR (CDCl3 75 MHz) δ 25.59, 26.21, 33.46, 34.34, 42.32, 51.68, 52.94, 62.47, 65.63, 98.02, 129.02, 136.07, 139.60, 144.07, 172.19. Tartrate salt had: mp 118-120 °C; [R]19D -80.60° (c 0.50, CH3OH). Anal. (C20H25ClINO8‚1.75H2O): C, H, N. 3β-(4′-Amino-3′-chlorophenyl)tropane-2β-carboxylic Acid Methyl Ester (7). A 50 mL flask equipped with a reflux condenser was charged with a solution of the 4-amino compound 6 (550 mg, 2 mmol) in reagent grade acetonitrile (20 mL). The solution was heated to 60 °C and N-chlorosuccinimide (NCS), 400 mg, 3 mmol) was added in one portion. The mixture was heated to reflux. After 5 h, the reaction mixture was allowed to cool to room temperature and concentrated under vacuum to give a dark residue, which was dissolved in methylene chloride, and washed by 10% aqueous ammonium hydroxide and water. Organic layers were combined and dried over sodium sulfate. Purification by flash chromatography (elution with 3:1 ethyl acetate-hexane with 1% TEA) gave 250 mg (40%) of the product. 1H NMR (CDCl3, 300 MHz) δ (ppm) 1.51-1.61 (m, 3H), 2.02-2.13 (m and s, 5H, NCH3), 2.42 (dt, 1H, H-4), 2.74-2.82 (m, 2H), 3.26 (m, 1H), 3.45 (s and m, 4H, CO2CH3 and H-1), 3.83 (br s, 2H, NH2), 6.59 (d, 1H, J ) 6.0 Hz, Ar H-5), 6.90 (dd, 1H, Ar H-6), 7.03 (d, 1H, J ) 2.1 Hz, Ar

Experimental Section Nuclear magnetic resonance (1H NMR and 13C NMR) spectra were recorded on a 300 MHz (Bruker AVANCE 300) spectrometer. Chemical shift data for the proton resonances were reported in parts per million (δ) relative to internal (CH3)4Si (δ 0.0). Optical rotations were measured on an AutoPol III polarimeter, purchased from Rudolf Research. Elemental analyses were performed by Atlantic Microlab, Norcross, GA. Analytical thin-layer chromatography (TLC) was

2770

Journal of Medicinal Chemistry, 2005, Vol. 48, No. 8

Carroll et al.

H-2). The amine 7 was used for the synthesis of 3e and 3h without further purification. 3β-(4′-Bromo-3′-chlorophenyl)tropane-2β-carboxylic Acid Methyl Ester (3e) Tartrate. Anhydrous copper(II) bromide (139 mg, 0.70 mmol), butyl nitite (102 µL, 0.87 mmol), and anhydrous acetonitrile (4 mL) were added to a threenecked round-bottom flask that was equipped with a reflux condenser, addition funnel, and a gas outlet tube. The resulting mixture was warmed to 65 °C. The amine (7, 180 mg, 0.58 mmol) in 1 mL of acetonitrile was added dropwise to the reaction solution. Lots of precipitate appeared, followed by the evolution of nitrogen. After 0.5 h, the reaction mixture was allowed to cool to room temperature, poured into 25 mL of 20% aqueous HCl, and basified by the addition of saturated sodium carbonate solution. The aqueous layer was extracted with methylene chloride and dried. Purification by flash column (elution with 1:1 ethyl acetate-hexane with 1% TEA) gave 120 mg (55%) of product 3e. 1H NMR (CDCl3, 300 MHz) δ (ppm) 1.55-1.74 (m, 3H), 2.07-2.26 (m and s, 5H, NCH3), 2.51 (dt, 1H, H-4), 2.86-2.96 (m, 2H), 3.35 (m, 1H), 3.53 (s, 3H, CO2CH3), 3.58 (m, 1H, H-1), 7.03 (dd, 1H, J ) 8.4 and 1.8 Hz, Ar H-6), 7.32 (d, 1H, J ) 1.8 Hz, Ar H-2), 7.48 (d, 1H, J ) 8.4 Hz, Ar H-5); 13C NMR (CDCl3 75 MHz) δ 25.56, 26.19, 33.71, 34.26, 42.28, 51.67, 52.84, 62.44, 65.60, 119.77, 127.38, 129.80, 133.44, 134.22, 144.84, 172.15. Tartrate salt had: mp 95-97 °C; [R]19D -75.00° (c 0.50, CH3OH). Anal. (C20H25BrClNO8‚ H2O): C, H, N. 3β-(3′,4′-Dibromophenyl)tropane-2β-carboxylic Acid Methyl Ester (3f) Tartrate. Anhydrous copper(II) bromide (134 mg, 0.67 mmol), butyl nitrite (98 µL, 0.84 mmol), and anhydrous acetonitrile (4 mL) were added to a three-necked round-bottom flask that was equipped with a reflux condenser, addition funnel, and a gas outlet tube. The resulting mixture was warmed to 65 °C. The amine (5, 200 mg, 0.56 mmol) in 1 mL of acetonitrile was added dropwise to the reaction solution. Lots of precipitate appeared, followed by the evolution of nitrogen. After 10 min, the reaction was complete. The reaction mixture was allowed to cool to room temperature, poured into 25 mL of 20% aqueous HCl, and neutralized by the addition of saturated sodium carbonate solution. The aqueous layer was extracted with methylene chloride and dried (Na2SO4). Purification by flash column (elution with 1:3 ethyl acetate-hexane with 1% TEA) gave 85 mg (36% of product 3f as a clear oil. 1H NMR (CDCl3, 300 MHz) δ (ppm) 1.57-1.69 (m, 3H), 2.012.22 (m and s, 5H, NCH3), 2.50 (dt, 1H, H-4), 2.85-2.89 (m, 2H), 3.34 (m, 1H), 3.52-3.59 (s and m, 4H, CO2CH3 and H-1), 7.08 (dd, 1H, J ) 8.4 and 2.1 Hz, Ar H-6), 7.45-7.50 (d and d, 2H, Ar H-2 and H5, overlap); 13C NMR (CDCl3 75 MHz) δ 25.56, 26.18, 33.56, 34.26, 42.30, 51.70, 52.85, 62.33, 65.60, 112.10, 124.62, 128.07, 133.11, 134.40, 144.89, 172.15. The tartrate salt had: mp 112-114 °C; [R]20D -82.4° (c 0.50, CH3OH). Anal. (C20H25BrNO8‚H2O): C, H, N. 3β-(4′-Bromo-3′-iodophenyl)tropane-2β-carboxylic Acid Methyl Ester (3g) Tartrate. Anhydrous copper(II) bromide (168 mg, 0.84 mmol), butyl nitrite (123 µL, 1.05 mmol), and anhydrous acetonitrile (4 mL) were added to a three-necked round-bottom flask that was equipped with a reflux condenser, addition funnel, and a gas outlet tube. The resulting mixture was warmed to 65 °C. The amine (4, 280 mg, 0.7 mmol) in 1 mL of acetonitrile was added dropwise to the reaction solution. Lots of precipitate appeared, followed by the evolution of nitrogen. After 10 min, the reaction mixture was allowed to cool to room temperature, poured into 25 mL of 20% aqueous HCl, and neutralized by the addition of saturated sodium carbonate solution. The aqueous layer was extracted with methylene chloride and dried (Na2SO4). Purification by flash column (elution with 3:1 ethyl acetate-hexane with 1% TEA) gave 250 mg (77%) of product 3g. 1H NMR (CDCl3, 300 MHz) δ (ppm) 1.57-1.73 (m, 3H), 2.09-2.21 (m and s, 5H, NCH3), 2.49 (dt, 1H, H-4), 2.84-2.91 (m, 2H), 3.35 (m, 1H), 3.53 (s, 3H, CO2CH3), 3.57 (m, 1H, H-1), 7.12 (dd, 1H, J ) 8.6 and 2.1 Hz, Ar H-6), 7.48 (d, 1H, J ) 8.4 Hz, Ar H-5), 7.73 (d, 1H, J ) 2.1 Hz, Ar H-2); 13C NMR (CDCl3 75 MHz) δ 25.56, 26.21, 33.52, 34.28, 42.32, 51.70, 52.88, 62.46, 65.63, 101.12, 127.09,

129.14, 132.40, 139.05, 144.65, 172.18. The tartrate salt had: mp 120-122 °C; [R]19D -73.0° (c 0.50, CH3OH). Anal. (C20H25BrINO8‚0.5H2O): C, H, N. 3β-(3′-Chloro-4′-iodophenyl)tropane-2β-carboxylic Acid Methyl Ester (3h) Tartrate. To a stirred solution of the starting material, 3β-(4′-amino-3′-chlorophenyl)tropane-2βcarboxylic acid methyl ester (7, 250 mg, 0.8 mmol), and diiodomethane (5 mL) under an atmosphere of nitrogen was added isoamyl nitrite (215 µL, 1.6 mmol) from a syringe. The reaction mixture was stirred at room temperature for 1 h under nitrogen and allowed to warm to 80 °C and continue to stir for another 2 h. Since the evaporation of the solvent, diiodomethane, was very difficult, the reaction mixture was directly applied on a column and purified with a flash column (elution with 1:1 ethyl acetate-hexane with 1% TEA) to give 110 mg (33%) of product 3h. 1H NMR (CDCl3, 300 MHz) δ (ppm) 1.59-1.71 (m, 3H), 2.05-2.24 (m and s, 5H, NCH3), 2.49 (dt, 1H, H-4), 2.88-2.93 (m, 2H), 3.34 (m, 1H), 3.53-3.58 (s and m, 4H, CO2CH3 and H-1), 6.87 (dd, 1H, J ) 8.2 and 1.8 Hz, Ar H-6), 7.32 (d, 1H, J ) 2.1 Hz, Ar H-2), 7.71 (d, 1H, J ) 8.1 Hz, Ar H-5); 13C NMR (CDCl3 75 MHz) δ 25.18, 25.74, 33.31, 33.81, 41.91, 51.31, 52.20, 61.96, 65.18, 94.50, 126.43, 127.16, 127.95, 139.52, 145.60, 171.78. The tartrate salt had: mp 120-122 °C; [R]19D -83.0° (c 0.50, CH3OH). Anal. (C20H25ClINO8‚H2O): C, H, N. 3β-(3′-Bromo-4′-iodophenyl)tropane-2β-carboxylic Acid Methyl Ester (3i) Tartrate. To a stirred solution of the starting material, 3β-(4′-amino-3′-bromophenyl)tropane-2βcarboxylic acid methyl ester (5, 320 mg, 0.9 mmol), and diiodomethane (5 mL) under an atmosphere of nitrogen was added isoamyl nitrite (242 µL, 1.8 mmol) from a syringe. The reaction mixture was stirred at room temperature for 1 h under nitrogen and allowed to warm to 80 °C and continue to stir for another 2 h. Since the evaporation of the solvent, diiodomethane was very difficult, the reaction mixture was directly applied on a column and purified by flash column (elution with 1:1 ethyl acetate-hexane with 1% TEA) to give 60 mg (14%) of product 3i. 1H NMR (CDCl3, 300 MHz) δ (ppm) 1.58-1.70 (m, 3H), 2.03-2.21 (m and s, 5H, NCH3), 2.49 (dt, 1H, H-4), 2.86-2.93 (m, 2H), 3.34 (m, 1H), 3.53-3.58 (s and m, 4H, CO2CH3 and H-1), 6.92 (dd, 1H, J ) 8.1 and 2.0 Hz, Ar H-6), 7.48 (d, 1H, J ) 1.8 Hz, Ar H-2), 7.72 (d, 1H, J ) 8.4 Hz, Ar H-5); 13C NMR (CDCl3 75 MHz) δ 25.58, 26.20, 33.76, 34.20, 42.30, 51.71, 52.84, 62.45, 66.62, 97.96, 126.30, 128.12, 129.63, 140.00, 145.99, 172.17. The tartrate salt had: mp 100-102 °C; [R]20D -81.6° (c 0.50, CH3OH). Anal. (C20H25BrINO8): C, H, N. 3β-(3′, 4′-Diiodophenyl)tropane-2β-carboxylic Acid Methyl Ester (3j) Hydrochloride. To a stirred solution of 3β-(4′-amino-3′-iodophenyl)tropane-2β-carboxylic acid methyl ester (4, 1.32 g, 33.05 mmol) in 16.5 diiodomethane under N2 was added 0.888 mL (0.774 g, 66.01 mmol) of isoamyl nitrite via syringe. The mixture was heated to 55 °C and stirred for 8 h. The solution was cooled and 150 mL of diethyl ether was added. The organic layer was extracted with 1 M aqueous hydrochloric acid (3×). The aqueous layers were basified with ammonium hydroxide and extracted with methylene chloride (3×). The combined organic layers were dried over sodium sulfate, filtered, and concentrated under reduced pressure. The crude dark yellow oil was purified by column chromatography on silica gel. Elution with 1:1 ethyl acetate-hexane with 2% TEA afforded 0.984 g (58%) of product 3j. 1H NMR (CDCl3, 300MHz) δ (ppm) 1.53-1.69 (m, 3H), 2.14-2.24 (m, 2H), 2.20 (s, 3H), 2.33 (t, 1H, J ) 8 Hz), 2.83-2.94 (m, 2H), 3.32 (bs, 1H), 3.34 (bs, 1H), 3.34 (s, 3H), 6.95 (dd, 1H, J ) 2.5 and 9.9 Hz), 7.71 (d, 1H, J ) 9.8 Hz), 7.71 (s, 1H). The hydrochloride salt had: mp 174 °C; [R]20D -59.7° (c 0.03, CH3OH); Anal. (C16H20ClI2NO2): C, H, N. 3β-(3′,4′-Dimethylphenyl)tropane-2β-carboxylic Acid Methyl Ester (3k) Tartrate. Magnesium turnings (3.21 g, 0.132 mol) were stirred under argon for 2 weeks to activate. The activated magnesium was covered with 20 mL of distilled ether and a small iodine crystal added. About 1/3 of a solution of 4-iodoxylene (17.05 mL, 0.120 mol) in 30 mL distilled ether

Monoamine Transporter Binding of Phenyltropane Analogues was added under argon, and mixture was heated slightly to initiate reaction. Addition continued at a dropwise rate to maintain reflux. After the addition was completed, the mixture was refluxed for 2-3 h and then stirred at room-temperature overnight. The Grignard reagent prepared above was cannulated into a (3 L) three-necked flask and rinsed in with 200 mL distilled ether. The flask was cooled to -45 °C in acetonitrile/dry ice bath, and anhydroecogonine methyl ester (8, 88.1 g, 48.9 mmol) in 100 mL of distilled ether was added at a slow dropwise rate over 1.5 h. After 3.5 h, the bath was exchanged for an acetone/dry ice bath and the reaction was quenched by the very slow addition of trifluoroacetic acid (37 mL, 0.48 mol) in 80 mL of distilled ether over 2 h. The dry ice bath was exchanged for ice/water bath and 200 mL of H2O added (pH ) 1.0). The aqueous layer was separated and the ether was washed with 1 N HCl (2 × 200 mL). The combined aqueous extracts were basified with concentrated NH4OH and filtered through a Celite pad to remove small amount of opaque material. The aqueous filtrate was washed with the ethyl ether (2×) and once with CH2Cl2. The combined organic extracts were washed with brine, dried over Na2SO4, filtered, and evaporated to give 8.48 g of crude material as an orange oil. The crude material was purified by flash chromatography using 15% (9:1 Et2O:Et3N)/ hexanes as eluent to give 0.68 g (5%) of the 3k. 1H NMR (CDCl3, 300 MHz) δ (ppm) 1.62-1.72 (m, 3H), 2.22 (s, 3H and s, 6H on top of m 2.16-2.25), 2.55 (dt, 1H, H-4), 2.90-2.91 (m, 2H), 3.47-3.68 (s and m, 4H, CO2CH3 and H-1), 6.977.39 (m, 3H). The tartrate salt had: mp 122-124 °C; [R]20D -97.2° (c 0.50, CH3OH). Anal. (C22H31NO8‚0.5H2O): C, H, N.

Acknowledgment. This research was supported by the National Institute on Drug Abuse Grants DA05477. We thank Fluvanna Josephson for the synthesis of 3j. Supporting Information Available: Elemental analysis. This material is available free of charge via the Internet at http://pubs.acs.org.

References (1) Ritz, M. C.; Lamb, R. J.; Goldberg, S. R.; Kuhar, M. J. Cocaine receptors on dopamine transporters are related to self-administration of cocaine. Science 1987, 237, 1219-1223. (2) Bergman, J.; Madras, B. K.; Johnson, S. E.; Spealman, R. D. Effects of cocaine and related drugs in nonhuman primates. III. Self-administration by squirrel monkeys. J. Pharmacol. Exp. Ther. 1989, 251, 150-155. (3) Kuhar, M. J.; Ritz, M. C.; Boja, J. W. The dopamine hypothesis of the reinforcing properties of cocaine. Trends Neurosci. 1991, 14, 299-302. (4) Wise, R. A.; Newton, P.; Leeb, K.; Burnette, B.; Pocock, D.; Justice, J. B., Jr. Fluctuations in nucleus accumbens dopamine concentration during intravenous cocaine self-administration in rats. Psychopharmacology (Berlin) 1995, 120, 10-20. (5) Carroll, F. I.; Lewin, A. H.; Boja, J. W.; Kuhar, M. J. Cocaine receptor: Biochemical characterization and structure-activity relationships for the dopamine transporter. J. Med. Chem. 1992, 35, 969-981. (6) Carroll, F. I.; Lewin, A. H.; Mascarella, S. W. Dopamine Transporter Uptake Blockers: Structure-Activity Relationships. Neurotransmitter Transporters: Structure, Function, and Regulation, 2nd ed.; Humana Press: Totowa, NJ, 2001; pp 381-432. (7) Carroll, F. I. 2002 Medicinal Chemistry Division Award address: monoamine transporters and opioid receptors. Targets for addiction therapy. J. Med. Chem. 2003, 46, 1775-1794. (8) Newman, A. H. Novel pharmacotherapies for cocaine abuse 1997-2000. Exp. Opin. Ther. Pat. 2000, 10, 1095-1122. (9) Dutta, A. K.; Zhang, S.; Kolhatkar, R.; Reith, M. E. Dopamine transporter as target for drug development of cocaine dependence medications. Eur. J. Pharmacol. 2003, 479, 93-106. (10) Carroll, F. I.; Gao, Y.; Rahman, M. A.; Abraham, P.; Lewin, A. H.; Boja, J. W.; Kuhar, M. J. Synthesis, ligand binding, QSAR,

Journal of Medicinal Chemistry, 2005, Vol. 48, No. 8 2771

(11)

(12)

(13) (14) (15)

(16) (17)

(18) (19)

(20)

(21) (22) (23)

(24) (25)

(26)

(27)

(28)

and CoMFA study of 3β-(p-substituted phenyl)tropan-2β-carboxylic acid methyl esters. J. Med. Chem. 1991, 34, 2719-2927. Carroll, F. I.; Kuzemko, M. A.; Gao, Y.; Abraham, P.; Lewin, A. H.; Boja, J. W.; Kuhar, M. J. Synthesis and ligand binding of 3β-(3-substituted phenyl)- and 3β-(3,4-disubstituted phenyl)tropane-2β-carboxylic acid methyl esters. Med. Chem. Res. 1992, 1, 382-387. Carroll, F. I.; Kotian, P.; Dehghani, A.; Gray, J. L.; Kuzemko, M. A.; Parham, K. A.; Abraham, P.; Lewin, A. H.; Boja, J. W.; Kuhar, M. J. Cocaine and 3β-(4′-substituted phenyl)tropane-2βcarboxylic acid ester and amide analogues. New high-affinity and selective compounds for the dopamine transporter. J. Med. Chem. 1995, 38, 379-388. Gainetdinov, R. R.; Caron, M. G. Monoamine transporters: from genes to behavior. Annu. Rev. Pharmacol. Toxicol. 2003, 43, 261-284. Mueller, C. P.; Carey, R. J.; Huston, J. P. Serotonin as an important mediator of cocaine’s behavioral effects. Drugs Today (Barc) 2003, 39, 497-511. Kleven, M. S.; Woolverton, W. L. Effects of three monoamine uptake inhibitors on behavior maintained by cocaine or food presentation in rhesus monkeys. Drug Alcohol Depend 1993, 31, 149-158. Howell, L. L.; Byrd, L. D. Serotonergic modulation of the behavioral effects of cocaine in the squirrel monkey. J. Pharmacol. Exp. Ther. 1995, 275, 1551-1559. Czoty, P. W.; Ginsburg, B. C.; Howell, L. L. Serotonergic attenuation of the reinforcing and neurochemical effects of cocaine in squirrel monkeys. J. Pharmacol. Exp. Ther. 2002, 300, 831-837. Mello, N. K.; Lukas, S. E.; Bree, M. P.; Mendelson, J. H. Desipramine effects on cocaine self-administration by rhesus monkeys. Drug Alcohol Depend. 1990, 26, 103-116. Carroll, F. I.; Mascarella, S. W.; Kuzemko, M. A.; Gao, Y.; Abraham, P.; Lewin, A. H.; Boja, J. W.; Kuhar, M. J. Synthesis, ligand binding, and QSAR (CoMFA and classical) study of 3β(3′-substituted phenyl)-, 3β-(4′-substituted phenyl)-, and 3β-(3′,4′disubstituted phenyl)tropane-2β-carboxylic acid methyl esters. J. Med. Chem. 1994, 37, 2865-2873. Nader, M. A.; Grant, K. A.; Davies, H. M.; Mach, R. H.; Childers, S. R. The reinforcing and discriminative stimulus effects of the novel cocaine analog 2β-propanoyl-3β-(4-tolyl)-tropane in rhesus monkeys. J. Pharmacol. Exp. Ther. 1997, 280, 541-550. Carroll, F. I.; Howell, L. L.; Kuhar, M. J. Pharmacotherapies for treatment of cocaine abuse: Preclinical aspects. J. Med. Chem. 1999, 42, 2721-2736. Howell, L. L.; Wilcox, K. M. The dopamine transporter and cocaine medication development: drug self-administration in nonhuman primates. J. Pharmacol. Exp. Ther. 2001, 298, 1-6. Newman, A. H.; Kulkarni, S. Probes for the dopamine transporter: new leads toward a cocaine-abuse therapeuticsA focus on analogues of benztropine and rimcazole. Med. Res. Rev. 2002, 22, 429-464. Carrera, M. R.; Meijler, M. M.; Janda, K. D. Cocaine pharmacology and current pharmacotherapies for its abuse. Bioorg. Med. Chem. 2004, 12, 5019-5030. Lindsey, K. P.; Wilcox, K. M.; Votaw, J. R.; Goodman, M. M.; Plisson, C.; Carroll, F. I.; Rice, K. C.; Howell, L. L. Effects of dopamine transporter inhibitors on cocaine self-administration in rhesus monkeys: relationship to transporter occupancy determined by positron emission tomography neuroimaging. J. Pharmacol. Exp. Ther. 2004, 309, 959-969. Wilcox, K. M.; Lindsey, K. P.; Votaw, J. R.; Goodman, M. M.; Martarello, L.; Carroll, F. I.; Howell, L. L. Self-administration of cocaine and the cocaine analog RTI-113: relationship to dopamine transporter occupancy determined by PET neuroimaging in rhesus monkeys. Synapse 2002, 43, 78-85. Howell, L. L.; Czoty, P. W.; Kuhar, M. J.; Carroll, F. I. Comparative behavioral pharmacology of cocaine and the selective dopamine uptake inhibitor, RTI-113 in the squirrel monkey. J. Pharmacol. Exp. Ther. 2000, 292, 521-529. Glowa, J. R.; Wojnicki, F. H. E.; Matecka, D.; Bacher, J. D.; Mansbach, R. S.; Balster, R. L.; Rice, K. C. Effects of dopamine reuptake inhibitors on food- and cocaine-maintained responding: I. Dependence on unit dose of cocaine. Exp. Clin. Psychopharmacol. 1995, 3, 219-231.

JM040185A